WorldWideScience

Sample records for picoliter volume droplets

  1. Printed droplet microfluidics for on demand dispensing of picoliter droplets and cells.

    Science.gov (United States)

    Cole, Russell H; Tang, Shi-Yang; Siltanen, Christian A; Shahi, Payam; Zhang, Jesse Q; Poust, Sean; Gartner, Zev J; Abate, Adam R

    2017-08-15

    Although the elementary unit of biology is the cell, high-throughput methods for the microscale manipulation of cells and reagents are limited. The existing options either are slow, lack single-cell specificity, or use fluid volumes out of scale with those of cells. Here we present printed droplet microfluidics, a technology to dispense picoliter droplets and cells with deterministic control. The core technology is a fluorescence-activated droplet sorter coupled to a specialized substrate that together act as a picoliter droplet and single-cell printer, enabling high-throughput generation of intricate arrays of droplets, cells, and microparticles. Printed droplet microfluidics provides a programmable and robust technology to construct arrays of defined cell and reagent combinations and to integrate multiple measurement modalities together in a single assay.

  2. On-chip real-time single-copy polymerase chain reaction in picoliter droplets

    Energy Technology Data Exchange (ETDEWEB)

    Beer, N R; Hindson, B; Wheeler, E; Hall, S B; Rose, K A; Kennedy, I; Colston, B

    2007-04-20

    The first lab-on-chip system for picoliter droplet generation and PCR amplification with real-time fluorescence detection has performed PCR in isolated droplets at volumes 10{sup 6} smaller than commercial real-time PCR systems. The system utilized a shearing T-junction in a silicon device to generate a stream of monodisperse picoliter droplets that were isolated from the microfluidic channel walls and each other by the oil phase carrier. An off-chip valving system stopped the droplets on-chip, allowing them to be thermal cycled through the PCR protocol without droplet motion. With this system a 10-pL droplet, encapsulating less than one copy of viral genomic DNA through Poisson statistics, showed real-time PCR amplification curves with a cycle threshold of {approx}18, twenty cycles earlier than commercial instruments. This combination of the established real-time PCR assay with digital microfluidics is ideal for isolating single-copy nucleic acids in a complex environment.

  3. Fast selective trapping and release of picoliter droplets in a 3D microfluidic PDMS multi-trap system with bubbles.

    Science.gov (United States)

    Rambach, Richard W; Biswas, Preetika; Yadav, Ashutosh; Garstecki, Piotr; Franke, Thomas

    2018-02-12

    The selective manipulation and incubation of individual picoliter drops in high-throughput droplet based microfluidic devices still remains challenging. We used a surface acoustic wave (SAW) to induce a bubble in a 3D designed multi-trap polydimethylsiloxane (PDMS) device to manipulate multiple droplets and demonstrate the selection, incubation and on-demand release of aqueous droplets from a continuous oil flow. By controlling the position of the acoustic actuation, individual droplets are addressed and selectively released from a droplet stream of 460 drops per s. A complete trapping and releasing cycle can be as short as 70 ms and has no upper limit for incubation time. We characterize the fluidic function of the hybrid device in terms of electric power, pulse duration and acoustic path.

  4. High-efficiency single cell encapsulation and size selective capture of cells in picoliter droplets based on hydrodynamic micro-vortices.

    Science.gov (United States)

    Kamalakshakurup, Gopakumar; Lee, Abraham P

    2017-12-05

    Single cell analysis has emerged as a paradigm shift in cell biology to understand the heterogeneity of individual cells in a clone for pathological interrogation. Microfluidic droplet technology is a compelling platform to perform single cell analysis by encapsulating single cells inside picoliter-nanoliter (pL-nL) volume droplets. However, one of the primary challenges for droplet based single cell assays is single cell encapsulation in droplets, currently achieved either randomly, dictated by Poisson statistics, or by hydrodynamic techniques. In this paper, we present an interfacial hydrodynamic technique which initially traps the cells in micro-vortices, and later releases them one-to-one into the droplets, controlled by the width of the outer streamline that separates the vortex from the flow through the streaming passage adjacent to the aqueous-oil interface (d gap ). One-to-one encapsulation is achieved at a d gap equal to the radius of the cell, whereas complete trapping of the cells is realized at a d gap smaller than the radius of the cell. The unique feature of this technique is that it can perform 1. high efficiency single cell encapsulations and 2. size-selective capturing of cells, at low cell loading densities. Here we demonstrate these two capabilities with a 50% single cell encapsulation efficiency and size selective separation of platelets, RBCs and WBCs from a 10× diluted blood sample (WBC capture efficiency at 70%). The results suggest a passive, hydrodynamic micro-vortex based technique capable of performing high-efficiency single cell encapsulation for cell based assays.

  5. Monodisperse Picoliter Droplets for Low-Bias and Contamination-Free Reactions in Single-Cell Whole Genome Amplification.

    Directory of Open Access Journals (Sweden)

    Yohei Nishikawa

    Full Text Available Whole genome amplification (WGA is essential for obtaining genome sequences from single bacterial cells because the quantity of template DNA contained in a single cell is very low. Multiple displacement amplification (MDA, using Phi29 DNA polymerase and random primers, is the most widely used method for single-cell WGA. However, single-cell MDA usually results in uneven genome coverage because of amplification bias, background amplification of contaminating DNA, and formation of chimeras by linking of non-contiguous chromosomal regions. Here, we present a novel MDA method, termed droplet MDA, that minimizes amplification bias and amplification of contaminants by using picoliter-sized droplets for compartmentalized WGA reactions. Extracted DNA fragments from a lysed cell in MDA mixture are divided into 105 droplets (67 pL within minutes via flow through simple microfluidic channels. Compartmentalized genome fragments can be individually amplified in these droplets without the risk of encounter with reagent-borne or environmental contaminants. Following quality assessment of WGA products from single Escherichia coli cells, we showed that droplet MDA minimized unexpected amplification and improved the percentage of genome recovery from 59% to 89%. Our results demonstrate that microfluidic-generated droplets show potential as an efficient tool for effective amplification of low-input DNA for single-cell genomics and greatly reduce the cost and labor investment required for determination of nearly complete genome sequences of uncultured bacteria from environmental samples.

  6. Capillary-based integrated digital PCR in picoliter droplets.

    Science.gov (United States)

    Chen, Jinyu; Luo, Zhaofeng; Li, Lin; He, Jinlong; Li, Luoquan; Zhu, Jianwei; Wu, Ping; He, Liqun

    2018-01-30

    The droplet digital polymerase chain reaction (ddPCR) is becoming more and more popular in diagnostic applications in academia and industry. In commercially available ddPCR systems, after they have been made by a generator, the droplets have to be transferred manually to modules for amplification and detection. In practice, some of the droplets (∼10%) are lost during manual transfer, leading to underestimation of the targets. In addition, the droplets are also at risk of cross-contamination during transfer. By contrast, in labs, some chip-based ddPCRs have been demonstrated where droplets always run in channels. However, the droplets easily coalesce to large ones in chips due to wall wetting as well as thermal oscillation. The loss of droplets becomes serious when such ddPCRs are applied to absolutely quantify rare mutations, such as in early diagnostics in clinical research or when measuring biological diversity at the cell level. Here, we propose a capillary-based integrated ddPCR system that is used for the first time to realize absolute quantification in this way. In this system, a HPLC T-junction is used to generate droplets and a long HPLC capillary connects the generator with both a capillary-based thermocycler and a capillary-based cytometer. The performance of the system is validated by absolute quantification of a gene specific to lung cancer (LunX). The results show that this system has very good linearity (0.9988) at concentrations ranging from NTC to 2.4 × 10 -4 copies per μL. As compared to qPCR, the all-in-one scheme is superior both in terms of the detection limit and the smaller fold changes measurement. The system of ddPCR might provide a powerful approach for clinical or academic applications where rare events are mostly considered.

  7. Droplet microfluidic platform for cell electrofusion

    NARCIS (Netherlands)

    Schoeman, R.M.

    2015-01-01

    In this thesis a lab on a chip platform is described which is capable of electrofusing cells in a picoliter droplet. The platform consist out of glass part containing recessed platinum electrodes plasma bonded to a PDMS slab containing microchannels. First the two cell populations are introduced

  8. Controllable picoliter pipetting using hydrophobic microfluidic valves

    Science.gov (United States)

    Zhang, M.; Huang, J.; Qian, X.; Mi, S.; Wang, X.

    2017-06-01

    A picoliter pipetting technique using the microfluidic method is presented. Utilizing the hydrophobic self-assembled monolayer films patterned in microchannels as pressure-controlled valves, a small volume of liquid can be separated by a designed channel trap and then ejected from the channel end at a higher pressure. The liquid trap section is composed of a T-shaped channel junction and a hydrophobic patch. The liquid volume can be precisely controlled by varying the distance of the hydrophobic patch from the T-junction. By this means, liquid less than 100 pl can be separated and pipetted. The developed device is potentially useful for sample dispensing in biological, medical, and chemical applications.

  9. Analytical detection techniques for droplet microfluidics—A review

    International Nuclear Information System (INIS)

    Zhu, Ying; Fang, Qun

    2013-01-01

    Graphical abstract: -- Highlights: •This is the first review paper focused on the analytical techniques for droplet-based microfluidics. •We summarized the analytical methods used in droplet-based microfluidic systems. •We discussed the advantage and disadvantage of each method through its application. •We also discuss the future development direction of analytical methods for droplet-based microfluidic systems. -- Abstract: In the last decade, droplet-based microfluidics has undergone rapid progress in the fields of single-cell analysis, digital PCR, protein crystallization and high throughput screening. It has been proved to be a promising platform for performing chemical and biological experiments with ultra-small volumes (picoliter to nanoliter) and ultra-high throughput. The ability to analyze the content in droplet qualitatively and quantitatively is playing an increasing role in the development and application of droplet-based microfluidic systems. In this review, we summarized the analytical detection techniques used in droplet systems and discussed the advantage and disadvantage of each technique through its application. The analytical techniques mentioned in this paper include bright-field microscopy, fluorescence microscopy, laser induced fluorescence, Raman spectroscopy, electrochemistry, capillary electrophoresis, mass spectrometry, nuclear magnetic resonance spectroscopy, absorption detection, chemiluminescence, and sample pretreatment techniques. The importance of analytical detection techniques in enabling new applications is highlighted. We also discuss the future development direction of analytical detection techniques for droplet-based microfluidic systems

  10. [Micro-droplet characterization and its application for amino acid detection in droplet microfluidic system].

    Science.gov (United States)

    Yuan, Huiling; Dong, Libing; Tu, Ran; Du, Wenbin; Ji, Shiru; Wang, Qinhong

    2014-01-01

    Recently, the droplet microfluidic system attracts interests due to its high throughput and low cost to detect and screen. The picoliter micro-droplets from droplet microfluidics are uniform with respect to the size and shape, and could be used as monodispensed micro-reactors for encapsulation and detection of single cell or its metabolites. Therefore, it is indispensable to characterize micro-droplet and its application from droplet microfluidic system. We first constructed the custom-designed droplet microfluidic system for generating micro-droplets, and then used the micro-droplets to encapsulate important amino acids such as glutamic acid, phenylalanine, tryptophan or tyrosine to test the droplets' properties, including the stability, diffusivity and bio-compatibility for investigating its application for amino acid detection and sorting. The custom-designed droplet microfluidic system could generate the uniformed micro-droplets with a controllable size between 20 to 50 microm. The micro-droplets could be stable for more than 20 h without cross-contamination or fusion each other. The throughput of detection and sorting of the system is about 600 micro-droplets per minute. This study provides a high-throughput platform for the analysis and screening of amino acid-producing microorganisms.

  11. Note: Development of a microfabricated sensor to measure thermal conductivity of picoliter scale liquid samples.

    Science.gov (United States)

    Park, Byoung Kyoo; Yi, Namwoo; Park, Jaesung; Kim, Dongsik

    2012-10-01

    This paper presents a thermal analysis device, which can measure thermal conductivity of picoliter scale liquid sample. We employ the three omega method with a microfabricated AC thermal sensor with nanometer width heater. The liquid sample is confined by a micro-well structure fabricated on the sensor surface. The performance of the instrument was verified by measuring the thermal conductivity of 27-picoliter samples of de-ionized (DI) water, ethanol, methanol, and DI water-ethanol mixtures with accuracies better than 3%. Furthermore, another analytical scheme allows real-time thermal conductivity measurement with 5% accuracy. To the best of our knowledge, this technique requires the smallest volume of sample to measure thermal property ever.

  12. Low-Cost Experimentation for the Study of Droplet Microfluidics

    Science.gov (United States)

    Bardin, David; Lee, Abraham P.

    2014-01-01

    The continued growth of microfluidics into industry settings in areas such as point-of-care diagnostics and targeted therapeutics necessitates a workforce trained in microfluidic technologies and experimental methods. Laboratory courses for students at the university and high school levels will require cost-effective in-class demonstrations that instruct in chip design, fabrication, and experimentation at the microscale. We present a hand-operated pressure pumping system to form monodisperse picoliter to nanoliter droplet streams at low cost, and a series of exercises aimed at instructing in the specific art of droplet formation. Using this setup, the student is able to generate and observe the modes of droplet formation in flow-focusing devices, and the effect of device dimensions on the characteristics of formed droplets. Lastly, at ultra-low cost we demonstrate large plug formation in a T-junction using coffee stirrers as a master mold substitute. Our method reduces the cost of experimentation to enable intuitive instruction in droplet formation, with additional implications for creating droplets in the field or at point-of-care. PMID:25133595

  13. Droplet Microfluidics Approach for Single-DNA Molecule Amplification and Condensation into DNA-Magnesium-Pyrophosphate Particles

    Directory of Open Access Journals (Sweden)

    Greta Zubaite

    2017-02-01

    Full Text Available Protein expression in vitro has broad applications in directed evolution, synthetic biology, proteomics and drug screening. However, most of the in vitro expression systems rely on relatively high DNA template concentrations to obtain sufficient amounts of proteins, making it harder to perform in vitro screens on gene libraries. Here, we report a technique for the generation of condensed DNA particles that can serve as efficient templates for in vitro gene expression. We apply droplet microfluidics to encapsulate single-DNA molecules in 3-picoliter (pL volume droplets and convert them into 1 μm-sized DNA particles by the multiple displacement amplification reaction driven by phi29 DNA polymerase. In the presence of magnesium ions and inorganic pyrophosphate, the amplified DNA condensed into the crystalline-like particles, making it possible to purify them from the reaction mix by simple centrifugation. Using purified DNA particles, we performed an in vitro transcription-translation reaction and successfully expressed complex enzyme β-galactosidase in droplets and in the 384-well format. The yield of protein obtained from DNA particles was significantly higher than from the corresponding amount of free DNA templates, thus opening new possibilities for high throughput screening applications.

  14. Investigation of molten metal droplet deposition and solidification for 3D printing techniques

    International Nuclear Information System (INIS)

    Wang, Chien-Hsun; Tsai, Ho-Lin; Wu, Yu-Che; Hwang, Weng-Sing

    2016-01-01

    This study investigated the transient transport phenomenon during the pile up of molten lead-free solder via the inkjet printing method. With regard to the droplet impact velocity, the distance from nozzle to substrate can be controlled by using the pulse voltage and distance control apparatus. A high-speed digital camera was used to record the solder impact and examine the accuracy of the pile up. These impact conditions correspond to We  =  2.1–15.1 and Oh  =  5.4  ×  10 −3 –3.8  ×  10 −3 . The effects of impact velocity and relative distance between two types of molten droplets on the shape of the impact mode are examined. The results show that the optimal parameters of the distance from nozzle to substrate and the spreading factor in this experiment are 0.5 mm and 1.33. The diameter, volume and velocity of the inkjet solder droplet are around 37–65 μ m, 25–144 picoliters, and 2.0–3.7 m s −1 , respectively. The vertical and inclined column structures of molten lead-free solder can be fabricated using piezoelectric ink-jet printing systems. The end-shapes of the 3D micro structure have been found to be dependent upon the distance from nozzle to substrate and the impact velocity of the molten lead-free solder droplet. (paper)

  15. Nanocapillaries for Open Tubular Chromatographic Separations of Proteins in Femtoliter to Picoliter Samples

    Science.gov (United States)

    Wang, Xiayan; Cheng, Chang; Wang, Shili; Zhao, Meiping; Dasgupta, Purnendu K.; Liu, Shaorong

    2009-01-01

    We have recently examined the potential of bare nanocapillaries for free solution DNA separations and demonstrated efficiencies exceeding 106 theoretical plates/m. In the present work, we demonstrate the use of bare and hydroxypropylcellulose (HPC) coated open tubular nanocapillaries for protein separations. Using 1.5 μm inner diameter (i.d.) capillary columns, hydrodynamically injecting femto to picoliter (fL-pL) volumes of fluorescent or fluorescent dye labeled protein samples, utilizing a pneumatically pressurized chamber containing 1.0 mM sodium tetraborate solution eluent (typ. 200 psi) as the pump and performing on-column detection using a simple laser-induced fluorescence detector, we demonstrate efficiencies of close to a million theoretical plates/m while generating single digit μL volumes of waste for a complete chromatographic run. We achieve baseline resolution for a protein mixture consisting of transferrin, α-lactalbumin, insulin, and α -2-macroglobulin. PMID:19663450

  16. A new technique for the deposition of standard solutions in total reflection X-ray fluorescence spectrometry (TXRF) using pico-droplets generated by inkjet printers and its applicability for aerosol analysis with SR-TXRF

    International Nuclear Information System (INIS)

    Fittschen, U.E.A.; Hauschild, S.; Amberger, M.A.; Lammel, G.; Streli, C.; Foerster, S.; Wobrauschek, P.; Jokubonis, C.; Pepponi, G.; Falkenberg, G.; Broekaert, J.A.C.

    2006-01-01

    A new technique for the deposition of standard solutions on particulate aerosol samples using pico-droplets for elemental determinations with total reflection X-ray fluorescence spectrometry (TXRF) is described. It enables short analysis times without influencing the sample structure and avoids time consuming scanning of the sample with the exciting beam in SR-TXRF analysis. Droplets of picoliter volume (∼ 5-130 pL) were generated with commercially available and slightly modified inkjet printers operated with popular image processing software. The size of the dried droplets on surfaces of different polarity namely silicone coated and untreated quartz reflectors, was determined for five different printer types and ten different cartridge types. The results show that droplets generated by inkjet printers are between 50 and 200 μm in diameter (corresponding to volumes of 5 to 130 pL) depending on the cartridge type, which is smaller than the width of the synchrotron beam used in the experiments (< 1 mm at an energy of 17 keV at the beamline L at HASYLAB, Hamburg). The precision of the printing of a certain amount of a single element standard solution was found to be comparable to aliquoting with micropipettes in TXRF, where for 2.5 ng of cobalt relative standard deviations of 12% are found. However, it could be shown that the printing of simple patterns is possible, which is important when structured samples have to be analysed

  17. Volume-of-fluid simulations in microfluidic T-junction devices: Influence of viscosity ratio on droplet size

    Science.gov (United States)

    Nekouei, Mehdi; Vanapalli, Siva A.

    2017-03-01

    We used volume-of-fluid (VOF) method to perform three-dimensional numerical simulations of droplet formation of Newtonian fluids in microfluidic T-junction devices. To evaluate the performance of the VOF method we examined the regimes of drop formation and determined droplet size as a function of system parameters. Comparison of the simulation results with four sets of experimental data from the literature showed good agreement, validating the VOF method. Motivated by the lack of adequate studies investigating the influence of viscosity ratio (λ) on the generated droplet size, we mapped the dependence of drop volume on capillary number (0.001 1. In addition, we find that at a given capillary number, the size of droplets does not vary appreciably when λ 1. We develop an analytical model for predicting the droplet size that includes a viscosity-dependent breakup time for the dispersed phase. This improved model successfully predicts the effects of the viscosity ratio observed in simulations. Results from this study are useful for the design of lab-on-chip technologies and manufacture of microfluidic emulsions, where there is a need to know how system parameters influence the droplet size.

  18. A combined volume-of-fluid method and low-Mach-number approach for DNS of evaporating droplets in turbulence

    Science.gov (United States)

    Dodd, Michael; Ferrante, Antonino

    2017-11-01

    Our objective is to perform DNS of finite-size droplets that are evaporating in isotropic turbulence. This requires fully resolving the process of momentum, heat, and mass transfer between the droplets and surrounding gas. We developed a combined volume-of-fluid (VOF) method and low-Mach-number approach to simulate this flow. The two main novelties of the method are: (i) the VOF algorithm captures the motion of the liquid gas interface in the presence of mass transfer due to evaporation and condensation without requiring a projection step for the liquid velocity, and (ii) the low-Mach-number approach allows for local volume changes caused by phase change while the total volume of the liquid-gas system is constant. The method is verified against an analytical solution for a Stefan flow problem, and the D2 law is verified for a single droplet in quiescent gas. We also demonstrate the schemes robustness when performing DNS of an evaporating droplet in forced isotropic turbulence.

  19. Microscale Rockets and Picoliter Containers Engineered from Electrospun Polymeric Microtubes.

    Science.gov (United States)

    Sitt, Amit; Soukupova, Jana; Miller, David; Verdi, David; Zboril, Radek; Hess, Henry; Lahann, Joerg

    2016-03-01

    Chemically functional core/shell microtubes made of biodegradable polymers are fabricated using coaxial electrospinning. The luminal walls are chemically functionalized, allowing for regioselective chemical binding or adsorption inside the microtube. Attaching catalytic nanoparticles or enzymes to the luminal walls converts the microtubes into bubble-propelled microrockets. Upon exposure to ultrasound, the microtubes undergo shape shifting, transforming them into picoliter-scale containers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. On-chip Magnetic Separation and Cell Encapsulation in Droplets

    Science.gov (United States)

    Chen, A.; Byvank, T.; Bharde, A.; Miller, B. L.; Chalmers, J. J.; Sooryakumar, R.; Chang, W.-J.; Bashir, R.

    2012-02-01

    The demand for high-throughput single cell assays is gaining importance because of the heterogeneity of many cell suspensions, even after significant initial sorting. These suspensions may display cell-to-cell variability at the gene expression level that could impact single cell functional genomics, cancer, stem-cell research and drug screening. The on-chip monitoring of individual cells in an isolated environment could prevent cross-contamination, provide high recovery yield and ability to study biological traits at a single cell level These advantages of on-chip biological experiments contrast to conventional methods, which require bulk samples that provide only averaged information on cell metabolism. We report on a device that integrates microfluidic technology with a magnetic tweezers array to combine the functionality of separation and encapsulation of objects such as immunomagnetically labeled cells or magnetic beads into pico-liter droplets on the same chip. The ability to control the separation throughput that is independent of the hydrodynamic droplet generation rate allows the encapsulation efficiency to be optimized. The device can potentially be integrated with on-chip labeling and/or bio-detection to become a powerful single-cell analysis device.

  1. Massively parallel whole genome amplification for single-cell sequencing using droplet microfluidics.

    Science.gov (United States)

    Hosokawa, Masahito; Nishikawa, Yohei; Kogawa, Masato; Takeyama, Haruko

    2017-07-12

    Massively parallel single-cell genome sequencing is required to further understand genetic diversities in complex biological systems. Whole genome amplification (WGA) is the first step for single-cell sequencing, but its throughput and accuracy are insufficient in conventional reaction platforms. Here, we introduce single droplet multiple displacement amplification (sd-MDA), a method that enables massively parallel amplification of single cell genomes while maintaining sequence accuracy and specificity. Tens of thousands of single cells are compartmentalized in millions of picoliter droplets and then subjected to lysis and WGA by passive droplet fusion in microfluidic channels. Because single cells are isolated in compartments, their genomes are amplified to saturation without contamination. This enables the high-throughput acquisition of contamination-free and cell specific sequence reads from single cells (21,000 single-cells/h), resulting in enhancement of the sequence data quality compared to conventional methods. This method allowed WGA of both single bacterial cells and human cancer cells. The obtained sequencing coverage rivals those of conventional techniques with superior sequence quality. In addition, we also demonstrate de novo assembly of uncultured soil bacteria and obtain draft genomes from single cell sequencing. This sd-MDA is promising for flexible and scalable use in single-cell sequencing.

  2. Rapid jetting status inspection and accurate droplet volume measurement for a piezo drop-on-demand inkjet print head using a scanning mirror for display applications

    Science.gov (United States)

    Shin, Dong-Youn; Kim, Minsung

    2017-02-01

    Despite the inherent fabrication simplicity of piezo drop-on-demand inkjet printing, the non-uniform deposition of colourants or electroluminescent organic materials leads to faulty display products, and hence, the importance of rapid jetting status inspection and accurate droplet volume measurement increases from a process perspective. In this work, various jetting status inspections and droplet volume measurement methods are reviewed by discussing their advantages and disadvantages, and then, the opportunities for the developed prototype with a scanning mirror are explored. This work demonstrates that jetting status inspection of 384 fictitious droplets can be performed within 17 s with maximum and minimum measurement accuracies of 0.2 ± 0.5 μ m for the fictitious droplets of 50 μ m in diameter and -1.2 ± 0.3 μ m for the fictitious droplets of 30 μ m in diameter, respectively. In addition to the new design of an inkjet monitoring instrument with a scanning mirror, two novel methods to accurately measure the droplet volume by amplifying a minute droplet volume difference and then converting to other physical properties are suggested and the droplet volume difference of ±0.3% is demonstrated to be discernible using numerical simulations, even with the low measurement accuracy of 1 μ m . When the fact is considered that the conventional vision-based method with a CCD camera requires the optical measurement accuracy less than 25 nm to measure the volume of an in-flight droplet in the nominal diameter of 50 μ m at the same volume measurement accuracy, the suggested method with the developed prototype offers a whole new opportunity to inkjet printing for display applications.

  3. Investigating the evolution of the phase behavior of AOT-based w/o microemulsions in dodecane as a function of droplet volume fraction.

    Science.gov (United States)

    Ganguly, R; Choudhury, N

    2012-04-15

    AOT-based water in oil (w/o) microemulsions are one of the most extensively studied reverse micellar systems because of their rich phase behavior and their ability to form in the absence of any co-surfactant. The aggregation characteristics and interaction of the microemulsion droplets in these systems are known to be governed by AOT-oil compatibility and water to AOT molar ratio (w). In this manuscript by using Dynamic Light Scattering (DLS) and viscometry techniques, we show that droplet volume fraction too plays an important role in shaping the phase behavior of these microemulsions in dodecane. The phase separation characteristics and the evolution of the viscosity and the hydrodynamic radius of the microemulsion droplets on approaching the cloud points have thus been found to undergo complete transformation as one goes from low to high droplet volume fraction even at a fixed 'w'. Modeling of the DLS data attributes this to the weakening of inter droplet attractive interaction caused by the growing dominance of the excluded volume effect with increase in droplet volume fraction. In the literature, the inter droplet attractive interaction driven phase separation in these microemulsions is explained based on gas-liquid type phase transition, conceptualized in the framework of Baxter adhesive hard sphere theory. The modeling of our viscosity data, however, does not support such proposition as the characteristic stickiness parameter (τ(-1)) of the microemulsion droplets in this system remains much lower than the critical value (τ(c)(-1)≈10.25) required to enforce such phase transition. Copyright © 2012 Elsevier Inc. All rights reserved.

  4. Control of the droplet generation by an infrared laser

    Directory of Open Access Journals (Sweden)

    Zhibin Wang

    2018-01-01

    Full Text Available In this work, the control of the droplet generation by a focused infrared (IR laser with a wavelength of 1550 nm was studied, in which the liquid water and the oil with the surfactant of Span 80 were employed as the disperse and continuous phases, respectively. The characteristics of the droplet generation controlled by the laser was explored under various flow rates, laser powers and spot positions and the comparison between the cases with/without the laser was also performed. The results showed that when the laser was focused on the region away from the outlet of the liquid water inflow channel, the droplet shedding was blocked due to the IR laser heating induced thermocapillary flow, leading to the increase of the droplet volume and the cycle time of the droplet generation as compared to the case without the laser. Decreasing the continuous phase flow rate led to the increase of the droplet volume, cycle time of the droplet generation and the volume increase ratio, while increasing the disperse phase flow rate led to the increase of the droplet volume and the decrease of the cycle time and volume increase ratio. For a given flow rate ratio between the continuous and disperse phases, the increase of the flow rates decreased the volume increase ratio. In addition, it is also found that the droplet volume, the cycle time and the volume increase ratio all increased with the laser power. When the laser was focused at the inlet of the downstream channel, the droplet volume, the cycle time and the volume increase ratio were the largest. Moving the laser spot to the downstream or upstream led to the decrease of them. When the laser was focused on the outlet of the liquid water inflow channel, the generated droplet volume and cycle time of the droplet generation were even lower than the case without the laser because of the lowered viscosity. This works provides a comprehensive understanding of the characteristics of the droplet generation controlled

  5. Characterization of surface position in a liquid dispensing orifice

    Energy Technology Data Exchange (ETDEWEB)

    Farahi, R H [ORNL; Passian, Ali [ORNL; Thundat, Thomas George [ORNL; Lereu, Aude L [ORNL; Tetard, Laurene [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL); Jones, Yolanda [ORNL

    2009-01-01

    Precision microdispencing technology delivers picoliter amounts of fluid for printing, electronic, optical, chemical and biomedical applications. In particular, microjetting is capable of accurate, flexible, and non-contact coating with polymers, thus allowing the functionalization of delicate microsensors such as microcantilevers. Information on various phases of droplet formation are important to control volume, uniformity, velocity and rate. One such aspect is the ringing of the meniscus after droplet breakoff which can affect subsequent drop formation. We present analysis of an optical characterization technique and experimental results on the behaviour of menisus oscillations in an orifice of a piezoelectric microjet.

  6. Desalting by crystallization: detection of attomole biomolecules in picoliter buffers by mass spectrometry.

    Science.gov (United States)

    Gong, Xiaoyun; Xiong, Xingchuang; Wang, Song; Li, Yanyan; Zhang, Sichun; Fang, Xiang; Zhang, Xinrong

    2015-10-06

    Sensitive detection of biomolecules in small-volume samples by mass spectrometry is, in many cases, challenging because of the use of buffers to maintain the biological activities of proteins and cells. Here, we report a highly effective desalting method for picoliter samples. It was based on the spontaneous separation of biomolecules from salts during crystallization of the salts. After desalting, the biomolecules were deposited in the tip of the quartz pipet because of the evaporation of the solvent. Subsequent detection of the separated biomolecules was achieved using solvent assisted electric field induced desorption/ionization (SAEFIDI) coupled with mass spectrometry. It allowed for direct desorption/ionization of the biomolecules in situ from the tip of the pipet. The organic component in the assistant solvent inhibited the desorption/ionization of salts, thus assured successful detection of biomolecules. Proteins and peptides down to 50 amol were successfully detected using our method even if there were 3 × 10(5) folds more amount of salts in the sample. The concentration and ion species of the salts had little influence on the detection results.

  7. High throughput miniature drug-screening platform using bioprinting technology

    International Nuclear Information System (INIS)

    Rodríguez-Dévora, Jorge I; Reyna, Daniel; Xu Tao; Zhang Bimeng; Shi Zhidong

    2012-01-01

    In the pharmaceutical industry, new drugs are tested to find appropriate compounds for therapeutic purposes for contemporary diseases. Unfortunately, novel compounds emerge at expensive prices and current target evaluation processes have limited throughput, thus leading to an increase of cost and time for drug development. This work shows the development of the novel inkjet-based deposition method for assembling a miniature drug-screening platform, which can realistically and inexpensively evaluate biochemical reactions in a picoliter-scale volume at a high speed rate. As proof of concept, applying a modified Hewlett Packard model 5360 compact disc printer, green fluorescent protein expressing Escherichia coli cells along with alginate gel solution have been arrayed on a coverslip chip under a repeatable volume of 180% ± 26% picoliters per droplet; subsequently, different antibiotic droplets were patterned on the spots of cells to evaluate the inhibition of bacteria for antibiotic screening. The proposed platform was compared to the current screening process, validating its effectiveness. The viability and basic function of the printed cells were evaluated, resulting in cell viability above 98% and insignificant or no DNA damage to human kidney cells transfected. Based on the reduction of investment and compound volume used by this platform, this technique has the potential to improve the actual drug discovery process at its target evaluation stage. (paper)

  8. Stick-Jump (SJ) Evaporation of Strongly Pinned Nanoliter Volume Sessile Water Droplets on Quick Drying, Micropatterned Surfaces.

    Science.gov (United States)

    Debuisson, Damien; Merlen, Alain; Senez, Vincent; Arscott, Steve

    2016-03-22

    We present an experimental study of stick-jump (SJ) evaporation of strongly pinned nanoliter volume sessile water droplets drying on micropatterned surfaces. The evaporation is studied on surfaces composed of photolithographically micropatterned negative photoresist (SU-8). The micropatterning of the SU-8 enables circular, smooth, trough-like features to be formed which causes a very strong pinning of the three phase (liquid-vapor-solid) contact line of an evaporating droplet. This is ideal for studying SJ evaporation as it contains sequential constant contact radius (CCR) evaporation phases during droplet evaporation. The evaporation was studied in nonconfined conditions, and forced convection was not used. Micropatterned concentric circles were defined having an initial radius of 1000 μm decreasing by a spacing ranging from 500 to 50 μm. The droplet evaporates, successively pinning and depinning from circle to circle. For each pinning radius, the droplet contact angle and volume are observed to decrease quasi-linearly with time. The experimental average evaporation rates were found to decrease with decreasing pining radii. In contrast, the experimental average evaporation flux is found to increase with decreasing droplet radii. The data also demonstrate the influence of the initial contact angle on evaporation rate and flux. The data indicate that the total evaporation time of a droplet depends on the specific micropattern spacing and that the total evaporation time on micropatterned surfaces is always less than on flat, homogeneous surfaces. Although the surface patterning is observed to have little effect on the average droplet flux-indicating that the underlying evaporation physics is not significantly changed by the patterning-the total evaporation time is considerably modified by patterning, up to a factor or almost 2 compared to evaporation on a flat, homogeneous surface. The closely spaced concentric circle pinning maintains a large droplet radius and

  9. Can a droplet break up under flow without elongating? Fragmentation of smectic monodisperse droplets

    Science.gov (United States)

    Courbin, L.; Engl, W.; Panizza, P.

    2004-06-01

    We study the fragmentation under shear flow of smectic monodisperse droplets at high volume fraction. Using small angle light scattering and optical microscopy, we reveal the existence of a break-up mechanism for which the droplets burst into daughter droplets of the same size. Surprisingly, this fragmentation process, which is strain controlled and occurs homogeneously in the cell, does not require any transient elongation of the droplets. Systematic experiments as a function of the initial droplet size and the applied shear rate show that the rupture is triggered by an instability of the inner droplet structure.

  10. Application of Compressible Volume of Fluid Model in Simulating the Impact and Solidification of Hollow Spherical ZrO2 Droplet on a Surface

    Science.gov (United States)

    Safaei, Hadi; Emami, Mohsen Davazdah; Jazi, Hamidreza Salimi; Mostaghimi, Javad

    2017-12-01

    Applications of hollow spherical particles in thermal spraying process have been developed in recent years, accompanied by attempts in the form of experimental and numerical studies to better understand the process of impact of a hollow droplet on a surface. During such process, volume and density of the trapped gas inside droplet change. The numerical models should be able to simulate such changes and their consequent effects. The aim of this study is to numerically simulate the impact of a hollow ZrO2 droplet on a flat surface using the volume of fluid technique for compressible flows. An open-source, finite-volume-based CFD code was used to perform the simulations, where appropriate subprograms were added to handle the studied cases. Simulation results were compared with the available experimental data. Results showed that at high impact velocities ( U 0 > 100 m/s), the compression of trapped gas inside droplet played a significant role in the impact dynamics. In such velocities, the droplet splashed explosively. Compressibility effects result in a more porous splat, compared to the corresponding incompressible model. Moreover, the compressible model predicted a higher spread factor than the incompressible model, due to planetary structure of the splat.

  11. Designing and simulating a nitinol-based micro ejector

    Directory of Open Access Journals (Sweden)

    Yesid Mora Sierra

    2012-01-01

    Full Text Available This paper describes pico-droplet ejector design and simulation. The actuation system was based on two interconnected nitinol membranes’ shape memory effect. Ejected volume was 12pL and it operated at 30°C to 64°C. Ejecting excitation voltage was 12V and the ejecting energy required by actuator operation was 26µJ per drop. These pico-liter ejectors could have applications in making, lubricating and cooling integrated circuits.

  12. Droplet based microfluidics

    International Nuclear Information System (INIS)

    Seemann, Ralf; Brinkmann, Martin; Pfohl, Thomas; Herminghaus, Stephan

    2012-01-01

    Droplet based microfluidics is a rapidly growing interdisciplinary field of research combining soft matter physics, biochemistry and microsystems engineering. Its applications range from fast analytical systems or the synthesis of advanced materials to protein crystallization and biological assays for living cells. Precise control of droplet volumes and reliable manipulation of individual droplets such as coalescence, mixing of their contents, and sorting in combination with fast analysis tools allow us to perform chemical reactions inside the droplets under defined conditions. In this paper, we will review available drop generation and manipulation techniques. The main focus of this review is not to be comprehensive and explain all techniques in great detail but to identify and shed light on similarities and underlying physical principles. Since geometry and wetting properties of the microfluidic channels are crucial factors for droplet generation, we also briefly describe typical device fabrication methods in droplet based microfluidics. Examples of applications and reaction schemes which rely on the discussed manipulation techniques are also presented, such as the fabrication of special materials and biophysical experiments.

  13. Evaporation of nanofluid droplet on heated surface

    Directory of Open Access Journals (Sweden)

    Yeung Chan Kim

    2015-04-01

    Full Text Available In this study, an experiment on the evaporation of nanofluid sessile droplet on a heated surface was conducted. A nanofluid of 0.5% volumetric concentration mixed with 80-nm-sized CuO powder and pure water were used for experiment. Droplet was applied to the heated surface, and images of the evaporation process were obtained. The recorded images were analyzed to find the volume, diameter, and contact angle of the droplet. In addition, the evaporative heat transfer coefficient was calculated from experimental result. The results of this study are summarized as follows: the base diameter of the droplet was maintained stably during the evaporation. The measured temperature of the droplet was increased rapidly for a very short time, then maintained constantly. The nanofluid droplet was evaporated faster than the pure water droplet under the experimental conditions of the same initial volume and temperature, and the average evaporative heat transfer coefficient of the nanofluid droplet was higher than that of pure water. We can consider the effects of the initial contact angle and thermal conductivity of nanofluid as the reason for this experimental result. However, the effect of surface roughness on the evaporative heat transfer of nanofluid droplet appeared unclear.

  14. Evaluation of droplet size distributions using univariate and multivariate approaches

    DEFF Research Database (Denmark)

    Gauno, M.H.; Larsen, C.C.; Vilhelmsen, T.

    2013-01-01

    of the distribution. The current study was aiming to compare univariate and multivariate approach in evaluating droplet size distributions. As a model system, the atomization of a coating solution from a two-fluid nozzle was investigated. The effect of three process parameters (concentration of ethyl cellulose...... in ethanol, atomizing air pressure, and flow rate of coating solution) on the droplet size and droplet size distribution using a full mixed factorial design was used. The droplet size produced by a two-fluid nozzle was measured by laser diffraction and reported as volume based size distribution....... Investigation of loading and score plots from principal component analysis (PCA) revealed additional information on the droplet size distributions and it was possible to identify univariate statistics (volume median droplet size), which were similar, however, originating from varying droplet size distributions...

  15. Electron probe microanalysis for clinical investigations: Microdrop and soft tissue analysis

    International Nuclear Information System (INIS)

    Ingram, M.J.; Ingram, F.D.

    1984-01-01

    The most important advantage offered by electron probe microanalysis (EPA) for clinical investigations is the ability to analyze smaller volumes of tissue than is possible with conventional techniques. The sample can be a biological soft tissue specimen, which involves subcellular localization, or a picoliter fluid droplet. In either case, the analysis can be nondestructive and permit multiple analyses for a number of elements in a given sample. The most highly developed electron microprobe analytical technique is fluid drop analysis, popularly referred to as microdrop analysis. This method provides the investigator with an analytic capability that has an accuracy of measurement often 1% or better on 20 to 30 picoliter fluid droplets. Electron microprobe techniques have been used for studies of animal hard tissue and for studies that involve insoluble inclusions. However, the development of techniques for studies of labile constituents in animal soft tissue has been much slower. It has been necessary not only to develop appropriate methods of tissue preparation, but also to establish sound techniques for tissue collection. Although there are adequate methods for collection of most types of tissue from laboratory animals, many of these methods are not suitable for human subjects. In order to provide the reader with a better understanding of the capabilities and potential for the application of electron microprobe methodology to problems in clinical medicine, the authors discuss some of their experiences with liquid droplet analysis and quantitative electrolyte distribution measurements in animal soft tissue

  16. Prediction of water droplet evaporation on zircaloy surface

    International Nuclear Information System (INIS)

    Lee, Chi Young; In, Wang Kee

    2014-01-01

    In the present experimental study, the prediction of water droplet evaporation on a zircaloy surface was investigated using various initial droplet sizes. To the best of our knowledge, this may be the first valuable effort for understanding the details of water droplet evaporation on a zircaloy surface. The initial contact diameters of the water droplets tested ranged from 1.76 to 3.41 mm. The behavior (i.e., time-dependent droplet volume, contact angle, droplet height, and contact diameter) and mode-transition time of the water droplet evaporation were strongly influenced by the initial droplet size. Using the normalized contact angle (θ*) and contact diameter (d*), the transitions between evaporation modes were successfully expressed by a single curve, and their criteria were proposed. To predict the temporal droplet volume change and evaporation rate, the range of θ* > 0.25 and d* > 0.9, which mostly covered the whole evaporation period and the initial contact diameter remained almost constant during evaporation, was targeted. In this range, the previous contact angle functions for the evaporation model underpredicted the experimental data. A new contact angle function of a zircaloy surface was empirically proposed, which represented the present experimental data within a reasonable degree of accuracy. (author)

  17. Electrostatic field and charge distribution in small charged dielectric droplets

    Science.gov (United States)

    Storozhev, V. B.

    2004-08-01

    The charge distribution in small dielectric droplets is calculated on the basis of continuum medium approximation. There are considered charged liquid spherical droplets of methanol in the range of nanometer sizes. The problem is solved by the following way. We find the free energy of some ion in dielectric droplet, which is a function of distribution of other ions in the droplet. The probability of location of the ion in some element of volume in the droplet is a function of its free energy in this element of volume. The same approach can be applied to other ions in the droplet. The obtained charge distribution differs considerably from the surface distribution. The curve of the charge distribution in the droplet as a function of radius has maximum near the surface. Relative concentration of charges in the vicinity of the center of the droplet does not equal to zero, and it is the higher, the less is the total charge of the droplet. According to the estimates the model is applicable if the droplet radius is larger than 10 nm.

  18. Electrostatic field and charge distribution in small charged dielectric droplets

    International Nuclear Information System (INIS)

    Storozhev, V.B.

    2004-01-01

    The charge distribution in small dielectric droplets is calculated on the basis of continuum medium approximation. There are considered charged liquid spherical droplets of methanol in the range of nanometer sizes. The problem is solved by the following way. We find the free energy of some ion in dielectric droplet, which is a function of distribution of other ions in the droplet. The probability of location of the ion in some element of volume in the droplet is a function of its free energy in this element of volume. The same approach can be applied to other ions in the droplet. The obtained charge distribution differs considerably from the surface distribution. The curve of the charge distribution in the droplet as a function of radius has maximum near the surface. Relative concentration of charges in the vicinity of the center of the droplet does not equal to zero, and it is the higher, the less is the total charge of the droplet. According to the estimates the model is applicable if the droplet radius is larger than 10 nm

  19. Infrared imaging and acoustic sizing of a bubble inside a micro-electro-mechanical system piezo ink channel

    NARCIS (Netherlands)

    van der Bos, J.A.; van der Bos, Arjan; Segers, Tim; Segers, T.J.; Jeurissen, R.J.M.; van den Berg, Marc; Reinten, Hans; Wijshoff, Herman; Wijshoff, H.; Versluis, Michel; Lohse, Detlef

    2011-01-01

    Piezo drop-on-demand inkjet printers are used in an increasing number of applications because of their reliable deposition of droplets onto a substrate. Droplets of a few picoliters are ejected from an inkjet nozzle at frequencies of up to 100 kHz. However, the entrapment of an air microbubble in

  20. Infrared imaging and acoustic sizing of a bubble inside a MEMS piezo ink channel

    NARCIS (Netherlands)

    Bos, van der A.; Segers, T.; Jeurissen, R.J.M.; Berg, van den M.; Reinten, H.; Wijshoff, H.M.A.; Versluis, M.; Lohse, D.

    2011-01-01

    Piezo drop-on-demand inkjet printers are used in an increasing number of applications because of their reliable deposition of droplets onto a substrate. Droplets of a few picoliters are ejected from an inkjet nozzle at frequencies of up to 100 kHz. However, the entrapment of an air microbubble in

  1. Evaporation of inclined water droplets

    Science.gov (United States)

    Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook

    2017-01-01

    When a drop is placed on a flat substrate tilted at an inclined angle, it can be deformed by gravity and its initial contact angle divides into front and rear contact angles by inclination. Here we study on evaporation dynamics of a pure water droplet on a flat solid substrate by controlling substrate inclination and measuring mass and volume changes of an evaporating droplet with time. We find that complete evaporation time of an inclined droplet becomes longer as gravitational influence by inclination becomes stronger. The gravity itself does not change the evaporation dynamics directly, whereas the gravity-induced droplet deformation increases the difference between front and rear angles, which quickens the onset of depinning and consequently reduces the contact radius. This result makes the evaporation rate of an inclined droplet to be slow. This finding would be important to improve understanding on evaporation dynamics of inclined droplets. PMID:28205642

  2. Rheological properties of soybean protein isolate gels containing emulsion droplets

    NARCIS (Netherlands)

    Kim, K.H.; Renkema, J.M.S.; Vliet, van T.

    2001-01-01

    Rheological properties of soybean protein gels containing various volume fractions oil droplets have been studied at small and large deformations. Dynamic viscoelastic properties of soybean protein isolate gels were determined as a function of the volume fraction of oil droplets stabilised by the

  3. Microfluidic droplet generator with controlled break-up mechanism

    KAUST Repository

    Gonzalez, David Conchouso

    2017-04-13

    Droplet generation devices and systems that parallelize droplet generation devices are provided. The droplet generation devices can include a symmetric block-and-break system and a tapered droplet generation zone. The symmetric block-and-break system can include a pair of break channels and a pair of bypass channels symmetrically arranged with respect to the dispersed-phase input channel and the output channel. The droplet generation devices can generate monodisperse droplets with a predefined volume over a range of flow rates, pressures, and fluid properties. The droplet generation devices are therefore capable of parallelization to achieve large-capacity droplet generation, e.g. greater than 1 L/hr, with small overall coefficients of variation.

  4. Air Entrapment and Drop Formation in Piezo Inkjet Printing

    NARCIS (Netherlands)

    van der Bos, J.A.

    2011-01-01

    Piezo drop-on-demand (DOD) inkjet printers are used in an increasing number of applications for their reliable deposition of droplets onto a substrate. Droplets of a few picoliters are ejected from an ink jet nozzle at a frequency of up to 50 kHz. However, entrapment of an air microbubble into the

  5. Direct numerical simulation of droplet-laden isotropic turbulence

    Science.gov (United States)

    Dodd, Michael S.

    Interaction of liquid droplets with turbulence is important in numerous applications ranging from rain formation to oil spills to spray combustion. The physical mechanisms of droplet-turbulence interaction are largely unknown, especially when compared to that of solid particles. Compared to solid particles, droplets can deform, break up, coalesce and have internal fluid circulation. The main goal of this work is to investigate using direct numerical simulation (DNS) the physical mechanisms of droplet-turbulence interaction, both for non-evaporating and evaporating droplets. To achieve this objective, we develop and couple a new pressure-correction method with the volume-of-fluid (VoF) method for simulating incompressible two-fluid flows. The method's main advantage is that the variable coefficient Poisson equation that arises in solving the incompressible Navier-Stokes equations for two-fluid flows is reduced to a constant coefficient equation. This equation can then be solved directly using, e.g., the FFT-based parallel Poisson solver. For a 10243 mesh, our new pressure-correction method using a fast Poisson solver is ten to forty times faster than the standard pressure-correction method using multigrid. Using the coupled pressure-correction and VoF method, we perform direct numerical simulations (DNS) of 3130 finite-size, non-evaporating droplets of diameter approximately equal to the Taylor lengthscale and with 5% droplet volume fraction in decaying isotropic turbulence at initial Taylor-scale Reynolds number Relambda = 83. In the droplet-laden cases, we vary one of the following three parameters: the droplet Weber number based on the r.m.s. velocity of turbulence (0.1 ≤ Werms ≤ 5), the droplet- to carrier-fluid density ratio (1 ≤ rhod/rho c ≤ 100) or the droplet- to carrier-fluid viscosity ratio (1 ≤ mud/muc ≤ 100). We derive the turbulence kinetic energy (TKE) equations for the two-fluid, carrier-fluid and droplet-fluid flow. These equations allow

  6. In-line characterization and identification of micro-droplets on-chip

    Directory of Open Access Journals (Sweden)

    Weber Emanuel

    2014-01-01

    Full Text Available We present an integrated optofluidic sensor system for in-line characterization of micro-droplets. The device provides information about the droplet generation frequency, the droplet volume, and the content of the droplet. Due to its simplicity this principle can easily be implemented with other microfluidic components on one and the same device. The sensor is based on total internal reflection phenomena. Droplets are pushed through a microfluidic channel which is hit by slightly diverging monochromatic light. At the solid-liquid interface parts of the rays experience total internal reflection while another part is transmitted. The ratio of reflected to transmitted light depends on the refractive index of the solution. Both signals are recorded simultaneously and provide a very stable output signal for the droplet characterization. With the proposed system passing droplets were counted up to 320 droplets per second and droplets with different volumes could be discriminated. In a final experiment droplets with different amounts of dissolved CaCl2 were distinguished based on their reflected and transmitted light pattern. This principle can be applied for the detection of any molecules in microdroplets which significantly influence the refractive index of the buffer solution.

  7. Dynamics of magnetic modulation of ferrofluid droplets for digital microfluidic applications

    Energy Technology Data Exchange (ETDEWEB)

    Sen, Uddalok; Chatterjee, Souvick [Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, 60607 (United States); Sen, Swarnendu [Mechanical Engineering Department, Jadavpur University, Kolkata, 700032 India (India); Tiwari, Manish K. [Department of Mechanical Engineering, University College London, London, WC1E 7JE UK (United Kingdom); Mukhopadhyay, Achintya [Mechanical Engineering Department, Jadavpur University, Kolkata, 700032 India (India); Ganguly, Ranjan, E-mail: ranjan@pe.jusl.ac.in [Department of Power Engineering, Jadavpur University, Kolkata, 700098 India (India)

    2017-01-01

    Active control of droplet generation in a microfluidic platform attracts interest for development of digital microfluidic devices ranging from biosensors to micro-reactors to point-of-care diagnostic devices. The present paper characterizes, through an unsteady three-dimensional Volume of Fluid (VOF) simulation, the active control of ferrofluid droplet generation in a microfluidic T-junction in presence of a non-uniform magnetic field created by an external magnetic dipole. Two distinctly different positions of the dipole were considered – one upstream of the junction and one downstream. While keeping the ferrofluid flow rate fixed, a parametric variation of the continuous phase capillary number, dipole strength, and dipole position was carried out. Differences in the flow behaviour in terms of dripping or jetting and the droplet characteristics in terms of droplet formation time period and droplet size were studied. The existence of a threshold dipole strength, below which the magnetic force was not able to influence the flow behaviour, was identified. It was also observed that, for dipoles placed upstream of the junction, droplet formation was suppressed at some higher dipole strengths, and this value was found to increase with increasing capillary number. Droplet time period was also found to increase with increasing dipole strength, along with droplet size, i.e. an increase in droplet volume. - Highlights: • Active control of ferrofluid droplet generation in a microfluidic T-junction is demonstrated. • Unsteady three-dimensional Volume of Fluid (VOF) simulation is adopted. • Capillary number, dipole strength and position influence droplet shedding behaviour. • Magnetic actuation of a microfluidic droplet generator is characterised.

  8. Droplet Growth

    Science.gov (United States)

    Marder, Michael Paolo

    When a mixture of two materials, such as aluminum and tin, or alcohol and water, is cooled below a certain temperature, the two components begin to separate. If one component is dilute in the other, it may separate out in the form of small spheres, and these will begin to enlarge, depleting the supersaturated material around them. If the dynamics is sufficiently slow, thermodynamics gives one considerable information about how the droplets grow. Two types of experiment have explored this behavior and given puzzling results. Nucleation experiments measure the rate at which droplets initially appear from a seemingly homogeneous mixture. Near the critical point in binary liquids, experiments conducted in the 1960's and early 1970's showed that nucleation was vastly slower than theory seemed to predict. The resolution of this problem arises by considering in detail the dynamics of growing droplets and comparing it with what experiments actually measure. Here will be presented a more detailed comparison of theory and experiment than has before been completed, obtaining satisfactory agreement with no free parameters needed. A second type of experiment measures droplet size distributions after long times. In the late stage, droplets compete with each other for material, a few growing at the expense of others. A theory first proposed by Lifshitz and Slyozov claims that this distribution, properly scaled, should be universal, and independent of properties of materials. Yet experimental measurements consistently find distributions that are more broad and squat than the theory would predict. Satisfactory agreement with experiment can be achieved by considering two points. First, one must study the complete time development of droplet size distributions, to understand when the asymptotic regime obtains. Second, droplet size distributions are spread by correlations between droplets. If one finds a small droplet, it is small because large droplets nearby are competing with it

  9. Droplet Translation Actuated by Photoelectrowetting.

    Science.gov (United States)

    Palma, Cesar; Deegan, Robert D

    2018-03-13

    In traditional electrowetting-on-dielectric (EWOD) devices, droplets are moved about a substrate using electric fields produced by an array of discrete electrodes. In this study, we show that a drop can be driven across a substrate with a localized light beam by exploiting the photoelectrowetting (PEW) effect, a light-activated variant of EWOD. Droplet transport actuated by PEW eliminates the need for electrode arrays and the complexities entailed in their fabrication and control, and offers a new approach for designing lab-on-a-chip applications. We report measurements of the maximum droplet speed as a function of frequency and magnitude of the applied bias, intensity of illumination, volume of the droplet, and viscosity and also introduce a model that reproduces these data.

  10. Absorption spectra of localized surface plasmon resonance observed in an inline/picoliter spectrometer cell fabricated by a near ultraviolet femtosecond laser

    Science.gov (United States)

    Shiraishi, Masahiko; Nishiyama, Michiko; Watanabe, Kazuhiro; Kubodera, Shoichi

    2018-03-01

    Absorption spectra based on localized surface plasmon resonance (LSPR) were obtained with an inline/picoliter spectrometer cell. The spectrometer cell was fabricated into an optical glass fiber by focusing a near UV (NUV) femtosecond laser pulses at a wavelength of 400 nm with an energy of 30 μJ. The laser beam was focused from two directions opposite to each other to fabricate a through-hole spectrometer cell. A diameter of the cell was approximately 3 μm, and the length was approximately 62.5 μm, which was nearly equal to the core diameter of the optical fiber. Liquid solution of gold nanoparticles (GNPs) with a diameter of 5-10 nm was injected into the spectrometer cell with its volume of 0.4 pL. The absorption peak centered at 518 nm was observed. An increase of absorption associated with the increase of the number of nanoparticles was in agreement with the numerical calculation based on the Lambert-Beer law.

  11. Evaluation of droplet size distributions using univariate and multivariate approaches.

    Science.gov (United States)

    Gaunø, Mette Høg; Larsen, Crilles Casper; Vilhelmsen, Thomas; Møller-Sonnergaard, Jørn; Wittendorff, Jørgen; Rantanen, Jukka

    2013-01-01

    Pharmaceutically relevant material characteristics are often analyzed based on univariate descriptors instead of utilizing the whole information available in the full distribution. One example is droplet size distribution, which is often described by the median droplet size and the width of the distribution. The current study was aiming to compare univariate and multivariate approach in evaluating droplet size distributions. As a model system, the atomization of a coating solution from a two-fluid nozzle was investigated. The effect of three process parameters (concentration of ethyl cellulose in ethanol, atomizing air pressure, and flow rate of coating solution) on the droplet size and droplet size distribution using a full mixed factorial design was used. The droplet size produced by a two-fluid nozzle was measured by laser diffraction and reported as volume based size distribution. Investigation of loading and score plots from principal component analysis (PCA) revealed additional information on the droplet size distributions and it was possible to identify univariate statistics (volume median droplet size), which were similar, however, originating from varying droplet size distributions. The multivariate data analysis was proven to be an efficient tool for evaluating the full information contained in a distribution.

  12. On-demand liquid-in-liquid droplet metering and fusion utilizing pneumatically actuated membrane valves

    International Nuclear Information System (INIS)

    Lin, Bo-Chih; Su, Yu-Chuan

    2008-01-01

    This paper presents an active emulsification scheme that is capable of producing micro-droplets with desired volumes and compositions on demand. Devices with pneumatically actuated membranes constructed on top of specially designed microfluidic channels are utilized to meter and fuse liquid-in-liquid droplets. By steadily pressurizing a fluid and intermittently blocking its flow, droplets with desired volumes are dispersed into another fluid. Furthermore, droplets from multiple sources are fused together to produce combined droplets with desired compositions. In the prototype demonstration, a three-layer PDMS molding and irreversible bonding process was employed to fabricate the proposed microfluidic devices. For a dispersed-phase flow that is normally blocked by a membrane valve, the relationship between the volume (V) of a metered droplet and the corresponding valve open time (T) is found to be approximately V = kT a , in which k and a are constants determined mainly by the fluid-driving pressures. In addition to the metering device, functional droplet entrapment, fusion and flow-switching devices were also integrated in the system to produce desired combined droplets and deliver them to intended destinations upon request. As such, the demonstrated microfluidic system could potentially realize the controllability on droplet volume, composition and motion, which is desired for a variety of chemical and biological applications

  13. Supersonic laser-induced jetting of aluminum micro-droplets

    International Nuclear Information System (INIS)

    Zenou, M.; Sa'ar, A.; Kotler, Z.

    2015-01-01

    The droplet velocity and the incubation time of pure aluminum micro-droplets, printed using the method of sub-nanosecond laser induced forward transfer, have been measured indicating the formation of supersonic laser-induced jetting. The incubation time and the droplet velocity were extracted by measuring a transient electrical signal associated with droplet landing on the surface of the acceptor substrate. This technique has been exploited for studying small volume droplets, in the range of 10–100 femto-litters for which supersonic velocities were measured. The results suggest elastic propagation of the droplets across the donor-to-acceptor gap, a nonlinear deposition dynamics on the surface of the acceptor and overall efficient energy transfer from the laser beam to the droplets

  14. Supersonic laser-induced jetting of aluminum micro-droplets

    Energy Technology Data Exchange (ETDEWEB)

    Zenou, M. [Racah Institute of Physics and the Harvey M. Kruger Family Center for Nano-science and Nanotechnology, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel); Additive Manufacturing Lab, Orbotech Ltd., P.O. Box 215, 81101 Yavne (Israel); Sa' ar, A. [Racah Institute of Physics and the Harvey M. Kruger Family Center for Nano-science and Nanotechnology, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel); Kotler, Z. [Additive Manufacturing Lab, Orbotech Ltd., P.O. Box 215, 81101 Yavne (Israel)

    2015-05-04

    The droplet velocity and the incubation time of pure aluminum micro-droplets, printed using the method of sub-nanosecond laser induced forward transfer, have been measured indicating the formation of supersonic laser-induced jetting. The incubation time and the droplet velocity were extracted by measuring a transient electrical signal associated with droplet landing on the surface of the acceptor substrate. This technique has been exploited for studying small volume droplets, in the range of 10–100 femto-litters for which supersonic velocities were measured. The results suggest elastic propagation of the droplets across the donor-to-acceptor gap, a nonlinear deposition dynamics on the surface of the acceptor and overall efficient energy transfer from the laser beam to the droplets.

  15. High-throughput controllable generation of droplet arrays with low consumption

    Science.gov (United States)

    Lin, Yinyin; Wu, Zhongsheng; Gao, Yibo; Wu, Jinbo; Wen, Weijia

    2018-06-01

    We describe a controllable sliding method for fabricating millions of isolated femto- to nanoliter-sized droplets with defined volume, geometry and position and a speed of up to 375 kHz. In this work, without using a superhydrophobic or superoleophobic surface, arrays of droplets are instantly formed on the patterned substrate by sliding a strip of liquid, including water, low-surface-tension organic solvents and solution, along the substrate. To precisely control the volume of the droplets, we systemically investigate the effects of the size of the wettable pattern, the viscosity of the liquid and sliding speed, which were found to vary independently to tune the height and volume of the droplets. Through this method, we successfully fabricated an oriented single metal-organic framework crystal array with control over their XY positioning on the surface, as characterized by microscopy and X-ray diffraction (XRD) techniques.

  16. Magnetophoretic velocimetry of manganese(II) in a single microdroplet in a flow system under a high gradient magnetic field generated with a superconducting magnet.

    Science.gov (United States)

    Suwa, Masayori; Watarai, Hitoshi

    2002-10-01

    An experimental system for magnetophoretic velocimetry, which could determine the volume magnetic susceptibility of a single particle dispersed in a liquid phase from a magnetophoretic velocity, has been developed. A micrometer-sized high-gradient magnetic field could be generated in a capillary by a pair of iron pole pieces in a superconducting magnet (10 T). The magnetophoretic behavior of a single particle in a capillary flow system was investigated under the inhomogeneous magnetic field. From the magnetophoretic velocity of a polystyrene latex particle dispersed in a MnCl2 aqueous solution, the product of the magnetic flux density and the gradient, B(dB/dx), was determined as a function of the position along the capillary. The maximum value of B(dB/dx) was 4.7 x 10(4) T2 m(-1), which was approximately 100 times higher than that obtained by two Nd-Fe-B permanent magnets (0.4 T). Organic droplets extracting manganese(II) with 2-thenoyltrifluoroacetone and tri-n-octylphosphine oxide from MnCl2 solution were used as test samples. The difference of the volume magnetic susceptibility between the droplet and the medium could be determined from the magnetophoretic velocity. This method allowed us to continuously measure a volume magnetic susceptibility of 10-6 level for a picoliter droplet and to determine manganese(II) in the single droplet at the attomole level.

  17. Transient heating and evaporation of moving mono-component liquid fuel droplets

    DEFF Research Database (Denmark)

    Yin, Chungen

    2016-01-01

    of which the flow and energy transport equations are numerically solved using the finite volume method. The computer code for the model is developed in a generic 3D framework and verified in different ways (e.g., by comparison against analytical solutions for simplified cases, and against experimental......This paper presents a complete description of a model for transient heating and evaporation of moving mono-component liquid fuel droplets. The model mainly consists of gas phase heat and mass transfer analysis, liquid phase analysis, and droplet dynamics analysis, which address the interaction...... between the moving droplets and free-stream flow, the flow and heat and mass transfer within the droplets, and the droplet dynamics and size, respectively. For the liquid phase analysis, the droplets are discretized into a number of control volumes along the radial, polar and azimuthal directions, on each...

  18. The precise and accurate production of millimetric water droplets using a superhydrophobic generating apparatus

    Science.gov (United States)

    Wood, Michael J.; Aristizabal, Felipe; Coady, Matthew; Nielson, Kent; Ragogna, Paul J.; Kietzig, Anne-Marie

    2018-02-01

    The production of millimetric liquid droplets has importance in a wide range of applications both in the laboratory and industrially. As such, much effort has been put forth to devise methods to generate these droplets on command in a manner which results in high diameter accuracy and precision, well-defined trajectories followed by successive droplets and low oscillations in droplet shape throughout their descents. None of the currently employed methods of millimetric droplet generation described in the literature adequately addresses all of these desired droplet characteristics. The reported methods invariably involve the cohesive separation of the desired volume of liquid from the bulk supply in the same step that separates the single droplet from the solid generator. We have devised a droplet generation device which separates the desired volume of liquid within a tee-apparatus in a step prior to the generation of the droplet which has yielded both high accuracy and precision of the diameters of the final droplets produced. Further, we have engineered a generating tip with extreme antiwetting properties which has resulted in reduced adhesion forces between the liquid droplet and the solid tip. This has yielded the ability to produce droplets of low mass without necessitating different diameter generating tips or the addition of surfactants to the liquid, well-defined droplet trajectories, and low oscillations in droplet volume. The trajectories and oscillations of the droplets produced have been assessed and presented quantitatively in a manner that has been lacking in the current literature.

  19. Electrostatic charging and control of droplets in microfluidic devices.

    Science.gov (United States)

    Zhou, Hongbo; Yao, Shuhuai

    2013-03-07

    Precharged droplets can facilitate manipulation and control of low-volume liquids in droplet-based microfluidics. In this paper, we demonstrate non-contact electrostatic charging of droplets by polarizing a neutral droplet and splitting it into two oppositely charged daughter droplets in a T-junction microchannel. We performed numerical simulation to analyze the non-contact charging process and proposed a new design with a notch at the T-junction in aid of droplet splitting for more efficient charging. We experimentally characterized the induced charge in droplets in microfabricated devices. The experimental results agreed well with the simulation. Finally, we demonstrated highly effective droplet manipulation in a path selection unit appending to the droplet charging. We expect our work could enable precision manipulation of droplets for more complex liquid handling in microfluidics and promote electric-force based manipulation in 'lab-on-a-chip' systems.

  20. Addressable droplet microarrays for single cell protein analysis.

    Science.gov (United States)

    Salehi-Reyhani, Ali; Burgin, Edward; Ces, Oscar; Willison, Keith R; Klug, David R

    2014-11-07

    Addressable droplet microarrays are potentially attractive as a way to achieve miniaturised, reduced volume, high sensitivity analyses without the need to fabricate microfluidic devices or small volume chambers. We report a practical method for producing oil-encapsulated addressable droplet microarrays which can be used for such analyses. To demonstrate their utility, we undertake a series of single cell analyses, to determine the variation in copy number of p53 proteins in cells of a human cancer cell line.

  1. Mathematical model for self-propelled droplets driven by interfacial tension

    Energy Technology Data Exchange (ETDEWEB)

    Nagai, Ken H. [School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292 (Japan); Tachibana, Kunihito; Tobe, Yuta; Kazama, Masaki [Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa 920-1192 (Japan); Kitahata, Hiroyuki [Department of Physics, Graduate School of Science, Chiba University, Chiba 263-8522 (Japan); Omata, Seiro [Faculty of Mathematics and Physics, Kanazawa University, Kanazawa, Ishikawa 920-1192 (Japan); Nagayama, Masaharu, E-mail: nagayama@es.hokudai.ac.jp [Research Institute for Electronic Science, Hokkaido University, Hokkaido 060-0812 (Japan); CREST, Japan Science and Technology Agency, Tokyo 102-0076 (Japan)

    2016-03-21

    We propose a model for the spontaneous motion of a droplet induced by inhomogeneity in interfacial tension. The model is derived from a variation of the Lagrangian of the system and we use a time-discretized Morse flow scheme to perform its numerical simulations. Our model can naturally simulate the dynamics of a single droplet, as well as that of multiple droplets, where the volume of each droplet is conserved. We reproduced the ballistic motion and fission of a droplet, and the collision of two droplets was also examined numerically.

  2. Application of rainbow refractometry for measurement of droplets with solid inclusions

    Science.gov (United States)

    Li, Can; Wu, Xue-cheng; Cao, Jian-zheng; Chen, Ling-hong; Gréhan, Gerard; Cen, Ke-fa

    2018-01-01

    Characterization of droplets with solid inclusions is of great research interest and has wide industrial applications. Reported here is a theoretical and experimental investigation of the measurement of droplets with solid inclusions using rainbow refractometry. A rainbow extinction model of a droplet with solid inclusions was deduced based on Beer-Lambert's Law. It takes into account the volume concentration, relative size, scattering efficiency of the solid inclusion, and liquid refractive index. An acoustic levitation system for a single droplet and a global rainbow instrumentation system for spray were integrated to study the effect of the H2O-CaCO3 suspension droplets on the rainbow signal and the measured parameters. The results showed that the rainbow encountered unusual disturbances, introduced by the solid inclusions, but its overall structure was not destroyed. Discoveries also included that for volume concentrations of 2.5% or less the CaCO3 particles with diameters below 4 μm had little effect on the measured parameters of the host droplet. The extinction characteristic was also analyzed. The rainbow extinction model failed to quantity the volume concentration of CaCO3, but succeeded in its qualitative analysis.

  3. Numerical study of impact and solidification of a droplet over a deposited frozen splat

    International Nuclear Information System (INIS)

    Ghafouri-Azar, R.; Mostaghimi, J.; Chandra, S.

    2002-01-01

    The impact and solidification of a molten tin droplet on another solidified splat was studied for varying offset spacing using a three-dimensional model of droplet impact. It was found the final shapes of impinging droplets were sensitive to the offset distance. The model applies a fixed-grid Eulerian control volume method to solve the fluid dynamics and heat transfer in the droplet. The model employs a Volume of Fluid (VOF) algorithm to track free surface deformation. Predictions of droplet shapes during impact from the model agreed well with experimental photographs. (author)

  4. Some Physics Inside Drying Droplets

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 19; Issue 2. Some Physics Inside Drying Droplets. Dileep Mampallil. General Article Volume 19 Issue 2 February 2014 pp 123-134. Fulltext. Click here to view fulltext PDF. Permanent link: https://www.ias.ac.in/article/fulltext/reso/019/02/0123-0134 ...

  5. Accurate, consistent, and fast droplet splitting and dispensing in electrowetting on dielectric digital microfluidics

    Science.gov (United States)

    Nikapitiya, N. Y. Jagath B.; Nahar, Mun Mun; Moon, Hyejin

    2017-12-01

    This letter reports two novel electrode design considerations to satisfy two very important aspects of EWOD operation—(1) Highly consistent volume of generated droplets and (2) Highly improved accuracy in the generated droplet volume. Considering the design principles investigated two novel designs were proposed; L-junction electrode design to offer high throughput droplet generation and Y-junction electrode design to split a droplet very fast while maintaining equal volume of each part. Devices of novel designs were fabricated and tested, and the results are compared with those of conventional approach. It is demonstrated that inaccuracy and inconsistency of droplet volume dispensed in the device with novel electrode designs are as low as 0.17 and 0.10%, respectively, while those of conventional approach are 25 and 0.76%, respectively. The dispensing frequency is enhanced from 4 to 9 Hz by using the novel design.

  6. Methanol Droplet Combustion in Oxygen-Inert Environments in Microgravity

    Science.gov (United States)

    Nayagam, Vedha; Dietrich, Daniel L.; Hicks, Michael C.; Williams, Forman A.

    2013-01-01

    The Flame Extinguishment (FLEX) experiment that is currently underway in the Combustion Integrated Rack facility onboard the International Space Station is aimed at understanding the effects of inert diluents on the flammability of condensed phase fuels. To this end, droplets of various fuels, including alkanes and alcohols, are burned in a quiescent microgravity environment with varying amounts of oxygen and inert diluents to determine the limiting oxygen index (LOI) for these fuels. In this study we report experimental observations of methanol droplets burning in oxygen-nitrogen-carbon dioxide and oxygen-nitrogen-helium gas mixtures at 0.7 and 1 atmospheric pressures. The initial droplet size varied between approximately 1.5 mm and 4 mm to capture both diffusive extinction brought about by insufficient residence time at the flame and radiative extinction caused by excessive heat loss from the flame zone. The ambient oxygen concentration varied from a high value of 30% by volume to as low as 12%, approaching the limiting oxygen index for the fuel. The inert dilution by carbon dioxide and helium varied over a range of 0% to 70% by volume. In these experiments, both freely floated and tethered droplets were ignited using symmetrically opposed hot-wire igniters and the burning histories were recorded onboard using digital cameras, downlinked later to the ground for analysis. The digital images yielded droplet and flame diameters as functions of time and subsequently droplet burning rate, flame standoff ratio, and initial and extinction droplet diameters. Simplified theoretical models correlate the measured burning rate constant and the flame standoff ratio reasonably well. An activation energy asymptotic theory accounting for time-dependent water dissolution or evaporation from the droplet is shown to predict the measured diffusive extinction conditions well. The experiments also show that the limiting oxygen index for methanol in these diluent gases is around 12% to

  7. Experimental test of liquid droplet radiator performance

    International Nuclear Information System (INIS)

    Mattick, A.T.; Simon, M.A.

    1986-01-01

    This liquid droplet radiator (LDR) is evolving rapidly as a lightweight system for heat rejection in space power systems. By using recirculating free streams of submillimeter droplets to radiate waste energy directly to space, the LDR can potentially be an order of magnitude lighter than conventional radiator systems which radiate from solid surfaces. The LDR is also less vulnerable to micrometeoroid damage than are conventional radiators, and it has a low transport volume. Three major development issues of this new heat rejection system are the ability to direct the droplet streams with sufficient precision to avoid fluid loss, radiative performance of the array of droplet streams which comprise the radiating elements of the LDR, and the efficacy of the droplet stream collector, again with respect to fluid loss. This paper reports experimental results bearing on the first two issues - droplet aiming in a multikilowatt-sized system, and radiated power from a large droplet array. Parallel efforts on droplet collection and LDR system design are being pursued by several research groups

  8. A Dewetting Model for Double-Emulsion Droplets

    Directory of Open Access Journals (Sweden)

    Zhanxiao Kang

    2016-11-01

    Full Text Available The evolution of double-emulsion droplets is of great importance for the application of microdroplets and microparticles. We study the driving force of the dewetting process, the equilibrium configuration and the dewetting time of double-emulsion droplets. Through energy analysis, we find that the equilibrium configuration of a partial engulfed droplet depends on a dimensionless interfacial tension determined by the three relevant interfacial tensions, and the engulfing part of the inner phase becomes larger as the volume of the outer phase increases. By introducing a dewetting boundary, the dewetting time can be calculated by balancing the driving force, caused by interfacial tensions, and the viscous force. Without considering the momentum change of the continuous phase, the dewetting time is an increasing function against the viscosity of the outer phase and the volume ratio between the outer phase and inner phase.

  9. Dynamics of magnetic modulation of ferrofluid droplets for digital microfluidic applications

    Science.gov (United States)

    Sen, Uddalok; Chatterjee, Souvick; Sen, Swarnendu; Tiwari, Manish K.; Mukhopadhyay, Achintya; Ganguly, Ranjan

    2017-01-01

    Active control of droplet generation in a microfluidic platform attracts interest for development of digital microfluidic devices ranging from biosensors to micro-reactors to point-of-care diagnostic devices. The present paper characterizes, through an unsteady three-dimensional Volume of Fluid (VOF) simulation, the active control of ferrofluid droplet generation in a microfluidic T-junction in presence of a non-uniform magnetic field created by an external magnetic dipole. Two distinctly different positions of the dipole were considered - one upstream of the junction and one downstream. While keeping the ferrofluid flow rate fixed, a parametric variation of the continuous phase capillary number, dipole strength, and dipole position was carried out. Differences in the flow behaviour in terms of dripping or jetting and the droplet characteristics in terms of droplet formation time period and droplet size were studied. The existence of a threshold dipole strength, below which the magnetic force was not able to influence the flow behaviour, was identified. It was also observed that, for dipoles placed upstream of the junction, droplet formation was suppressed at some higher dipole strengths, and this value was found to increase with increasing capillary number. Droplet time period was also found to increase with increasing dipole strength, along with droplet size, i.e. an increase in droplet volume.

  10. Sensitive and predictable separation of microfluidic droplets by size using in-line passive filter.

    Science.gov (United States)

    Ding, Ruihua; Ung, W Lloyd; Heyman, John A; Weitz, David A

    2017-01-01

    Active manipulation of droplets is crucial in droplet microfluidics. However, droplet polydispersity decreases the accuracy of active manipulation. We develop a microfluidic "droplet filter" that accurately separates droplets by size. The droplet filter has a sharp size cutoff and is capable of distinguishing droplets differing in volume by 20%. A simple model explains the behavior of the droplets as they pass through the filter. We show application of the filter in improving dielectric sorting efficiency.

  11. All-electronic droplet generation on-chip with real-time feedback control for EWOD digital microfluidics.

    Science.gov (United States)

    Gong, Jian; Kim, Chang-Jin C J

    2008-06-01

    Electrowetting-on-dielectric (EWOD) actuation enables digital (or droplet) microfluidics where small packets of liquids are manipulated on a two-dimensional surface. Due to its mechanical simplicity and low energy consumption, EWOD holds particular promise for portable systems. To improve volume precision of the droplets, which is desired for quantitative applications such as biochemical assays, existing practices would require near-perfect device fabrication and operation conditions unless the droplets are generated under feedback control by an extra pump setup off of the chip. In this paper, we develop an all-electronic (i.e., no ancillary pumping) real-time feedback control of on-chip droplet generation. A fast voltage modulation, capacitance sensing, and discrete-time PID feedback controller are integrated on the operating electronic board. A significant improvement is obtained in the droplet volume uniformity, compared with an open loop control as well as the previous feedback control employing an external pump. Furthermore, this new capability empowers users to prescribe the droplet volume even below the previously considered minimum, allowing, for example, 1 : x (x < 1) mixing, in comparison to the previously considered n : m mixing (i.e., n and m unit droplets).

  12. ALL-ELECTRONIC DROPLET GENERATION ON-CHIP WITH REAL-TIME FEEDBACK CONTROL FOR EWOD DIGITIAL MICROFLUIDICS

    Science.gov (United States)

    Gong, Jian; Kim, Chang-Jin “CJ”

    2009-01-01

    Electrowetting-on-dielectric (EWOD) actuation enables digital (or droplet) microfluidics where small packets of liquids are manipulated on a two-dimensional surface. Due to its mechanical simplicity and low energy consumption, EWOD holds particular promise for portable systems. To improve volume precision of the droplets, which is desired for quantitative applications such as biochemical assays, existing practices would require near-perfect device fabricaion and operation conditions unless the droplets are generated under feedback control by an extra pump setup off of the chip. In this paper, we develop an all-electronic (i.e., no ancillary pumping) real-time feedback control of on-chip droplet generation. A fast voltage modulation, capacitance sensing, and discrete-time PID feedback controller are integrated on the operating electronic board. A significant improvement is obtained in the droplet volume uniformity, compared with an open loop control as well as the previous feedback control employing an external pump. Furthermore, this new capability empowers users to prescribe the droplet volume even below the previously considered minimum, allowing, for example, 1:x (x < 1) mixing, in comparison to the previously considered n:m mixing (i.e., n and m unit droplets). PMID:18497909

  13. Multiple and high-throughput droplet reactions via combination of microsampling technique and microfluidic chip

    KAUST Repository

    Wu, Jinbo

    2012-11-20

    Microdroplets offer unique compartments for accommodating a large number of chemical and biological reactions in tiny volume with precise control. A major concern in droplet-based microfluidics is the difficulty to address droplets individually and achieve high throughput at the same time. Here, we have combined an improved cartridge sampling technique with a microfluidic chip to perform droplet screenings and aggressive reaction with minimal (nanoliter-scale) reagent consumption. The droplet composition, distance, volume (nanoliter to subnanoliter scale), number, and sequence could be precisely and digitally programmed through the improved sampling technique, while sample evaporation and cross-contamination are effectively eliminated. Our combined device provides a simple model to utilize multiple droplets for various reactions with low reagent consumption and high throughput. © 2012 American Chemical Society.

  14. Modeling Evaporation and Particle Assembly in Colloidal Droplets.

    Science.gov (United States)

    Zhao, Mingfei; Yong, Xin

    2017-06-13

    Evaporation-induced assembly of nanoparticles in a drying droplet is of great importance in many engineering applications, including printing, coating, and thin film processing. The investigation of particle dynamics in evaporating droplets can provide fundamental hydrodynamic insight for revealing the processing-structure relationship in the particle self-organization induced by solvent evaporation. We develop a free-energy-based multiphase lattice Boltzmann method coupled with Brownian dynamics to simulate evaporating colloidal droplets on solid substrates with specified wetting properties. The influence of interface-bound nanoparticles on the surface tension and evaporation of a flat liquid-vapor interface is first quantified. The results indicate that the particles at the interface reduce surface tension and enhance evaporation flux. For evaporating particle-covered droplets on substrates with different wetting properties, we characterize the increase of evaporate rate via measuring droplet volume. We find that droplet evaporation is determined by the number density and circumferential distribution of interfacial particles. We further correlate particle dynamics and assembly to the evaporation-induced convection in the bulk and on the surface of droplet. Finally, we observe distinct final deposits from evaporating colloidal droplets with bulk-dispersed and interface-bound particles. In addition, the deposit pattern is also influenced by the equilibrium contact angle of droplet.

  15. Three-axis acoustic device for levitation of droplets in an open gas stream and its application to examine sulfur dioxide absorption by water droplets.

    Science.gov (United States)

    Stephens, Terrance L; Budwig, Ralph S

    2007-01-01

    Two acoustic devices to stabilize a droplet in an open gas stream (single-axis and three-axis levitators) have been designed and tested. The gas stream was provided by a jet apparatus with a 64 mm exit diameter and a uniform velocity profile. The acoustic source used was a Langevin vibrator with a concave reflector. The single-axis levitator relied primarily on the radial force from the acoustic field and was shown to be limited because of significant droplet wandering. The three-axis levitator relied on a combination of the axial and radial forces. The three-axis levitator was applied to examine droplet deformation and circulation and to investigate the uptake of SO(2) from the gas stream to the droplet. Droplets ranging in diameters from 2 to 5 mm were levitated in gas streams with velocities up to 9 ms. Droplet wandering was on the order of a half droplet diameter for a 3 mm diameter droplet. Droplet circulation ranged from the predicted Hadamard-Rybczynski pattern to a rotating droplet pattern. Droplet pH over a central volume of the droplet was measured by planar laser induced fluorescence. The results for the decay of droplet pH versus time are in general agreement with published theory and experiments.

  16. The influence of material hardness on liquid droplet impingement erosion

    International Nuclear Information System (INIS)

    Fujisawa, Nobuyuki; Yamagata, Takayuki; Takano, Shotaro; Saito, Kengo; Morita, Ryo; Fujiwara, Kazutoshi; Inada, Fumio

    2015-01-01

    Highlights: • Liquid droplet impingement erosion is studied for various metal materials. • Average power dependency on droplet velocity is found as 7. • Power dependency on Vickers hardness is found as −4.5. • An empirical formula is constructed for erosion rates of metal materials. • Predicted erosion rate is well correlated with experiment within a factor of 1.5. - Abstract: This paper describes the experimental study on the liquid droplet impingement erosion of metal materials to understand the influence of material hardness on the erosion rate. The experiment is carried out using a water spray jet apparatus with a condition of relatively thin liquid film thickness. The metal materials tested are pure aluminum, aluminum alloy, brass, mild steel, carbon steel and stainless steel. The liquid droplets considered are 30 ± 5 μm in volume average diameter of water, which is the same order of droplet diameter in the actual pipeline in nuclear/fossil power plants. In order to understand the influence of material hardness on the liquid droplet impingement erosion, the scanning electron microscope (SEM) observation on the eroded surface and the measurement of erosion rate are carried out in the terminal stage of erosion. The experimental results indicate that the erosion rates are expressed by the droplet velocity, volume flux, Vickers hardness and the liquid film thickness, which are fundamentals of the liquid droplet impingement erosion. The empirical formula shows that the power index for droplet velocity dependency is found to be 7 with a scattering from 5 to 9 depending on the materials, while the power index for Vickers hardness dependency is found as −4.5

  17. The influence of material hardness on liquid droplet impingement erosion

    Energy Technology Data Exchange (ETDEWEB)

    Fujisawa, Nobuyuki, E-mail: fujisawa@eng.niigata-u.ac.jp [Visualization Research Center, Niigata University, 8050, Ikarashi 2-Nocho, Nishi-ku, Niigata 950-2181 (Japan); Yamagata, Takayuki, E-mail: yamagata@eng.niigata-u.ac.jp [Visualization Research Center, Niigata University, 8050, Ikarashi 2-Nocho, Nishi-ku, Niigata 950-2181 (Japan); Takano, Shotaro; Saito, Kengo [Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-Nocho, Nishi-ku, Niigata 950-2181 (Japan); Morita, Ryo; Fujiwara, Kazutoshi; Inada, Fumio [Central Research Institute of Electric Power Industry, 2-11-1, Iwatokita, Komae, Tokyo 201-8511 (Japan)

    2015-07-15

    Highlights: • Liquid droplet impingement erosion is studied for various metal materials. • Average power dependency on droplet velocity is found as 7. • Power dependency on Vickers hardness is found as −4.5. • An empirical formula is constructed for erosion rates of metal materials. • Predicted erosion rate is well correlated with experiment within a factor of 1.5. - Abstract: This paper describes the experimental study on the liquid droplet impingement erosion of metal materials to understand the influence of material hardness on the erosion rate. The experiment is carried out using a water spray jet apparatus with a condition of relatively thin liquid film thickness. The metal materials tested are pure aluminum, aluminum alloy, brass, mild steel, carbon steel and stainless steel. The liquid droplets considered are 30 ± 5 μm in volume average diameter of water, which is the same order of droplet diameter in the actual pipeline in nuclear/fossil power plants. In order to understand the influence of material hardness on the liquid droplet impingement erosion, the scanning electron microscope (SEM) observation on the eroded surface and the measurement of erosion rate are carried out in the terminal stage of erosion. The experimental results indicate that the erosion rates are expressed by the droplet velocity, volume flux, Vickers hardness and the liquid film thickness, which are fundamentals of the liquid droplet impingement erosion. The empirical formula shows that the power index for droplet velocity dependency is found to be 7 with a scattering from 5 to 9 depending on the materials, while the power index for Vickers hardness dependency is found as −4.5.

  18. Shear-driven redistribution of surfactant affects enzyme activity in well-mixed femtoliter droplets.

    Science.gov (United States)

    Liu, Yu; Jung, Seung-Yong; Collier, C Patrick

    2009-06-15

    We developed a microfluidic platform for splitting well-mixed, femtoliter-volume droplets from larger water-in-oil plugs, where the sizes of the daughter droplets were not limited by channel width. These droplets were separated from mother plugs at a microfabricated T-junction, which enabled the study of how increased confinement affected enzyme kinetics in droplets 4-10 microm in diameter. Initial rates for enzyme catalysis in the mother plugs and the largest daughter drops were close to the average bulk rate, while the rates in smaller droplets decreased linearly with increasing surface to volume ratio. Rates in the smallest droplets decreased by a factor of 4 compared to the bulk rate. Traditional methods for detecting nonspecific adsorption at the water-oil interface were unable to detect evidence of enzyme adsorption, including pendant drop tensiometry, laser scanning confocal microscopy of drops containing labeled proteins in microemulsions, and epifluorescence microscopy of plugs and drops generated on-chip. We propose the slowing of enzyme reaction kinetics in the smaller droplets was the result of increased adsorption and inactivation of enzymes at the water-oil interface arising from transient interfacial shear stresses imparted on the daughter droplets as they split from the mother plugs and passed through the constricted opening of the T-junction. Such stresses are known to modulate the interfacial area and density of surfactant molecules that can passivate the interface. Bright field images of the splitting processes at the junction indicate that these stresses scaled with increasing surface to volume ratios of the droplets but were relatively insensitive to the average flow rate of plugs upstream of the junction.

  19. Numerical Study for a Large Volume Droplet on the Dual-rough Surface: Apparent Contact Angle, Contact Angle Hysteresis and Transition Barrier.

    Science.gov (United States)

    Dong, Jian; Jin, Yanli; Dong, He; Liu, Jiawei; Ye, Senbin

    2018-06-14

    The profile, apparent contact angle (ACA), contact angle hysteresis (CAH) and wetting state transmission energy barrier (WSTEB) are important static and dynamic properties of a large volume droplet on the hierarchical surface. Understanding them can provide us with important insights to functional surfaces and promote the application in corresponding areas. In this paper, we established three theoretical models (Model 1, Model 2 and Model 3) and corresponding numerical methods, which were obtained by the free energy minimization and the nonlinear optimization algorithm, to predict the profile, ACA, CAH and WSTEB of a large volume droplet on the horizontal regular dual-rough surface. In consideration of the gravity, the energy barrier on the contact circle, the dual heterogenous structures and their roughness on the surface, the models are more universal and accurate than previous models. It showed that the predictions of the models were in good agreement with the results from the experiment or literature. The models are promising to become novel design approaches of functional surfaces, which are frequently applied in microfluidic chips, water self-catchment system and dropwise condensation heat transfer system.

  20. Simple and reusable picoinjector for liquid delivery via nanofluidics approach

    KAUST Repository

    Li, Shunbo; Cao, Wenbin; Hui, Yu Sanna; Wen, Weijia

    2014-01-01

    Precise control of sample volume is one of the most important functions in lab-on-a-chip (LOC) systems, especially for chemical and biological reactions. The common approach used for liquid delivery involves the employment of capillaries and microstructures for generating a droplet which has a volume in the nanoliter or picoliter range. Here, we report a novel approach for constructing a picoinjector which is based on well-controlled electroosmotic (EO) flow to electrokinetically drive sample solutions. This picoinjector comprises an array of interconnected nanochannels for liquid delivery. Such technique for liquid delivery has the advantages of well-controlled sample volume and reusable nanofluidic chip, and it was reported for the first time. In the study of the pumping process for this picoinjector, the EO flow rate was determined by the intensity of the fluorescent probe. The influence of ion concentration in electrolyte solutions over the EO flow rate was also investigated and discussed. The application of this EO-driven picoinjector for chemical reactions was demonstrated by the reaction between Fluo-4 and calcium chloride with the reaction cycle controlled by the applied square waves of different duty cycles. The precision of our device can reach down to picoliter per second, which is much smaller than that of most existing technologies. This new approach, thus, opens further possibilities of adopting nanofluidics for well-controlled chemical reactions with particular applications in nanoparticle synthesis, bimolecular synthesis, drug delivery, and diagnostic testing.

  1. Simple and reusable picoinjector for liquid delivery via nanofluidics approach

    KAUST Repository

    Li, Shunbo

    2014-03-25

    Precise control of sample volume is one of the most important functions in lab-on-a-chip (LOC) systems, especially for chemical and biological reactions. The common approach used for liquid delivery involves the employment of capillaries and microstructures for generating a droplet which has a volume in the nanoliter or picoliter range. Here, we report a novel approach for constructing a picoinjector which is based on well-controlled electroosmotic (EO) flow to electrokinetically drive sample solutions. This picoinjector comprises an array of interconnected nanochannels for liquid delivery. Such technique for liquid delivery has the advantages of well-controlled sample volume and reusable nanofluidic chip, and it was reported for the first time. In the study of the pumping process for this picoinjector, the EO flow rate was determined by the intensity of the fluorescent probe. The influence of ion concentration in electrolyte solutions over the EO flow rate was also investigated and discussed. The application of this EO-driven picoinjector for chemical reactions was demonstrated by the reaction between Fluo-4 and calcium chloride with the reaction cycle controlled by the applied square waves of different duty cycles. The precision of our device can reach down to picoliter per second, which is much smaller than that of most existing technologies. This new approach, thus, opens further possibilities of adopting nanofluidics for well-controlled chemical reactions with particular applications in nanoparticle synthesis, bimolecular synthesis, drug delivery, and diagnostic testing.

  2. Numerical Investigations on Electric Field Characteristics with Respect to Capacitive Detection of Free-Flying Droplets

    Directory of Open Access Journals (Sweden)

    Peter Koltay

    2012-08-01

    Full Text Available In this paper a multi-disciplinary simulation of a capacitive droplet sensor based on an open plate capacitor as transducing element is presented. The numerical simulations are based on the finite volume method (FVM, including calculations of an electric field which changes according to the presence of a liquid droplet. The volume of fluid (VOF method is applied for the simulation of the ejection process of a liquid droplet out of a dispenser nozzle. The simulations were realised using the computational fluid dynamic (CFD software CFD ACE+. The investigated capacitive sensing principle enables to determine the volume of a micro droplet passing the sensor capacitor due to the induced change in capacity. It could be found that single droplets in the considered volume range of 5 nL < Vdrop < 100 nL lead to a linear change of the capacity up to ΔQ < 30 fC. The sensitivity of the focused capacitor geometry was evaluated to be Si = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement.

  3. Performance of droplet generator and droplet collector in liquid droplet radiator under microgravity

    Science.gov (United States)

    Totani, T.; Itami, M.; Nagata, H.; Kudo, I.; Iwasaki, A.; Hosokawa, S.

    2002-06-01

    The Liquid Droplet Radiator (LDR) has an advantage over comparable conventional radiators in terms of the rejected heat power-weight ratio. Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems that will be prerequisite for large space structures. The performance of the LDR under microgravity condition has been studied from the viewpoint of operational space use of the LDR in the future. In this study, the performances of a droplet generator and a droplet collector in the LDR are investigated using drop shafts in Japan: MGLAB and JAMIC. As a result, it is considered that (1) the droplet generator can produce uniform droplet streams in the droplet diameter range from 200 to 280 [µm] and the spacing range from 400 to 950 [µm] under microgravity condition, (2) the droplet collector with the incidence angle of 35 degrees can prevent a uniform droplet stream, in which droplet diameter is 250 [µm] and the velocity is 16 [m/s], from splashing under microgravity condition, whereas splashes may occur at the surface of the droplet collector in the event that a nonuniform droplet stream collides against it.

  4. Universal evaporation dynamics of a confined sessile droplet

    Science.gov (United States)

    Bansal, Lalit; Hatte, Sandeep; Basu, Saptarshi; Chakraborty, Suman

    2017-09-01

    Droplet evaporation under confinement is ubiquitous to multitude of applications such as microfluidics, surface patterning, and ink-jet printing. However, the rich physics governing the universality in the underlying dynamics remains grossly elusive. Here, we bring out hitherto unexplored universal features of the evaporation dynamics of a sessile droplet entrapped in a 3D confined fluidic environment. We show, through extensive set of experiments and theoretical formulations, that the evaporation timescale for such a droplet can be represented by a unique function of the initial conditions. Moreover, using same theoretical considerations, we are able to trace and universally merge the volume evolution history of the droplets along with evaporation lifetimes, irrespective of the extent of confinement. We also showcase the internal flow transitions caused by spatio-temporal variation of evaporation flux due to confinement. These findings may be of profound importance in designing functionalized droplet evaporation devices for emerging engineering and biomedical applications.

  5. Impinging Water Droplets on Inclined Glass Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Armijo, Kenneth Miguel [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lance, Blake [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ho, Clifford K. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-09-01

    Multiphase computational models and tests of falling water droplets on inclined glass surfaces were developed to investigate the physics of impingement and potential of these droplets to self-clean glass surfaces for photovoltaic modules and heliostats. A multiphase volume-of-fluid model was developed in ANSYS Fluent to simulate the impinging droplets. The simulations considered different droplet sizes (1 mm and 3 mm), tilt angles (0°, 10°, and 45°), droplet velocities (1 m/s and 3 m/s), and wetting characteristics (wetting=47° contact angle and non-wetting = 93° contact angle). Results showed that the spread factor (maximum droplet diameter during impact divided by the initial droplet diameter) decreased with increasing inclination angle due to the reduced normal force on the surface. The hydrophilic surface yielded greater spread factors than the hydrophobic surface in all cases. With regard to impact forces, the greater surface tilt angles yielded lower normal forces, but higher shear forces. Experiments showed that the experimentally observed spread factor (maximum droplet diameter during impact divided by the initial droplet diameter) was significantly larger than the simulated spread factor. Observed spread factors were on the order of 5 - 6 for droplet velocities of ~3 m/s, whereas the simulated spread factors were on the order of 2. Droplets were observed to be mobile following impact only for the cases with 45° tilt angle, which matched the simulations. An interesting phenomenon that was observed was that shortly after being released from the nozzle, the water droplet oscillated (like a trampoline) due to the "snapback" caused by the surface tension of the water droplet being released from the nozzle. This oscillation impacted the velocity immediately after the release. Future work should evaluate the impact of parameters such as tilt angle and surface wettability on the impact of particle/soiling uptake and removal to investigate ways that

  6. Vapor-droplet flow equations

    International Nuclear Information System (INIS)

    Crowe, C.T.

    1975-01-01

    General features of a vapor-droplet flow are discussed and the equations expressing the conservation of mass, momentum, and energy for the vapor, liquid, and mixture using the control volume approach are derived. The phenomenological laws describing the exchange of mass, momentum, and energy between phases are also reviewed. The results have application to development of water-dominated geothermal resources

  7. A New Concept to Transport a Droplet on Horizontal Hydrophilic/Hydrophobic Surfaces

    International Nuclear Information System (INIS)

    Myong, Hyon Kook

    2014-01-01

    A fluid transport technique is a key issue for the development of microfluidic systems. In this paper, a new concept for transporting a droplet without external power sources is proposed and verified numerically. The proposed device is a heterogeneous surface which has both hydrophilic and hydrophobic horizontal surfaces. The numerical simulation to demonstrate the new concept is conducted by an in-house solution code (PowerCFD) which employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. It is found that the proposed concept for droplet transport shows superior performance for droplet transport in microfluidic systems

  8. Development of Two Way Coupled Euler – Euler Droplets Model

    Directory of Open Access Journals (Sweden)

    Vojtěch BĚTÁK

    2010-12-01

    Full Text Available A development of droplet solver for 3D complex geometry is described in this work. This solver is composed of solvers for turbulent flow field and droplets. This code is based on the finite volume method. An open source CFD code OpenFOAM was chosen for its first implementation and first results are shown.

  9. Droplet size in flow: Theoretical model and application to polymer blends

    Science.gov (United States)

    Fortelný, Ivan; Jůza, Josef

    2017-05-01

    The paper is focused on prediction of the average droplet radius, R, in flowing polymer blends where the droplet size is determined by dynamic equilibrium between the droplet breakup and coalescence. Expressions for the droplet breakup frequency in systems with low and high contents of the dispersed phase are derived using available theoretical and experimental results for model blends. Dependences of the coalescence probability, Pc, on system parameters, following from recent theories, is considered and approximate equation for Pc in a system with a low polydispersity in the droplet size is proposed. Equations for R in systems with low and high contents of the dispersed phase are derived. Combination of these equations predicts realistic dependence of R on the volume fraction of dispersed droplets, φ. Theoretical prediction of the ratio of R to the critical droplet radius at breakup agrees fairly well with experimental values for steadily mixed polymer blends.

  10. Behaviour of Water Droplets Under the Influence of a Uniform Electric Field in Nanocomposite Samples of Epoxy Resin/TiO2

    Directory of Open Access Journals (Sweden)

    Α. Bairaktari

    2013-10-01

    Full Text Available In this paper nanocomposite samples of epoxy resin and TiO2 nanoparticles were investigated with water droplets on their surface. A uniform electric field was applied and the behaviour of the water droplets was observed. Parameters that were studied were the water conductivity, the droplet volume, the number of droplets and the droplet positioning with respect to (w.r.t. the electrodes. All above mentioned parameters influence the flashover voltage of the samples. It is to be noted that – at least in some cases – the water droplet positioning w.r.t. the electrodes was more important in determining the flashover voltage than the droplet volume.

  11. High-throughput deterministic single-cell encapsulation and droplet pairing, fusion, and shrinkage in a single microfluidic device.

    Science.gov (United States)

    Schoeman, Rogier M; Kemna, Evelien W M; Wolbers, Floor; van den Berg, Albert

    2014-02-01

    In this article, we present a microfluidic device capable of successive high-yield single-cell encapsulation in droplets, with additional droplet pairing, fusion, and shrinkage. Deterministic single-cell encapsulation is realized using Dean-coupled inertial ordering of cells in a Yin-Yang-shaped curved microchannel using a double T-junction, with a frequency over 2000 Hz, followed by controlled droplet pairing with a 100% success rate. Subsequently, droplet fusion is realized using electrical actuation resulting in electro-coalescence of two droplets, each containing a single HL60 cell, with 95% efficiency. Finally, volume reduction of the fused droplet up to 75% is achieved by a triple pitchfork structure. This droplet volume reduction is necessary to obtain close cell-cell membrane contact necessary for final cell electrofusion, leading to hybridoma formation, which is the ultimate aim of this research. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Atomization of Impinging Droplets on Superheated Superhydrophobic Surfaces

    Science.gov (United States)

    Emerson, Preston; Crockett, Julie; Maynes, Daniel

    2017-11-01

    Water droplets impinging smooth superheated surfaces may be characterized by dynamic vapor bubbles rising to the surface, popping, and causing a spray of tiny droplets to erupt from the droplet. This spray is called secondary atomization. Here, atomization is quantified experimentally for water droplets impinging superheated superhydrophobic surfaces. Smooth hydrophobic and superhydrophobic surfaces with varying rib and post microstructuring were explored. Each surface was placed on an aluminum heating block, and impingement events were captured with a high speed camera at 3000 fps. For consistency among tests, all events were normalized by the maximum atomization found over a range of temperatures on a smooth hydrophobic surface. An estimate of the level of atomization during an impingement event was created by quantifying the volume of fluid present in the atomization spray. Droplet diameter and Weber number were held constant, and atomization was found for a range of temperatures through the lifetime of the impinging droplet. The Leidenfrost temperature was also determined and defined to be the lowest temperature at which atomization ceases to occur. Both atomization and Leidenfrost temperature increase with decreasing pitch (distance between microstructures).

  13. Evaporation and crystallization of a droplet of desulfurization wastewater from a coal-fired power plant

    International Nuclear Information System (INIS)

    Liang, Zhengxing; Zhang, Li; Yang, Zhongqing; Qiang, Tang; Pu, Ge; Ran, Jingyu

    2017-01-01

    Highlights: • Evaporation and crystallization characteristics of the droplets of desulfurization wastewater. • TGA and DSC methods were used to investigate the evaporation and crystallization processes. • Evaporation and crystallization rates increase with the increase of temperature increasing rate. • Increasing volume of the droplet increases the evaporation rate, but decreases the crystallization rate. • Structure of the crystals changes significantly when the temperature increasing rate and the volume of the droplet change. - Abstract: Relationship between evaporation and crystallization characteristics of a droplet of desulfurization wastewater from a coal-fired power plant and some operating conditions was studied experimentally using a thermogravimetric analyzer (TGA) with differential scanning calorimetry (DSC) function and a scanning electron microscope (SEM). The results shows that, between 15 °C/min and 45 °C/min, a higher temperature increasing rate leads to higher evaporation and crystallization rates. The increment in the evaporation rate, caused by the same increment of temperature increasing rate, is larger, when the temperature increasing rate is lower. In addition, the final temperatures, ranging from 90 °C to 150 °C, have little impact on the evaporation and crystallization rates of the 0.5 μL droplet. Ultimately, for the droplets, ranging from 0.2 μL to 2.5 μL, evaporation rate increases with increasing volumes of the droplets, but the crystallization rate decreases. From the SEM results, it can be observed that the quantity of cracks on the surface of the crystals also declines with the increase in volumes. Furthermore, the Stefan flow becomes a significant and unneglectable factor in order to decrease the evaporation rate at the end of the evaporation period.

  14. Multiple and high-throughput droplet reactions via combination of microsampling technique and microfluidic chip

    KAUST Repository

    Wu, Jinbo; Zhang, Mengying; Li, Xiaolin; Wen, Weijia

    2012-01-01

    Microdroplets offer unique compartments for accommodating a large number of chemical and biological reactions in tiny volume with precise control. A major concern in droplet-based microfluidics is the difficulty to address droplets individually

  15. Ammonia Released by Streptomyces aburaviensis Induces Droplet Formation in Streptomyces violaceoruber.

    Science.gov (United States)

    Schmidt, Kathrin; Spiteller, Dieter

    2017-08-01

    Streptomyces violaceoruber grown in co-culture with Streptomyces aburaviensis produces an about 17-fold higher volume of droplets on its aerial mycelium than in single-culture. Physical separation of the Streptomyces strains by either a plastic barrier or by a dialysis membrane, which allowed communication only by the exchange of volatile compounds or diffusible compounds in the medium, respectively, still resulted in enhanced droplet formation. The application of molecular sieves to bioassays resulted in the attenuation of the droplet-inducing effect of S. aburaviensis indicating the absorption of the compound. 1 H-NMR analysis of molecular-sieve extracts and the selective indophenol-blue reaction revealed that the volatile droplet-inducing compound is ammonia. The external supply of ammonia in biologically relevant concentrations of ≥8 mM enhanced droplet formation in S. violaceoruber in a similar way to S. aburaviensis. Ammonia appears to trigger droplet production in many Streptomyces strains because four out of six Streptomyces strains exposed to ammonia exhibited induced droplet production.

  16. Transient Droplet Behavior and Droplet Breakup during Bulk and Confined Shear Flow in Blends with One Viscoelastic Component: Experiments, Modelling and Simulations

    Science.gov (United States)

    Cardinaels, Ruth; Verhulst, Kristof; Renardy, Yuriko; Moldenaers, Paula

    2008-07-01

    The transient droplet deformation and droplet orientation after inception of shear, the shape relaxation after cessation of shear and droplet breakup during shear, are microscopically studied, both under bulk and confined conditions. The studied blends contain one viscoelastic Boger fluid phase. A counter rotating setup, based on a Paar Physica MCR300, is used for the droplet visualisation. For bulk shear flow, it is shown that the droplet deformation during startup of shear flow and the shape relaxation after cessation of shear flow are hardly influenced by droplet viscoelasticity, even at moderate to high capillary and Deborah numbers. The effects of droplet viscoelasticity only become visible close to the critical conditions and a novel break-up mechanism is observed. Matrix viscoelasticity has a more pronounced effect, causing overshoots in the deformation and significantly inhibiting relaxation. However, different applied capillary numbers prior to cessation of shear flow, with the Deborah number fixed, still result in a single master curve for shape retraction, as in fully Newtonian systems. The long tail in the droplet relaxation can be qualitatively described with a phenomenological model for droplet deformation, when using a 5-mode Giesekus model for the fluid rheology. It is found that the shear flow history significantly affects the droplet shape evolution and the breakup process in blends with one viscoelastic component. Confining a droplet between two plates accelerates the droplet deformation kinetics, similar to fully Newtonian systems. However, the increased droplet deformation, due to wall effects, causes the steady state to be reached at a later instant in time. Droplet relaxation is less sensitive to confinement, leading to slower relaxation kinetics only for highly confined droplets. For the blend with a viscoelastic droplet, a non-monotonous trend is found for the critical capillary number as a function of the confinement ratio. Finally

  17. Transient Droplet Behavior and Droplet Breakup during Bulk and Confined Shear Flow in Blends with One Viscoelastic Component: Experiments, Modelling and Simulations

    International Nuclear Information System (INIS)

    Cardinaels, Ruth; Verhulst, Kristof; Moldenaers, Paula; Renardy, Yuriko

    2008-01-01

    The transient droplet deformation and droplet orientation after inception of shear, the shape relaxation after cessation of shear and droplet breakup during shear, are microscopically studied, both under bulk and confined conditions. The studied blends contain one viscoelastic Boger fluid phase. A counter rotating setup, based on a Paar Physica MCR300, is used for the droplet visualisation. For bulk shear flow, it is shown that the droplet deformation during startup of shear flow and the shape relaxation after cessation of shear flow are hardly influenced by droplet viscoelasticity, even at moderate to high capillary and Deborah numbers. The effects of droplet viscoelasticity only become visible close to the critical conditions and a novel break-up mechanism is observed. Matrix viscoelasticity has a more pronounced effect, causing overshoots in the deformation and significantly inhibiting relaxation. However, different applied capillary numbers prior to cessation of shear flow, with the Deborah number fixed, still result in a single master curve for shape retraction, as in fully Newtonian systems. The long tail in the droplet relaxation can be qualitatively described with a phenomenological model for droplet deformation, when using a 5-mode Giesekus model for the fluid rheology. It is found that the shear flow history significantly affects the droplet shape evolution and the breakup process in blends with one viscoelastic component. Confining a droplet between two plates accelerates the droplet deformation kinetics, similar to fully Newtonian systems. However, the increased droplet deformation, due to wall effects, causes the steady state to be reached at a later instant in time. Droplet relaxation is less sensitive to confinement, leading to slower relaxation kinetics only for highly confined droplets. For the blend with a viscoelastic droplet, a non-monotonous trend is found for the critical capillary number as a function of the confinement ratio. Finally

  18. Direct numerical simulation of water droplet coalescence in the oil

    International Nuclear Information System (INIS)

    Mohammadi, Mehdi; Shahhosseini, Shahrokh; Bayat, Mahmoud

    2012-01-01

    Highlights: ► VOF computational technique has been used to simulate coalescence of two water droplets in oil. ► The model was validated with the experimental data for binary droplet coalescence. ► Based on the CFD simulation results a correlation has been proposed to predict the coalescence time. - Abstract: Coalescence of two water droplets in the oil was simulated using Computational Fluid Dynamics (CFD) techniques. The finite volume numerical method was applied to solve the Navier–Stokes equations in conjunction with the Volume of Fluid (VOF) approach for interface tracking. The effects of some parameters consisting of the collision velocity, off-center collision parameter, oil viscosity and water–oil interfacial tension on the coalescence time were investigated. The simulation results were validated against the experimental data available in the literature. The results revealed that quicker coalescence could be achieved if the head-on collisions occur or the droplets approach each other with a high velocity. In addition, low oil viscosities or large water–oil interfacial tensions cause less coalescence time. Moreover, a correlation was developed to predict coalescence efficiency as a function of the mentioned parameters.

  19. A Numerical Analysis of Droplet Breakup in Asymmetric T-Junctions with Different Outlet Pressure Gradients

    Science.gov (United States)

    Cheng, Way Lee; Han, Arum; Sadr, Reza

    2016-11-01

    Droplet splitting is the breakup of a parent droplet into two or more daughter droplets of desired sizes. It is done to improve production efficiency and investigational capacity in microfluidic devices. Passive splitting is the breakup of droplets into precise volume ratios at predetermined locations without external power sources. In this study, a 3-D simulation was conducted using the Volume-of-Fluid method to analysis the breakup process of a droplet in asymmetric T-junctions with different outlet arm lengths. The arrangement allows a droplet to be split into two smaller droplets of different sizes, where the volumetric ratio of the daughter droplets depends on the length ratios of the outlet arms. The study identified different breakup regimes such as primary, transition, bubble and non-breakup under different flow conditions and channel configurations. Furthermore, a close analysis to the primary breakup regimes were done to determine the breakup mechanisms at various flow conditions. The analysis show that the breakup mechanisms in asymmetric T-junctions is different than a regular split. A pseudo-phenomenological model for the breakup criteria was presented at the end. The model was an expanded version to a theoretically derived model for the symmetric droplet breakup. The Qatar National Research Fund (a member of the Qatar Founda- tion), under Grant NPRP 5-671-2-278, supported this work.

  20. Water droplets' internal fluidity during horizontal motion on a superhydrophobic surface with an external electric field.

    Science.gov (United States)

    Sakai, Munetoshi; Kono, Hiroki; Nakajima, Akira; Sakai, Hideki; Abe, Masahiko; Fujishima, Akira

    2010-02-02

    On a superhydrophobic surface, the internal fluidity of water droplets with different volumes (15, 30 microL) and their horizontal motion in an external electric field were evaluated using particle image velocimetry (PIV). For driving of water droplets on a superhydrophobic coating between parallel electrodes, it was important to place them at appropriate positions. Droplets moved with slipping. Small droplets showed deformation that is more remarkable. Results show that the dielectrophoretic force induced the initial droplet motion and that the surface potential gradient drove the droplets after reaching the middle point between electrodes.

  1. Capacitive sensor for continuous monitoring of high-volume droplet microfluidic generation

    KAUST Repository

    Conchouso Gonzalez, David

    2016-12-19

    This paper presents a capacitive sensor for monitoring parallel microfluidic droplet generation. The great electric permittivity difference between common droplet microfluidic fluids such as air, oil and water (ϵoil ≈ 2–3 and ϵwater ≈ 80.4), allows for accurate detection of water in oil concentration changes. Capacitance variations as large as 10 pF between a channel filled with water or dodecane, are used to continuously monitor the output of a parallelization system producing 150 µl/min of water in dodecane emulsions. We also discuss a low cost fabrication process to manufacture these capacitive sensors, which can be integrated to different substrates.

  2. Measurement of nanoscale molten polymer droplet spreading using atomic force microscopy

    Science.gov (United States)

    Soleymaniha, Mohammadreza; Felts, Jonathan R.

    2018-03-01

    We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures using atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μm diameters at 115-175 °C on sapphire, silicon oxide, and mica. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The contact angle evolution follows a power law with time with experimentally determined values of -0.29 ± 0.01, -0.08 ± 0.02, and -0.21 ± 0.01 for sapphire, silicon oxide, and mica, respectively. The non-zero steady state contact angles result in a slower evolution of contact angle with time consistent with theories combining molecular kinetic and hydrodynamic models. Monitoring the cantilever phase provides additional information about the local mechanics of the droplet surface. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 °C to 175 °C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means.

  3. Framework for simulating droplet vaporization in turbulent flows

    Science.gov (United States)

    Palmore, John; Desjardins, Olivier

    2017-11-01

    A framework for performing direct numerical simulations of droplet vaporization is presented. The work is motivated by spray combustion in engines wherein fuel droplets vaporize in a turbulent gas flow. The framework is built into a conservative finite volume code for simulating low Mach number turbulent multiphase flows. Phase tracking is performed using a discretely conservative geometric volume of fluid method, while the transport of mass fraction and temperature is performed using the BQUICK scheme. Special attention is given to the implementation of transport equations near the interface to ensure the consistency between fluxes of mass, momentum, and scalars. The effect of evaporation on the flow appears as a system of coupled source terms which depend on the local thermodynamic equilibrium between the phases. The sources are implemented implicitly using an unconditionally stable, monotone scheme. Two methodologies for resolving the system's thermodynamic equilibrium are compared for their accuracy, robustness, and computational expense. Verification is performed by comparing results to known solutions in one and three dimensions. Finally, simulations of droplets vaporizing in turbulence are demonstrated, and trends for mass fraction and temperature fields are discussed.

  4. Flashing liquid jets and two-phase droplet dispersion I. Experiments for derivation of droplet atomisation correlations.

    Science.gov (United States)

    Cleary, Vincent; Bowen, Phil; Witlox, Henk

    2007-04-11

    The large-scale release of a liquid contained at upstream conditions above its local atmospheric boiling point is a scenario often given consideration in process industry risk analysis. Current-hazard quantification software often employs simplistic equilibrium two-phase approaches. Scaled water experiments have been carried out measuring droplet velocity and droplet size distributions for a range of exit orifice aspect ratios (L/d) and conditions representing low to high superheat. 2D Phase-Doppler Anemometry has been utilised to characterise droplet kinematics and spray quality. Droplet size correlations have been developed for non-flashing, the transition between non-flashing and flashing, and fully flashing jets. Using high-speed shadowography, transition between regimes is defined in terms of criteria identified in the external flow structure. An overview companion paper provides a wider overview of the problem and reports implementation of these correlations into consequence models and subsequent validation. The fluid utilised throughout is water, hence droplet correlations are developed in non-dimensional form to allow extrapolation to other fluids through similarity scaling, although verification of model performance for other fluids is required in future studies. Data is reduced via non-dimensionalisation in terms of the Weber number and Jakob number, essentially representing the fluid mechanics and thermodynamics of the system, respectively. A droplet-size distribution correlation has also been developed, conveniently presented as a volume undersize distribution based on the Rosin-Rammler distribution. Separate correlations are provided for sub-cooled mechanical break-up and fully flashing jets. This form of correlation facilitates rapid estimates of likely mass rainout quantities, as well as full distribution information for more rigorous two-phase thermodynamic modelling in the future.

  5. The dynamics of milk droplet-droplet collisions

    Science.gov (United States)

    Finotello, Giulia; Kooiman, Roeland F.; Padding, Johan T.; Buist, Kay A.; Jongsma, Alfred; Innings, Fredrik; Kuipers, J. A. M.

    2018-01-01

    Spray drying is an important industrial process to produce powdered milk, in which concentrated milk is atomized into small droplets and dried with hot gas. The characteristics of the produced milk powder are largely affected by agglomeration, combination of dry and partially dry particles, which in turn depends on the outcome of a collision between droplets. The high total solids (TS) content and the presence of milk proteins cause a relatively high viscosity of the fed milk concentrates, which is expected to largely influence the collision outcomes of drops inside the spray. It is therefore of paramount importance to predict and control the outcomes of binary droplet collisions. Only a few studies report on droplet collisions of high viscous liquids and no work is available on droplet collisions of milk concentrates. The current study therefore aims to obtain insight into the effect of viscosity on the outcome of binary collisions between droplets of milk concentrates. To cover a wide range of viscosity values, three milk concentrates (20, 30 and 46% TS content) are investigated. An experimental set-up is used to generate two colliding droplet streams with consistent droplet size and spacing. A high-speed camera is used to record the trajectories of the droplets. The recordings are processed by Droplet Image Analysis in MATLAB to determine the relative velocities and the impact geometries for each individual collision. The collision outcomes are presented in a regime map dependent on the dimensionless impact parameter and Weber ( We) number. The Ohnesorge ( Oh) number is introduced to describe the effect of viscosity from one liquid to another and is maintained constant for each regime map by using a constant droplet diameter ( d ˜ 700 μ m). In this work, a phenomenological model is proposed to describe the boundaries demarcating the coalescence-separation regimes. The collision dynamics and outcome of milk concentrates are compared with aqueous glycerol

  6. Operating range, hold-up, droplet size and axial mixing of pulsed plate columns in highly disperse and low-continuity volume flows

    International Nuclear Information System (INIS)

    Schmidt, H.; Miller, H.

    Operating behavior, hold-up, droplet size and axial mixing are investigated in highly disperse and slightly continuous volume flows in a pulsed plate column. The geometry of the column of 4-m length and 10-cm inside diameter was held constant. The hole shape of the column bases was changed, wherby the cylindrical, sharp-edge drilled hole is compared with the punched, nozzle-shaped hole in their effects on the fluid-dynamic behavior. In this case we varied the volume flows, the ratio of volume flows, the pulse frequency and the operating temperature. The operation was held constant for the aqueous, the organic, the continuous and the disperse phases. The objective was to demonstrate the applicability of pulsed plate columns with very large differences between the organic disperse and the aqueous continuous volume flow, to obtain design data for such columns and to perform a scale-up to industrial reprocessing plant-size. 18 references, 11 figures, 3 tables

  7. Block-and-break generation of microdroplets with fixed volume

    Science.gov (United States)

    van Steijn, Volkert; Korczyk, Piotr M.; Derzsi, Ladislav; Abate, Adam R.; Weitz, David A.; Garstecki, Piotr

    2013-01-01

    We introduce a novel type of droplet generator that produces droplets of a volume set by the geometry of the droplet generator and not by the flow rates of the liquids. The generator consists of a classic T-junction with a bypass channel. This bypass directs the continuous fluid around the forming droplets, so that they can fill the space between the inlet of the dispersed phase and the exit of the bypass without breaking. Once filled, the dispersed phase blocks the exit of the bypass and is squeezed by the continuous fluid and broken off from the junction. We demonstrate the fixed-volume droplet generator for (i) the formation of monodisperse droplets from a source of varying flow rates, (ii) the formation of monodisperse droplets containing a gradation of solute concentration, and (iii) the parallel production of monodisperse droplets. PMID:24404013

  8. Model-based Adjustment of Droplet Characteristic for 3D Electronic Printing

    Directory of Open Access Journals (Sweden)

    Lin Na

    2017-01-01

    Full Text Available The major challenge in 3D electronic printing is the print resolution and accuracy. In this paper, a typical mode - lumped element modeling method (LEM - is adopted to simulate the droplet jetting characteristic. This modeling method can quickly get the droplet velocity and volume with a high accuracy. Experimental results show that LEM has a simpler structure with the sufficient simulation and prediction accuracy.

  9. Isothermal titration calorimetry in nanoliter droplets with subsecond time constants.

    Science.gov (United States)

    Lubbers, Brad; Baudenbacher, Franz

    2011-10-15

    We reduced the reaction volume in microfabricated suspended-membrane titration calorimeters to nanoliter droplets and improved the sensitivities to below a nanowatt with time constants of around 100 ms. The device performance was characterized using exothermic acid-base neutralizations and a detailed numerical model. The finite element based numerical model allowed us to determine the sensitivities within 1% and the temporal dynamics of the temperature rise in neutralization reactions as a function of droplet size. The model was used to determine the optimum calorimeter design (membrane size and thickness, junction area, and thermopile thickness) and sensitivities for sample volumes of 1 nL for silicon nitride and polymer membranes. We obtained a maximum sensitivity of 153 pW/(Hz)(1/2) for a 1 μm SiN membrane and 79 pW/(Hz)(1/2) for a 1 μm polymer membrane. The time constant of the calorimeter system was determined experimentally using a pulsed laser to increase the temperature of nanoliter sample volumes. For a 2.5 nanoliter sample volume, we experimentally determined a noise equivalent power of 500 pW/(Hz)(1/2) and a 1/e time constant of 110 ms for a modified commercially available infrared sensor with a thin-film thermopile. Furthermore, we demonstrated detection of 1.4 nJ reaction energies from injection of 25 pL of 1 mM HCl into a 2.5 nL droplet of 1 mM NaOH. © 2011 American Chemical Society

  10. Explosive Leidenfrost droplets

    Science.gov (United States)

    Colinet, Pierre; Moreau, Florian; Dorbolo, Stéphane

    2017-11-01

    We show that Leidenfrost droplets made of an aqueous solution of surfactant undergo a violent explosion in a wide range of initial volumes and concentrations. This unexpected behavior turns out to be triggered by the formation of a gel-like shell, followed by a sharp temperature increase. Comparing a simple model of the radial surfactant distribution inside a spherical droplet with experiments allows highlighting the existence of a critical surface concentration for the shell to form. The temperature rise (attributed to boiling point elevation with surface concentration) is a key feature leading to the explosion, instead of the implosion (buckling) scenario reported by other authors. Indeed, under some conditions, this temperature increase is shown to be sufficient to trigger nucleation and growth of vapor bubbles in the highly superheated liquid bulk, stretching the surrounding elastic shell up to its rupture limit. The successive timescales characterizing this explosion sequence are also discussed. Funding sources: F.R.S. - FNRS (ODILE and DITRASOL projects, RD and SRA positions of P. Colinet and S. Dorbolo), BELSPO (IAP 7/38 MicroMAST project).

  11. Cool-flame Extinction During N-Alkane Droplet Combustion in Microgravity

    Science.gov (United States)

    Nayagam, Vedha; Dietrich, Daniel L.; Hicks, Michael C.; Williams, Forman A.

    2014-01-01

    Recent droplet combustion experiments onboard the International Space Station (ISS) have revealed that large n-alkane droplets can continue to burn quasi-steadily following radiative extinction in a low-temperature regime, characterized by negative-temperaturecoefficient (NTC) chemistry. In this study we report experimental observations of n-heptane, n-octane, and n-decane droplets of varying initial sizes burning in oxygen/nitrogen/carbon dioxide and oxygen/helium/nitrogen environments at 1.0, 0.7, and 0.5 atmospheric pressures. The oxygen concentration in these tests varied in the range of 14% to 25% by volume. Large n-alkane droplets exhibited quasi-steady low-temperature burning and extinction following radiative extinction of the visible flame while smaller droplets burned to completion or disruptively extinguished. A vapor-cloud formed in most cases slightly prior to or following the "cool flame" extinction. Results for droplet burning rates in both the hot-flame and cool-flame regimes as well as droplet extinction diameters at the end of each stage are presented. Time histories of radiant emission from the droplet captured using broadband radiometers are also presented. Remarkably the "cool flame" extinction diameters for all the three n-alkanes follow a trend reminiscent of the ignition delay times observed in previous studies. The similarities and differences among the n-alkanes during "cool flame" combustion are discussed using simplified theoretical models of the phenomenon

  12. Quantification of protein interaction kinetics in a micro droplet

    Energy Technology Data Exchange (ETDEWEB)

    Yin, L. L. [Center for Bioelectronics and Biosensors, Biodesign Institute, Arizona State University, Tempe, Arizona 85287 (United States); College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044 (China); Wang, S. P., E-mail: shaopeng.wang@asu.edu, E-mail: njtao@asu.edu; Shan, X. N.; Tao, N. J., E-mail: shaopeng.wang@asu.edu, E-mail: njtao@asu.edu [Center for Bioelectronics and Biosensors, Biodesign Institute, Arizona State University, Tempe, Arizona 85287 (United States); Zhang, S. T. [College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044 (China)

    2015-11-15

    Characterization of protein interactions is essential to the discovery of disease biomarkers, the development of diagnostic assays, and the screening for therapeutic drugs. Conventional flow-through kinetic measurements need relative large amount of sample that is not feasible for precious protein samples. We report a novel method to measure protein interaction kinetics in a single droplet with sub microliter or less volume. A droplet in a humidity-controlled environmental chamber is replacing the microfluidic channels as the reactor for the protein interaction. The binding process is monitored by a surface plasmon resonance imaging (SPRi) system. Association curves are obtained from the average SPR image intensity in the center area of the droplet. The washing step required by conventional flow-through SPR method is eliminated in the droplet method. The association and dissociation rate constants and binding affinity of an antigen-antibody interaction are obtained by global fitting of association curves at different concentrations. The result obtained by this method is accurate as validated by conventional flow-through SPR system. This droplet-based method not only allows kinetic studies for proteins with limited supply but also opens the door for high-throughput protein interaction study in a droplet-based microarray format that enables measurement of many to many interactions on a single chip.

  13. Effect of surfactant concentration on the evaporation of droplets on cotton (Gossypium hirsutum L.) leaves.

    Science.gov (United States)

    Zhou, Zhaolu; Cao, Chong; Cao, Lidong; Zheng, Li; Xu, Jun; Li, Fengmin; Huang, Qiliang

    2018-04-05

    The evaporation kinetics of pesticide droplets deposited on a leaf surface can affect their application efficiency. Evaporation of droplets on the hydrophobic leaves has received considerable attention, but little is known about hydrophilic leaf surfaces. In this study, the effect of surfactant concentration on the evaporation of droplets deposited on cotton leaves was investigated. The evaporation time is roughly decreased for concentrations ranging from 0% to 0.01% and increased from 0.01% to 0.10%. Contrary to the widely held belief that pesticide retention on target crops can rapidly be formed only with surfactant concentrations exceeding the CMC (critical micelle concentration), this study demonstrates that, on hydrophilic cotton leaves, fast evaporation of the droplet at surfactant concentrations of 0.01% (CMC) can reduce the volume quickly, lower the loss point and enhance pesticide retention. In addition, the evolution of droplet volume, height and contact angle on the cotton leaf surface were measured to confirm this conclusion. The result presented herein can be used to guide the use of surfactants and pesticides in agriculture. Copyright © 2018 Elsevier B.V. All rights reserved.

  14. Study of droplet entrainment from bubbling surface in a bubble column

    International Nuclear Information System (INIS)

    Ramirez de Santiago, M.

    1991-05-01

    In a bubble column droplets are ejected from the free surface by bubble bursting or splashing. Depending on their size, the droplets are partly carried away by the streaming gas or fall back to the bubbling surface by gravity force. Experiments have been carried out to determine the void fraction in the column by means of an optical probe. In the interfacial zone the bubble bursting process was captured with a high-speed video camera. Simultaneous measurements were made of size and velocity of droplets at several distances from the bubbling surface with a Phase-Doppler Anemometry. The bubble column can be divided into three regions: A lower zone with a flat profile of the local void fraction, a central zone where the flow regime is steady and an upper zone where the local void fraction grows rapidly. A two-parameter log-normal distribution function was proposed in order to describe the polydisperse distribution of droplet-size. Results were obtained concerning the entrainment, concentration, volume fraction and interfacial area of droplets. Finally, it was found that the turbulence intensity affects the droplet terminal velocity for droplets smaller than the Kolmogorov microscale [fr

  15. Acoustic droplet vaporization of vascular droplets in gas embolotherapy

    Science.gov (United States)

    Bull, Joseph

    2016-11-01

    This work is primarily motivated by a developmental gas embolotherapy technique for cancer treatment. In this methodology, infarction of tumors is induced by selectively formed vascular gas bubbles that arise from the acoustic vaporization of vascular droplets. Additionally, micro- or nano-droplets may be used as vehicles for localized drug delivery, with or without flow occlusion. In this talk, we examine the dynamics of acoustic droplet vaporization through experiments and theoretical/computational fluid mechanics models, and investigate the bioeffects of acoustic droplet vaporization on endothelial cells and in vivo. Functionalized droplets that are targeted to tumor vasculature are examined. The influence of fluid mechanical and acoustic parameters, as well as droplet functionalization, is explored. This work was supported by NIH Grant R01EB006476.

  16. Numerical simulation of liquid droplet breakup in supersonic flows

    Science.gov (United States)

    Liu, Nan; Wang, Zhenguo; Sun, Mingbo; Wang, Hongbo; Wang, Bing

    2018-04-01

    A five-equation model based on finite-difference frame was utilized to simulate liquid droplet breakup in supersonic flows. To enhance the interface-capturing quality, an anti-diffusion method was introduced as a correction of volume-fraction after each step of calculation to sharpen the interface. The robustness was guaranteed by the hybrid variable reconstruction in which the second-order and high-order method were respectively employed in discontinuous and continuous flow fields. According to the recent classification of droplet breakup regimes, the simulations lay in the shear induced entrainment regime. Comparing to the momentum of the high-speed air flows, surface tension and viscid force were negligible in both two-dimensional and three-dimensional simulations. The inflow conditions were set as Mach 1.2, 1.5 and 1.8 to reach different dynamic pressure with the liquid to gas density ratio being 1000 initially. According to the results of simulations, the breakup process was divided into three stages which were analyzed in details with the consideration of interactions between gas and liquid. The shear between the high-speed gas flow and the liquid droplet was found to be the sources of surface instabilities on windward, while the instabilities on the leeward side were originated by vortices. Movement of the liquid mass center was studied, and the unsteady acceleration was observed. In addition, the characteristic breakup time was around 1.0 based on the criterion of either droplet thickness or liquid volume fraction.

  17. Application of volume of fluid method for simulation of a droplet impacting a fiber

    Directory of Open Access Journals (Sweden)

    M. Khalili

    2016-06-01

    Full Text Available In the present work, impact of a Newtonian drop on horizontal thin fibers with circular cross section is simulated in 2D views. The numerical simulations of the phenomena are carried out using volume of fluid (VOF method for tracking the free surface motion. Impacting of a Newtonian droplet on a circular thin fiber (350μm radius investigated numerically. The main focus of this simulation is to acquire threshold radius and velocity of a drop which is entirely captured by the fiber. The model agrees well with the experiments and demonstrates the threshold radius decreased generally with the increase of impact velocity. In other words, for velocity larger than threshold velocity of capture perhaps only a small portion of fluid is stuck on the solid and the rest of the drop is ejected for impact velocity smaller than critical velocity the drop is totally captured. This threshold velocity has been determined when the impact is centered.

  18. Effect of droplet size on the droplet behavior on the heterogeneous surface

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Ho Yeon; Son, Sung Wan; Ha, ManYeong [Pusan National University, Busan (Korea, Republic of); Park, Yong Gap [Pusan National University, Busan (Korea, Republic of)

    2017-06-15

    The characteristics of a three-dimensional hemispherical droplet on a heterogeneous surface were studied using the Lattice Boltzmann method (LBM). The hydrophilic surface has a hydrophobic part at the center. The hemispherical droplets are located at the center of the heterogeneous surface. According to the contact angles of hydrophilic and hydrophobic bottom surfaces, the droplet either separates or reaches a new equilibrium state. The separation time varies according to the change in droplet size, and it affects the status of droplet separation. The droplet separation behavior was investigated by analyzing the velocity vector around the phase boundary line. The shape and separation time of a droplet are determined by the contact angle of each surface. The speed of droplet separation increases as the difference in contact angle increases between the hydrophobic surface and hydrophilic surface. The separation status and the separation time of a droplet are also determined by the change of the droplet size. As the size of the droplet decreases, the effect of surface tension decreases, and the separation time of the droplet also decreases. On the other hand, as the droplet becomes larger, the effect of surface tension increases and the time required for the droplet to separate also increases.

  19. Droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling for simpler and faster PCR assay using wire-guided manipulations.

    Science.gov (United States)

    You, David J; Yoon, Jeong-Yeol

    2012-09-04

    A computer numerical control (CNC) apparatus was used to perform droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling on a single superhydrophobic surface and a multi-chambered PCB heater. Droplets were manipulated using "wire-guided" method (a pipette tip was used in this study). This methodology can be easily adapted to existing commercial robotic pipetting system, while demonstrated added capabilities such as vibrational mixing, high-speed centrifuging of droplets, simple DNA extraction utilizing the hydrophobicity difference between the tip and the superhydrophobic surface, and rapid thermocycling with a moving droplet, all with wire-guided droplet manipulations on a superhydrophobic surface and a multi-chambered PCB heater (i.e., not on a 96-well plate). Serial dilutions were demonstrated for diluting sample matrix. Centrifuging was demonstrated by rotating a 10 μL droplet at 2300 round per minute, concentrating E. coli by more than 3-fold within 3 min. DNA extraction was demonstrated from E. coli sample utilizing the disposable pipette tip to cleverly attract the extracted DNA from the droplet residing on a superhydrophobic surface, which took less than 10 min. Following extraction, the 1500 bp sequence of Peptidase D from E. coli was amplified using rapid droplet thermocycling, which took 10 min for 30 cycles. The total assay time was 23 min, including droplet centrifugation, droplet DNA extraction and rapid droplet thermocycling. Evaporation from of 10 μL droplets was not significant during these procedures, since the longest time exposure to air and the vibrations was less than 5 min (during DNA extraction). The results of these sequentially executed processes were analyzed using gel electrophoresis. Thus, this work demonstrates the adaptability of the system to replace many common laboratory tasks on a single platform (through re-programmability), in rapid succession (using droplets), and with a high level of

  20. Effects of droplet interactions on droplet transport at intermediate Reynolds numbers

    Science.gov (United States)

    Shuen, Jian-Shun

    1987-01-01

    Effects of droplet interactions on drag, evaporation, and combustion of a planar droplet array, oriented perpendicular to the approaching flow, are studied numerically. The three-dimensional Navier-Stokes equations, with variable thermophysical properties, are solved using finite-difference techniques. Parameters investigated include the droplet spacing, droplet Reynolds number, approaching stream oxygen concentration, and fuel type. Results are obtained for the Reynolds number range of 5 to 100, droplet spacings from 2 to 24 diameters, oxygen concentrations of 0.1 and 0.2, and methanol and n-butanol fuels. The calculations show that the gasification rates of interacting droplets decrease as the droplet spacings decrease. The reduction in gasification rates is significant only at small spacings and low Reynolds numbers. For the present array orientation, the effects of interactions on the gasification rates diminish rapidly for Reynolds numbers greater than 10 and spacings greater than 6 droplet diameters. The effects of adjacent droplets on drag are shown to be small.

  1. Droplet size effects on film drainage between droplet and substrate.

    Science.gov (United States)

    Steinhaus, Benjamin; Spicer, Patrick T; Shen, Amy Q

    2006-06-06

    When a droplet approaches a solid surface, the thin liquid film between the droplet and the surface drains until an instability forms and then ruptures. In this study, we utilize microfluidics to investigate the effects of film thickness on the time to film rupture for water droplets in a flowing continuous phase of silicone oil deposited on solid poly(dimethylsiloxane) (PDMS) surfaces. The water droplets ranged in size from millimeters to micrometers, resulting in estimated values of the film thickness at rupture ranging from 600 nm down to 6 nm. The Stefan-Reynolds equation is used to model film drainage beneath both millimeter- and micrometer-scale droplets. For millimeter-scale droplets, the experimental and analytical film rupture times agree well, whereas large differences are observed for micrometer-scale droplets. We speculate that the differences in the micrometer-scale data result from the increases in the local thin film viscosity due to confinement-induced molecular structure changes in the silicone oil. A modified Stefan-Reynolds equation is used to account for the increased thin film viscosity of the micrometer-scale droplet drainage case.

  2. Morphing and vectoring impacting droplets by means of wettability-engineered surfaces.

    Science.gov (United States)

    Schutzius, Thomas M; Graeber, Gustav; Elsharkawy, Mohamed; Oreluk, James; Megaridis, Constantine M

    2014-11-13

    Driven by its importance in nature and technology, droplet impact on solid surfaces has been studied for decades. To date, research on control of droplet impact outcome has focused on optimizing pre-impact parameters, e.g., droplet size and velocity. Here we follow a different, post-impact, surface engineering approach yielding controlled vectoring and morphing of droplets during and after impact. Surfaces with patterned domains of extreme wettability (high or low) are fabricated and implemented for controlling the impact process during and even after rebound--a previously neglected aspect of impact studies on non-wetting surfaces. For non-rebound cases, droplets can be morphed from spheres to complex shapes--without unwanted loss of liquid. The procedure relies on competition between surface tension and fluid inertial forces, and harnesses the naturally occurring contact-line pinning mechanisms at sharp wettability changes to create viable dry regions in the spread liquid volume. Utilizing the same forces central to morphing, we demonstrate the ability to rebound orthogonally-impacting droplets with an additional non-orthogonal velocity component. We theoretically analyze this capability and derive a We(-.25) dependence of the lateral restitution coefficient. This study offers wettability-engineered surfaces as a new approach to manipulate impacting droplet microvolumes, with ramifications for surface microfluidics and fluid-assisted templating applications.

  3. Evaporation kinetics of surfactant solution droplets on rice (Oryza sativa) leaves

    Science.gov (United States)

    Cao, Li-Dong; Zheng, Li; Xu, Jun; Li, Feng-Min; Huang, Qi-Liang

    2017-01-01

    The dynamics of evaporating sessile droplets on hydrophilic or hydrophobic surfaces is widely studied, and many models for these processes have been developed based on experimental evidence. However, few research has been explored on the evaporation of sessile droplets of surfactant or pesticide solutions on target crop leaves. Thus, in this paper the impact of surfactant concentrations on contact angle, contact diameter, droplet height, and evolution of the droplets’ evaporative volume on rice leaf surfaces have been investigated. The results indicate that the evaporation kinetics of surfactant droplets on rice leaves were influenced by both the surfactant concentrations and the hydrophobicity of rice leaf surfaces. When the surfactant concentration is lower than the surfactant CMC (critical micelle concentration), the droplet evaporation time is much longer than that of the high surfactant concentration. This is due to the longer existence time of a narrow wedge region under the lower surfactant concentration, and such narrow wedge region further restricts the droplet evaporation. Besides, our experimental data are shown to roughly collapse onto theoretical curves based on the model presented by Popov. This study could supply theoretical data on the evaporation of the adjuvant or pesticide droplets for practical applications in agriculture. PMID:28472108

  4. Synthesis of colloidal metal nanocrystals in droplet reactors: the pros and cons of interfacial adsorption.

    Science.gov (United States)

    Zhang, Lei; Wang, Yi; Tong, Limin; Xia, Younan

    2014-07-09

    Droplet reactors have received considerable attention in recent years as an alternative route to the synthesis and potentially high-volume production of colloidal metal nanocrystals. Interfacial adsorption will immediately become an important issue to address when one seeks to translate a nanocrystal synthesis from batch reactors to droplet reactors due to the involvement of higher surface-to-volume ratios for the droplets and the fact that nanocrystals tend to be concentrated at the water-oil interface. Here we report a systematic study to compare the pros and cons of interfacial adsorption of metal nanocrystals during their synthesis in droplet reactors. On the one hand, interfacial adsorption can be used to generate nanocrystals with asymmetric shapes or structures, including one-sixth-truncated Ag octahedra and Au-Ag nanocups. On the other hand, interfacial adsorption has to be mitigated to obtain nanocrystals with uniform sizes and controlled shapes. We confirmed that Triton X-100, a nonionic surfactant, could effectively alleviate interfacial adsorption while imposing no impact on the capping agent typically needed for a shape-controlled synthesis. With the introduction of a proper surfactant, droplet reactors offer an attractive platform for the continuous production of colloidal metal nanocrystals.

  5. Methanol Droplet Extinction in Carbon-Dioxide-Enriched Environments in Microgravity

    Science.gov (United States)

    Hicks, Michael C.; Nayagam, Vedha; Williams, Forman A.

    2010-01-01

    Diffusive extinction of methanol droplets with initial diameters between 1.25 mm and 1.72 mm, burning in a quiescent microgravity environment at one atmosphere pressure, was obtained experimentally for varying levels of ambient carbon-dioxide concentrations with a fixed oxygen concentration of 21% and a balance of nitrogen. These experiments serve as precursors to those which are beginning to be performed on the International Space Station and are motivated by the need to understand the effectiveness of carbon-dioxide as a fire suppressant in low-gravity environments. In these experiments, the flame standoff distance, droplet diameter, and flame radiation are measured as functions of time. The results show that the droplet extinction diameter depends on both the initial droplet diameter and the ambient concentration of carbon dioxide. Increasing the initial droplet diameter leads to an increased extinction diameter, while increasing the carbon-dioxide concentration leads to a slight decrease in the extinction diameter. These results are interpreted using a critical Damk hler number for extinction as predicted by an earlier theory, which is extended here to be applicable in the presence of effects of heat conduction along the droplet support fibers and of the volume occupied by the support beads

  6. Sensible Heat Transfer during Droplet Cooling: Experimental and Numerical Analysis

    Directory of Open Access Journals (Sweden)

    Emanuele Teodori

    2017-06-01

    Full Text Available This study presents the numerical reproduction of the entire surface temperature field resulting from a water droplet spreading on a heated surface, which is compared with experimental data. High-speed infrared thermography of the back side of the surface and high-speed images of the side view of the impinging droplet were used to infer on the solid surface temperature field and on droplet dynamics. Numerical reproduction of the phenomena was performed using OpenFOAM CFD toolbox. An enhanced volume of fluid (VOF model was further modified for this purpose. The proposed modifications include the coupling of temperature fields between the fluid and the solid regions, to account for transient heat conduction within the solid. The results evidence an extremely good agreement between the temporal evolution of the measured and simulated spreading factors of the considered droplet impacts. The numerical and experimental dimensionless surface temperature profiles within the solid surface and along the droplet radius, were also in good agreement. Most of the differences were within the experimental measurements uncertainty. The numerical results allowed relating the solid surface temperature profiles with the fluid flow. During spreading, liquid recirculation within the rim, leads to the appearance of different regions of heat transfer that can be correlated with the vorticity field within the droplet.

  7. Internal flow inside droplets within a concentrated emulsion during droplet rearrangement

    Science.gov (United States)

    Leong, Chia Min; Gai, Ya; Tang, Sindy K. Y.

    2018-03-01

    Droplet microfluidics, in which each droplet serves as a micro-reactor, has found widespread use in high-throughput biochemical screening applications. These droplets are often concentrated at various steps to form a concentrated emulsion. As part of a serial interrogation and sorting process, such concentrated emulsions are typically injected into a tapered channel leading to a constriction that fits one drop at a time for the probing of droplet content in a serial manner. The flow physics inside the droplets under these flow conditions are not well understood but are critical for predicting and controlling the mixing of reagents inside the droplets as reactors. Here we investigate the flow field inside droplets of a concentrated emulsion flowing through a tapered microchannel using micro-particle image velocimetry. The confining geometry of the channel forces the number of rows of drops to reduce by one at specific and uniformly spaced streamwise locations, which are referred to as droplet rearrangement zones. Within each rearrangement zone, the phase-averaged velocity results show that the motion of the droplets involved in the rearrangement process, also known as a T1 event, creates vortical structures inside themselves and their adjacent droplets. These flow structures increase the circulation inside droplets up to 2.5 times the circulation in droplets at the constriction. The structures weaken outside of the rearrangement zones suggesting that the flow patterns created by the T1 process are transient. The time scale of circulation is approximately the same as the time scale of a T1 event. Outside of the rearrangement zones, flow patterns in the droplets are determined by the relative velocity between the continuous and disperse phases.

  8. Droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling for simpler and faster PCR assay using wire-guided manipulations

    Directory of Open Access Journals (Sweden)

    You David J

    2012-09-01

    Full Text Available Abstract A computer numerical control (CNC apparatus was used to perform droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling on a single superhydrophobic surface and a multi-chambered PCB heater. Droplets were manipulated using “wire-guided” method (a pipette tip was used in this study. This methodology can be easily adapted to existing commercial robotic pipetting system, while demonstrated added capabilities such as vibrational mixing, high-speed centrifuging of droplets, simple DNA extraction utilizing the hydrophobicity difference between the tip and the superhydrophobic surface, and rapid thermocycling with a moving droplet, all with wire-guided droplet manipulations on a superhydrophobic surface and a multi-chambered PCB heater (i.e., not on a 96-well plate. Serial dilutions were demonstrated for diluting sample matrix. Centrifuging was demonstrated by rotating a 10 μL droplet at 2300 round per minute, concentrating E. coli by more than 3-fold within 3 min. DNA extraction was demonstrated from E. coli sample utilizing the disposable pipette tip to cleverly attract the extracted DNA from the droplet residing on a superhydrophobic surface, which took less than 10 min. Following extraction, the 1500 bp sequence of Peptidase D from E. coli was amplified using rapid droplet thermocycling, which took 10 min for 30 cycles. The total assay time was 23 min, including droplet centrifugation, droplet DNA extraction and rapid droplet thermocycling. Evaporation from of 10 μL droplets was not significant during these procedures, since the longest time exposure to air and the vibrations was less than 5 min (during DNA extraction. The results of these sequentially executed processes were analyzed using gel electrophoresis. Thus, this work demonstrates the adaptability of the system to replace many common laboratory tasks on a single platform (through re-programmability, in rapid succession (using droplets

  9. Multi-scale simulation of droplet-droplet interactions and coalescence

    CSIR Research Space (South Africa)

    Musehane, Ndivhuwo M

    2016-10-01

    Full Text Available Conference on Computational and Applied Mechanics Potchefstroom 3–5 October 2016 Multi-scale simulation of droplet-droplet interactions and coalescence 1,2Ndivhuwo M. Musehane?, 1Oliver F. Oxtoby and 2Daya B. Reddy 1. Aeronautic Systems, Council... topology changes that result when droplets interact. This work endeavours to eliminate the need to use empirical correlations based on phenomenological models by developing a multi-scale model that predicts the outcome of a collision between droplets from...

  10. Preventing droplet deformation during dielectrophoretic centering of a compound emulsion droplet

    Science.gov (United States)

    Randall, Greg; Blue, Brent

    2012-11-01

    Compound droplets, or droplets-within-droplets, are traditionally key components in applications ranging from drug delivery to the food industry. Presently, millimeter-sized compound droplets are precursors for shell targets in inertial fusion energy work. However, a key constraint in target fabrication is a uniform shell wall thickness, which in turn requires a centered core droplet in the compound droplet precursor. Previously, Bei et al. (2009, 2010) have shown that compound droplets could be centered in a static fluid using an electric field of 0.7 kV/cm at 20 MHz. Randall et al. (2012) developed a process to center the core of a moving compound droplet, though the ~kV/cm field induced small (fluid mechanics and interfacial rheology perspective and we discuss the effective interfacial charge from an emulsifier and its impact on centering. Work funded by General Atomics Internal R&D.

  11. Pronounced limb and fibre type differences in subcellular lipid droplet content and distribution in elite skiers before and after exhaustive exercise.

    Science.gov (United States)

    Koh, Han-Chow E; Nielsen, Joachim; Saltin, Bengt; Holmberg, Hans-Christer; Ørtenblad, Niels

    2017-09-01

    Although lipid droplets in skeletal muscle are an important energy source during endurance exercise, our understanding of lipid metabolism in this context remains incomplete. Using transmission electron microscopy, two distinct subcellular pools of lipid droplets can be observed in skeletal muscle - one beneath the sarcolemma and the other between myofibrils. At rest, well-trained leg muscles of cross-country skiers contain 4- to 6-fold more lipid droplets than equally well-trained arm muscles, with a 3-fold higher content in type 1 than in type 2 fibres. During exhaustive exercise, lipid droplets between the myofibrils but not those beneath the sarcolemma are utilised by both type 1 and 2 fibres. These findings provide insight into compartmentalisation of lipid metabolism within skeletal muscle fibres. Although the intramyocellular lipid pool is an important energy store during prolonged exercise, our knowledge concerning its metabolism is still incomplete. Here, quantitative electron microscopy was used to examine subcellular distribution of lipid droplets in type 1 and 2 fibres of the arm and leg muscles before and after 1 h of exhaustive exercise. Intermyofibrillar lipid droplets accounted for 85-97% of the total volume fraction, while the subsarcolemmal pool made up 3-15%. Before exercise, the volume fractions of intermyofibrillar and subsarcolemmal lipid droplets were 4- to 6-fold higher in leg than in arm muscles (P exercise, intermyofibrillar lipid droplet volume fraction was 53% lower (P = 0.0082) in both fibre types in arm, but not leg muscles. This reduction was positively associated with the corresponding volume fraction prior to exercise (R 2  = 0.84, P exercise-induced change in the subsarcolemmal pool could be detected. These findings indicate clear differences in the subcellular distribution of lipid droplets in the type 1 and 2 fibres of well-trained arm and leg muscles, as well as preferential utilisation of the intermyofibrillar pool

  12. Theoretical model of droplet wettability on a low-surface-energy solid under the influence of gravity.

    Science.gov (United States)

    Yonemoto, Yukihiro; Kunugi, Tomoaki

    2014-01-01

    The wettability of droplets on a low surface energy solid is evaluated experimentally and theoretically. Water-ethanol binary mixture drops of several volumes are used. In the experiment, the droplet radius, height, and contact angle are measured. Analytical equations are derived that incorporate the effect of gravity for the relationships between the droplet radius and height, radius and contact angle, and radius and liquid surface energy. All the analytical equations display good agreement with the experimental data. It is found that the fundamental wetting behavior of the droplet on the low surface energy solid can be predicted by our model which gives geometrical information of the droplet such as the contact angle, droplet radius, and height from physical values of liquid and solid.

  13. An experimental investigation of evaporating sessile droplet on super-hydrophobic surface

    International Nuclear Information System (INIS)

    Shin, Dong Hwan; Lee, Seong Hyuk; Yoo, Jung Yul

    2008-01-01

    The objective of this study is to investigate the evaporation process of a water droplet on hydrophobic and hydrophilic surfaces. Time-dependent contact angle, height, radius, surface area, and volume were measured for three different surfaces, such as glass, OctadecylTrichloroSilane(OTS), and AlkylKetene Dimmer(AKD) using a digital image analysis technique. For hydrophilic surfaces, the measured contact angle, liquid volume, and height are also compared with numerical estimation. It is found that for super-hydrophobic surfaces, the contact line becomes no longer pinned during evaporation, and three distinct stages for hydrophobic surface cannot be found. For the super-hydrophobic surface, it takes the longest time for evaporation because the droplet maintains spherical shape even near the end of evaporation process

  14. Numerical Simulation on Head-On Binary Collision of Gel Propellant Droplets

    Directory of Open Access Journals (Sweden)

    Zejun Liu

    2013-01-01

    Full Text Available Binary collision of droplets is a fundamental form of droplet interaction in the spraying flow field. In order to reveal the central collision mechanism of two gel droplets with equal diameters, an axi-symmetric form of the Navier-Stokes equations are firstly solved and the method of VOF (volume of fluid is utilized to track the evolution of the gas-liquid free interface. Then, the numerical computation model is validated with Qian’s experimental results on Newtonian liquids. Phenomena of rebound, coalescence and reflexive separation of droplets after collision are investigated, and structures of the complicated flow fields during the collision process are also analyzed in detail. Results show that the maximum shear rate will appear at the point where the flow is redirected and accelerated. Rebound of droplets is determined by the Weber number and viscosity of the fluid together. It can be concluded that the gel droplets are easier to rebound in comparison with the base fluid droplets. The results also show that the alternant appearance along with the deformation of droplets in the radial and axial direction is the main characteristic of the droplet coalescence process, and the deformation amplitude attenuates gradually. Moreover, the reflexive separation process of droplets can be divided into three distinctive stages including the radial expansion, the recovery of the spherical shape, and the axial extension and reflexive separation. The variation trend of the kinetic energy is opposite to that of the surface energy. The maximum deformation of droplets appears in the radial expansion stage; in the case of a low Weber number, the minimum central thickness of a droplet appears later than its maximum deformation, however, this result is on the contrary in the case of a high Weber number.

  15. Droplet Microfluidic and Magnetic Particles Platform for Cancer Typing.

    Science.gov (United States)

    Ferraro, Davide; Champ, Jérôme; Teste, Bruno; Serra, M; Malaquin, Laurent; Descroix, Stéphanie; de Cremoux, Patricia; Viovy, Jean-Louis

    2017-01-01

    Analyses of nucleic acids are routinely performed in hospital laboratories to detect gene alterations for cancer diagnosis and treatment decision. Among the different possible investigations, mRNA analysis provides information on abnormal levels of genes expression. Standard laboratory methods are still not adapted to the isolation and quantitation of low mRNA amounts and new techniques needs to be developed in particular for rare subsets analysis. By reducing the volume involved, time process, and the contamination risks, droplet microfluidics provide numerous advantages to perform analysis down to the single cell level.We report on a droplet microfluidic platform based on the manipulation of magnetic particles that allows the clinical analysis of tumor tissues. In particular, it allows the extraction of mRNA from the total-RNA sample, Reverse Transcription, and cDNA amplification, all in droplets.

  16. Modelling of heating and evaporation of n-Heptane droplets

    DEFF Research Database (Denmark)

    Yin, Chungen

    2015-01-01

    This study is a part of a project that is targeted to optimize the pyrolysis process of biomass pellets for bio-oil production and to develop new technology to upgrade the bio-oil for use in transportation. Among others, study of pyrolysis of the biomass pellets and evaporation of the pyrolysis bio...... and azimuthal directions, respectively, on each of which the flow, heat and mass transfer are numerically solved using the finite volume method. During the transient heating and evaporation process, the interaction between the moving droplets and free-stream flow are properly considered. Droplet dynamics...

  17. Magnetic Tools for Lab-on-a-chip Technologies

    Energy Technology Data Exchange (ETDEWEB)

    Pekas, Nikola Slobodan [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    This study establishes a set of magnetics-based tools that have been integrated with microfluidic systems. The overall impact of the work begins to enable the rapid and efficient manipulation and detection of magnetic entities such as particles, picoliter-sized droplets, or bacterial cells. Details of design, fabrication, and theoretical and experimental assessments are presented. The manipulation strategy has been demonstrated in the format of a particle diverter, whereby micron-sized particles are actively directed into desired flow channels at a split-flow junction by means of integrated microelectromagnets. Magnetic detection has been realized by deploying Giant Magnetoresistance (GMR) sensors--microfabricated structures originally developed for use as readout elements in computer hard-drives. We successfully transferred the GMR technology to the lab-on-a-chip arena, and demonstrated the versatility of the concept in several important areas: real-time, integrated monitoring of the properties of multiphase droplet flows; rapid quantitative determination of the concentration of magnetic nanoparticles in droplets of ferrofluids; and high-speed detection of individual magnetic microparticles and magnetotactic bacteria. The study also includes novel schemes for hydrodynamic flow focusing that work in conjunction with GMR-based detection to ensure precise navigation of the sample stream through the GMR detection volume, therefore effectively establishing a novel concept of a microfabricated magnetic flow cytometer.

  18. Evaluation method for radiative heat transfer in polydisperse water droplets

    International Nuclear Information System (INIS)

    Maruyama, Shigenao; Nakai, Hirotaka; Sakurai, Atsushi; Komiya, Atsuki

    2008-01-01

    Simplifications of the model for nongray radiative heat transfer analysis in participating media comprised of polydisperse water droplets are presented. Databases of the radiative properties for a water droplet over a wide range of wavelengths and diameters are constructed using rigorous Mie theory. The accuracy of the radiative properties obtained from the database interpolation is validated by comparing them with those obtained from the Mie calculations. The radiative properties of polydisperse water droplets are compared with those of monodisperse water droplets with equivalent mean diameters. Nongray radiative heat transfer in the anisotropic scattering fog layer, including direct and diffuse solar irradiations and infrared sky flux, is analyzed using REM 2 . The radiative heat fluxes within the fog layer containing polydisperse water droplets are compared with those in the layer containing monodisperse water droplets. Through numerical simulation of the radiative heat transfer, polydisperse water droplets can be approximated by using the Sauter diameter, a technique that can be useful in several research fields, such as engineering and atmospheric science. Although this approximation is valid in the case of pure radiative transfer problems, the Sauter diameter is reconfirmed to be the appropriate diameter for approximating problems in radiative heat transfer, although volume-length mean diameter shows better accordance in some cases. The CPU time for nongray radiative heat transfer analysis with a fog model is evaluated. It is proved that the CPU time is decreased by using the databases and the approximation method for polydisperse particulate media

  19. Development of a millimetrically scaled biodiesel transesterification device that relies on droplet-based co-axial fluidics

    Science.gov (United States)

    Yeh, S. I.; Huang, Y. C.; Cheng, C. H.; Cheng, C. M.; Yang, J. T.

    2016-07-01

    In this study, we investigated a fluidic system that adheres to new concepts of energy production. To improve efficiency, cost, and ease of manufacture, a millimetrically scaled device that employs a droplet-based co-axial fluidic system was devised to complete alkali-catalyzed transesterification for biodiesel production. The large surface-to-volume ratio of the droplet-based system, and the internal circulation induced inside the moving droplets, significantly enhanced the reaction rate of immiscible liquids used here - soybean oil and methanol. This device also decreased the molar ratio between methanol and oil to near the stoichiometric coefficients of a balanced chemical equation, which enhanced the total biodiesel volume produced, and decreased the costs of purification and recovery of excess methanol. In this work, the droplet-based co-axial fluidic system performed better than other methods of continuous-flow production. We achieved an efficiency that is much greater than that of reported systems. This study demonstrated the high potential of droplet-based fluidic chips for energy production. The small energy consumption and low cost of the highly purified biodiesel transesterification system described conforms to the requirements of distributed energy (inexpensive production on a moderate scale) in the world.

  20. Effect of single aerosol droplets on plasma impedance in the inductively coupled plasma

    Energy Technology Data Exchange (ETDEWEB)

    Chan, George C.-Y., E-mail: gcchan@indiana.edu; Zhu, Zhenli; Hieftje, Gary M.

    2012-10-15

    The impedance of an inductively coupled plasma was indirectly monitored by two different means-through a RF-probe coil placed inside the torch housing and from tapping the phase-detector signal of the impedance-matching network. During single-droplet introduction, temporal spikes in both the RF-probe coil and the phase-detector signals were readily observed, indicating a momentary change in plasma impedance. The changes in plasma impedance were found to be due solely to plasma perturbation by droplet introduction, and not to an artifact caused by imperfect automatic impedance matching. The temporal changes in plasma impedance were found to be directly proportional to the temporally integrated atomic emission of hydrogen, which is assumed in turn to be directly proportional to the volume of the introduced droplet. A small satellite droplet, with an estimated diameter of 27 {mu}m (i.e., {approx} 10 pL in volume), caused a readily measurable change in plasma impedance. By assuming that the change in RF-probe voltage is directly proportional to the variation in RF power delivered by the load coil, the instantaneous power change coupled to the plasma during single-droplet introduction was estimated. Typical increases in peak RF power and total energy coupled to the plasma, for a single 50-{mu}m droplet introduction, were thereby estimated to be around 8 to 11 W and 0.03 to 0.04 J, respectively. This impedance change was also exploited as a trigger to signal the droplet-introduction event into the plasma. This trigger signal was obtained through a combination of the RF-probe and the phase-detector signals and offered typical jitter from 1 to 2 ms. With the proper choice of a trigger threshold, no trigger misfire resulted and the achievable efficiencies of the trigger signal were 99.95, 97.18 and 74.33% for plasma forward power levels of 900, 1200, and 1500 W, respectively. The baseline noise on the RF-probe coil and the phase-detector signals, which increase with plasma

  1. Comparison of capacitive and radio frequency resonator sensors for monitoring parallelized droplet microfluidic production

    KAUST Repository

    Conchouso Gonzalez, David

    2016-06-28

    Scaled-up production of microfluidic droplets, through the parallelization of hundreds of droplet generators, has received a lot of attention to bring novel multiphase microfluidics research to industrial applications. However, apart from droplet generation, other significant challenges relevant to this goal have never been discussed. Examples include monitoring systems, high-throughput processing of droplets and quality control procedures among others. In this paper, we present and compare capacitive and radio frequency (RF) resonator sensors as two candidates that can measure the dielectric properties of emulsions in microfluidic channels. By placing several of these sensors in a parallelization device, the stability of the droplet generation at different locations can be compared, and potential malfunctions can be detected. This strategy enables for the first time the monitoring of scaled-up microfluidic droplet production. Both sensors were prototyped and characterized using emulsions with droplets of 100-150 μm in diameter, which were generated in parallelization devices at water-in-oil volume fractions (φ) between 11.1% and 33.3%.Using these sensors, we were able to measure accurately increments as small as 2.4% in the water volume fraction of the emulsions. Although both methods rely on the dielectric properties of the emulsions, the main advantage of the RF resonator sensors is the fact that they can be designed to resonate at multiple frequencies of the broadband transmission line. Consequently with careful design, two or more sensors can be parallelized and read out by a single signal. Finally, a comparison between these sensors based on their sensitivity, readout cost and simplicity, and design flexibility is also discussed. © 2016 The Royal Society of Chemistry.

  2. Interaction mechanisms between ceramic particles and atomized metallic droplets

    Science.gov (United States)

    Wu, Yue; Lavernia, Enrique J.

    1992-10-01

    The present study was undertaken to provide insight into the dynamic interactions that occur when ceramic particles are placed in intimate contact with a metallic matrix undergoing a phase change. To that effect, Al-4 wt pct Si/SiCp composite droplets were synthesized using a spray atomization and coinjection approach, and their solidification microstructures were studied both qualitatively and quantitatively. The present results show that SiC particles (SiCp) were incor- porated into the matrix and that the extent of incorporation depends on the solidification con- dition of the droplets at the moment of SiC particle injection. Two factors were found to affect the distribution and volume fraction of SiC particles in droplets: the penetration of particles into droplets and the entrapment and/or rejection of particles by the solidification front. First, during coinjection, particles collide with the atomized droplets with three possible results: they may penetrate the droplets, adhere to the droplet surface, or bounce back after impact. The extent of penetration of SiC particles into droplets was noted to depend on the kinetic energy of the particles and the magnitude of the surface energy change in the droplets that occurs upon impact. In liquid droplets, the extent of penetration of SiC particles was shown to depend on the changes in surface energy, ΔEs, experienced by the droplets. Accordingly, large SiC particles encoun- tered more resistance to penetration relative to small ones. In solid droplets, the penetration of SiC particles was correlated with the dynamic pressure exerted by the SiC particles on the droplets during impact and the depth of the ensuing crater. The results showed that no pene- tration was possible in such droplets. Second, once SiC particles have penetrated droplets, their final location in the microstructure is governed by their interactions with the solidification front. As a result of these interactions, both entrapment and rejection of

  3. Coalescence-induced jumping of micro-droplets on heterogeneous superhydrophobic surfaces

    Science.gov (United States)

    Attarzadeh, Reza; Dolatabadi, Ali

    2017-01-01

    The phenomenon of droplets coalescence-induced self-propelled jumping on homogeneous and heterogeneous superhydrophobic surfaces was numerically modeled using the volume of fluid method coupled with a dynamic contact angle model. The heterogeneity of the surface was directly modeled as a series of micro-patterned pillars. To resolve the influence of air around a droplet and between the pillars, extensive simulations were performed for different droplet sizes on a textured surface. Parallel computations with the OpenMP algorithm were used to accelerate computation speed to meet the convergence criteria. The composition of the air-solid surface underneath the droplet facilitated capturing the transition from a no-slip/no-penetration to a partial-slip with penetration as the contact line at triple point started moving to the air pockets. The wettability effect from the nanoscopic roughness and the coating was included in the model by using the intrinsic contact angle obtained from a previously published study. As the coalescence started, the radial velocity of the coalescing liquid bridge was partially reverted to the upward direction due to the counter-action of the surface. However, we found that the velocity varied with the size of the droplets. A part of the droplet kinetic energy was dissipated as the merged droplet started penetrating into the cavities. This was due to a different area in contact between the liquid and solid and, consequently, a higher viscous dissipation rate in the system. We showed that the effect of surface roughness is strongly significant when the size of the micro-droplet is comparable with the size of the roughness features. In addition, the relevance of droplet size to surface roughness (critical relative roughness) was numerically quantified. We also found that regardless of the viscous cutoff radius, as the relative roughness approached the value of 44, the direct inclusion of surface topography was crucial in the modeling of the

  4. Highly efficient capillary polymerase chain reaction using an oscillation droplet microreactor

    International Nuclear Information System (INIS)

    Liu Dayu; Liang Guangtie; Lei Xiuxia; Chen Bin; Wang Wei; Zhou Xiaomian

    2012-01-01

    Graphical abstract: An oscillation-flow approach using a droplet reactor was developed to fully explore the potential of continuous-flow PCR. By fully utilizing interfacial chemistry, a water-in-oil (w/o) droplet was automatically generated by allowing an oil–water plug to flow through a polytetrafluoroethylene (PTFE) capillary. Due to the movement of aqueous phase relative to the oil phase, the droplet moves further into the middle of the oil plug with increase in migration distance. The resulting droplet was transported spanning the two heating zones and was employed as the reactor of oscillating-flow PCR. Highlights: ► Droplet formation in a capillary. ► Transport the droplet using oscillation-flow. ► Oscillation droplet PCR. ► Improved reaction efficiency. - Abstract: The current work presents the development of a capillary-based oscillation droplet approach to maximize the potential of a continuous-flow polymerase chain reaction (PCR). Through the full utilization of interfacial chemistry, a water-in-oil (w/o) droplet was generated by allowing an oil–water plug to flow along a polytetrafluoroethylene (PTFE) capillary. The w/o droplet functioned as the reactor for oscillating-flow PCR to provide a stable reaction environment, accelerate reagent mixing, and eliminate surface adsorption. The capillary PCR approach proposed in the current research offers high amplification efficiency, fast reaction speed, and easy system control attributable to the oscillation droplet reactor. Experimental results show that the droplet-based micro-PCR assay requires lower reaction volume (2 μL) and shorter reaction time (12 min) compared with conventional PCR methods. Taking the amplification of the New Delhi metallo-beta-lactamase (NDM-1) gene as an example, the present work demonstrates that the oscillation droplet PCR assay is capable of achieving high efficiency up to 89.5% and a detection limit of 10 DNA copies. The miniature PCR protocol developed in the current

  5. Fluid Mechanics Of Molten Metal Droplets In Additive Manufacturing

    Czech Academy of Sciences Publication Activity Database

    Tesař, Václav; Šonský, Jiří

    2016-01-01

    Roč. 4, č. 4 (2016), s. 403-412 ISSN 2046-0546 R&D Projects: GA ČR GA13-23046S Institutional support: RVO:61388998 Keywords : additive manufacturing * droplets * molten metal Subject RIV: BK - Fluid Dynamics http://www.witpress.com/elibrary/cmem-volumes/4/4/1545

  6. Droplet Breakup in Asymmetric T-Junctions at Intermediate to Large Capillary Numbers

    Science.gov (United States)

    Sadr, Reza; Cheng, Way Lee

    2017-11-01

    Splitting of a parent droplet into multiple daughter droplets of desired sizes is usually desired to enhance production and investigational efficiency in microfluidic devices. This can be done in an active or passive mode depending on whether an external power sources is used or not. In this study, three-dimensional simulations were done using the Volume-of-Fluid (VOF) method to analyze droplet splitting in asymmetric T-junctions with different outlet lengths. The parent droplet is divided into two uneven portions the volumetric ratio of the daughter droplets, in theory, depends on the length ratios of the outlet branches. The study identified various breakup modes such as primary, transition, bubble and non-breakup under various flow conditions and the configuration of the T-junctions. In addition, an analysis with the primary breakup regimes were conducted to study the breakup mechanisms. The results show that the way the droplet splits in an asymmetric T-junction is different than the process in a symmetric T-junction. A model for the asymmetric breakup criteria at intermediate or large Capillary number is presented. The proposed model is an expanded version to a theoretically derived model for the symmetric droplet breakup under similar flow conditions.

  7. Evaporation of sessile droplets affected by graphite nanoparticles and binary base fluids.

    Science.gov (United States)

    Zhong, Xin; Duan, Fei

    2014-11-26

    The effects of ethanol component and nanoparticle concentration on evaporation dynamics of graphite-water nanofluid droplets have been studied experimentally. The results show that the formed deposition patterns vary greatly with an increase in ethanol concentration from 0 to 50 vol %. Nanoparticles have been observed to be carried to the droplet surface and form a large piece of aggregate. The volume evaporation rate on average increases as the ethanol concentration increases from 0 to 50 vol % in the binary mixture nanofluid droplets. The evaporation rate at the initial stage is more rapid than that at the late stage to dry, revealing a deviation from a linear fitting line, standing for a constant evaporation rate. The deviation is more intense with a higher ethanol concentration. The ethanol-induced smaller liquid-vapor surface tension leads to higher wettability of the nanofluid droplets. The graphite nanoparticles in ethanol-water droplets reinforce the pinning effect in the drying process, and the droplets with more ethanol demonstrate the depinning behavior only at the late stage. The addition of graphite nanoparticles in water enhances a droplet baseline spreading at the beginning of evaporation, a pinning effect during evaporation, and the evaporation rate. However, with a relatively high nanoparticle concentration, the enhancement is attenuated.

  8. Evaporation dynamics of a sessile droplet on glass surfaces with fluoropolymer coatings: focusing on the final stage of thin droplet evaporation.

    Science.gov (United States)

    Gatapova, Elizaveta Ya; Shonina, Anna M; Safonov, Alexey I; Sulyaeva, Veronica S; Kabov, Oleg A

    2018-03-07

    The evaporation dynamics of a water droplet with an initial volume of 2 μl from glass surfaces with fluoropolymer coatings are investigated using the shadow technique and an optical microscope. The droplet profile for a contact angle of less than 5° is constructed using an image-analyzing interference technique, and evaporation dynamics are investigated at the final stage. We coated the glass slides with a thin film of a fluoropolymer by the hot-wire chemical vapor deposition method at different deposition modes depending on the deposition pressure and the temperature of the activating wire. The resulting surfaces have different structures affecting the wetting properties. Droplet evaporation from a constant contact radius mode in the early stage of evaporation was found followed by the mode where both contact angle and contact radius simultaneously vary in time (final stage) regardless of wettability of the coated surfaces. We found that depinning occurs at small contact angles of 2.2-4.7° for all samples, which are smaller than the measured receding contact angles. This is explained by imbibition of the liquid into the developed surface of the "soft" coating that leads to formation of thin droplets completely wetting the surface. The final stage, which is little discussed in the literature, is also recorded. We have singled out a substage where the contact line velocity is abruptly increasing for all coated and uncoated surfaces. The critical droplet height corresponding to the transition to this substage is about 2 μm with R/h = 107. The duration of this substage is the same for all coated and uncoated surfaces. Droplets observed at this substage for all the tested surfaces are axisymmetric. The specific evaporation rate clearly demonstrates an abrupt increase at the final substage of the droplet evaporation. The classical R 2 law is justified for the complete wetting situation where the droplet is disappearing in an axisymmetric manner.

  9. High-Energy Laser Interaction with Gases, Droplets, and Bulk Liquids.

    Science.gov (United States)

    Jarzembski, Maurice Anthony

    Breakdown threshold intensities (I_ {rm TH}) were measured as functions of wavelengths and pressure for air, He, Ar, and Xe using a Nd:YAG pulsed laser. Multiphoton absorption dominates in the UV and cascade collision ionization dominates in the IR; however, both can be affected by other electron gain and loss processes. Presence of droplets lowers breakdown of gases due to field enhancements. Breakdown is initiated either in the droplet material or in the gas. At lambda = 0.532mum for a 50 μm dia. water droplet in He, Ar, and air for p pressure. For droplet -in-Xe, at p pressure. For droplet-in-Xe, at p 140 Torr, breakdown occurs outside the droplet and is dependent on gas pressure. Pressure dependence of breakdown was observed for 120mum dia. water droplets in Ar at p > 400 Torr. The required intensity for breakdown of droplet depends on I_{ rm TH} of bulk liquid and the effective field enhancement created by the droplet. The I _{rm TH} of droplet-in-air provides an upper limit to the propagation of a high energy laser beam in the atmosphere containing particles. By geometrical optics approach, a significant field enhancement located at the critical ring region, encircling the axis of the sphere in the forward direction at angle theta_{c}, was discovered where nonlinear processes can occur. This was confirmed experimentally and by Mie theory. Field enhancements calculated at the critical ring for water droplets of different sizes agree well with measurements. For a droplet of given size and real refractive index, the effective field enhancement and the volume over which it occurs are two important factors governing the occurrence of breakdown in droplets for both off resonance and on resonance conditions. Measurements of wavelength dependence of breakdown showed that in the UV, I_{rm TH} for droplets and bulk liquids were comparable and lower by few orders of magnitude from that of air. Transmittance and reflectance of bulk liquids in the UV change with

  10. Evaporation of Liquid Droplet in Nano and Micro Scales from Statistical Rate Theory.

    Science.gov (United States)

    Duan, Fei; He, Bin; Wei, Tao

    2015-04-01

    The statistical rate theory (SRT) is applied to predict the average evaporation flux of liquid droplet after the approach is validated in the sessile droplet experiments of the water and heavy water. The steady-state experiments show a temperature discontinuity at the evaporating interface. The average evaporation flux is evaluated by individually changing the measurement at a liquid-vapor interface, including the interfacial liquid temperature, the interfacial vapor temperature, the vapor-phase pressure, and the droplet size. The parameter study shows that a higher temperature jump would reduce the average evaporation flux. The average evaporation flux can significantly be influenced by the interfacial liquid temperature and the vapor-phase pressure. The variation can switch the evaporation into condensation. The evaporation flux is found to remain relative constant if the droplet is larger than a micro scale, while the smaller diameters in nano scale can produce a much higher evaporation flux. In addition, a smaller diameter of droplets with the same liquid volume has a larger surface area. It is suggested that the evaporation rate increases dramatically as the droplet shrinks into nano size.

  11. Isotropically etched radial micropore for cell concentration, immobilization, and picodroplet generation.

    Science.gov (United States)

    Perroud, Thomas D; Meagher, Robert J; Kanouff, Michael P; Renzi, Ronald F; Wu, Meiye; Singh, Anup K; Patel, Kamlesh D

    2009-02-21

    To enable several on-chip cell handling operations in a fused-silica substrate, small shallow micropores are radially embedded in larger deeper microchannels using an adaptation of single-level isotropic wet etching. By varying the distance between features on the photolithographic mask (mask distance), we can precisely control the overlap between two etch fronts and create a zero-thickness semi-elliptical micropore (e.g. 20 microm wide, 6 microm deep). Geometrical models derived from a hemispherical etch front show that micropore width and depth can be expressed as a function of mask distance and etch depth. These models are experimentally validated at different etch depths (25.03 and 29.78 microm) and for different configurations (point-to-point and point-to-edge). Good reproducibility confirms the validity of this approach to fabricate micropores with a desired size. To illustrate the wide range of cell handling operations enabled by micropores, we present three on-chip functionalities: continuous-flow particle concentration, immobilization of single cells, and picoliter droplet generation. (1) Using pressure differentials, particles are concentrated by removing the carrier fluid successively through a series of 44 shunts terminated by 31 microm wide, 5 microm deep micropores. Theoretical values for the concentration factor determined by a flow circuit model in conjunction with finite volume modeling are experimentally validated. (2) Flowing macrophages are individually trapped in 20 microm wide, 6 microm deep micropores by hydrodynamic confinement. The translocation of transcription factor NF-kappaB into the nucleus upon lipopolysaccharide stimulation is imaged by fluorescence microscopy. (3) Picoliter-sized droplets are generated at a 20 microm wide, 7 microm deep micropore T-junction in an oil stream for the encapsulation of individual E. coli bacteria cells.

  12. Flashing liquid jets and two-phase droplet dispersion

    International Nuclear Information System (INIS)

    Cleary, Vincent; Bowen, Phil; Witlox, Henk

    2007-01-01

    The large-scale release of a liquid contained at upstream conditions above its local atmospheric boiling point is a scenario often given consideration in process industry risk analysis. Current-hazard quantification software often employs simplistic equilibrium two-phase approaches. Scaled water experiments have been carried out measuring droplet velocity and droplet size distributions for a range of exit orifice aspect ratios (L/d) and conditions representing low to high superheat. 2D Phase-Doppler Anemometry has been utilised to characterise droplet kinematics and spray quality. Droplet size correlations have been developed for non-flashing, the transition between non-flashing and flashing, and fully flashing jets. Using high-speed shadowography, transition between regimes is defined in terms of criteria identified in the external flow structure. An overview companion paper provides a wider overview of the problem and reports implementation of these correlations into consequence models and subsequent validation. The fluid utilised throughout is water, hence droplet correlations are developed in non-dimensional form to allow extrapolation to other fluids through similarity scaling, although verification of model performance for other fluids is required in future studies. Data is reduced via non-dimensionalisation in terms of the Weber number and Jakob number, essentially representing the fluid mechanics and thermodynamics of the system, respectively. A droplet-size distribution correlation has also been developed, conveniently presented as a volume undersize distribution based on the Rosin-Rammler distribution. Separate correlations are provided for sub-cooled mechanical break-up and fully flashing jets. This form of correlation facilitates rapid estimates of likely mass rainout quantities, as well as full distribution information for more rigorous two-phase thermodynamic modelling in the future

  13. Deformation pathways and breakup modes in acoustically levitated bicomponent droplets under external heating

    Science.gov (United States)

    Pathak, Binita; Basu, Saptarshi

    2016-03-01

    Controlled breakup of droplets using heat or acoustics is pivotal in applications such as pharmaceutics, nanoparticle production, and combustion. In the current work we have identified distinct thermal acoustics-induced deformation regimes (ligaments and bubbles) and breakup dynamics in externally heated acoustically levitated bicomponent (benzene-dodecane) droplets with a wide variation in volatility of the two components (benzene is significantly more volatile than dodecane). We showcase the physical mechanism and universal behavior of droplet surface caving in leading to the inception and growth of ligaments. The caving of the top surface is governed by a balance between the acoustic pressure field and the restrictive surface tension of the droplet. The universal collapse of caving profiles for different benzene concentration (70 % by volume). The findings are portable to any similar bicomponent systems with differential volatility.

  14. Pulsed Direct Current Electrospray: Enabling Systematic Analysis of Small Volume Sample by Boosting Sample Economy.

    Science.gov (United States)

    Wei, Zhenwei; Xiong, Xingchuang; Guo, Chengan; Si, Xingyu; Zhao, Yaoyao; He, Muyi; Yang, Chengdui; Xu, Wei; Tang, Fei; Fang, Xiang; Zhang, Sichun; Zhang, Xinrong

    2015-11-17

    We had developed pulsed direct current electrospray ionization mass spectrometry (pulsed-dc-ESI-MS) for systematically profiling and determining components in small volume sample. Pulsed-dc-ESI utilized constant high voltage to induce the generation of single polarity pulsed electrospray remotely. This method had significantly boosted the sample economy, so as to obtain several minutes MS signal duration from merely picoliter volume sample. The elongated MS signal duration enable us to collect abundant MS(2) information on interested components in a small volume sample for systematical analysis. This method had been successfully applied for single cell metabolomics analysis. We had obtained 2-D profile of metabolites (including exact mass and MS(2) data) from single plant and mammalian cell, concerning 1034 components and 656 components for Allium cepa and HeLa cells, respectively. Further identification had found 162 compounds and 28 different modification groups of 141 saccharides in a single Allium cepa cell, indicating pulsed-dc-ESI a powerful tool for small volume sample systematical analysis.

  15. Macroscopic investigation of water volume effects on interfacial dynamic behaviors between clathrate hydrate and water.

    Science.gov (United States)

    Cha, Minjun; Couzis, Alexander; Lee, Jae W

    2013-05-14

    This study investigated the effects of the water volume on the interfacial dynamics between cyclopentane (CP) hydrate and water droplet in a CP/n-decane oil mixture. The adhesion force between CP hydrate and various water droplets was determined using the z-directional microbalance. Through repetition of precise measurements over several cycles from contact to detachment, we observed abnormal wetting behaviors in the capillary bridge during the retraction process when the water drop volume is larger than 100 μL. With the increase in water droplet volumes, the contact force between CP hydrate and water also increases up to 300 μL. However, there is a dramatic reduction of increasing rate in the contact forces over 300 μL of water droplet. With the addition of the surfactants of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) to the water droplet, the contact force between CP hydrate and solution droplet exhibits a lower value and a transition volume of the contact force comes with a smaller solution volume of 200 μL. The water volume effects on the liquid wetting of the probe and the size of capillary bridges provide important insight into hydrate growth and aggregation/agglomeration in the presence of free water phase inside gas/oil pipelines.

  16. Multiscale Simulation of Gas Film Lubrication During Liquid Droplet Collision

    Science.gov (United States)

    Chen, Xiaodong; Khare, Prashant; Ma, Dongjun; Yang, Vigor

    2012-02-01

    Droplet collision plays an elementary role in dense spray combustion process. When two droplets approach each other, a gas film forms in between. The pressure generated within the film prevents motion of approaching droplets. This fluid mechanics is fluid film lubrication that occurs when opposing bearing surfaces are completely separated by fluid film. The lubrication flow in gas film decides the collision outcome, coalescence or bouncing. Present study focuses on gas film drainage process over a wide range of Weber numbers during equal- and unequal-sized droplet collision. The formulation is based on complete set of conservation equations for both liquid and surrounding gas phases. An improved volume-of-fluid technique, augmented by an adaptive mesh refinement algorithm, is used to track liquid/gas interfaces. A unique thickness-based refinement algorithm based on topology of interfacial flow is developed and implemented to efficiently resolve the multiscale problem. The grid size on interface is up O(10-4) of droplet size with a max resolution of 0.015 μm. An advanced visualization technique using the Ray-tracing methodology is used to gain direct insights to detailed physics. Theories are established by analyzing the characteristics of shape changing and flow evolution.

  17. Numerical study of droplet evaporation in coupled high-temperature and electrostatic fields

    Directory of Open Access Journals (Sweden)

    Ziwen Zuo

    2015-03-01

    Full Text Available The evaporation of a sessile water droplet under the coupled electrostatic and high-temperature fields is studied numerically. The leaky dielectric model and boiling point evaporation model are used for calculating the electric force and heat mass transfer. The free surface is captured using the volume of fluid method accounting for the variable surface tension and the transition of physical properties across the interface. The flow behaviors and temperature evolutions in different applied fields are predicted. It shows that in the coupled fields, the external electrostatic field restrains the flow inside the droplet and keeps a steady circulation. The flow velocity is reduced due to the interaction between electric body force and the force caused by temperature gradient. The heat transfer from air into the droplet is reduced by the lower flow velocity. The evaporation rate of the droplet in the high-temperature field is decreased.

  18. Droplet generating device for droplet-based μTAS using electro-conjugate fluid

    Science.gov (United States)

    Iijima, Y.; Takemura, K.; Edamura, K.

    2017-05-01

    Droplet-based μTAS, which carries out biochemical inspection and synthesis by handling samples as droplets on a single chip, has been attracting attentions in recent years. Although miniaturization of a chip is progressed, there are some problems in miniaturization of a whole system because of the necessity to connect syringe pumps to the chip. Thus, this study aims to realize a novel droplets generating device for droplet-based μTAS using electro-conjugate fluid (ECF). The ECF is a dielectric liquid generating a powerful flow when subjected to high DC voltage. The ECF flow generation allows us to realize a tiny hydraulic power source. Using the ECF flow, we can develop a droplet generating device for droplet-based μTAS by placing minute electrode pairs in flow channels. The device contains two channels filled with the ECF, which are dispersed and continuous phases meeting at a T-junction. When a sample in the dispersed phase is injected by the ECF flow to the continuous phase at T-junction, droplets are generated by shearing force between the two phases. We conducted droplet generating experiment and confirmed that droplets are successfully generated when the flow rate of the continuous phase is between 90 and 360 mm3 s-1, and the flow rate of the dispersed phase is between 10 and 40 mm3 s-1. We also confirmed that the droplet diameter and the droplet production rate are controllable by tuning the applied voltage to the electrode pairs.

  19. Lossless droplet transfer of droplet-based microfluidic analysis

    Science.gov (United States)

    Kelly, Ryan T [West Richland, WA; Tang, Keqi [Richland, WA; Page, Jason S [Kennewick, WA; Smith, Richard D [Richland, WA

    2011-11-22

    A transfer structure for droplet-based microfluidic analysis is characterized by a first conduit containing a first stream having at least one immiscible droplet of aqueous material and a second conduit containing a second stream comprising an aqueous fluid. The interface between the first conduit and the second conduit can define a plurality of apertures, wherein the apertures are sized to prevent exchange of the first and second streams between conduits while allowing lossless transfer of droplets from the first conduit to the second conduit through contact between the first and second streams.

  20. Temporal and spatial effects of ablation plume on number density distribution of droplets in an aerosol measured by laser-induced breakdown

    International Nuclear Information System (INIS)

    Yashiro, H.; Kakehata, M.

    2013-01-01

    We proposed and experimentally demonstrated a novel method of evaluating the number density of droplets in an aerosol by laser-induced breakdown. The number density of droplets is evaluated from the volume in which the laser intensity exceeds the breakdown threshold intensity for droplets, and the number of droplets in this volume, which is evaluated by the experimentally observed breakdown probability. This measurement method requires a large number of laser shots for not only precise measurement but also highly temporally and spatially resolved density distribution in aerosol. Laser ablation plumes ejected from liquid droplets generated by breakdown disturb the density around the measurement points. Therefore, the recovery time of the density determines the maximum repetition rate of the probe laser irradiating a fixed point. The expansion range of the ablation plume determines the minimum distance at which the measurement points are unaffected by a neighboring breakdown when multiple laser beams are simultaneously irradiated. These laser irradiation procedures enable the measurement of the number density distribution of droplets in an aerosol at a large number of points within a short measurement time.

  1. Temporal and spatial effects of ablation plume on number density distribution of droplets in an aerosol measured by laser-induced breakdown

    Energy Technology Data Exchange (ETDEWEB)

    Yashiro, H.; Kakehata, M. [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2013-05-07

    We proposed and experimentally demonstrated a novel method of evaluating the number density of droplets in an aerosol by laser-induced breakdown. The number density of droplets is evaluated from the volume in which the laser intensity exceeds the breakdown threshold intensity for droplets, and the number of droplets in this volume, which is evaluated by the experimentally observed breakdown probability. This measurement method requires a large number of laser shots for not only precise measurement but also highly temporally and spatially resolved density distribution in aerosol. Laser ablation plumes ejected from liquid droplets generated by breakdown disturb the density around the measurement points. Therefore, the recovery time of the density determines the maximum repetition rate of the probe laser irradiating a fixed point. The expansion range of the ablation plume determines the minimum distance at which the measurement points are unaffected by a neighboring breakdown when multiple laser beams are simultaneously irradiated. These laser irradiation procedures enable the measurement of the number density distribution of droplets in an aerosol at a large number of points within a short measurement time.

  2. Dissolution and degradation of crude oil droplets by different bacterial species and consortia by microcosm microfluidics

    Science.gov (United States)

    Jalali, Maryam; Sheng, Jian

    2017-11-01

    Bacteria are involved in cleanup and degradation of crude oil in polluted marine and soil environments. A number of bacterial species have been identified for consuming petroleum hydrocarbons with diverse metabolic capabilities. We conducted laboratory experiments to investigate bacterial consumption by monitoring the volume change to oil droplets as well as effects of oil droplet size on this process. To conduct our study, we developed a micro-bioassay containing an enclosed chamber with bottom substrate printed with stationary oil microdroplets and a digital holographic interferometer (DHI). The morphology of microdroplets was monitored in real time over 100 hours and instantaneous flow field was also measured by digital holographic microscope. The substrates with printed oil droplets were further evaluated with atomic force microscopy (AFM) at the end of each experiment. Three different bacteria species, Pseudomonas sp, Alcanivorax borkumensis, and Marinobacter hydrocarbonoclasticus, as well as six bacterial consortia were used in this study. The results show that droplets smaller than 20µm in diameter are not subject to bacterial degradation and the volume of droplet did not change beyond dissolution. Substantial species-specific behaviors have been observed in isolates. The experiments of consortia and various flow shears on biodegradation and dissolution are ongoing and will be reported.

  3. Numerical investigation of micro-pore formation during substrate impact of molten droplets in spraying processes

    International Nuclear Information System (INIS)

    Liu, H.; Lavernia, E.J.; Rangel, R.H.; Muehlberger, E.; Sickinger, A.

    1994-01-01

    The porosity that is commonly associated with discrete droplet processes, such as plasma spraying and spray deposition, effectively degrades the quality of the sprayed material. In the present study, micro-pore formation during the deformation and interaction of molten tungsten droplets impinging onto a flat substrate in spraying processes is numerically investigated. The numerical simulation is accomplished on the basis of the full Navier-Stokes equations and the Volume Of Fluid (VOF) function by using a 2-domain method for the thermal field and solidification problem and a two-phase flow continuum model for the flow problem with a growing solid layer. The possible mechanisms governing the formation of micro-pores are discussed. The effects of important processing parameters, such as droplet impact velocity, droplet temperature, substrate temperature, and droplet viscosity, on the micro-pore formation are addressed

  4. Block-and-break generation of microdroplets with fixed volume

    NARCIS (Netherlands)

    Van Steijn, V.; Korczyk, P.M.; Derzsi, L.; Abate, A.R.; Weitz, D.A.; Garstecki, P.

    2013-01-01

    We introduce a novel type of droplet generator that produces droplets of a volume set by the geometry of the droplet generator and not by the flow rates of the liquids. The generator consists of a classic T-junction with a bypass channel. This bypass directs the continuous fluid around the forming

  5. Oxidation of SO{sub 2} and formation of water droplets under irradiation of 20 MeV protons in N{sub 2}/H{sub 2}O/SO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Tomita, Shigeo [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Nakai, Yoichi, E-mail: nakaiy@riken.jp [Radioactive Isotope Physics Laboratory, RIKEN Nishina Center, Wako, Saitama 351-0198 (Japan); Funada, Shuhei; Tanikawa, Hideomi; Harayama, Isao [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Kobara, Hitomi [National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8569 (Japan); Sasa, Kimikazu [Tandem Accelerator Complex, University of Tsukuba, Tsukuba, Ibaraki 305-8577 (Japan); Pedersen, Jens Olaf Pepke [National Space Institute, Technical University of Denmark, DK-2800 Kgs. Lyngby (Denmark); Hvelplund, Preben [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark)

    2015-12-15

    We have performed an experiment on charged droplet formation in a humidified N{sub 2} gas with trace SO{sub 2} concentration and induced by 20 MeV proton irradiation. It is thought that SO{sub 2} reacts with the chemical species, such as OH radicals, generated through the reactions triggered by N{sub 2}{sup +} production. Both droplet number and droplet size increased with SO{sub 2} consumption for the proton irradiation. The total charged droplet numbers entering the differential mobility analyzer per unit time were proportional to the 0.68 power of the SO{sub 2} consumption. These two findings suggest that coagulation among the small droplets contributes to the formation of the droplets. The charged droplet volume detected per unit time is proportional to the SO{sub 2} consumption, which indicates that a constant amount of sulfur atoms is contained in a unit volume of droplet, regardless of different droplet-size distributions depending on the SO{sub 2} consumption.

  6. Why droplet dimension can be larger than, equal to, or smaller than the nanowire dimension

    Science.gov (United States)

    Mohammad, S. Noor

    2009-11-01

    Droplets play central roles in the nanowire (NW) growth by vapor phase mechanisms. These mechanisms include vapor-liquid-solid (VLS), vapor-solid-solid or vapor-solid (VSS), vapor-quasisolid-solid or vapor-quasiliquid-solid (VQS), oxide-assisted growth (OAG), and self-catalytic growth (SCG) mechanisms. Fundamentals of the shape, size, characteristics, and dynamics of droplets and the impacts of them on the NW growth, have been studied. The influence of growth techniques, growth parameters (e.g., growth temperature, partial pressure, gas flow rates, etc.), thermodynamic conditions, surface and interface energy, molar volume, chemical potentials, etc. have been considered on the shapes and sizes of droplets. A model has been presented to explain why droplets can be larger than, equal to, or smaller than the associated NWs. Various growth techniques have been analyzed to understand defects created in NWs. Photoluminescence characteristics have been presented to quantify the roles of droplets in the creation of NW defects. The study highlights the importance of the purity of the droplet material. It attests to the superiority of the SCG mechanism, and clarifies the differences between the VSS, VQS, VLS, and SCG mechanisms. It explains why droplets produced by some mechanisms are visible but droplets produced by some other mechanisms are not visible. It elucidates the formation mechanisms of very large and very small droplets, and discusses the ground rules for droplets creating necked NWs. It puts forth reasons to demonstrate that very large droplets may not behave as droplets.

  7. A random-access microarray for programmable droplet storage, retrieval and manipulation

    International Nuclear Information System (INIS)

    Tseng, Yi-Ming; Wang, Jhih-Jhe; Su, Yu-Chuan

    2012-01-01

    This article presents an integrated microfluidic system that is capable of programmably metering, entrapping, coalescing, addressably storing, retrieving and manipulating emulsion droplets. A multilayer, flexible PDMS chip with specially designed fluidic channels dynamically reconfigured by pneumatically actuated diaphragms is utilized to integrate a variety of droplet manipulation schemes. Once droplets are formed, their motions are coordinated by a 2D multiplexing scheme, which exploits the bidirectional movement of diaphragms to implement a random-access microarray. In the prototype demonstration, a PDMS molding and bonding process is used to fabricate the proposed microfluidic system. Emulsion droplets with desired volumes and compositions are produced, addressably stored, manipulated and retrieved from a 4 × 4 array, which employs just 4 (= 2 × log 2 4) control inputs for the operation. It has been demonstrated that (1) the integration of droplet manipulation and 2D multiplexing schemes can be achieved readily using bidirectional diaphragm valves, (2) multiplexing of an N × N array could be realized utilizing only 2 × log 2 N control inputs and (3) a multifunctional, random-access microarray can be accomplished employing a multilayer PDMS chip. As such, the demonstrated random-access microarray could potentially serve as a platform for continuous tracking and multistep processing of emulsion droplets, which is desired for various biological and chemical applications. (paper)

  8. Dynamics of wetting explored with inkjet printing

    Directory of Open Access Journals (Sweden)

    Völkel Simeon

    2017-01-01

    Full Text Available An inkjet printer head, which is capable of depositing liquid droplets with a resolution of 22 picoliters and high repeatability, is employed to investigate the wetting dynamics of drops printed on a horizontal plane as well as on a granular monolayer. For a sessile drop on a horizontal plane, we characterize the contact angle hysteresis, drop volume and contact line dynamics from side view images. We show that the evaporation rate scales with the dimension of the contact line instead of the surface area of the drop. We demonstrate that the system evolves into a closed cycle upon repeating the depositing-evaporating process, owing to the high repeatability of the printing facility. Finally, we extend the investigation to a granular monolayer in order to explore the interplay between liquid deposition and granular particles.

  9. Hydrodynamics and PIV study in the impingement zone formed by a droplet train

    Science.gov (United States)

    Kanjirakat, Anoop; Sadr, Reza; Zhang, Taolue; Muthusamy, Jayaveera; Alvarado, Jorge; Texas A; M University at Qatar Collaboration; Texas A; M University College Station Collaboration

    2016-11-01

    Droplet impingement is encountered in numerous technical applications, such as ink jet printing, spray cooling, and fuel injection in internal combustion engines. Even though many studies in droplet impingement were conducted in past, not many have measured the near-wall velocities in the droplet impingement zone. With the goal of gaining a better understanding of the hydrodynamics in the impingement zone, well-controlled experiments are performed in combination with micro-PIV measurements and numerical simulations. Hydrodynamics of HFE-7100 droplets generated using a piezoelectric droplet generator, impinging on a pre-wetted surface is investigated. Micro-PIV studies in the high-velocity impingement zone are performed using one-micron meter fluorescent particles dispersed in HFE-7100 along with the double exposed images. Three-dimensional and 2D-axisymmetric numerical modeling for a transient droplet crown development is performed. The interface between the gas and the liquid is modeled using a Volume of Fluid (VOF) method. Numerical simulation results obtained are observed to be in good agreement with that of the experimental observations. Supported by National Priority Research Program (NPRP) of Qatar National Research Fund (QNRF), Grant No.: NPRP 6-1304-2-525.

  10. Comparison of capacitive and radio frequency resonator sensors for monitoring parallelized droplet microfluidic production

    KAUST Repository

    Conchouso Gonzalez, David; McKerricher, Garret; Carreno, Armando Arpys Arevalo; Castro, David; Shamim, Atif; Foulds, Ian G.

    2016-01-01

    with droplets of 100-150 μm in diameter, which were generated in parallelization devices at water-in-oil volume fractions (φ) between 11.1% and 33.3%.Using these sensors, we were able to measure accurately increments as small as 2.4% in the water volume fraction

  11. Black liquor devolatilization and swelling - a detailed droplet model and experimental validation

    International Nuclear Information System (INIS)

    Jaervinen, M.; Zevenhoven, R.; Vakkilainen, E.; Forssen, M.

    2003-01-01

    In this paper, we present results from a new detailed physical model for single black liquor droplet pyrolysis and swelling, and validate them against experimental data from a non-oxidizing environment using two different reactor configurations. In the detailed model, we solve for the heat transfer and gas phase mass transfer in the droplet and thereby, the intra-particle gas-char and gas-gas interactions during drying and devolatilization can be studied. In the experimental part, the mass change, the swelling behaviour, and the volume fraction of larger voids, i.e. cenospheres in the droplets were determined in a non-oxidizing environment. The model gave a good correlation with experimental swelling and mass loss data. Calculations suggest that a considerable amount of the char can be consumed before the entire droplet has experienced the devolatilization and drying stages of combustion. Char formed at the droplet surface layer is generally consumed by gasification with H 2 O flowing outwards from the droplet interior. The extent of char conversion during devolatilization and the rate of devolatilization are greatly affected by swelling and the formation of larger voids in the particle. The more the particle swells and the more homogeneous the particle structure is, the larger is the conversion of char at the end of devolatilization

  12. Integrated optics nano-opto-fluidic sensor based on whispering gallery modes for picoliter volume refractometry

    International Nuclear Information System (INIS)

    Gilardi, Giovanni; Beccherelli, Romeo

    2013-01-01

    We propose and numerically investigate an integrated optics refractometric nano-opto-fluidic sensor based on whispering gallery modes in sapphire microspheres. A measurand fluid is injected in a micromachined reservoir defined in between the microsphere and an optical waveguide. The wavelength shift due to changes in the refractive index of the measurand fluid are studied for a set of different configurations by the finite element method and a high sensitivity versus fluid volume is found. The proposed device can be tailored to work with a minimum fluid volume of 1 pl and a sensitivity up of 2000 nm/(RIU·nl). We introduce a figure of merit which quantifies the amplifying effect on the sensitivity of high quality factor resonators and allows us to compare different devices. (paper)

  13. Heteroaggregation of lipid droplets coated with sodium caseinate and lactoferrin.

    Science.gov (United States)

    de Figueiredo Furtado, Guilherme; Michelon, Mariano; de Oliveira, Davi Rocha Bernardes; da Cunha, Rosiane Lopes

    2016-11-01

    Formation and characterization of droplet heteroaggregates were investigated by mixing two emulsions previously stabilized by proteins oppositely charged. Emulsions were composed of 5vol.% of sunflower oil and 95vol.% of sodium caseinate or lactoferrin aqueous dispersions. They were produced using ultrasound with fixed power (300W) and sonication time (6min). Different volume ratios (0-100%) of sodium caseinate-stabilized emulsion (droplet diameter around 1.75μm) to lactoferrin-stabilized emulsion (droplet diameter around 1.55μm) were mixed under conditions that both proteins showed opposite charges (pH7). Influence of ionic strength (0-400mM NaCl) on the heteroaggregates stability was also evaluated. Creaming stability, zeta potential, microstructure, mean particle diameter and rheological properties of the heteroaggregates were measured. These properties depended on the volume ratio (0-100%) of sodium caseinate to lactoferrin-stabilized emulsion (C:L) and the ionic strength. In the absence of salt, different zeta potential values were obtained, rheological properties (viscosity and elastic moduli) were improved and the largest heteroaggregates were formed at higher content of lactoferrin-stabilized emulsion (60-80%). The system containing 40 and 60vol.% of sodium caseinate and lactoferrin stabilized emulsion, respectively, presented good stability against phase separation besides showing enhanced rheological and size properties due to extensive droplets aggregation. Phase separation was observed only in the absence of sodium caseinate, demonstrating the higher susceptibility of lactoferrin to NaCl. The heteroaggregates produced may be useful functional agents for texture modification and controlled release since different rheological properties and sizes can be achieved depending on protein concentrations. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Motion of water droplets in the counter flow of high-temperature combustion products

    Science.gov (United States)

    Volkov, R. S.; Strizhak, P. A.

    2018-01-01

    This paper presents the experimental studies of the deceleration, reversal, and entrainment of water droplets sprayed in counter current flow to a rising stream of high-temperature (1100 K) combustion gases. The initial droplets velocities 0.5-2.5 m/s, radii 10-230 μm, relative volume concentrations 0.2·10-4-1.8·10-4 (m3 of water)/(m3 of gas) vary in the ranges corresponding to promising high-temperature (over 1000 K) gas-vapor-droplet applications (for example, polydisperse fire extinguishing using water mist, fog, or appropriate water vapor-droplet veils, thermal or flame treatment of liquids in the flow of combustion products or high-temperature air; creating coolants based on flue gas, vapor and water droplets; unfreezing of granular media and processing of the drossed surfaces of thermal-power equipment; ignition of liquid and slurry fuel droplets). A hardware-software cross-correlation complex, high-speed (up to 105 fps) video recording tools, panoramic optical techniques (Particle Image Velocimetry, Particle Tracking Velocimetry, Interferometric Particle Imagine, Shadow Photography), and the Tema Automotive software with the function of continuous monitoring have been applied to examine the characteristics of the processes under study. The scale of the influence of initial droplets concentration in the gas flow on the conditions and features of their entrainment by high-temperature gases has been specified. The dependencies Red = f(Reg) and Red' = f(Reg) have been obtained to predict the characteristics of the deceleration of droplets by gases at different droplets concentrations.

  15. A numerical study on the dynamics of droplet formation in a microfluidic double T-junction.

    Science.gov (United States)

    Ngo, Ich-Long; Dang, Trung-Dung; Byon, Chan; Joo, Sang Woo

    2015-03-01

    In this study, droplet formations in microfluidic double T-junctions (MFDTD) are investigated based on a two-dimensional numerical model with volume of fluid method. Parametric ranges for generating alternating droplet formation (ADF) are identified. A physical background responsible for the ADF is suggested by analyzing the dynamical stability of flow system. Since the phase discrepancy between dispersed flows is mainly caused by non-symmetrical breaking of merging droplet, merging regime becomes the alternating regime at appropriate conditions. In addition, the effects of channel geometries on droplet formation are studied in terms of relative channel width. The predicted results show that the ADF region is shifted toward lower capillary numbers when channel width ratio is less than unity. The alternating droplet size increases with the increase of channel width ratio. When this ratio reaches unity, alternating droplets can be formed at very high water fraction (wf = 0.8). The droplet formation in MFDTD depends significantly on the viscosity ratio, and the droplet size in ADF decreases with the increase of the viscosity ratio. The understanding of underlying physics of the ADF phenomenon is useful for many applications, including nanoparticle synthesis with different concentrations, hydrogel bead generation, and cell transplantation in biomedical therapy.

  16. Fast electric control of the droplet size in a microfluidic T-junction droplet generator

    Science.gov (United States)

    Shojaeian, Mostafa; Hardt, Steffen

    2018-05-01

    The effect of DC electric fields on the generation of droplets of water and xanthan gum solutions in sunflower oil at a microfluidic T-junction is experimentally studied. The electric field leads to a significant reduction of the droplet diameter, by about a factor of 2 in the case of water droplets. The droplet size can be tuned by varying the electric field strength, an effect that can be employed to produce a stream of droplets with a tailor-made size sequence. Compared to the case of purely hydrodynamic droplet production without electric fields, the electric control has about the same effect on the droplet size if the electric stress at the liquid/liquid interface is the same as the hydrodynamic stress.

  17. Dual-nozzle microfluidic droplet generator

    Science.gov (United States)

    Choi, Ji Wook; Lee, Jong Min; Kim, Tae Hyun; Ha, Jang Ho; Ahrberg, Christian D.; Chung, Bong Geun

    2018-05-01

    The droplet-generating microfluidics has become an important technique for a variety of applications ranging from single cell analysis to nanoparticle synthesis. Although there are a large number of methods for generating and experimenting with droplets on microfluidic devices, the dispensing of droplets from these microfluidic devices is a challenge due to aggregation and merging of droplets at the interface of microfluidic devices. Here, we present a microfluidic dual-nozzle device for the generation and dispensing of uniform-sized droplets. The first nozzle of the microfluidic device is used for the generation of the droplets, while the second nozzle can accelerate the droplets and increase the spacing between them, allowing for facile dispensing of droplets. Computational fluid dynamic simulations were conducted to optimize the design parameters of the microfluidic device.

  18. The Investigation of Intermediate Stage of Template Etching with Metal Droplets by Wetting Angle Analysis on (001 GaAs Surface

    Directory of Open Access Journals (Sweden)

    Lyamkina AA

    2011-01-01

    Full Text Available Abstract In this work, we study metal droplets on a semiconductor surface that are the initial stage for both droplet epitaxy and local droplet etching. The distributions of droplet geometrical parameters such as height, radius and volume help to understand the droplet formation that strongly influences subsequent nanohole etching. To investigate the etching and intermixing processes, we offer a new method of wetting angle analysis. The aspect ratio that is defined as the ratio of the height to radius was used as an estimation of wetting angle which depends on the droplet material. The investigation of the wetting angle and the estimation of indium content revealed significant materials intermixing during the deposition time. AFM measurements reveal the presence of two droplet groups that is in agreement with nanohole investigations. To explain this observation, we consider arsenic evaporation and consequent change in the initial substrate. On the basis of our analysis, we suggest the model of droplet evolution and the formation of two droplet groups.

  19. Velocity and size distribution measurement of suspension droplets using PDPA technique

    Science.gov (United States)

    Amiri, Shahin; Akbarnozari, Ali; Moreau, Christian; Dolatabadi, Ali

    2015-11-01

    The creation of fine and uniform droplets from a bulk of liquid is a vital process in a variety of engineering applications, such as atomization in suspension plasma spray (SPS) in which the submicron coating materials are injected to the plasma gas through the suspension droplets. The size and velocity of these droplets has a great impact on the interaction of the suspension with the gas flow emanating from a plasma torch and can consequently affect the mechanical and chemical properties of the resultant coatings. In the current study, an aqueous suspension of small glass particles (2-8 μm) was atomized by utilizing an effervescent atomizer of 1 mm orifice diameter which involves bubbling gas (air) directly into the liquid stream. The gas to liquid ratio (GLR) was kept constant at 6% throughout this study. The mass concentration of glass particles varied in the range between 0.5 to 5% in order to investigate the effect of suspension viscosity and surface tension on the droplet characteristics, such as velocity and size distributions. These characteristics were simultaneously measured by using a non-intrusive optical technique, Phase Doppler Particle Anemometry (PDPA), which is based on the light signal scattered from the droplets moving in a measurement volume. The velocity and size distribution of suspension droplets were finally compared to those of distilled water under identical conditions. The results showed a different atomization behaviors due to the reduction in surface tension of the suspension spray.

  20. Electrical actuation of dielectric droplets

    International Nuclear Information System (INIS)

    Kumari, N; Bahadur, V; Garimella, S V

    2008-01-01

    Electrical actuation of liquid droplets at the microscale offers promising applications in the fields of microfluidics and lab-on-a-chip devices. Much prior research has targeted the electrical actuation of electrically conducting liquid droplets; however, the actuation of dielectric droplets has remained relatively unexplored, despite the advantages associated with the use of a dielectric droplet. This paper presents modeling and experimental results on the electrical actuation of dielectric droplets between two flat plates. A first-order analytical model, based on the energy-minimization principle, is developed to estimate the electrical actuation force on a dielectric droplet as it moves between two flat plates. Two versions of this analytical model are benchmarked for their suitability and accuracy against a detailed numerical model. The actuation force prediction is then combined with available semi-analytical expressions for predicting the forces opposing droplet motion to develop a model that predicts transient droplet motion under electrical actuation. Electrical actuation of dielectric droplets is experimentally demonstrated by moving transformer oil droplets between two flat plates under the influence of an actuation voltage. Droplet velocities and their dependence on the plate spacing and the applied voltage are experimentally measured and showed reasonable agreement with predictions from the models developed

  1. Fabrication of hemispherical liquid encapsulated structures based on droplet molding

    Science.gov (United States)

    Ishizuka, Hiroki; Miki, Norihisa

    2015-12-01

    We have developed and demonstrated a method for forming spherical structures of a thin polydimethylsiloxane (PDMS) membrane encapsulating a liquid. Liquid encapsulation can enhance the performance of microelectromechanical systems (MEMS) devices by providing deformability and improved dielectric properties. Parylene deposition and wafer bonding are applied to encapsulate liquid into a MEMS device. In parylene deposition, a parylene membrane is directly formed onto a liquid droplet. However, since the parylene membrane is stiff, the membrane is fragile. Although wafer bonding can encapsulate liquid between two substrates, the surface of the fabricated structure is normally flat. We propose a new liquid encapsulation method by dispensing liquid droplets. At first, a 20 μl PDMS droplet is dispensed on ethylene glycol. A 70 μl glycerin droplet is dispensed into a PDMS casting solution layer. The droplet forms a layer on heated ethylene glycol. Glycerin and ethylene glycol are chosen for their high boiling points. Additionally, a glycerin droplet is dispensed on the layer and surrounded by a thin PDMS casting solution film. The film is baked for 1 h at 75 °C. As the result, a structure encapsulating a liquid in a flexible PDMS membrane is obtained. We investigate the effects of the volume, surface tension, and guide thickness on the shape of the formed structures. We also evaluated the effect of the structure diameter on miniaturization. The structure can be adapted for various functions by changing the encapsulated liquid. We fabricated a stiffness-tunable structure by dispensing a magnetorheoligical fluid droplet with a stiffness that can be changed by an external magnetic field. We also confirmed that the proposed structure can produce stiffness differences that are distinguishable by humans.

  2. Optical calorimetry in microfluidic droplets.

    Science.gov (United States)

    Chamoun, Jacob; Pattekar, Ashish; Afshinmanesh, Farzaneh; Martini, Joerg; Recht, Michael I

    2018-05-29

    A novel microfluidic calorimeter that measures the enthalpy change of reactions occurring in 100 μm diameter aqueous droplets in fluoropolymer oil has been developed. The aqueous reactants flow into a microfluidic droplet generation chip in separate fluidic channels, limiting contact between the streams until immediately before they form the droplet. The diffusion-driven mixing of reactants is predominantly restricted to within the droplet. The temperature change in droplets due to the heat of reaction is measured optically by recording the reflectance spectra of encapsulated thermochromic liquid crystals (TLC) that are added to one of the reactant streams. As the droplets travel through the channel, the spectral characteristics of the TLC represent the internal temperature, allowing optical measurement with a precision of ≈6 mK. The microfluidic chip and all fluids are temperature controlled, and the reaction heat within droplets raises their temperature until thermal diffusion dissipates the heat into the surrounding oil and chip walls. Position resolved optical temperature measurement of the droplets allows calculation of the heat of reaction by analyzing the droplet temperature profile over time. Channel dimensions, droplet generation rate, droplet size, reactant stream flows and oil flow rate are carefully balanced to provide rapid diffusional mixing of reactants compared to thermal diffusion, while avoiding thermal "quenching" due to contact between the droplets and the chip walls. Compared to conventional microcalorimetry, which has been used in this work to provide reference measurements, this new continuous flow droplet calorimeter has the potential to perform titrations ≈1000-fold faster while using ≈400-fold less reactants per titration.

  3. Metal Droplet Formation in Gas Metal Arc Welding

    International Nuclear Information System (INIS)

    Haidar, J.

    2000-01-01

    A two-dimensional dynamic treatment has been developed for description of arc and electrode properties in gas metal arc welding (GMAW). The theory is a unified treatment of the arc the welding wire anode and the cathode, and includes a detailed account of sheath effects near the anode. The wire anode is included as a dynamic entity and the volume of fluid method is used to handle the movement of the free surface of the molten metal at the tip of the wire, accounting for effects of surface tension, inertia, gravity, arc pressure, viscous drag force of the plasma, magnetic forces and Marangoni effect, and also for the effects of wire feed rate in GMAW. Results of calculations made for a mild steel wire of diameter 0.16 cm are in good agreement with experimental measurements of droplet diameter and droplet detachment frequency at currents between 150 and 330 A, which includes the transition between ''globular'' and ''spray'' transfer. Quantitative predictions are also made of the amount of metal vapour that is generated from the welding droplets at the tip of the welding wire. (author)

  4. Real Time Monitoring of Containerless Microreactions in Acoustically Levitated Droplets via Ambient Ionization Mass Spectrometry.

    Science.gov (United States)

    Crawford, Elizabeth A; Esen, Cemal; Volmer, Dietrich A

    2016-09-06

    Direct in-droplet (in stillo) microreaction monitoring using acoustically levitated micro droplets has been achieved by combining acoustic (ultrasonic) levitation for the first time with real time ambient tandem mass spectrometry (MS/MS). The acoustic levitation and inherent mixing of microliter volumes of reactants (3 μL droplets), yielding total reaction volumes of 6 μL, supported monitoring the acid-catalyzed degradation reaction of erythromycin A. This reaction was chosen to demonstrate the proof-of-principle of directly monitoring in stillo microreactions via hyphenated acoustic levitation and ambient ionization mass spectrometry. The microreactions took place completely in stillo over 30, 60, and 120 s within the containerless stable central pressure node of an acoustic levitator, thus readily promoting reaction miniaturization. For the evaluation of the miniaturized in stillo reactions, the degradation reactions were also carried out in vials (in vitro) with a total reaction volume of 400 μL. The reacted in vitro mixtures (6 μL total) were similarly introduced into the acoustic levitator prior to ambient ionization MS/MS analysis. The in stillo miniaturized reactions provided immediate real-time snap-shots of the degradation process for more accurate reaction monitoring and used a fraction of the reactants, while the larger scale in vitro reactions only yielded general reaction information.

  5. Theoretical analysis and simulation of obstructed breakup of micro-droplet in T-junction under an asymmetric pressure difference

    Science.gov (United States)

    Fu, Yuhang; Bai, Lin; Jin, Yong; Cheng, Yi

    2017-03-01

    Asymmetric droplet breakup under a pressure difference at two outlets of a T-junction is investigated theoretically and numerically in this study. An accurate analysis of the evolution of droplet dynamics during the obstructed breakup process has been conducted. Meanwhile, the lattice Boltzmann method based on color gradient model is employed to simulate the system with the verification of the theoretical results. It is demonstrated that the Zou-He boundary setting at each outlet is advantageous for modifying the pressure drop of the two branches of T-junction. The results reveal that asymmetric breakup of the unequally sized droplets follows two steps, namely, the filling stage and the breakup stage. Then a universal parameter is proposed to describe the asymmetric condition of droplet breakup in T-junction, which plays a key role to characterize the temporal evolution of volume ratio and the droplet length of formed smaller droplets.

  6. Microfluidic passive permeability assay using nanoliter droplet interface lipid bilayers.

    Science.gov (United States)

    Nisisako, Takasi; Portonovo, Shiva A; Schmidt, Jacob J

    2013-11-21

    Membrane permeability assays play an important role in assessing drug transport activities across biological membranes. However, in conventional parallel artificial membrane permeability assays (PAMPA), the membrane model used is dissimilar to biological membranes physically and chemically. Here, we describe a microfluidic passive permeability assay using droplet interface bilayers (DIBs). In a microfluidic network, nanoliter-sized donor and acceptor aqueous droplets are alternately formed in cross-flowing oil containing phospholipids. Subsequently, selective removal of oil through hydrophobic pseudo-porous sidewalls induces the contact of the lipid monolayers, creating arrayed planar DIBs between the donor and acceptor droplets. Permeation of fluorescein from the donor to the acceptor droplets was fluorometrically measured. From the measured data and a simple diffusion model we calculated the effective permeabilities of 5.1 × 10(-6) cm s(-1), 60.0 × 10(-6) cm s(-1), and 87.6 × 10(-6) cm s(-1) with donor droplets at pH values of 7.5, 6.4 and 5.4, respectively. The intrinsic permeabilities of specific monoanionic and neutral fluorescein species were obtained similarly. We also measured the permeation of caffeine in 10 min using UV microspectroscopy, obtaining a permeability of 20.8 × 10(-6) cm s(-1). With the small solution volumes, short measurement time, and ability to measure a wide range of compounds, this device has considerable potential as a platform for high-throughput drug permeability assays.

  7. Lithography-free nanofluidic concentrator based on droplets-on-demand system

    Science.gov (United States)

    Yu, Miao; Zhou, Hongbo; Yao, Shuhuai

    2013-11-01

    Biomarkers are usually low-abundance proteins in biofluids and below detection limit of conventional biosensors. Nanofluidic concentration devices allow efficient biomolecules trapping by utilizing ion concentration polarization near nanochannels. However, once the electric field is turned off, the electrokinetic concentration plug cannot maintain its concentration status and starts to diffuse. In order to maintain the high concentration and extract the concentrated sample for further analysis, a good approach is to encapsulate these plugs into water-in-oil droplets. Here we developed a nanofluidic concentrator based on droplet-on-demand generator to encapsulate concentrated sample in nL droplets. The lithography-free nanochannels were patterned by thermal cracking on the surface of PS Petri-dish. The resulting nanochannel arrays were 30 nm in depth. In combination with microchannels on PDMS, the micro-nano hybrid chip was developed. We used FITC solution to demonstrate that the chip significantly increased the sample concentration for more than 100 folds within 5 minutes. By tuning the pulsed pressure imposed by the solenoid valve connected to the concentration channel, the system can generate a desired volume of droplet with a target sample concentration at a prescribed time. This work was supported by the Research Grants Council of Hong Kong under General Research Fund (Grant No. 621110).

  8. An infrared scattering by evaporating droplets at the initial stage of a pool fire suppression by water sprays

    Science.gov (United States)

    Dombrovsky, Leonid A.; Dembele, Siaka; Wen, Jennifer X.

    2018-06-01

    The computational analysis of downward motion and evaporation of water droplets used to suppress a typical transient pool fire shows local regions of a high volume fraction of relatively small droplets. These droplets are comparable in size with the infrared wavelength in the range of intense flame radiation. The estimated scattering of the radiation by these droplets is considerable throughout the entire spectrum except for a narrow region in the vicinity of the main absorption peak of water where the anomalous refraction takes place. The calculations of infrared radiation field in the model pool fire indicate the strong effect of scattering which can be observed experimentally to validate the fire computational model.

  9. Optimization of digital droplet polymerase chain reaction for quantification of genetically modified organisms.

    Science.gov (United States)

    Gerdes, Lars; Iwobi, Azuka; Busch, Ulrich; Pecoraro, Sven

    2016-03-01

    Digital PCR in droplets (ddPCR) is an emerging method for more and more applications in DNA (and RNA) analysis. Special requirements when establishing ddPCR for analysis of genetically modified organisms (GMO) in a laboratory include the choice between validated official qPCR methods and the optimization of these assays for a ddPCR format. Differentiation between droplets with positive reaction and negative droplets, that is setting of an appropriate threshold, can be crucial for a correct measurement. This holds true in particular when independent transgene and plant-specific reference gene copy numbers have to be combined to determine the content of GM material in a sample. Droplets which show fluorescent units ranging between those of explicit positive and negative droplets are called 'rain'. Signals of such droplets can hinder analysis and the correct setting of a threshold. In this manuscript, a computer-based algorithm has been carefully designed to evaluate assay performance and facilitate objective criteria for assay optimization. Optimized assays in return minimize the impact of rain on ddPCR analysis. We developed an Excel based 'experience matrix' that reflects the assay parameters of GMO ddPCR tests performed in our laboratory. Parameters considered include singleplex/duplex ddPCR, assay volume, thermal cycler, probe manufacturer, oligonucleotide concentration, annealing/elongation temperature, and a droplet separation evaluation. We additionally propose an objective droplet separation value which is based on both absolute fluorescence signal distance of positive and negative droplet populations and the variation within these droplet populations. The proposed performance classification in the experience matrix can be used for a rating of different assays for the same GMO target, thus enabling employment of the best suited assay parameters. Main optimization parameters include annealing/extension temperature and oligonucleotide concentrations. The

  10. Entropy Analyses of Droplet Combustion in Convective Environment with Small Reynolds Number

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xiaobin; ZHANG Wei; ZHANG Xuejun

    2013-01-01

    This paper analyzes the entropy generation rate of simple pure droplet combustion in a temperature-elevated air convective environment based on the solutions of flow,and heat and mass transfer between the two phases.The flow-field calculations are carried out by solving the respective conservation equations for each phase,accounting for the droplet deformation with the axisymmetric model.The effects of the temperature,velocity and oxygen fraction of the free stream air on the total entropy generation rate in the process of the droplet combustion are investigated.Special attention is given to analyze the quantitative effects of droplet deformation.The results reveal that the entropy generation rate due to chemical reaction occupies a large fraction of the total entropy generated,as a result of the large areas covered by the flame.Although,the magnitude of the entropy generation rate per volume due to heat transfer and combined mass and heat transfer has a magnitude of one order greater than that due to chemical reaction,they cover a very limited area,leading to a small fraction of the total entropy generated.The entropy generation rate due to mass transfer is negligible.High temperature and high velocity of the free stream are advantageous to increase the exergy efficiency in the range of small Reynolds number (<1) from the viewpoint of the second-law analysis over the droplet lifetime.The effect of droplet deformation on the total entropy generation is the modest.

  11. Hydrophobic polymer covered by a grating electrode for converting the mechanical energy of water droplets into electrical energy

    Science.gov (United States)

    Helseth, L. E.; Guo, X. D.

    2016-04-01

    Water contact electric harvesting has a great potential as a new energy technology for powering small-scale electronics, but a better understanding of the dynamics governing the conversion from mechanical to electrical energy on the polymer surfaces is needed. Important questions are how current correlates with droplet kinetic energy and what happens to the charge dynamics when a large number of droplets are incident on the polymer simultaneously. Here we address these questions by studying the current that is generated in an external electrical circuit when water droplets impinge on hydrophobic fluorinated ethylene propylene film containing a grating electrode on the back side. Droplets moving down an inclined polymer plane exhibit a characteristic periodic current time trace, and it is found that the peak current scales with sine of the inclination angle. For single droplets in free fall impinging onto the polymer, it is found that the initial peak current scales with the height of the free fall. The transition from individual droplets to a nearly continuous stream was investigated using the spectral density of the current signal. In both regimes, the high frequency content of the spectral density scales as f -2. For low frequencies, the low frequency content at low volume rates was noisy but nearly constant, whereas for high volume rates an increase with frequency is observed. It is demonstrated that the output signal from the system exposed to water droplets from a garden hose can be rectified and harvested by a 33 μF capacitor, where the stored energy increases at a rate of about 20 μJ in 100 s.

  12. A Burke-Schumann Analysis of Dual-Flame Structure Supported by a Burning Droplet

    Science.gov (United States)

    Nayagam, V.; Dietrich, D.; Williams, F. A.

    2016-01-01

    Droplet combustion experiments carried out onboard the International Space Station (ISS), using pure fuels and fuel mixtures, have shown that quasi-steady burning can be sustained by a non-traditional flame configuration, namely a "cool flame" burning in the "partial-burning" regime where both fuel and oxygen leak through the low-temperature controlled flame-sheet. Recent experiments involving large, bi-component fuel (n-decane and hexanol, 50/50 by volume) droplets at elevated pressures show that the visible, hot flame becomes extremely weak while the burning rate remains relatively high, suggesting the possibility of simultaneous presence of "cool" and "hot" flames of roughly equal importance. The radiant output from these bi-component droplets is relatively high and cannot be accounted for only by the presence of a visible hot-flame. In this analysis we explore the theoretical possibility of a dual-flame structure, where one flame lies close to the droplet surface called the "cool-flame," and other farther away from the droplet surface, termed the "hot-flame." A Burke-Schumann analysis of this dual-structure seems to indicate such flame structures are possible over a narrow range of initial conditions. Theoretical results can be compared against available experimental data for pure and bi-component fuel droplet combustion to test how realistic the model may be.

  13. Butschli Dynamic Droplet System

    DEFF Research Database (Denmark)

    Armstrong, R.; Hanczyc, M.

    2013-01-01

    Dynamical oil-water systems such as droplets display lifelike properties and may lend themselves to chemical programming to perform useful work, specifically with respect to the built environment. We present Butschli water-in-oil droplets as a model for further investigation into the development...... reconstructed the Butschli system and observed its life span under a light microscope, observing chemical patterns and droplet behaviors in nearly three hundred replicate experiments. Self-organizing patterns were observed, and during this dynamic, embodied phase the droplets provided a means of introducing...... temporal and spatial order in the system with the potential for chemical programmability. The authors propose that the discrete formation of dynamic droplets, characterized by their lifelike behavior patterns, during a variable window of time (from 30 s to 30 min after the addition of alkaline water...

  14. Comparison of various droplet breakup models in gas-liquid flows in high-pressure environments

    International Nuclear Information System (INIS)

    Khaleghi, H.; Ganji, D. D.; Omidvar, A.

    2008-01-01

    Droplet breakup affects spray penetration and evaporation, and plays a critical role in engine efficiency. The purpose of this research was to examine the rate of penetration and evaporation of droplets in a combustion chamber, and the efficiency of the engine when liquid jet is injected into the compressed gas chamber in an axi-symmetrical fashion leading to a turbulent and unsteady flow. As a result of interaction with the highly compressed air in the chamber, the liquid jet breaks up and forms minute droplets. These particles will in turn breakup because of aerodynamic forces, producing even smaller droplets. A number of models are available for analyzing the breakup of droplets; however, each model is typically reliable only over a limited parameter range. In this research three well-known models are applied for droplet breakup modeling and their results are compared. To obtain the details of the flow field, the Eulerian gas phase mass, momentum and energy conservation equations, as well as equations governing the transport of turbulence and fuel vapor mass fraction are solved together with equations of trajectory, momentum, mass and energy conservation for liquid droplets in Lagrangian form. The numerical solution is performed using the finite volume method and EPISO (Engine-PISO) algorithm. The results obtained from the models show that the breakup process in a high pressure environment significantly affects the penetration and evaporation rates of the spray, and the droplet size is determined by the balance between breakup and coalescence processes. It is also shown that the details of atomization in the nozzle do not significantly influence the ultimate size of droplets. It should be mentioned that droplet collision modeling has been taken into account in the computer code and is activated wherever necessary

  15. Shock wave-induced evaporation of water droplets in a gas-droplet mixture 646

    NARCIS (Netherlands)

    Goossens, H.W.J.; Cleijne, J.W.; Smolders, H.J.; Dongen, van M.E.H.

    1988-01-01

    A model is presented for the droplet evaporation process induced by a shock wave propagating in a fog. The model is based on the existence of a quasi-steady wet bulb state of the droplets during evaporation. It is shown that for moderate shock strength, Ma = <2,=" and=" droplet=" radii=" in=" the="

  16. Experimental and numerical investigations of liquid mercury droplet impacts

    International Nuclear Information System (INIS)

    Naoe, Takashi; Futakawa, Masatoshi; Kenny, Richard Gerrard; Otsuki, Masato

    2014-01-01

    A broad investigation into the hydrodynamics of liquid mercury has been motivated of late by its use in MW-scale spallation neutron sources. One area of particular concern relates to the erosion suffered by vessel walls from the cumulative effects of liquid mercury droplet impacts arising from the collapse of cavitation bubbles. The low speed (< 5 m/s) range of such events forms the focus of this paper and to this end a series of experiments is conducted on spherical droplets of diameter 2.5 mm impacting upon a dry quartz surface. A reasonable simulation of such impacts is made possible by using the VOF (volume of fluid) solver interFoam (a part of the open source package OpenFOAM) in combination with an empirical expression for the dynamic contact angle of the air-mercury-quartz system. This latter represents a 'best fit' to data obtained from high resolution imaging of the droplet profile for a range of contact line velocities. Experiment and simulation are subsequently compared throughout the stages of initial deposition, spread, recession with break-up and, finally, bounce. (author)

  17. Dependence of the Internal Structure on Water/Particle Volume Ratio in an Amphiphilic Janus Particle-Water-Oil Ternary System: From Micelle-like Clusters to Emulsions of Spherical Droplets.

    Science.gov (United States)

    Noguchi, Tomohiro G; Iwashita, Yasutaka; Kimura, Yasuyuki

    2017-01-31

    Amphiphilic Janus particles (AJP), composed of hydrophilic and hydrophobic hemispheres, are one of the simplest anisotropic colloids, and they exhibit higher surface activities than particles with homogeneous surface properties. Consequently, a ternary system of AJP, water, and oil can form extremely stable Pickering emulsions, with internal structures that depend on the Janus structure of the particles and the system composition. However, the detail of these structures has not been fully explored, especially for the composition range where the amount of the minority liquid phase and AJP are comparable, where one would expect the Janus characteristics to be directly reflected. In this study, we varied the volume ratio of the particles and the minority liquid phase, water, by 2 orders of magnitude around the comparable composition range, and observed the resultant structures at the resolution of the individual particle dimensions by optical microscopy. When the volume ratio of water is smaller than that of the Janus particles, capillary interactions between the hydrophilic hemispheres of the particles induce micelle-like clusters in which the hydrophilic sides of the particles face inward. With increasing water content, these clusters grow into a rodlike morphology. When the water volume exceeds that of the particles, the structure transforms into an emulsion state composed of spherical droplets, colloidosomes, because of the surface activity of particles at the liquid-liquid interface. Thus, we found that a change in volume fraction alters the mechanism of structure formation in the ternary system, and large resulting morphological changes in the self-assembled structures reflect the anisotropy of the particles. The self-assembly shows essential commonalities with that in microemulsions of surfactant molecules, however the AJP system is stabilized only kinetically. Analysis of the dependence of the emulsion droplet size on composition shows that almost all the

  18. Growth and dissolution of liquid 3He droplets in solid 4He matrix

    International Nuclear Information System (INIS)

    Gan'shin, A.N.; Grigor'ev, V.N.; Majdanov, V.A.; Penzev, A.A.; Rudavskij, Eh.Ya.; Rybalko, A.S.

    2000-01-01

    The phase separation kinetics of solid 3 He - 4 He mixtures was investigated using pressure measurements in the conditions when the two-phase system formed consists of concentrated phase liquid droplets (almost pure 3 He) in the dilute phase crystal matrix (almost pure 4 He). It is shown that the liquid droplet growth may be described by a sum of two exponential processes with small and large time contacts as cooling down step by step. This is a result of the strong influence of strains which appear in the crystal at the phase separation due to a large difference in molar volume between the phases and probably give rise to plastic deformation of the matrix and to non-equilibrium 3 He concentration in it. The 3 He atom transfer occurs only to the extent of strain relaxation. It is found that the cyclic growth and dissolution of the liquid droplets affect the crystal quality and lead to pressure increase. The coexistence of liquid and solid phases in droplets is speculated to be possible

  19. Investigation of Different Droplet Formation Regimes in a T-junction Microchannel Using the VOF Technique in OpenFOAM

    Science.gov (United States)

    Malekzadeh, Shima; Roohi, Ehsan

    2015-06-01

    Here we aimed to investigate various droplet formation regimes in a two-dimensional T-junction microchannel geometry using the open source software OpenFOAM. Two incompressible fluids, continuous phase in the main channel and dispersed phase in the lateral channel, have been considered. The interFoam solver was used to simulate laminar flow with two incompressible and isothermal phases. We evaluated the capability of "Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM)" volume of fluid (VOF) technique of the OpenFOAM for modeling of the droplet formation and movement in different regimes. The flow behavior in the T-junction microchannel over a wide range of capillary numbers (0.006 to 0.12), volume flow rate ratio (0.125, 0.25, 0.5), and contact angle (130° to 180°) in the squeezing, dripping and jetting regimes were examined.The importance of parameters such as contact angle, capillary number, flow rate ratio, and Reynolds number at the time of separation, as well as the formation of droplets, was investigated in different regimes. We found that droplet detachment time increases by increasing the contact angle in the squeezing regime while increasing the contact angle in the dripping regime results in a decrease in the droplet detachment time. We compare the role of pressure gradient and shear stress forces in the droplet formation process in both dripping and squeezing regimes in details. We also provide a classification of two-phase flow regimes in the investigated T-junction microchannel in terms of three main parameters of, e.g., flow rate ratio, contact angle, and capillary number.

  20. A numerical study of three-dimensional droplets spreading on chemically patterned surfaces

    KAUST Repository

    Zhong, Hua

    2016-09-26

    We study numerically the three-dimensional droplets spreading on physically flat chemically patterned surfaces with periodic squares separated by channels. Our model consists of the Navier-Stokes-Cahn-Hilliard equations with the generalized Navier boundary conditions. Stick-slip behavior and con-tact angle hysteresis are observed. Moreover, we also study the relationship between the effective advancing/receding angle and the two intrinsic angles of the surface patterns. By increasing the volume of droplet gradually, we find that the advancing contact line tends gradually to an equiangular octagon with the length ratio of the two adjacent sides equal to a fixed value that depends on the geometry of the pattern.

  1. Droplet behavior analysis in consideration of droplet entrainment from liquid film in annular dispersed flow

    International Nuclear Information System (INIS)

    Matsuura, Keizo; Otake, Hiroshi; Kataoka, Isao; Serizawa, Akimi

    2000-01-01

    A method of droplet behavior simulation in an annular dispersed flow has been developed. In this method, both droplet deposition and entrainment from liquid film are considered. The Lagrangian method and stochastic model are used to analyze droplet diffusion and deposition behavior in a turbulent flow, and droplet entrainment from liquid film is calculated by an entrainment correlation. For the verification of this method, Gill's experiment is analyzed, in which the transition from annular flow with no entrainment to equilibrium annular dispersed flow was observed. Analysis results can also show the similar transition tendency. The experimental results of radial distribution of droplet mass flux are compared with analysis results. The agreement is good for low liquid flow rate, but entrainment rate must be adjusted for high liquid flow rate, in which gas turbulence is thought to be modified by high droplet density. In future work the effect of high droplet density on turbulence should be considered. (author)

  2. Microfluidic Fabrication of Porous Polymer Microspheres: Dual Reactions in Single Droplets

    KAUST Repository

    Gong, Xiuqing

    2009-06-16

    We report the microfluidic fabrication of macroporous polymer microspheres via the simultaneous reactions within single droplets, induced by LTV irradiation. The aqueous phase of the reaction is the decomposition of H 2O2 to yield oxygen, whereas the organic phase is the polymerization of NO A 61, ethylene glycol dimethacrylate (EGDMA), and tri (propylene glycol) diacrylate (TPGDA) precursors. We first used a liquid polymer precursor to encapsulate a multiple number of magnetic Fe3O 4 colloidal suspension (MCS) droplets in a core-shell structure, for the purpose of studying the number of such encapsulated droplets that can be reliably controlled through the variation of flow rates. It was found that the formation of one shell with one, two, three, or more encapsulated droplets is possible. Subsequently, the H2O2 solution was encapsulated in the same way, after which we investigated its decomposition under UV irradiation, which simultaneously induces the polymerization of the encapsulating shell. Because the H2O2 decomposition leads to the release of oxygen, porous microspheres were obtained from a combined H2O2 decomposition/polymer precursor polymerization reaction. The multiplicity of the initially encapsulated H2O 2 droplets ensures the homogeneous distribution of the pores. The pores inside the micrometer-sized spheres range from several micrometers to tens of micrometers, and the maximum internal void volume fraction can attain 70%, similar to that of high polymerized high internal phase emulsion (polyHIPE). © 2009 American Chemical Society.

  3. Simulation of High-Speed Droplet Impact Against Dry Substrates with Partial Velocity Slip

    Science.gov (United States)

    Kondo, Tomoki; Ando, Keita

    2017-11-01

    High-speed droplet impact can be used to clean substrates such as silicon wafers. Radially spreading shear flow after the impact may allow for mechanically removing contaminant particles at substrate surfaces. Since it is a big challenge to experimentally explore such complicated flow that exhibits contact line motion and water hammer, its flow feature is not well understood. Here, we aim to numerically evaluate shear flow caused by the impact of a spherical water droplet (of submillimeter sizes) at high speed (up to 50 m/s) against a dry rigid wall. We model the flow based on compressible Navier-Stokes equations with Stokes' hypothesis and solve them by a high-order-accurate finite volume method equipped with shock and interface capturing. To treat the motion of a contact line between the three phases (the droplet, the rigid wall, and the ambient air) in a robust manner, we permit velocity slip at the wall with Navier's model, for wall slip is known to come into play under steep velocity gradients that can arise from high-speed droplet impact. In our presentation, we will examine radially spreading flow after the droplet impact and the resulting wall shear stress generation from the simulation. This work was supported by JSPS KAKENHI Grant Number JP17J02211.

  4. Electrohydrodynamic simulation of electrically controlled droplet generation

    International Nuclear Information System (INIS)

    Ouedraogo, Yun; Gjonaj, Erion; Weiland, Thomas; Gersem, Herbert De; Steinhausen, Christoph; Lamanna, Grazia; Weigand, Bernhard

    2017-01-01

    Highlights: • We develop a full electrohydrodynamic simulation approach which allows for the accurate modeling of droplet dynamics under the influence of transient electric fields. The model takes into account conductive, capacitive as well as convective electrical currents in the fluid. • Simulation results are shown for an electrically driven droplet generator using highly conductive acetone droplets and low conductivity pentane droplets, respectively. Excellent agreement with measurement is found. • We investigate the operation characteristic of the droplet generator by computing droplet sizes and detachment times with respect to the applied voltage. • The droplet charging effect is demonstrated for pentane droplets as well as for acetone droplets under long voltage pulses. We show that due to the very different relaxation times, the charging behavior of the two liquids is very different. • We demonstrate that due to this behavior, also the detachment mechanisms for acetone and pentane droplets are different. For low conductivity (pentane) droplets, droplet detachment is only possible after the electric fields are switched off. This is because the effective electric polarization force points upwards, thus, inhibiting the detachment of the droplet from the capillary tip. - Abstract: An electrohydrodynamic model for the simulation of droplet formation, detachment and motion in an electrically driven droplet generator is introduced. The numerical approach is based on the coupled solution of the multiphase flow problem with the charge continuity equation. For the latter, a modified convection-conduction model is applied, taking into account conductive, capacitive as well as convective electrical currents in the fluid. This allows for a proper description of charge relaxation phenomena in the moving fluid. In particular, the charge received by the droplet after detachment is an important parameter influencing the droplet dynamics in the test chamber

  5. Arrested of coalescence of emulsion droplets of arbitrary size

    Science.gov (United States)

    Mbanga, Badel L.; Burke, Christopher; Blair, Donald W.; Atherton, Timothy J.

    2013-03-01

    With applications ranging from food products to cosmetics via targeted drug delivery systems, structured anisotropic colloids provide an efficient way to control the structure, properties and functions of emulsions. When two fluid emulsion droplets are brought in contact, a reduction of the interfacial tension drives their coalescence into a larger droplet of the same total volume and reduced exposed area. This coalescence can be partially or totally hindered by the presence of nano or micron-size particles that coat the interface as in Pickering emulsions. We investigate numerically the dependance of the mechanical stability of these arrested shapes on the particles size, their shape anisotropy, their polydispersity, their interaction with the solvent, and the particle-particle interactions. We discuss structural shape changes that can be induced by tuning the particles interactions after arrest occurs, and provide design parameters for the relevant experiments.

  6. Global rainbow refractometry for droplet temperature measurement

    Energy Technology Data Exchange (ETDEWEB)

    Pascal Lemaitre; Emmanuel Porcheron; Amandine Nuboer; Philippe Brun; Pierre Cornet; Jeanne Malet; Jacques Vendel; Laurent Bouilloux [Institut de Radioprotection et de Surete Nucleaire DSU/SERAC, BP 68, 91192 Gif-sur-Yvette Cedex (France); Gerard Grehan [UMR 6614 CORIA, Laboratoire d' Electromagnetisme et Systemes Particulaires Site Universitaire du Madrillet, Avenue de l' universite BP 12, 76 801 Saint Etienne du Rouvray Cedex, (France)

    2005-07-01

    Full text of publication follows: In order to establish an accurate database to characterize the heat and mass transfers between a spray and the atmosphere with thermal-hydraulic conditions representative of a hypothetical nuclear reactor accident in the containment enclosure of a pressurized water reactor (PWR), the French Institut de Radioprotection et de Surete Nucleaire (IRSN) has developed the TOSQAN experimental facility. This experiment is highly instrumented with non-intrusive diagnostics allowing to measure droplet size and velocity and gas concentrations [1]. The aim of this work is to present the Global Rainbow Thermometry (GRT), which is an advanced non-intrusive optical diagnostic, developed to measure the mean temperature of a set of falling droplets, in a measurement volume of 1 cm{sup 3}. The final paper will be divided in three parts. In the first one, we will explain the principle of the rainbow formation and how droplet temperature can be deduced from the rainbow analysis [2]. This part will be illustrated with the theoretical background on the rainbow and numerical simulations of the global rainbow. The second part will be devoted to present the global rainbow experimental set-up we have developed on optical table, its experimental qualification and finally its implementation on the TOSQAN facility [3]. Finally, we will present the temperature measurements achieved in TOSQAN for thermal-hydraulic conditions representative of a hypothetical nuclear reactor accident. These measurements are useful to characterize the heat and mass transfers between the spraying droplets and the air-steam mixture composing the atmosphere. This analysis will be exposed in a two companion papers. References: [1] E. Porcheron, P. Brun, P. Cornet, J. Malet, J. Vendel. Optical diagnostics applied for single and multi-phase flow characterization in the TOSQAN facility dedicated for thermal hydraulic containment studies. NURETH-10 Seoul, Korea, October 5-9, 2003. [2] P

  7. Global rainbow refractometry for droplet temperature measurement

    International Nuclear Information System (INIS)

    Pascal Lemaitre; Emmanuel Porcheron; Amandine Nuboer; Philippe Brun; Pierre Cornet; Jeanne Malet; Jacques Vendel; Laurent Bouilloux; Gerard Grehan

    2005-01-01

    Full text of publication follows: In order to establish an accurate database to characterize the heat and mass transfers between a spray and the atmosphere with thermal-hydraulic conditions representative of a hypothetical nuclear reactor accident in the containment enclosure of a pressurized water reactor (PWR), the French Institut de Radioprotection et de Surete Nucleaire (IRSN) has developed the TOSQAN experimental facility. This experiment is highly instrumented with non-intrusive diagnostics allowing to measure droplet size and velocity and gas concentrations [1]. The aim of this work is to present the Global Rainbow Thermometry (GRT), which is an advanced non-intrusive optical diagnostic, developed to measure the mean temperature of a set of falling droplets, in a measurement volume of 1 cm 3 . The final paper will be divided in three parts. In the first one, we will explain the principle of the rainbow formation and how droplet temperature can be deduced from the rainbow analysis [2]. This part will be illustrated with the theoretical background on the rainbow and numerical simulations of the global rainbow. The second part will be devoted to present the global rainbow experimental set-up we have developed on optical table, its experimental qualification and finally its implementation on the TOSQAN facility [3]. Finally, we will present the temperature measurements achieved in TOSQAN for thermal-hydraulic conditions representative of a hypothetical nuclear reactor accident. These measurements are useful to characterize the heat and mass transfers between the spraying droplets and the air-steam mixture composing the atmosphere. This analysis will be exposed in a two companion papers. References: [1] E. Porcheron, P. Brun, P. Cornet, J. Malet, J. Vendel. Optical diagnostics applied for single and multi-phase flow characterization in the TOSQAN facility dedicated for thermal hydraulic containment studies. NURETH-10 Seoul, Korea, October 5-9, 2003. [2] P

  8. Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

    Directory of Open Access Journals (Sweden)

    Fedorov A

    2010-01-01

    Full Text Available Abstract We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background.

  9. Uniform-droplet spray forming

    Energy Technology Data Exchange (ETDEWEB)

    Blue, C.A.; Sikka, V.K. [Oak Ridge National Lab., TN (United States); Chun, Jung-Hoon [Massachusetts Institute of Technology, Cambridge, MA (United States); Ando, T. [Tufts Univ., Medford, MA (United States)

    1997-04-01

    The uniform-droplet process is a new method of liquid-metal atomization that results in single droplets that can be used to produce mono-size powders or sprayed-on to substrates to produce near-net shapes with tailored microstructure. The mono-sized powder-production capability of the uniform-droplet process also has the potential of permitting engineered powder blends to produce components of controlled porosity. Metal and alloy powders are commercially produced by at least three different methods: gas atomization, water atomization, and rotating disk. All three methods produce powders of a broad range in size with a very small yield of fine powders with single-sized droplets that can be used to produce mono-size powders or sprayed-on substrates to produce near-net shapes with tailored microstructures. The economical analysis has shown the process to have the potential of reducing capital cost by 50% and operating cost by 37.5% when applied to powder making. For the spray-forming process, a 25% savings is expected in both the capital and operating costs. The project is jointly carried out at Massachusetts Institute of Technology (MIT), Tuffs University, and Oak Ridge National Laboratory (ORNL). Preliminary interactions with both finished parts and powder producers have shown a strong interest in the uniform-droplet process. Systematic studies are being conducted to optimize the process parameters, understand the solidification of droplets and spray deposits, and develop a uniform-droplet-system (UDS) apparatus appropriate for processing engineering alloys.

  10. Hydrodynamics of a quark droplet

    DEFF Research Database (Denmark)

    Bjerrum-Bohr, Johan J.; Mishustin, Igor N.; Døssing, Thomas

    2012-01-01

    We present a simple model of a multi-quark droplet evolution based on the hydrodynamical description. This model includes collective expansion of the droplet, effects of the vacuum pressure and surface tension. The hadron emission from the droplet is described following Weisskopf's statistical...

  11. Numerical evaluation of droplet sizing based on the ratio of fluorescent and scattered light intensities (LIF/Mie technique)

    International Nuclear Information System (INIS)

    Charalampous, Georgios; Hardalupas, Yannis

    2011-01-01

    The dependence of fluorescent and scattered light intensities from spherical droplets on droplet diameter was evaluated using Mie theory. The emphasis is on the evaluation of droplet sizing, based on the ratio of laser-induced fluorescence and scattered light intensities (LIF/Mie technique). A parametric study is presented, which includes the effects of scattering angle, the real part of the refractive index and the dye concentration in the liquid (determining the imaginary part of the refractive index). The assumption that the fluorescent and scattered light intensities are proportional to the volume and surface area of the droplets for accurate sizing measurements is not generally valid. More accurate sizing measurements can be performed with minimal dye concentration in the liquid and by collecting light at a scattering angle of 60 deg. rather than the commonly used angle of 90 deg. Unfavorable to the sizing accuracy are oscillations of the scattered light intensity with droplet diameter that are profound at the sidescatter direction (90 deg.) and for droplets with refractive indices around 1.4.

  12. Liquid droplet radiator technology issues

    International Nuclear Information System (INIS)

    Mattick, A.T.; Hertzberg, A.

    1985-01-01

    The operation of the liquid droplet radiator (LDR) is analyzed to establish design constraints for the LDR components and to predict the performance of an integrated LDR system. The design constraints largely result from mass loss considerations: fluid choice is governed by evaporation loss; droplet generation techniques must be capable of precise aiming of >10 5 droplet streams; and collection losses must be less than 1 droplet in 10 7 . Concepts for droplet generation and collection components are discussed and incorporated into a mass model for an LDR system. This model predicts that LDR's using lithium, Dow 705 silicone fluid, or NaK may be several times lighter than heat pipe radiators. 13 refs

  13. Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100

    Directory of Open Access Journals (Sweden)

    J. K. Spiegel

    2012-09-01

    Full Text Available Droplet size spectra measurements are crucial to obtain a quantitative microphysical description of clouds and fog. However, cloud droplet size measurements are subject to various uncertainties. This work focuses on the error analysis of two key measurement uncertainties arising during cloud droplet size measurements with a conventional droplet size spectrometer (FM-100: first, we addressed the precision with which droplets can be sized with the FM-100 on the basis of the Mie theory. We deduced error assumptions and proposed a new method on how to correct measured size distributions for these errors by redistributing the measured droplet size distribution using a stochastic approach. Second, based on a literature study, we summarized corrections for particle losses during sampling with the FM-100. We applied both corrections to cloud droplet size spectra measured at the high alpine site Jungfraujoch for a temperature range from 0 °C to 11 °C. We showed that Mie scattering led to spikes in the droplet size distributions using the default sizing procedure, while the new stochastic approach reproduced the ambient size distribution adequately. A detailed analysis of the FM-100 sampling efficiency revealed that particle losses were typically below 10% for droplet diameters up to 10 μm. For larger droplets, particle losses can increase up to 90% for the largest droplets of 50 μm at ambient wind speeds below 4.4 m s−1 and even to >90% for larger angles between the instrument orientation and the wind vector (sampling angle at higher wind speeds. Comparisons of the FM-100 to other reference instruments revealed that the total liquid water content (LWC measured by the FM-100 was more sensitive to particle losses than to re-sizing based on Mie scattering, while the total number concentration was only marginally influenced by particle losses. Consequently, for further LWC measurements with the FM-100 we strongly recommend to consider (1 the

  14. Liquid droplet sensing using twisted optical fiber couplers fabricated by hydrofluoric acid flow etching

    Science.gov (United States)

    Son, Gyeongho; Jung, Youngho; Yu, Kyoungsik

    2017-04-01

    We report a directional-coupler-based refractive index sensor and its cost-effective fabrication method using hydrofluoric acid droplet wet-etching and surface-tension-driven liquid flows. The proposed fiber sensor consists of a pair of twisted tapered optical fibers with low excess losses. The fiber cores in the etched microfiber region are exposed to the surrounding medium for efficient interaction with the guided light. We observe that the etching-based low-loss fiber-optic sensors can measure the water droplet volume by detecting the refractive index changes of the surrounding medium around the etched fiber core region.

  15. A parameterization of cloud droplet nucleation

    International Nuclear Information System (INIS)

    Ghan, S.J.; Chuang, C.; Penner, J.E.

    1993-01-01

    Droplet nucleation is a fundamental cloud process. The number of aerosols activated to form cloud droplets influences not only the number of aerosols scavenged by clouds but also the size of the cloud droplets. Cloud droplet size influences the cloud albedo and the conversion of cloud water to precipitation. Global aerosol models are presently being developed with the intention of coupling with global atmospheric circulation models to evaluate the influence of aerosols and aerosol-cloud interactions on climate. If these and other coupled models are to address issues of aerosol-cloud interactions, the droplet nucleation process must be adequately represented. Here we introduce a droplet nucleation parametrization that offers certain advantages over the popular Twomey (1959) parameterization

  16. 1-Million droplet array with wide-field fluorescence imaging for digital PCR.

    Science.gov (United States)

    Hatch, Andrew C; Fisher, Jeffrey S; Tovar, Armando R; Hsieh, Albert T; Lin, Robert; Pentoney, Stephen L; Yang, David L; Lee, Abraham P

    2011-11-21

    Digital droplet reactors are useful as chemical and biological containers to discretize reagents into picolitre or nanolitre volumes for analysis of single cells, organisms, or molecules. However, most DNA based assays require processing of samples on the order of tens of microlitres and contain as few as one to as many as millions of fragments to be detected. Presented in this work is a droplet microfluidic platform and fluorescence imaging setup designed to better meet the needs of the high-throughput and high-dynamic-range by integrating multiple high-throughput droplet processing schemes on the chip. The design is capable of generating over 1-million, monodisperse, 50 picolitre droplets in 2-7 minutes that then self-assemble into high density 3-dimensional sphere packing configurations in a large viewing chamber for visualization and analysis. This device then undergoes on-chip polymerase chain reaction (PCR) amplification and fluorescence detection to digitally quantify the sample's nucleic acid contents. Wide-field fluorescence images are captured using a low cost 21-megapixel digital camera and macro-lens with an 8-12 cm(2) field-of-view at 1× to 0.85× magnification, respectively. We demonstrate both end-point and real-time imaging ability to perform on-chip quantitative digital PCR analysis of the entire droplet array. Compared to previous work, this highly integrated design yields a 100-fold increase in the number of on-chip digitized reactors with simultaneous fluorescence imaging for digital PCR based assays.

  17. Control of charged droplets using electrohydrodynamic repulsion for circular droplet patterning

    International Nuclear Information System (INIS)

    Kim, Bumjoo; Sung, Jungwoo; Lim, Geunbae; Nam, Hyoryung; Kim, Sung Jae; Joo, Sang W

    2011-01-01

    We report a novel method to form a circular pattern of monodisperse microdroplets using an electrohydrodynamic repulsion (EDR) mechanism. EDR is a phenomenon of electrostatical bounced microdroplets from an accumulated droplet on a bottom substrate. In addition to a regular EDR system, by placing a ring electrode between the capillary and ground substrate, two separate regions were created. A parameter study of two regions was carried out for droplet formation and falling velocity to control the radius of the generated droplets and the circular patterns independently. Based on energy conservation theory, our experimental results showed that the free-falling region exerted crucial influences on the sizes of the circular patterns

  18. Selfbound quantum droplets

    Science.gov (United States)

    Langen, Tim; Wenzel, Matthias; Schmitt, Matthias; Boettcher, Fabian; Buehner, Carl; Ferrier-Barbut, Igor; Pfau, Tilman

    2017-04-01

    Self-bound many-body systems are formed through a balance of attractive and repulsive forces and occur in many physical scenarios. Liquid droplets are an example of a self-bound system, formed by a balance of the mutual attractive and repulsive forces that derive from different components of the inter-particle potential. On the basis of the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, it was predicted that three-dimensional self-bound quantum droplets of magnetic atoms should exist. Here we report on the observation of such droplets using dysprosium atoms, with densities 108 times lower than a helium droplet, in a trap-free levitation field. We find that this dilute magnetic quantum liquid requires a minimum, critical number of atoms, below which the liquid evaporates into an expanding gas as a result of the quantum pressure of the individual constituents. Consequently, around this critical atom number we observe an interaction-driven phase transition between a gas and a self-bound liquid in the quantum degenerate regime with ultracold atoms.

  19. Chip-based droplet sorting

    Energy Technology Data Exchange (ETDEWEB)

    Beer, Neil Reginald; Lee, Abraham; Hatch, Andrew

    2017-11-21

    A non-contact system for sorting monodisperse water-in-oil emulsion droplets in a microfluidic device based on the droplet's contents and their interaction with an applied electromagnetic field or by identification and sorting.

  20. OCS in He droplets

    Energy Technology Data Exchange (ETDEWEB)

    Grebenev, V.

    2000-06-01

    Phenomenon of superfluidity of para-hydrogen (pH{sub 2}){sub 1-17} and helium {sup 4}He{sub 1-7000} systems doped with an OCS chromophore molecule was investigated in this work. The study of such systems became possible after the development of the depletion spectroscopy technique in helium droplets. The droplets can be easily created and doped with up to 100 particles such as OCS, para-hydrogen or ortho-hydrogen molecules and {sup 4}He atoms. The measured infrared depletion spectra give the information about the temperature of the droplets and their aggregate state. The depletion spectrum of OCS in pure {sup 4}He droplets was comprehensively studied. The rovibrational OCS spectrum shows well resolved narrow lines. The spectrum is shifted to the red relative to the corresponding gas phase spectrum and the rotational constant of OCS in {sup 4}He droplet is three times smaller than that for free molecule. Different models of OCS rotation in the helium environment were discussed. It was shown that the shapes of the rovibrational lines are defined mainly by inhomogeneous broadening due to the droplet size distribution. The sub-rotational structure of the OCS rovibrational lines was revealed in microwave-infrared double resonance experiments. This structure arises due to the interaction of the OCS with the He environment. However, the information obtained in the experiments was not enough to understand the nature of this interaction. (orig.)

  1. Sheet, ligament and droplet formation in swirling primary atomization

    Directory of Open Access Journals (Sweden)

    Changxiao Shao

    2018-04-01

    Full Text Available We report direct numerical simulations of swirling liquid atomization to understand the physical mechanism underlying the sheet breakup of a non-turbulent liquid swirling jet which lacks in-depth investigation. The volume-of-fluid (VOF method coupled with adapted mesh refinement (AMR technique in GERRIS code is employed in the present simulation. The mechanisms of sheet, ligament and droplet formation are investigated. It is observed that the olive-shape sheet structure is similar to the experimental result qualitatively. The numerical results show that surface tension, pressure difference and swirling effect contribute to the contraction and extension of liquid sheet. The ligament formation is partially at the sheet rim or attributed to the extension of liquid hole. Especially, the movement of hairpin vortex exerts by an anti-radial direction force to the sheet surface and leads to the sheet thinness. In addition, droplet formation is attributed to breakup of ligament and central sheet.

  2. Sheet, ligament and droplet formation in swirling primary atomization

    Science.gov (United States)

    Shao, Changxiao; Luo, Kun; Chai, Min; Fan, Jianren

    2018-04-01

    We report direct numerical simulations of swirling liquid atomization to understand the physical mechanism underlying the sheet breakup of a non-turbulent liquid swirling jet which lacks in-depth investigation. The volume-of-fluid (VOF) method coupled with adapted mesh refinement (AMR) technique in GERRIS code is employed in the present simulation. The mechanisms of sheet, ligament and droplet formation are investigated. It is observed that the olive-shape sheet structure is similar to the experimental result qualitatively. The numerical results show that surface tension, pressure difference and swirling effect contribute to the contraction and extension of liquid sheet. The ligament formation is partially at the sheet rim or attributed to the extension of liquid hole. Especially, the movement of hairpin vortex exerts by an anti-radial direction force to the sheet surface and leads to the sheet thinness. In addition, droplet formation is attributed to breakup of ligament and central sheet.

  3. Electronic desalting for controlling the ionic environment in droplet-based biosensing platforms

    Energy Technology Data Exchange (ETDEWEB)

    Swaminathan, Vikhram Vilasur [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Dak, Piyush; Alam, Muhammad A., E-mail: rbashir@illinois.edu, E-mail: alam@purdue.edu [School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Reddy, Bobby; Duarte-Guevara, Carlos; Zhong, Yu [Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Salm, Eric [Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Fischer, Andrew [Abbott Laboratories, 1921 Hurd Drive, Dept. 8482 LC2 M/S 2-33, Irving, Texas 75038 (United States); Liu, Yi-Shao [Taiwan Semiconductor Manufacturing Company, Hsinchu 300-78, Taiwan (China); Bashir, Rashid, E-mail: rbashir@illinois.edu, E-mail: alam@purdue.edu [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

    2015-02-02

    The ability to control the ionic environment in saline waters and aqueous electrolytes is useful for desalination as well as electronic biosensing. We demonstrate a method of electronic desalting at micro-scale through on-chip micro electrodes. We show that, while desalting is limited in bulk solutions with unlimited availability of salts, significant desalting of ≥1 mM solutions can be achieved in sub-nanoliter volume droplets with diameters of ∼250 μm. Within these droplets, by using platinum-black microelectrodes and electrochemical surface treatments, we can enhance the electrode surface area to achieve >99% and 41% salt removal in 1 mM and 10 mM salt concentrations, respectively. Through self-consistent simulations and experimental measurements, we demonstrate that conventional double-layer theory over-predicts the desalting capacity and, hence, cannot be used to model systems that are mass limited or undergoing significant salt removal from the bulk. Our results will provide a better understanding of capacitive desalination, as well as a method for salt manipulation in high-throughput droplet-based microfluidic sensing platforms.

  4. Dancing droplets: Contact angle, drag, and confinement

    Science.gov (United States)

    Benusiglio, Adrien; Cira, Nate; Prakash, Manu

    2015-11-01

    When deposited on a clean glass slide, a mixture of water and propylene glycol forms a droplet of given contact angle, when both pure liquids spread. (Cira, Benusiglio, Prakash: Nature, 2015). The droplet is stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow from the border to the apex of the droplets. The apparent contact angle of the droplets depends on both their composition and the external humidity as captured by simple models. These droplets present remarkable properties such as lack of a large pinning force. We discuss the drag on these droplets as a function of various parameters. We show theoretical and experimental results of how various confinement geometries change the vapor gradient and the dynamics of droplet attraction.

  5. In situ X-ray scattering studies of protein solution droplets drying on micro- and nanopatterned superhydrophobic PMMA surfaces.

    Science.gov (United States)

    Accardo, Angelo; Gentile, Francesco; Mecarini, Federico; De Angelis, Francesco; Burghammer, Manfred; Di Fabrizio, Enzo; Riekel, Christian

    2010-09-21

    Superhydrophobic poly(methyl methacrylate) surfaces with contact angles of ∼170° and high optical and X-ray transparencies have been fabricated through the use of optical lithography and plasma etching. The surfaces contain either a microscale pattern of micropillars or a random nanofibrillar pattern. Nanoscale asperities on top of the micropillars closely resemble Nelumbo nucifera lotus leaves. The evolution of the contact angle of water and lysozyme solution droplets during evaporation was studied on the micro- and nanopatterned surfaces, showing in particular contact-line pinning for the protein solution droplet on the nanopatterned surface. The microstructural evolution of lysozyme solution droplets was studied on both types of surfaces in situ under nearly contact-free conditions by synchrotron radiation microbeam wide-angle and small-angle X-ray scattering revealing the increasing protein concentration and the onset of precipitation. The solid residuals show hollow sphere morphologies. Rastermicrodiffraction of the detached residuals suggests about a 1/3 volume fraction of ≥17 nm lysozyme nanocrystalline domains and about a 2/3 short-range-order volume fraction. About 5-fold larger nanocrystalline domains were observed at the attachment points of the sphere to the substrates, which is attributed to particle growth in a shear flow. Such surfaces represent nearly contact-free sample supports for studies of inorganic and organic solution droplets, which find applications in biochips.

  6. Particle Manipulation Methods in Droplet Microfluidics.

    Science.gov (United States)

    Tenje, Maria; Fornell, Anna; Ohlin, Mathias; Nilsson, Johan

    2018-02-06

    This Feature describes the different particle manipulation techniques available in the droplet microfluidics toolbox to handle particles encapsulated inside droplets and to manipulate whole droplets. We address the advantages and disadvantages of the different techniques to guide new users.

  7. Colliding droplets: A short film presentation

    Science.gov (United States)

    Hendricks, C. D.

    1981-12-01

    A series of experiments were performed in which liquid droplets were caused to collide. Impact velocities to several meters per second and droplet diameters up to 600 micrometers were used. The impact parameters in the collisions vary from zero to greater than the sum of the droplet radii. Photographs of the collisions were taken with a high speed framing camera in order to study the impacts and subsequent behavior of the droplets.

  8. Numerical Study of High-Speed Droplet Impact on Surfaces and its Physical Cleaning Effects

    Science.gov (United States)

    Kondo, Tomoki; Ando, Keita

    2015-11-01

    Spurred by the demand for cleaning techniques of low environmental impact, one favors physical cleaning that does not rely on any chemicals. One of the promising candidates is based on water jets that often involve fission into droplet fragments and collide with target surfaces to which contaminant particles (often micron-sized or even smaller) stick. Hydrodynamic force (e.g., shearing and lifting) arising from the droplet impact will play a role to remove the particles, but its detailed mechanism is still unknown. To explore the role of high-speed droplet impact in physical cleaning, we solve compressible Navier-Stokes equations with a finite volume method that is designed to capture both shocks and material interfaces in accurate and robust manners. Water hammer and shear flow accompanied by high-speed droplet impact at a rigid wall is simulated to evaluate lifting force and rotating torque, which are relevant to the application of particle removal. For the simulation, we use the numerical code recently developed by Computational Flow Group lead by Tim Colonius at Caltech. The first author thanks Jomela Meng for her help in handling the code during his stay at Caltech.

  9. Self-propelled oil droplets consuming "fuel" surfactant

    DEFF Research Database (Denmark)

    Toyota, Taro; Maru, Naoto; Hanczyc, Martin M

    2009-01-01

    A micrometer-sized oil droplet of 4-octylaniline containing 5 mol % of an amphiphilic catalyst exhibited a self-propelled motion, producing tiny oil droplets, in an aqueous dispersion of an amphiphilic precursor of 4-octylaniline. The tiny droplets on the surface of the self-propelled droplet wer...

  10. Direct numerical simulations of evaporating droplets in turbulence

    Science.gov (United States)

    Palmore, John; Desjardins, Olivier

    2015-11-01

    This work demonstrates direct numerical simulations of evaporating two phase flows, with applications to studying combustion in aircraft engines. Inside the engine, liquid fuel is injected into the combustion chamber where it atomizes into droplets and evaporates. Combustion occurs as the fuel vapor mixes with the surrounding flow of turbulent gas. Understanding combustion, therefore, requires studying evaporation in a turbulent flow and the resulting vapor distribution. We study the problem using a finite volume framework to solve the Navier-Stokes and scalar transport equations under a low-Mach assumption [Desjardins et al., J. Comp. Phys., 2008]. The liquid-gas interface is tracked using a conservative level-set method [Desjardins et al., J. Comp. Phys., 2008] which allows for a sharp reconstruction of the discontinuity across the interface. Special care is taken in the discretization of cells near the liquid-gas interface to ensure the stability and accuracy of the solution. Results are discussed for non-reacting simulations of liquid droplets evaporating into a turbulent field of inert gas.

  11. Droplets, Bubbles and Ultrasound Interactions.

    Science.gov (United States)

    Shpak, Oleksandr; Verweij, Martin; de Jong, Nico; Versluis, Michel

    2016-01-01

    The interaction of droplets and bubbles with ultrasound has been studied extensively in the last 25 years. Microbubbles are broadly used in diagnostic and therapeutic medical applications, for instance, as ultrasound contrast agents. They have a similar size as red blood cells, and thus are able to circulate within blood vessels. Perfluorocarbon liquid droplets can be a potential new generation of microbubble agents as ultrasound can trigger their conversion into gas bubbles. Prior to activation, they are at least five times smaller in diameter than the resulting bubbles. Together with the violent nature of the phase-transition, the droplets can be used for local drug delivery, embolotherapy, HIFU enhancement and tumor imaging. Here we explain the basics of bubble dynamics, described by the Rayleigh-Plesset equation, bubble resonance frequency, damping and quality factor. We show the elegant calculation of the above characteristics for the case of small amplitude oscillations by linearizing the equations. The effect and importance of a bubble coating and effective surface tension are also discussed. We give the main characteristics of the power spectrum of bubble oscillations. Preceding bubble dynamics, ultrasound propagation is introduced. We explain the speed of sound, nonlinearity and attenuation terms. We examine bubble ultrasound scattering and how it depends on the wave-shape of the incident wave. Finally, we introduce droplet interaction with ultrasound. We elucidate the ultrasound-focusing concept within a droplets sphere, droplet shaking due to media compressibility and droplet phase-conversion dynamics.

  12. Droplet Vaporization In A Levitating Acoustic Field

    Science.gov (United States)

    Ruff, G. A.; Liu, S.; Ciobanescu, I.

    2003-01-01

    Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. To eliminate the effect of the fiber, several researchers have conducted microgravity experiments using unsupported droplets. Jackson and Avedisian investigated single, unsupported drops while Nomura et al. studied droplet clouds formed by a condensation technique. The overall objective of this research is to extend the study of unsupported drops by investigating the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would provide unique experimental data for the verification and improvement of spray combustion models. In this work, the formation of drop clusters is precisely controlled using an acoustic levitation system so that dilute, as well as dense clusters can be created and stabilized before combustion in microgravity is begun. While the low-gravity test facility is being completed, tests have been conducted in 1-g to characterize the effect of the acoustic field on the vaporization of single and multiple droplets. This is important because in the combustion experiment, the droplets will be formed and

  13. Fusion of microlitre water-in-oil droplets for simple, fast and green chemical assays.

    Science.gov (United States)

    Chiu, S-H; Urban, P L

    2015-08-07

    A simple format for microscale chemical assays is proposed. It does not require the use of test tubes, microchips or microtiter plates. Microlitre-range (ca. 0.7-5.0 μL) aqueous droplets are generated by a commercial micropipette in a non-polar matrix inside a Petri dish. When two droplets are pipetted nearby, they spontaneously coalesce within seconds, priming a chemical reaction. Detection of the reaction product is accomplished by colorimetry, spectrophotometry, or fluorimetry using simple light-emitting diode (LED) arrays as the sources of monochromatic light, while chemiluminescence detection of the analytes present in single droplets is conducted in the dark. A smartphone camera is used as the detector. The limits of detection obtained for the developed in-droplet assays are estimated to be: 1.4 nmol (potassium permanganate by colorimetry), 1.4 pmol (fluorescein by fluorimetry), and 580 fmol (sodium hypochlorite by chemiluminescence detection). The format has successfully been used to monitor the progress of chemical and biochemical reactions over time with sub-second resolution. A semi-quantitative analysis of ascorbic acid using Tillman's reagent is presented. A few tens of individual droplets can be scanned in parallel. Rapid switching of the LED light sources with different wavelengths enables a spectral analysis of multiple droplets. Very little solid waste is produced. The assay matrix is readily recycled, thus the volume of liquid waste produced each time is also very small (typically, 1-10 μL per analysis). Various water-immiscible translucent liquids can be used as the reaction matrix: including silicone oil, 1-octanol as well as soybean cooking oil.

  14. Mass spectrometry of acoustically levitated droplets.

    Science.gov (United States)

    Westphall, Michael S; Jorabchi, Kaveh; Smith, Lloyd M

    2008-08-01

    Containerless sample handling techniques such as acoustic levitation offer potential advantages for mass spectrometry, by eliminating surfaces where undesired adsorption/desorption processes can occur. In addition, they provide a unique opportunity to study fundamental aspects of the ionization process as well as phenomena occurring at the air-droplet interface. Realizing these advantages is contingent, however, upon being able to effectively interface levitated droplets with a mass spectrometer, a challenging task that is addressed in this report. We have employed a newly developed charge and matrix-assisted laser desorption/ionization (CALDI) technique to obtain mass spectra from a 5-microL acoustically levitated droplet containing peptides and an ionic matrix. A four-ring electrostatic lens is used in conjunction with a corona needle to produce bursts of corona ions and to direct those ions toward the droplet, resulting in droplet charging. Analyte ions are produced from the droplet by a 337-nm laser pulse and detected by an atmospheric sampling mass spectrometer. The ion generation and extraction cycle is repeated at 20 Hz, the maximum operating frequency of the laser employed. It is shown in delayed ion extraction experiments that both positive and negative ions are produced, behavior similar to that observed for atmospheric pressure matrix-assisted laser absorption/ionization. No ion signal is observed in the absence of droplet charging. It is likely, although not yet proven, that the role of the droplet charging is to increase the strength of the electric field at the surface of the droplet, reducing charge recombination after ion desorption.

  15. Leidenfrost boiling of water droplet

    Directory of Open Access Journals (Sweden)

    Orzechowski Tadeusz

    2017-01-01

    Full Text Available The investigations concerned a large water droplet at the heating surface temperature above the Leidenfrost point. The heating cylinder was the main component of experimental stand on which investigations were performed. The measurement system was placed on the high-sensitivity scales. Data transmission was performed through RS232 interface. The author-designed program, with extended functions to control the system, was applied. The present paper examines the behaviour of a large single drop levitating over a hot surface, unsteady mass of the drop, and heat transfer. In computations, the dependence, available in the literature, for the orthogonal droplet projection on the heating surface as a function of time was employed. It was confirmed that the local value of the heat transfer coefficient is a power function of the area of the droplet surface projection. Also, a linear relationship between the flux of mass evaporated from the droplet and the droplet orthogonal projection was observed.

  16. Leidenfrost boiling of water droplet

    Science.gov (United States)

    Orzechowski, Tadeusz

    The investigations concerned a large water droplet at the heating surface temperature above the Leidenfrost point. The heating cylinder was the main component of experimental stand on which investigations were performed. The measurement system was placed on the high-sensitivity scales. Data transmission was performed through RS232 interface. The author-designed program, with extended functions to control the system, was applied. The present paper examines the behaviour of a large single drop levitating over a hot surface, unsteady mass of the drop, and heat transfer. In computations, the dependence, available in the literature, for the orthogonal droplet projection on the heating surface as a function of time was employed. It was confirmed that the local value of the heat transfer coefficient is a power function of the area of the droplet surface projection. Also, a linear relationship between the flux of mass evaporated from the droplet and the droplet orthogonal projection was observed.

  17. Droplet generation during core reflood

    International Nuclear Information System (INIS)

    Kocamustafaogullari, G.; De Jarlais, G.; Ishii, M.

    1983-01-01

    The process of entrainment and disintegration of liquid droplets by a flow of steam has considerable practical importance in calculating the effectivenes of the emergency core cooling system. Liquid entrainment is also important in determination of the critical heat flux point in general. Thus the analysis of the reflooding phase of a LOCA requires detailed knowledge of droplet size. Droplet size is mainly determined by the droplet generation mechanisms involved. To study these mechanisms, data generated in the PWR FLECHT SEASET series of experiments was analyzed. In addition, an experiment was performed in which the hydrodynamics of low quality post-CHF flow (inverted annular flow) were simulated in an adiabatic test section

  18. Influence of film dimensions on film droplet formation.

    Science.gov (United States)

    Holmgren, Helene; Ljungström, Evert

    2012-02-01

    Aerosol particles may be generated from rupturing liquid films through a droplet formation mechanism. The present work was undertaken with the aim to throw some light on the influence of film dimensions on droplet formation with possible consequences for exhaled breath aerosol formation. The film droplet formation process was mimicked by using a purpose-built device, where fluid films were spanned across holes of known diameters. As the films burst, droplets were formed and the number and size distributions of the resulting droplets were determined. No general relation could be found between hole diameter and the number of droplets generated per unit surface area of fluid film. Averaged over all film sizes, a higher surface tension yielded higher concentrations of droplets. Surface tension did not influence the resulting droplet diameter, but it was found that smaller films generated smaller droplets. This study shows that small fluid films generate droplets as efficiently as large films, and that droplets may well be generated from films with diameters below 1 mm. This has implications for the formation of film droplets from reopening of closed airways because human terminal bronchioles are of similar dimensions. Thus, the results provide support for the earlier proposed mechanism where reopening of closed airways is one origin of exhaled particles.

  19. Parallelization of Droplet Microfluidic Systems for the Sustainable Production of Micro-Reactors at Industrial Scale

    KAUST Repository

    Conchouso Gonzalez, David

    2017-04-01

    At the cutting edge of the chemical and biological research, innovation takes place in a field referred to as Lab on Chip (LoC), a multi-disciplinary area that combines biology, chemistry, electronics, microfabrication, and fluid mechanics. Within this field, droplets have been used as microreactors to produce advanced materials like quantum dots, micro and nanoparticles, active pharmaceutical ingredients, etc. The size of these microreactors offers distinct advantages, which were not possible using batch technologies. For example, they allow for lower reagent waste, minimal energy consumption, increased safety, as well as better process control of reaction conditions like temperature regulation, residence times, and response times among others. One of the biggest drawbacks associated with this technology is its limited production volume that prevents it from reaching industrial applications. The standard production rates for a single droplet microfluidic device is in the range of 1-10mLh-1, whereas industrial applications usually demand production rates several orders of magnitude higher. Although substantial work has been recently undertaken in the development scaled-out solutions, which run in parallel several droplet generators. Complex fluid mechanics and limitations on the manufacturing capacity have constrained these works to explore only in-plane parallelization. This thesis investigates a three-dimensional parallelization by proposing a microfluidic system that is comprised of a stack of droplet generation layers working on the liquid-liquid ow regime. Its realization implied a study of the characteristics of conventional droplet generators and the development of a fabrication process for 3D networks of microchannels. Finally, the combination of these studies resulted in a functional 3D parallelization system with the highest production rate (i.e. 1 Lh-1) at the time of its publication. Additionally, this architecture can reach industrially relevant

  20. A compact and facile microfluidic droplet creation device using a piezoelectric diaphragm micropump for droplet digital PCR platforms.

    Science.gov (United States)

    Okura, Naoaki; Nakashoji, Yuta; Koshirogane, Toshihiro; Kondo, Masaki; Tanaka, Yugo; Inoue, Kohei; Hashimoto, Masahiko

    2017-10-01

    We have exploited a compact and facile microfluidic droplet creation device consisting of a poly(dimethylsiloxane) microfluidic chip possessing T-junction channel geometry, two inlet reservoirs, and one outlet reservoir, and a piezoelectric (PZT) diaphragm micropump with controller. Air was evacuated from the outlet reservoir using the PZT pump, reducing the pressure inside. The reduced pressure within the outlet reservoir pulled oil and aqueous solution preloaded in the inlet reservoirs into the microchannels, which then merged at the T-junction, successfully forming water-in-oil emulsion droplets at a rate of ∼1000 per second with minimal sample loss. We confirmed that the onset of droplet formation occurred immediately after turning on the pump (<1 s). Over repeated runs, droplet formation was highly reproducible, with droplet size purity (polydispersity, <4%) comparable to that achieved using other microfluidic droplet preparation techniques. We also demonstrated single-molecule PCR amplification in the created droplets, suggesting that the device could be used for effective droplet digital PCR platforms in most laboratories without requiring great expense, space, or time for acquiring technical skills. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Measurement of dew droplets in initial deposition at dew point by using a phase-shift interference microscope

    Science.gov (United States)

    Matsumoto, Shigeaki; Toyooka, Satoru; Hoshino, Mitsuo

    2002-09-01

    In order to measure the total mass per unit area of dew droplets deposited on a metal plate in the dew-point hygrometer, the shape of a dew droplet deposited on a copper plate was measured accurately by using an interference microscope that employed a phase-shift technique. The microscope was constructed by adding a piezoelectric transducer to an usual interference microscope. A simple method that uses a conventional speaker horn and an optical fiber cable was introduced to depress speckle noise. The shape of a dew droplet deposited on the copper plate surface with 0.1 μm in average roughness was measured with an accuracy of +/-3nm. The mass of a dew droplet could be calculated numerically from the volume of its shape and was of the order of 10-9 g. The total mass of dew droplets deposited per unit area and the deposition velocity were obtained under a gentle wind. The total mass was the order of 10-5 g/cm2 at the beginning of deposition and the deposition velocity was ranged from 2x10-6 to 6x10-5 g/cm2.min.

  2. Hydrodynamics of Leidenfrost droplets in one-component fluids

    KAUST Repository

    Xu, Xinpeng; Qian, Tiezheng

    2013-01-01

    Using the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], we numerically investigate the hydrodynamics of Leidenfrost droplets under gravity in two dimensions. Some recent theoretical predictions and experimental observations are confirmed in our simulations. A Leidenfrost droplet larger than a critical size is shown to be unstable and break up into smaller droplets due to the Rayleigh-Taylor instability of the bottom surface of the droplet. Our simulations demonstrate that an evaporating Leidenfrost droplet changes continuously from a puddle to a circular droplet, with the droplet shape controlled by its size in comparison with a few characteristic length scales. The geometry of the vapor layer under the droplet is found to mainly depend on the droplet size and is nearly independent of the substrate temperature, as reported in a recent experimental study [Phys. Rev. Lett. 109, 074301 (2012)]. Finally, our simulations demonstrate that a Leidenfrost droplet smaller than a characteristic size takes off from the hot substrate because the levitating force due to evaporation can no longer be balanced by the weight of the droplet, as observed in a recent experimental study [Phys. Rev. Lett. 109, 034501 (2012)].

  3. Binary particle separation in droplet microfluidics using acoustophoresis

    Science.gov (United States)

    Fornell, Anna; Cushing, Kevin; Nilsson, Johan; Tenje, Maria

    2018-02-01

    We show a method for separation of two particle species with different acoustic contrasts originally encapsulated in the same droplet in a continuous two-phase system. This was realized by using bulk acoustic standing waves in a 380 μm wide silicon-glass microfluidic channel. Polystyrene particles (positive acoustic contrast particles) and in-house synthesized polydimethylsiloxane (PDMS) particles (negative acoustic contrast particles) were encapsulated inside water-in-oil droplets either individually or in a mixture. At acoustic actuation of the system at the fundamental resonance frequency, the polystyrene particles were moved to the center of the droplet (pressure node), while the PDMS particles were moved to the sides of the droplet (pressure anti-nodes). The acoustic particle manipulation step was combined in series with a trifurcation droplet splitter, and as the original droplet passed through the splitter and was divided into three daughter droplets, the polystyrene particles were directed into the center daughter droplet, while the PDMS particles were directed into the two side daughter droplets. The presented method expands the droplet microfluidics tool-box and offers new possibilities to perform binary particle separation in droplet microfluidic systems.

  4. Hydrodynamics of Leidenfrost droplets in one-component fluids

    KAUST Repository

    Xu, Xinpeng

    2013-04-24

    Using the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], we numerically investigate the hydrodynamics of Leidenfrost droplets under gravity in two dimensions. Some recent theoretical predictions and experimental observations are confirmed in our simulations. A Leidenfrost droplet larger than a critical size is shown to be unstable and break up into smaller droplets due to the Rayleigh-Taylor instability of the bottom surface of the droplet. Our simulations demonstrate that an evaporating Leidenfrost droplet changes continuously from a puddle to a circular droplet, with the droplet shape controlled by its size in comparison with a few characteristic length scales. The geometry of the vapor layer under the droplet is found to mainly depend on the droplet size and is nearly independent of the substrate temperature, as reported in a recent experimental study [Phys. Rev. Lett. 109, 074301 (2012)]. Finally, our simulations demonstrate that a Leidenfrost droplet smaller than a characteristic size takes off from the hot substrate because the levitating force due to evaporation can no longer be balanced by the weight of the droplet, as observed in a recent experimental study [Phys. Rev. Lett. 109, 034501 (2012)].

  5. The collaborative work of droplet assembly.

    Science.gov (United States)

    Chen, Xiao; Goodman, Joel M

    2017-10-01

    Three proteins have been implicated in the assembly of cytoplasmic lipid droplets: seipin, FIT2, and perilipin. This review examines the current theories of seipin function as well as the evidence for the involvement of all three proteins in droplet biogenesis, and ends with a proposal of how they collaborate to regulate the formation of droplets. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Droplet collisions in turbulence

    NARCIS (Netherlands)

    Oldenziel, G.

    2014-01-01

    Liquid droplets occur in many natural phenomena and play an important role in a large number of industrial applications. One of the distinct properties of droplets as opposed to solid particles is their ability to merge, or coalesce upon collision. Coalescence of liquid drops is of importance in for

  7. Computational Thermodynamics Analysis of Vaporizing Fuel Droplets in the Human Upper Airways

    Science.gov (United States)

    Zhang, Zhe; Kleinstreuer, Clement

    The detailed knowledge of air flow structures as well as particle transport and deposition in the human lung for typical inhalation flow rates is an important precursor for dosimetry-and-health-effect studies of toxic particles as well as for targeted drug delivery of therapeutic aerosols. Focusing on highly toxic JP-8 fuel aerosols, 3-D airflow and fluid-particle thermodynamics in a human upper airway model starting from mouth to Generation G3 (G0 is the trachea) are simulated using a user-enhanced and experimentally validated finite-volume code. The temperature distributions and their effects on airflow structures, fuel vapor deposition and droplet motion/evaporation are discussed. The computational results show that the thermal effect on vapor deposition is minor, but it may greatly affect droplet deposition in human airways.

  8. Colliding droplets: a short film presentation

    International Nuclear Information System (INIS)

    Hendricks, C.D.

    1981-01-01

    A series of experiments were performed in which liquid droplets were caused to collide. Impact velocities to several meters per second and droplet diameters up to 600 micrometers were used. The impact parameters in the collisions vary from zero to greater than the sum of the droplet radii. Photographs of the collisions were taken with a high speed framing camera in order to study the impacts and subsequent behavior of the droplets. The experiments will be discussed and a short movie film presentation of some of the impacts will be shown

  9. Settling of fixed erythrocyte suspension droplets

    Science.gov (United States)

    Omenyi, S. N.; Snyder, R. S.

    1983-01-01

    It is pointed out that when particles behave collectively rather than individually, the fractionation of micron-size particles on the basis of size, density, and surface characteristics by centrifugation and electrophoresis is hindered. The formation and sedimentation of droplets containing particles represent an extreme example of collective behavior and pose a major problem for these separation methods when large quantities of particles need to be fractionated. Experiments are described that measure droplet sizes and settling rates for a variety of particles and droplets. Expressions relating the particle concentration in a drop to measurable quantities of the fluids and particles are developed. The number of particles in each droplet is then estimated, together with the effective droplet density. Red blood cells from different animals fixed in glutaraldehyde provide model particle groups.

  10. Multicomponent droplet vaporization in a convecting environment

    International Nuclear Information System (INIS)

    Megaridis, C.M.; Sirignano, W.A.

    1990-01-01

    In this paper a parametric study of the fundamental exchange processes for energy, mass and momentum between the liquid and gas phases of multicomponent liquid vaporizing droplets is presented. The model, which examines an isolated, vaporizing, multicomponent droplet in an axisymmetric, convecting environment, considers the different volatilities of the liquid components, the alteration of the liquid-phase properties due to the spatial/temporal variations of the species concentrations and also the effects of multicomponent diffusion. In addition, the model accounts for variable thermophysical properties, surface blowing and droplet surface regression due to vaporization, transient droplet heating with internal liquid circulation, and finally droplet deceleration with respect to the free flow due to drag. The numerical calculation employs finite-difference techniques and an iterative solution procedure that provides time-varying spatially-resolved data for both phases. The effects of initial droplet composition, ambient temperature, initial Reynolds number (based on droplet diameter), and volatility differential between the two liquid components are investigated for a liquid droplet consisting of two components with very different volatilities. It is found that mixtures with higher concentration of the less volatile substance actually vaporize faster on account of intrinsically higher liquid heating rates

  11. Collisions of droplets on spherical particles

    Science.gov (United States)

    Charalampous, Georgios; Hardalupas, Yannis

    2017-10-01

    Head-on collisions between droplets and spherical particles are examined for water droplets in the diameter range between 170 μm and 280 μm and spherical particles in the diameter range between 500 μm and 2000 μm. The droplet velocities range between 6 m/s and 11 m/s, while the spherical particles are fixed in space. The Weber and Ohnesorge numbers and ratio of droplet to particle diameter were between 92 deposition and splashing regimes, a regime is observed in the intermediate region, where the droplet forms a stable crown, which does not breakup but propagates along the particle surface and passes around the particle. This regime is prevalent when the droplets collide on small particles. The characteristics of the collision at the onset of rim instability are also described in terms of the location of the film on the particle surface and the orientation and length of the ejected crown. Proper orthogonal decomposition identified that the first 2 modes are enough to capture the overall morphology of the crown at the splashing threshold.

  12. Velocity and rotation measurements in acoustically levitated droplets

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Abhishek [University of Central Florida, Orlando, FL 32816 (United States); Basu, Saptarshi [Indian Institute of Science, Bangalore 560012 (India); Kumar, Ranganathan, E-mail: ranganathan.kumar@ucf.edu [University of Central Florida, Orlando, FL 32816 (United States)

    2012-10-01

    The velocity scale inside an acoustically levitated droplet depends on the levitator and liquid properties. Using Particle Imaging Velocimetry (PIV), detailed velocity measurements have been made in a levitated droplet of different diameters and viscosity. The maximum velocity and rotation are normalized using frequency and amplitude of acoustic levitator, and droplet viscosity. The non-dimensional data are fitted for micrometer- and millimeter-sized droplets levitated in different levitators for different viscosity fluids. It is also shown that the rotational speed of nanosilica droplets at an advanced stage of vaporization compares well with that predicted by exponentially fitted parameters. -- Highlights: ► Demonstrates the importance of rotation in a levitated droplet that leads to controlled morphology. ► Provides detailed measurements of Particle Image Velocimetry inside levitated droplets. ► Shows variation of vortex strength with the droplet diameter and viscosity of the liquid.

  13. Velocity and rotation measurements in acoustically levitated droplets

    International Nuclear Information System (INIS)

    Saha, Abhishek; Basu, Saptarshi; Kumar, Ranganathan

    2012-01-01

    The velocity scale inside an acoustically levitated droplet depends on the levitator and liquid properties. Using Particle Imaging Velocimetry (PIV), detailed velocity measurements have been made in a levitated droplet of different diameters and viscosity. The maximum velocity and rotation are normalized using frequency and amplitude of acoustic levitator, and droplet viscosity. The non-dimensional data are fitted for micrometer- and millimeter-sized droplets levitated in different levitators for different viscosity fluids. It is also shown that the rotational speed of nanosilica droplets at an advanced stage of vaporization compares well with that predicted by exponentially fitted parameters. -- Highlights: ► Demonstrates the importance of rotation in a levitated droplet that leads to controlled morphology. ► Provides detailed measurements of Particle Image Velocimetry inside levitated droplets. ► Shows variation of vortex strength with the droplet diameter and viscosity of the liquid.

  14. Levitated droplet dye laser

    DEFF Research Database (Denmark)

    Azzouz, H.; Alkafadiji, L.; Balslev, Søren

    2006-01-01

    a high quality optical resonator. Our 750 nL lasing droplets consist of Rhodamine 6G dissolved in ethylene glycol, at a concentration of 0.02 M. The droplets are optically pumped at 532 nm light from a pulsed, frequency doubled Nd:YAG laser, and the dye laser emission is analyzed by a fixed grating...

  15. Water Entry by a Train of Droplets

    Science.gov (United States)

    Ohl, Claus-Dieter; Huang, Xin; Chan, Chon U.; Frommhold, Philipp Erhard; Lippert, Alexander

    2014-11-01

    The impact of single droplets on a deep pool is a well-studied phenomenon which reveals reach fluid mechanics. Lesser studied is the impact of a train of droplet and the accompanied formation of largely elongated cavities, in particular for well controlled droplets. The droplets with diameters of 20-40 μm and velocities of approx. 20 m/s are generated with a piezo-actuated nozzle at rates of 200-300 kHz. Individual droplets are selected by electric charging and deflection and the impact is visualized with stroboscopic photography and high-speed videos. We study in particular the formation and shape of the cavity as by varying the number of droplets from one to 64. The cavities reach centimetres in length with lateral diameters of the order of 100 of micrometres.

  16. Charge Transfer into Aqueous Droplets via Kilovolt Potentials

    Science.gov (United States)

    Hamlin, B. S.; Rosenberg, E. R.; Ristenpart, W. D.

    2012-11-01

    When an aqueous droplet immersed in an insulating oil contacts an electrified surface, the droplet acquires net charge. For sufficiently large field strengths, the charged droplet is driven back and forth electrophoretically between the electrodes, in essence ``bouncing'' between them. Although it is clear that the droplet acquires charge, the underlying mechanism controlling the charge transfer process has been unclear. Here we demonstrate that the chemical species present in the droplet strongly affect the charge transfer process into the drop. Using two independent charge measurement techniques, high speed video velocimetry and direct current measurement, we show that the charge acquired during contact is strongly influenced by the droplet pH. We also provide physical evidence that the electrodes undergo electroplating or corrosion for droplets with appropriate chemical species present. Together, the observations strongly suggest that electrochemical reactions govern the charge transfer process into the droplet.

  17. Steady State Droplet Deformation and Orientation during Bulk and Confined Shear Flow in Blends with One Viscoelastic Component: Experiments, Modeling and Simulations

    Science.gov (United States)

    Verhulst, Kristof; Cardinaels, Ruth; Renardy, Yuriko; Moldenaers, Paula

    2008-07-01

    The steady deformation and orientation of droplets in shear flow, both under bulk and confined conditions, is microscopically studied for blends with one viscoelastic phase and a viscosity ratio of 1.5. The experiments are performed with a Linkam shearing cell and a counter rotating setup, based on a Paar Physica MCR300. For bulk shear flow, it is shown that matrix viscoelasticity suppresses droplet deformation and promotes droplet orientation towards the flow direction. Interestingly, these effects saturate at Deborah numbers above 2. For ellipsoidal droplets, viscoelasticity of the droplet fluid hardly affects the droplet deformation and droplet orientation, even up to Deborah numbers as high as 16. When the droplet is confined between two plates, the droplet deformation and the orientation towards the flow direction increase with confinement ratio, as in fully Newtonian systems. At a Deborah number of 1, the effect of component viscoelasticity under confined conditions remains qualitatively the same as under bulk conditions, at least up to a confinement ratio 2R/H of 0.6. The experiments under bulk conditions are compared with the predictions of phenomenological models, such as the Maffettone-Minale model, for droplet deformation. The Shapira-Haber model, which analytically describes the effects of the walls on the droplet deformation for fully Newtonian systems, is used to describe the experimental results under confinement. Here, this model is combined with the bulk phenomenological models to include bulk viscoelasticity effects. Under the present conditions, the adapted Shapira-Haber model describes the steady droplet deformation under confinement rather well. Finally, the experimentally obtained droplet shapes are compared with the results of 3D simulations, performed with a volume-of-fluid algorithm.

  18. Magnetic fluid droplet in a harmonic electric field

    Energy Technology Data Exchange (ETDEWEB)

    Kvasov, D., E-mail: kvasovdmitry@gmail.com [Lomonosov Moscow State University, Moscow (Russian Federation); Naletova, V. [Lomonosov Moscow State University, Moscow (Russian Federation); Beketova, E.; Dikanskii, Yu. [North-Caucasus Federal University, Stavropol (Russian Federation)

    2017-06-01

    A magnetic fluid droplet immersed in oil in an applied harmonic electric field is studied experimentally and theoretically. It is shown that deformations of the droplet observed experimentally are not described by the well-known theory. New double-layer droplet model which describes experimental data well is proposed. - Highlights: • The magnetic fluid droplet in the oil in a harmonic electric field is studied. • The paradoxical flattening effect of the droplet is observed experimentally. • For explaining this effect the model of the double-layer droplet is proposed. • Numerical and experimental data coincide qualitatively and quantitatively.

  19. Oleoplaning droplets on lubricated surfaces

    Science.gov (United States)

    Daniel, Dan; Timonen, Jaakko V. I.; Li, Ruoping; Velling, Seneca J.; Aizenberg, Joanna

    2017-10-01

    Recently, there has been much interest in using lubricated surfaces to achieve extreme liquid repellency: a foreign droplet immiscible with the underlying lubricant layer was shown to slide off at a small tilt angle behaviour was hypothesized to arise from a thin lubricant overlayer film sandwiched between the droplet and solid substrate, but this has not been observed experimentally. Here, using thin-film interference, we are able to visualize the intercalated film under both static and dynamic conditions. We further demonstrate that for a moving droplet, the film thickness follows the Landau-Levich-Derjaguin law. The droplet is therefore oleoplaning--akin to tyres hydroplaning on a wet road--with minimal dissipative force and no contact line pinning. The techniques and insights presented in this study will inform future work on the fundamentals of wetting for lubricated surfaces and enable their rational design.

  20. Lipidomic and proteomic analysis of Caenorhabditis elegans lipid droplets and identification of ACS-4 as a lipid droplet-associated protein

    Energy Technology Data Exchange (ETDEWEB)

    Vrablik, Tracy L. [Washington State Univ., Pullman, WA (United States); Petyuk, Vladislav A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Larson, Emily M. [Washington State Univ., Pullman, WA (United States); Smith, Richard D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Watts, Jennifer [Washington State Univ., Pullman, WA (United States)

    2015-06-27

    Lipid droplets are cytoplasmic organelles that store neutral lipids for membrane synthesis and energy reserves. In this study, we characterized the lipid and protein composition of purified C. elegans lipid droplets. These lipid droplets are composed mainly of triacylglycerols, surrounded by a phospholipid monolayer composed primarily of phosphatidylcholine and phosphatidylethanolamine. The fatty acid composition of the triacylglycerols was rich in fatty acid species obtained from the dietary E. coli, including cyclopropane fatty acids and cis-vaccenic acid. Unlike other organisms, C. elegans lipid droplets contain very little cholesterol or cholesterol esters. Comparison of the lipid droplet proteomes of wild type and high-fat daf-2 mutant strains shows a relative decrease of MDT-28 abundance in lipid droplets isolated from daf-2 mutants. Functional analysis of lipid droplet proteins identified in our proteomic studies indicated an enrichment of proteins required for growth and fat homeostasis in C. elegans.

  1. Estimativa da deposição de agrotóxicos por análise de gotas Estimates of pesticide deposition by droplet size analysis

    Directory of Open Access Journals (Sweden)

    Aldemir Chaim

    1999-06-01

    Full Text Available As quantificações dos agrotóxicos que atingem os alvos são feitas com metodologias onerosas ou sofisticadas. Assim, o objetivo deste trabalho foi comparar dois métodos para quantificar as deposições de agrotóxicos: um, por análise de gotas, e o outro, por análise química de traçador. As gotas de uma calda cúprica foram amostradas com papel sensível a água, lâmina de microscópio recoberta com óxido de magnésio e cartões de papel-filtro. No método de análise de gotas, o volume depositado em determinada área foi calculado considerando-se os diâmetros das manchas ou impressões, fatores de espalhamento e densidade de deposição. No outro método, o volume depositado foi obtido mediante análise de resíduo do traçador encontrado nos alvos e pela concentração da calda da pulverização. Não houve diferenças estatísticas entre os volumes estimados pelos dois métodos.The available methodologies for analysing the pesticide reaching the target are sophisticated or expensive. The objective of this work was to compare two methods to quantify the pesticide deposition. One of them by droplets analysis and the other by chemical tracer analysis. The droplets of a fungicide spray were sampled using water sensitive papers, slides with oxide magnesium and cards of filter paper. In the droplet analysis method, the volume of spray deposited on a delimited area was estimated considering the diameters of stains or craters, spread factors and droplet density. In the chemical tracer analysis method the volume was calculated by the residue deposited on sampling target and spray concentration. There were no statistic differences in the volumes estimated by the two methods.

  2. Janus droplet as a catalytic micromotor

    Science.gov (United States)

    Shklyaev, Sergey

    2015-06-01

    Self-propulsion of a Janus droplet in a solution of surfactant, which reacts on a half of a drop surface, is studied theoretically. The droplet acts as a catalytic motor creating a concentration gradient, which generates its surface-tension-driven motion; the self-propulsion speed is rather high, 60 μ \\text{m/s} and more. This catalytic motor has several advantages over other micromotors: simple manufacturing, easily attained neutral buoyancy. In contrast to a single-fluid droplet, which demonstrates a self-propulsion as a result of symmetry breaking instability, for the Janus one no stability threshold exists; hence, the droplet radius can be scaled down to micrometers.

  3. Interface-Resolving Simulation of Collision Efficiency of Cloud Droplets

    Science.gov (United States)

    Wang, Lian-Ping; Peng, Cheng; Rosa, Bodgan; Onishi, Ryo

    2017-11-01

    Small-scale air turbulence could enhance the geometric collision rate of cloud droplets while large-scale air turbulence could augment the diffusional growth of cloud droplets. Air turbulence could also enhance the collision efficiency of cloud droplets. Accurate simulation of collision efficiency, however, requires capture of the multi-scale droplet-turbulence and droplet-droplet interactions, which has only been partially achieved in the recent past using the hybrid direct numerical simulation (HDNS) approach. % where Stokes disturbance flow is assumed. The HDNS approach has two major drawbacks: (1) the short-range droplet-droplet interaction is not treated rigorously; (2) the finite-Reynolds number correction to the collision efficiency is not included. In this talk, using two independent numerical methods, we will develop an interface-resolved simulation approach in which the disturbance flows are directly resolved numerically, combined with a rigorous lubrication correction model for near-field droplet-droplet interaction. This multi-scale approach is first used to study the effect of finite flow Reynolds numbers on the droplet collision efficiency in still air. Our simulation results show a significant finite-Re effect on collision efficiency when the droplets are of similar sizes. Preliminary results on integrating this approach in a turbulent flow laden with droplets will also be presented. This work is partially supported by the National Science Foundation.

  4. Development of an imaging system for single droplet characterization using a droplet generator.

    Science.gov (United States)

    Minov, S Vulgarakis; Cointault, F; Vangeyte, J; Pieters, J G; Hijazi, B; Nuyttens, D

    2012-01-01

    The spray droplets generated by agricultural nozzles play an important role in the application accuracy and efficiency of plant protection products. The limitations of the non-imaging techniques and the recent improvements in digital image acquisition and processing increased the interest in using high speed imaging techniques in pesticide spray characterisation. The goal of this study was to develop an imaging technique to evaluate the characteristics of a single spray droplet using a piezoelectric single droplet generator and a high speed imaging technique. Tests were done with different camera settings, lenses, diffusers and light sources. The experiments have shown the necessity for having a good image acquisition and processing system. Image analysis results contributed in selecting the optimal set-up for measuring droplet size and velocity which consisted of a high speed camera with a 6 micros exposure time, a microscope lens at a working distance of 43 cm resulting in a field of view of 1.0 cm x 0.8 cm and a Xenon light source without diffuser used as a backlight. For measuring macro-spray characteristics as the droplet trajectory, the spray angle and the spray shape, a Macro Video Zoom lens at a working distance of 14.3 cm with a bigger field of view of 7.5 cm x 9.5 cm in combination with a halogen spotlight with a diffuser and the high speed camera can be used.

  5. Phase rainbow refractometry for accurate droplet variation characterization.

    Science.gov (United States)

    Wu, Yingchun; Promvongsa, Jantarat; Saengkaew, Sawitree; Wu, Xuecheng; Chen, Jia; Gréhan, Gérard

    2016-10-15

    We developed a one-dimensional phase rainbow refractometer for the accurate trans-dimensional measurements of droplet size on the micrometer scale as well as the tiny droplet diameter variations at the nanoscale. The dependence of the phase shift of the rainbow ripple structures on the droplet variations is revealed. The phase-shifting rainbow image is recorded by a telecentric one-dimensional rainbow imaging system. Experiments on the evaporating monodispersed droplet stream show that the phase rainbow refractometer can measure the tiny droplet diameter changes down to tens of nanometers. This one-dimensional phase rainbow refractometer is capable of measuring the droplet refractive index and diameter, as well as variations.

  6. Spray Droplet Characterization from a Single Nozzle by High Speed Image Analysis Using an In-Focus Droplet Criterion.

    Science.gov (United States)

    Minov, Sofija Vulgarakis; Cointault, Frédéric; Vangeyte, Jürgen; Pieters, Jan G; Nuyttens, David

    2016-02-06

    Accurate spray characterization helps to better understand the pesticide spray application process. The goal of this research was to present the proof of principle of a droplet size and velocity measuring technique for different types of hydraulic spray nozzles using a high speed backlight image acquisition and analysis system. As only part of the drops of an agricultural spray can be in focus at any given moment, an in-focus criterion based on the gray level gradient was proposed to decide whether a given droplet is in focus or not. In a first experiment, differently sized droplets were generated with a piezoelectric generator and studied to establish the relationship between size and in-focus characteristics. In a second experiment, it was demonstrated that droplet sizes and velocities from a real sprayer could be measured reliably in a non-intrusive way using the newly developed image acquisition set-up and image processing. Measured droplet sizes ranged from 24 μm to 543 μm, depending on the nozzle type and size. Droplet velocities ranged from around 0.5 m/s to 12 m/s. The droplet size and velocity results were compared and related well with the results obtained with a Phase Doppler Particle Analyzer (PDPA).

  7. Freezing of Water Droplet due to Evaporation

    Science.gov (United States)

    Satoh, Isao; Fushinobu, Kazuyoshi; Hashimoto, Yu

    In this study, the feasibility of cooling/freezing of phase change.. materials(PCMs) due to evaporation for cold storage systems was experimentally examined. A pure water was used as the test PCM, since the latent heat due to evaporation of water is about 7 times larger than that due to freezing. A water droplet, the diameter of which was 1-4 mm, was suspended in a test cell by a fine metal wire (O. D.= 100μm),and the cell was suddenly evacuated up to the pressure lower than the triple-point pressure of water, so as to enhance the evaporation from the water surface. Temperature of the droplet was measured by a thermocouple, and the cooling/freezing behavior and the temperature profile of the droplet surface were captured by using a video camera and an IR thermo-camera, respectively. The obtained results showed that the water droplet in the evacuated cell is effectively cooled by the evaporation of water itself, and is frozen within a few seconds through remarkable supercooling state. When the initial temperature of the droplet is slightly higher than the room temperature, boiling phenomena occur in the droplet simultaneously with the freezing due to evaporation. Under such conditions, it was shown that the degree of supercooling of the droplet is reduced by the bubbles generated in the droplet.

  8. Droplet phase characteristics in liquid-dominated steam--water nozzle flow

    International Nuclear Information System (INIS)

    Alger, T.W.

    1978-01-01

    An experimental study was undertaken to determine the droplet size distribution, the droplet spatial distribution and the mean droplet velocity in low-quality, steam-water flow from a rectangular cross-section, converging-diverging nozzle. A unique forward light scattering technique was developed for droplet size distribution measurements. Droplet spatial variations were investigated using light transmission measurements, and droplet velocities were measured with a laser-Doppler velocimeter (LDV) system incorporating a confocal Fabry-Perot interferometer. Nozzle throat radius of curvature and height were varied to investigte their effects on droplet size. Droplet size distribution measurements yielded a nominal Sauter mean droplet diameter of 1.7 μm and a nominal mass-mean droplet diameter of 2.4 μm. Neither the throat radius of curvature nor the throat height were found to have a significant effect upon the nozzle exit droplet size. The light transmission and LDV measurement results confirmed both the droplet size measurements and demonstrated high spatial uniformity of the droplet phase within the nozzle jet flow. One-dimensional numerical calculations indicated that both the dynamic breakup (thermal equilibrium based on a critical Weber number of 6.0) and the boiling breakup (thermal nonequilibrium based on average droplet temperature) models predicted droplet diameters on the order of 7.5 μm, which are approximately equal to the maximum stable droplet diameters within the nozzle jet flow

  9. Droplet sizes, dynamics and deposition in vertical annular flow

    International Nuclear Information System (INIS)

    Lopes, J.C.B.; Dukler, A.E.

    1985-10-01

    The role of droplets in vertical upwards annular flow is investigated, focusing on the droplet size distributions, dynamics, and deposition phenomena. An experimental program was performed based on a new laser optical technique developed in these laboratories and implemented here for annular flow. This permitted the simultaneous measurement of droplet size, axial and radial velocity. The dependence of droplet size distributions on flow conditions is analyzed. The Upper-Log Normal function proves to be a good model for the size distribution. The mechanism controlling the maximum stable drop size was found to result from the interaction of the pressure fluctuations of the turbulent flow of the gas core with the droplet. The average axial droplet velocity showed a weak dependence on gas rates. This can be explained once the droplet size distribution and droplet size-velocity relationship are analyzed simultaneously. The surprising result from the droplet conditional analysis is that larger droplet travel faster than smaller ones. This dependence cannot be explained if the drag curves used do not take into account the high levels of turbulence present in the gas core in annular flow. If these are considered, then interesting new situations of multiplicity and stability of droplet terminal velocities are encountered. Also, the observed size-velocity relationship can be explained. A droplet deposition is formulated based on the particle inertia control. This permitted the calculation of rates of drop deposition directly from the droplet size and velocities data

  10. Packaging a liquid metal ESD with micro-scale Mercury droplet.

    Energy Technology Data Exchange (ETDEWEB)

    Barnard, Casey Anderson

    2011-08-01

    A liquid metal ESD is being developed to provide electrical switching at different acceleration levels. The metal will act as both proof mass and electric contact. Mercury is chosen to comply with operation parameters. There are many challenges surrounding the deposition and containment of micro scale mercury droplets. Novel methods of micro liquid transfer are developed to deliver controllable amounts of mercury to the appropriate channels in volumes under 1 uL. Issues of hermetic sealing and avoidance of mercury contamination are also addressed.

  11. Dynamics of deformation and pinch-off of a migrating compound droplet in a tube

    Science.gov (United States)

    Borthakur, Manash Pratim; Biswas, Gautam; Bandyopadhyay, Dipankar

    2018-04-01

    A computational fluid dynamic investigation has been carried out to study the dynamics of a moving compound droplet inside a tube. The motions associated with such a droplet is uncovered by solving the axisymmetric Navier-Stokes equations in which the spatiotemporal evolution of a pair of twin-deformable interfaces has been tracked employing the volume-of-fluid approach. The deformations at the interfaces and their subsequent dynamics are found to be stimulated by the subtle interplay between the capillary and viscous forces. The simulations uncover that when a compound drop composed of concentric inner and outer interfaces migrates inside a tube, initially in the unsteady domain of evolution, the inner drop shifts away from the concentric position to reach a morphology of constant eccentricity at the steady state. The coupled motions of the droplets in the unsteady regime causes a continuous deformation of the inner and outer interfaces to obtain a configuration with a (an) prolate (oblate) shaped outer (inner) interface. The magnitudes of capillary number and viscosity ratio are found to have significant influence on the temporal evolution of the interfacial deformations as well as the eccentricity of the droplets. Further, the simulations uncover that, following the asymmetric deformation of the interfaces, the migrating compound droplet can undergo an uncommon breakup stimulated by a rather irregular pinch-off of the outer shell. The breakup is found to initiate with the thinning of the outer shell followed by the pinch-off. Interestingly, the kinetics of the thinning of outer shell is found to follow two distinct power-law regimes—a swiftly thinning stage at the onset followed by a rate limiting stage before pinch-off, which eventually leads to the uncommon breakup of the migrating compound droplets.

  12. Emulsion droplet interactions: a front-tracking treatment

    Science.gov (United States)

    Mason, Lachlan; Juric, Damir; Chergui, Jalel; Shin, Seungwon; Craster, Richard V.; Matar, Omar K.

    2017-11-01

    Emulsion coalescence influences a multitude of industrial applications including solvent extraction, oil recovery and the manufacture of fast-moving consumer goods. Droplet interaction models are vital for the design and scale-up of processing systems, however predictive modelling at the droplet-scale remains a research challenge. This study simulates industrially relevant moderate-inertia collisions for which a high degree of droplet deformation occurs. A hybrid front-tracking/level-set approach is used to automatically account for interface merging without the need for `bookkeeping' of interface connectivity. The model is implemented in Code BLUE using a parallel multi-grid solver, allowing both film and droplet-scale dynamics to be resolved efficiently. Droplet interaction simulations are validated using experimental sequences from the literature in the presence and absence of background turbulence. The framework is readily extensible for modelling the influence of surfactants and non-Newtonian fluids on droplet interaction processes. EPSRC, UK, MEMPHIS program Grant (EP/K003976/1), RAEng Research Chair (OKM), PETRONAS.

  13. Experimental test of liquid droplet radiator performance

    Science.gov (United States)

    Mattick, A. T.; Simon, M. A.

    The liquid droplet radiator (LDR) is a heat rejection system for space power systems wherein an array of heated liquid droplets radiates energy directly to space. The use of submillimeter droplets provides large radiating area-to-mass ratio, resulting in radiator systems which are several times lighter than conventional solid surface radiators. An experiment is described in which the power radiated by an array of 2300 streams of silicone oil droplets is measured to test a previously developed theory of the LDR radiation process. This system would be capable of rejecting several kW of heat in space. Furthermore, it would be suitable as a modular unit of an LDR designed for 100-kW power levels. The experiment provided confirmation of the theoretical dependence of droplet array emissivity on optical depth. It also demonstrated the ability to create an array of more than 1000 droplet streams having a divergence less than 1 degree.

  14. Millifluidic droplet analyser for microbiology

    NARCIS (Netherlands)

    Baraban, L.; Bertholle, F.; Salverda, M.L.M.; Bremond, N.; Panizza, P.; Baudry, J.; Visser, de J.A.G.M.; Bibette, J.

    2011-01-01

    We present a novel millifluidic droplet analyser (MDA) for precisely monitoring the dynamics of microbial populations over multiple generations in numerous (=103) aqueous emulsion droplets (100 nL). As a first application, we measure the growth rate of a bacterial strain and determine the minimal

  15. Targeting the motor regulator Klar to lipid droplets

    Directory of Open Access Journals (Sweden)

    Einstein Jenifer

    2011-02-01

    Full Text Available Abstract Background In Drosophila, the transport regulator Klar displays tissue-specific localization: In photoreceptors, it is abundant on the nuclear envelope; in early embryos, it is absent from nuclei, but instead present on lipid droplets. Differential targeting of Klar appears to be due to isoform variation. Droplet targeting, in particular, has been suggested to occur via a variant C-terminal region, the LD domain. Although the LD domain is necessary and sufficient for droplet targeting in cultured cells, lack of specific reagents had made it previously impossible to analyze its role in vivo. Results Here we describe a new mutant allele of klar with a lesion specifically in the LD domain; this lesion abolishes both droplet localization of Klar and the ability of Klar to regulate droplet motion. It does not disrupt Klar's function for nuclear migration in photoreceptors. Using a GFP-LD fusion, we show that the LD domain is not only necessary but also sufficient for droplet targeting in vivo; it mediates droplet targeting in embryos, in ovaries, and in a number of somatic tissues. Conclusions Our analysis demonstrates that droplet targeting of Klar occurs via a cis-acting sequence and generates a new tool for monitoring lipid droplets in living tissues of Drosophila.

  16. Investigation on Electrostatical Breakup of Bio-Oil Droplets

    Directory of Open Access Journals (Sweden)

    John Z. Wen

    2012-10-01

    Full Text Available In electrostatic atomization, the input electrical energy causes breaking up of the droplet surface by utilizing a mutual repulsion of net charges accumulating on that surface. In this work a number of key parameters controlling the bio-oil droplet breakup process are identified and these correlations among the droplet size distribution, specific charges of droplets and externally applied electrical voltages are quantified. Theoretical considerations of the bag or strip breakup mechanism of biodiesel droplets experiencing electrostatic potential are compared to experimental outcomes. The theoretical analysis suggests the droplet breakup process is governed by the Rayleigh instability condition, which reveals the effects of droplets size, specific charge, surface tension force, and droplet velocities. Experiments confirm that the average droplet diameters decrease with increasing specific charges and this decreasing tendency is non-monotonic due to the motion of satellite drops in the non-uniform electrical field. The measured specific charges are found to be smaller than the theoretical values. And the energy transformation from the electrical energy to surface energy, in addition to the energy loss, Taylor instability breakup, non-excess polarization and some system errors, accounts for this discrepancy. The electrostatic force is the dominant factor controlling the mechanism of biodiesel breakup in electrostatic atomization.

  17. Research on the porous flow of the mechanism of viscous-elastic fluids displacing residual oil droplets in micro pores

    Science.gov (United States)

    Dong, Guanyu

    2018-03-01

    In order to analyze the microscopic stress field acting on residual oil droplets in micro pores, calculate its deformation, and explore the hydrodynamic mechanism of viscous-elastic fluids displacing oil droplets, the viscous-elastic fluid flow equations in micro pores are established by choosing the Upper Convected Maxwell constitutive equation; the numerical solutions of the flow field are obtained by volume control and Alternate Direction Implicit methods. From the above, the velocity field and microscopic stress field; the forces acting on residual oil droplets; the deformations of residual oil droplets by various viscous-elastic displacing fluids and at various Wiesenberg numbers are calculated and analyzed. The result demonstrated that both the normal stress and horizontal force acting on the residual oil droplets by viscous-elastic fluids are much larger compared to that of inelastic fluid; the distribution of normal stress changes abruptly; under the condition of the same pressure gradient in the system under investigation, the ratio of the horizontal forces acting on the residual oil droplets by different displacing fluids is about 1:8:20, which means that under the above conditions, the driving force on a oil droplet is 20 times higher for a viscous-elastic fluid compared to that of a Newtonian Fluid. The conclusions are supportive of the mechanism that viscous-elastic driving fluids can increase the Displacement Efficiency. This should be of help in designing new chemicals and selecting Enhanced Oil Recovery systems.

  18. In situ observation on the dynamic process of evaporation and crystallization of sodium nitrate droplets on a ZnSe substrate by FTIR-ATR.

    Science.gov (United States)

    Zhang, Qing-Nuan; Zhang, Yun; Cai, Chen; Guo, Yu-Cong; Reid, Jonathan P; Zhang, Yun-Hong

    2014-04-17

    Sodium nitrate is a main component of aging sea salt aerosol, and its phase behavior has been studied repeatedly with wide ranges observed in the efflorescence relative humidity (RH) in particular. Studies of the efflorescence dynamics of NaNO3 droplets deposited on a ZnSe substrate are reported, using an in situ Fourier transform infrared attenuated total reflection (FTIR-ATR) technique. The time-dependence of the infrared spectra of NaNO3 aerosols accompanying step changes in RH have been measured with high signal-to-noise ratio. From the IR difference spectra recorded, changes of the time-dependent absorption peak area of the O-H stretching band (ν-OH, ∼3400 cm(-1)) and the nitrate out-of-plane bending band (ν2-NO3(-), ∼836 cm(-1)) are obtained. From these measurements, changes in the IR signatures can be attributed to crystalline and solution phase nitrate ions, allowing the volume fraction of the solution droplets that have crystallized to be determined. Then, using these clear signatures of the volume fraction of droplets that have yet to crystallize, the homogeneous and heterogeneous nucleation kinetics can be studied from conventional measurements using a steady decline in RH. The nucleation rate measurements confirm that the rate of crystallization in sodium nitrate droplets is considerably less than in ammonium sulfate droplets at any particular degree of solute supersaturation, explaining the wide range of efflorescence RHs observed for sodium nitrate in previous studies. We demonstrate that studying nucleation kinetics using the FTIR-ATR approach has many advantages over brightfield imaging studies on smaller numbers of larger droplets or measurements made on single levitated particles.

  19. Some Lipid Droplets Are More Equal Than Others: Different Metabolic Lipid Droplet Pools in Hepatic Stellate Cells.

    Science.gov (United States)

    Molenaar, Martijn R; Vaandrager, Arie B; Helms, J Bernd

    2017-01-01

    Hepatic stellate cells (HSCs) are professional lipid-storing cells and are unique in their property to store most of the retinol (vitamin A) as retinyl esters in large-sized lipid droplets. Hepatic stellate cell activation is a critical step in the development of chronic liver disease, as activated HSCs cause fibrosis. During activation, HSCs lose their lipid droplets containing triacylglycerols, cholesteryl esters, and retinyl esters. Lipidomic analysis revealed that the dynamics of disappearance of these different classes of neutral lipids are, however, very different from each other. Although retinyl esters steadily decrease during HSC activation, triacylglycerols have multiple pools one of which becomes transiently enriched in polyunsaturated fatty acids before disappearing. These observations are consistent with the existence of preexisting "original" lipid droplets with relatively slow turnover and rapidly recycling lipid droplets that transiently appear during activation of HSCs. Elucidation of the molecular machinery involved in the regulation of these distinct lipid droplet pools may open new avenues for the treatment of liver fibrosis.

  20. Droplet ejection and sliding on a flapping film

    Directory of Open Access Journals (Sweden)

    Xi Chen

    2017-03-01

    Full Text Available Water recovery and subsequent reuse are required for human consumption as well as industrial, and agriculture applications. Moist air streams, such as cooling tower plumes and fog, represent opportunities for water harvesting. In this work, we investigate a flapping mechanism to increase droplet shedding on thin, hydrophobic films for two vibrational cases (e.g., ± 9 mm and 11 Hz; ± 2 mm and 100 Hz. Two main mechanisms removed water droplets from the flapping film: vibrational-induced coalescence/sliding and droplet ejection from the surface. Vibrations mobilized droplets on the flapping film, increasing the probability of coalescence with neighboring droplets leading to faster droplet growth. Droplet departure sizes of 1–2 mm were observed for flapping films, compared to 3–4 mm on stationary films, which solely relied on gravity for droplet removal. Additionally, flapping films exhibited lower percentage area coverage by water after a few seconds. The second removal mechanism, droplet ejection was analyzed with respect to surface wave formation and inertia. Smaller droplets (e.g., 1-mm diameter were ejected at a higher frequency which is associated with a higher acceleration. Kinetic energy of the water was the largest contributor to energy required to flap the film, and low energy inputs (i.e., 3.3 W/m2 were possible. Additionally, self-flapping films could enable novel water collection and condensation with minimal energy input.

  1. Droplet size in a rectangular Venturi scrubber

    OpenAIRE

    Costa, M. A. M.; Henrique, P. R.; Gonçalves, J. A. S.; Coury, J.R.

    2004-01-01

    The Venturi scrubber is a device which uses liquid in the form of droplets to efficiently remove fine particulate matter from gaseous streams. Droplet size is of fundamental importance for the scrubber performance. In the present experimental study, a laser diffraction technique was used in order to measure droplet size in situ in a Venturi scrubber with a rectangular cross section. Droplet size distribution was measured as a function of gas velocity (58.3 to 74.9 m/s), liquid-to-gas ratio (0...

  2. New models for droplet heating and evaporation

    KAUST Repository

    Sazhin, Sergei S.

    2013-02-01

    A brief summary of new models for droplet heating and evaporation, developed mainly at the Sir Harry Ricardo Laboratory of the University of Brighton during 2011-2012, is presented. These are hydrodynamic models for mono-component droplet heating and evaporation, taking into account the effects of the moving boundary due to evaporation, hydrodynamic models of multi-component droplet heating and evaporation, taking and not taking into account the effects of the moving boundary, new kinetic models of mono-component droplet heating and evaporation, and a model for mono-component droplet evaporation, based on molecular dynamics simulation. The results, predicted by the new models are compared with experimental data and the prehctions of the previously developed models where possible. © 2013 Asian Network for Scientific Information.

  3. An experimental study on suspended sodium droplet combustion

    International Nuclear Information System (INIS)

    Sato, Kenji

    2003-03-01

    As part of studies for phenomenological investigation of sodium droplet burning behavior, in our previous experimental studies, ignition process and succeeding combustion of suspended single sodium droplet had been investigated by using high speed movie camera, and a temperature measurement system feasible for the experiment had been developed. In the present study, by using 4 mm diam. suspended sodium droplet, combustion experiments were performed for the free-stream velocity of dry air flow of 20 to 60 cm/s, and for the initial droplet temperature of 280 to 400degC, and the effects of the free-stream velocity and initial droplet temperature on the ignition behavior and droplet temperature variation with time were examined by using high speed movie camera and sheath-type fine thermocouple. The experimental results are as follows: (1) When the initial droplet temperature is less than 290degC, before ignition the oxide film accompanied with vertical streak appeared and the droplet turned to teardrop shape. (2) The ignition delay time defined as the time to evolution of orange color light emission zone or flame zone decreases with the increase o the free-stream velocity or of initial droplet temperature. Examples of typical ignition time are 1.4 s at the free-stream velocity 20 cm/s and initial droplet temperature 300degC, and 0.65 s at 60 cm/s and 400degC. (3) the dependence of the ignition delay time on the free-stream velocity decreases as the free stream velocity increases. (4) The droplet temperatures at the moment of melting extending all over the surface and at the moment of ignition are around 460degC and 500 to 600degC (mostly around 575degC), respectively. These values are essentially independent of the free-stream velocity and initial droplet temperature. (5) The rate of temperature rise does not change through the moment of ignition. (6) The asymptotic droplet temperature at approaching to quasi-steady combustion state following ignition is independent of

  4. Thermal management of metallic surfaces: evaporation of sessile water droplets on polished and patterned stainless steel

    Science.gov (United States)

    Czerwiec, T.; Tsareva, S.; Andrieux, A.; Bortolini, G. A.; Bolzan, P. H.; Castanet, G.; Gradeck, M.; Marcos, G.

    2017-10-01

    This communication focus on the evaporation of sessile water droplets on different states of austenitic stainless steel surfaces: mirror polished, mirror polished and aged and patterned by sputtering. The evolution of the contact angle and of the droplet diameter is presented as a function of time at room temperature. For all the surface states, a constant diameter regime (CCR) is observed. An important aging effect on the contact angle is measured on polished surfaces due to atmospheric contamination. The experimental observations are compared to a quasi-static evaporation model assuming spherical caps. The evolution of the droplet volume as a function of time is almost linear with the evaporation time for all the observed surfaces. This is in accordance with the model prediction for the CCR mode for small initial contact angles. In our experiments, the evaporation time is found to be linearly dependent on the initial contact angle. This dependence is not correctly described by the evaporation model

  5. Liquid droplet radiator performance studies

    Science.gov (United States)

    Mattick, A. T.; Hertzberg, A.

    By making use of droplets rather than solid surfaces to radiate waste heat in space, the liquid droplet radiator (LDR) achieves a radiating area/mass much larger than that of conventional radiators which use fins or heat pipes. The lightweight potential of the LDR is shown to be limited primarily by the radiative properties of the droplets. The requirement that the LDR heat transfer fluid have a very low vapor pressure limits the choice of fluids to relatively few—several liquid metals and Dow 705 silicone fluid are the only suitable candidates so far identified. An experimental determination of the emittance of submillimeter droplets of Dow 705 fluid indicates than an LDR using this fluid at temperatures of 275-335 K would be ⋍ 10 times lighter than the lightest solid surface radiators. Although several liquid metals appear to offer excellent performance in LDR applications at temperatures between 200 K and 975 K, experimental determination of liquid metal emissivities is needed for a conclusive assessment.

  6. Enhancing Protease Activity Assay in Droplet-Based Microfluidics Using a Biomolecule Concentrator

    Science.gov (United States)

    Chen, Chia-Hung; Sarkar, Aniruddh; Song, Yong-Ak; Miller, Miles A.; Kim, Sung Jae; Griffith, Linda G.; Lauffenburger, Douglas A.; Han, Jongyoon

    2011-01-01

    We introduce an integrated microfluidic device consisting of a biomolecule concentrator and a microdroplet generator, which enhances the limited sensitivity of low-abundance enzyme assays by concentrating biomolecules before encapsulating them into droplet microreactors. We used this platform to detect ultra low levels of matrix metalloproteinases (MMPs) from diluted cellular supernatant and showed that it significantly (∼10-fold) reduced the time required to complete the assay and the sample volume used. PMID:21671557

  7. An experimental study on suspended sodium droplet combustion (3)

    International Nuclear Information System (INIS)

    Sato, Kenji

    2005-03-01

    As part of studies for phenomenological investigation of sodium droplet burning behavior, in our previous experimental studies for suspended single sodium droplet, behavior of ignition process and succeeding combustion, ignition delay time, and droplet temperature history had been investigated. In this study, combustion experiments of suspended sodium droplet were performed in upward dry air flow by expanding the range of free-stream velocity U of air flow into 400 cm/s with initial droplet temperature Ti=300, 350, and 400degC and initial droplet diameter 4 mm at first. Then, the combustion experiments were also performed by changing the initial droplet diameter from 2.3 to 4.4 mm with Ti=350 and 400degC and U=100 cm/s. From the experimental results, the effects of free-stream velocity, initial droplet temperature, and initial droplet diameter on the ignition/burning behavior and ignition delay time were examined. The obtained results are as follows: (1) Ignition phenomena of suspended droplet were observed for all examined experimental conditions up to 400 cm/s. The orange emission observed at the moment of ignition occurs simultaneously over whole droplet surface except the top region of it. (2) The feature of the dependence of ignition delay time on the free-stream velocity is independent of the initial droplet temperature. With the increase of the free-stream velocity, up to 300 cm/s the ignition delay time decreases with decreasing dependency, and then the dependency increases more. (3) The ignition delay time increases with the increase of initial droplet diameter. The dependency increases as the initial droplet diameter increases. The ignition delay time extrapolated toward zero diameters from the obtained results becomes to be essentially zero. (author)

  8. Droplet size in a rectangular Venturi scrubber

    Directory of Open Access Journals (Sweden)

    M. A. M. Costa

    2004-06-01

    Full Text Available The Venturi scrubber is a device which uses liquid in the form of droplets to efficiently remove fine particulate matter from gaseous streams. Droplet size is of fundamental importance for the scrubber performance. In the present experimental study, a laser diffraction technique was used in order to measure droplet size in situ in a Venturi scrubber with a rectangular cross section. Droplet size distribution was measured as a function of gas velocity (58.3 to 74.9 m/s, liquid-to-gas ratio (0.07 to 0.27 l/m³, and distance from liquid injection point (64 to 173 mm. It was found that all these variables significantly affect droplet size. The results were compared with the predictions from correlations found in the literature.

  9. Droplet electrospray ionization mass spectrometry for high throughput screening for enzyme inhibitors.

    Science.gov (United States)

    Sun, Shuwen; Kennedy, Robert T

    2014-09-16

    High throughput screening (HTS) is important for identifying molecules with desired properties. Mass spectrometry (MS) is potentially powerful for label-free HTS due to its high sensitivity, speed, and resolution. Segmented flow, where samples are manipulated as droplets separated by an immiscible fluid, is an intriguing format for high throughput MS because it can be used to reliably and precisely manipulate nanoliter volumes and can be directly coupled to electrospray ionization (ESI) MS for rapid analysis. In this study, we describe a "MS Plate Reader" that couples standard multiwell plate HTS workflow to droplet ESI-MS. The MS plate reader can reformat 3072 samples from eight 384-well plates into nanoliter droplets segmented by an immiscible oil at 4.5 samples/s and sequentially analyze them by MS at 2 samples/s. Using the system, a label-free screen for cathepsin B modulators against 1280 chemicals was completed in 45 min with a high Z-factor (>0.72) and no false positives (24 of 24 hits confirmed). The assay revealed 11 structures not previously linked to cathepsin inhibition. For even larger scale screening, reformatting and analysis could be conducted simultaneously, which would enable more than 145,000 samples to be analyzed in 1 day.

  10. Droplet Epitaxy Image Contrast in Mirror Electron Microscopy

    Science.gov (United States)

    Kennedy, S. M.; Zheng, C. X.; Jesson, D. E.

    2017-01-01

    Image simulation methods are applied to interpret mirror electron microscopy (MEM) images obtained from a movie of GaAs droplet epitaxy. Cylindrical symmetry of structures grown by droplet epitaxy is assumed in the simulations which reproduce the main features of the experimental MEM image contrast, demonstrating that droplet epitaxy can be studied in real-time. It is therefore confirmed that an inner ring forms at the droplet contact line and an outer ring (or skirt) occurs outside the droplet periphery. We believe that MEM combined with image simulations will be increasingly used to study the formation and growth of quantum structures.

  11. Micro-Particles Motion in an Evaporating Droplet

    International Nuclear Information System (INIS)

    Jung, Jung Yeul; Yoo, Jung Yul; Kim, Young Won

    2007-01-01

    Nano-particles (on the order of 1 to 100 nm) contained within the droplet are moved by liquid flow and stacked at the contact line. The self-pinned contact line under the evaporating droplet is very interesting in the field of patterning and separation of particles and biocells. Models accounting for the nano-particles' flow and deposit patterns have been reported and verified by various experiments. Here, we report for the first time a phenomenon where micro-particles (on the order of 1 μm) in the colloid droplet flow to the center of droplet. There are three modes of fluid and particle flow in the evaporating droplet. In the first mode, a self-pinned contact line is maintained and the fluid and micro/nano-particles flow to the contact line. In the second mode, micro/nano-particles self-assemble at the near contact line, as reported by Jung and Kwak. In the final mode, only micro-particles are adverted to the center of the droplet due to movement of the contact line

  12. Enhancing physicochemical properties of emulsions by heteroaggregation of oppositely charged lactoferrin coated lutein droplets and whey protein isolate coated DHA droplets.

    Science.gov (United States)

    Li, Xin; Wang, Xu; Xu, Duoxia; Cao, Yanping; Wang, Shaojia; Wang, Bei; Sun, Baoguo; Yuan, Fang; Gao, Yanxiang

    2018-01-15

    The formation and physicochemical stability of mixed functional components (lutein & DHA) emulsions through heteroaggregation were studied. It was formed by controlled heteroaggregation of oppositely charged lutein and DHA droplets coated by cationic lactoferrin (LF) and anionic whey protein isolate (WPI), respectively. Heteroaggregation was induced by mixing the oppositely charged LF-lutein and WPI-DHA emulsions together at pH 6.0. Droplet size, zeta-potential, transmission-physical stability, microrheological behavior and microstructure of the heteroaggregates formed were measured as a function of LF-lutein to WPI-DHA droplet ratio. Lutein degradation and DHA oxidation by measurement of lipid hydroperoxides and thiobarbituric acid reactive substances were determined. Upon mixing the two types of bioactive compounds droplets together, it was found that the largest aggregates and highest physical stability occurred at a droplet ratio of 40% LF-lutein droplets to 60% WPI-DHA droplets. Heteroaggregates formation altered the microrheological properties of the mixed emulsions mainly by the special network structure of the droplets. When LF-coated lutein droplets ratios were more than 30% and less than 60%, the mixed emulsions exhibited distinct decreases in the Mean Square Displacement, which indicated that their limited scope of Brownian motion and stable structure. Mixed emulsions with LF-lutein/WPI-DHA droplets ratio of 4:6 exhibited Macroscopic Viscosity Index with 13 times and Elasticity Index with 3 times of magnitudes higher than the individual emulsions from which they were prepared. Compared with the WPI-DHA emulsion or LF-lutein emulsion, the oxidative stability of the heteroaggregate of LF-lutein/WPI-DHA emulsions was improved. Heteroaggregates formed by oppositely charged bioactive compounds droplets may be useful for creating specific food structures that lead to desirable physicochemical properties, such as microrheological property, physical and chemical

  13. Droplet morphometry and velocimetry (DMV): a video processing software for time-resolved, label-free tracking of droplet parameters.

    Science.gov (United States)

    Basu, Amar S

    2013-05-21

    Emerging assays in droplet microfluidics require the measurement of parameters such as drop size, velocity, trajectory, shape deformation, fluorescence intensity, and others. While micro particle image velocimetry (μPIV) and related techniques are suitable for measuring flow using tracer particles, no tool exists for tracking droplets at the granularity of a single entity. This paper presents droplet morphometry and velocimetry (DMV), a digital video processing software for time-resolved droplet analysis. Droplets are identified through a series of image processing steps which operate on transparent, translucent, fluorescent, or opaque droplets. The steps include background image generation, background subtraction, edge detection, small object removal, morphological close and fill, and shape discrimination. A frame correlation step then links droplets spanning multiple frames via a nearest neighbor search with user-defined matching criteria. Each step can be individually tuned for maximum compatibility. For each droplet found, DMV provides a time-history of 20 different parameters, including trajectory, velocity, area, dimensions, shape deformation, orientation, nearest neighbour spacing, and pixel statistics. The data can be reported via scatter plots, histograms, and tables at the granularity of individual droplets or by statistics accrued over the population. We present several case studies from industry and academic labs, including the measurement of 1) size distributions and flow perturbations in a drop generator, 2) size distributions and mixing rates in drop splitting/merging devices, 3) efficiency of single cell encapsulation devices, 4) position tracking in electrowetting operations, 5) chemical concentrations in a serial drop dilutor, 6) drop sorting efficiency of a tensiophoresis device, 7) plug length and orientation of nonspherical plugs in a serpentine channel, and 8) high throughput tracking of >250 drops in a reinjection system. Performance metrics

  14. Interaction of Droplets Separated by an Elastic Film.

    Science.gov (United States)

    Liu, Tianshu; Xu, Xuejuan; Nadermann, Nichole; He, Zhenping; Jagota, Anand; Hui, Chung-Yuen

    2017-01-10

    The Laplace pressure of a droplet placed on one side of an elastic thin film can cause significant deformation in the form of a bulge on its opposite side. Here, we show that this deformation can be detected by other droplets suspended on the opposite side of the film, leading to interaction between droplets separated by the solid (but deformable) film. The interaction is repulsive when the drops have a large overlap and attractive when they have a small overlap. Thus, if two identical droplets are placed right on top of each other (one on either side of the thin film), they tend to repel each other, eventually reaching an equilibrium configuration where there is a small overlap. This observation can be explained by analyzing the energy landscape of the droplets interacting via an elastically deformed film. We further demonstrate this idea by designing a pattern comprising a big central drop with satellite droplets. This phenomenon can lead to techniques for directed motion of droplets confined to one side of a thin elastic membrane by manipulations on the other side.

  15. Experimental investigation of flash pyrolysis oil droplet combustion

    DEFF Research Database (Denmark)

    Ibrahim, Norazana; Jensen, Peter A.; Dam-Johansen, Kim

    2013-01-01

    at a temperature ranging between 1000 and 1400°C with an initial gas velocity of 1.6 m/s and oxygen concentration of 3%. The evolution of combustion of bio-oil droplets was recorded by a digital video camera. It was observed that the combustion behaviour of pyrolysis oil droplet differ from the heavy oil in terms......The aim of this work is to investigate and compare the combustion behaviour of a single droplet of pyrolysis oil derived from wheat straw and heavy fossil oil in a single droplet combustion chamber. The initial oil droplet diameters were in between 500 μm to 2500 μm. The experiments were performed...

  16. The Lipid Droplet – A Well-Connected Organelle

    Directory of Open Access Journals (Sweden)

    Qiang eGao

    2015-08-01

    Full Text Available Our knowledge of inter-organellar communication has grown exponentially in recent years. This review focuses on the interactions that cytoplasmic lipid droplets have with other organelles. Twenty-five years ago droplets were considered simply particles of coalesced fat. Ten years ago there were hints from proteomics studies that droplets might interact with other structures to share lipids and proteins. Now it is clear that the droplets interact with many if not most cellular structures to maintain cellular homeostasis and to buffer against insults such as starvation. The evidence for this statement, as well as probes to understand the nature and results of droplet interactions, are presented.

  17. Spin lattices of walking droplets

    Science.gov (United States)

    Saenz, Pedro; Pucci, Giuseppe; Goujon, Alexis; Dunkel, Jorn; Bush, John

    2017-11-01

    We present the results of an experimental investigation of the spontaneous emergence of collective behavior in spin lattice of droplets walking on a vibrating fluid bath. The bottom topography consists of relatively deep circular wells that encourage the walking droplets to follow circular trajectories centered at the lattice sites, in one direction or the other. Wave-mediated interactions between neighboring drops are enabled through a thin fluid layer between the wells. The sense of rotation of the walking droplets may thus become globally coupled. When the coupling is sufficiently strong, interactions with neighboring droplets may result in switches in spin that lead to preferred global arrangements, including correlated (all drops rotating in the same direction) or anti-correlated (neighboring drops rotating in opposite directions) states. Analogies with ferromagnetism and anti-ferromagnetism are drawn. Different spatial arrangements are presented in 1D and 2D lattices to illustrate the effects of topological frustration. This work was supported by the US National Science Foundation through Grants CMMI-1333242 and DMS-1614043.

  18. Study of the Internal Flow and Evaporation Characteristic Inside a Water Droplet on a Vertical Vibrating Hydrophobic Surface

    Energy Technology Data Exchange (ETDEWEB)

    Park, Chang-Seok; Lim, Hee-Chang [Pusan Nat’l Univ., Busan (Korea, Republic of)

    2017-01-15

    Thermal Marangoni flow has been observed inside droplets on heated surfaces, finally resulting in a coffee stain effect. This study aims to visualize and control the thermal Marangoni flow by employing periodic vertical vibration. The variations in the contact angle and internal volume of the droplet as it evaporates is observed by using a combination of continuous light and a still camera. With regard to the internal velocity, the particle image velocimetry system is applied to visualize the internal thermal Marangoni flow. In order to estimate the internal temperature gradient and surface tension on the surface of a droplet, the theoretical model based on the conduction and convection theory of heat transfer is applied. Thus, the internal velocity increases with an increase in plate temperature. The flow directions of the Marangoni and gravitational flows are opposite, and hence, it may be possible to control the coffee stain effect.

  19. Preparation and nucleation of spherical metallic droplet

    Directory of Open Access Journals (Sweden)

    Bing-ge Zhao

    2015-03-01

    Full Text Available The preparation and solidification of metallic droplets attract more and more attention for their significance in both engineering and scientific fields. In this paper, the preparation and characterization of Sn-based alloy droplets using different methods such as atomization and consumable electrode direct current arc (CDCA technique are reviewed. The morphology and structure of these droplets were determined by optical microscopy, X-ray diffraction (XRD and scanning electron microscopy (SEM. The solidification behavior of single droplet was systematically studied by means of scanning calorimetry (DSC, and the nucleation kinetics was also calculated. In particular, the development of fast scanning calorimetry (FSC made it possible to investigate the evolution of undercooling under ultrafast but controllable heating and cooling conditions. The combination of CDCA technique and FSC measurements opens up a new door for quantitative studies on droplet solidification, which is accessible to demonstrate some theories by experiments.

  20. Dynamics of droplet breakup in a T-junction

    NARCIS (Netherlands)

    Hoang, D.A.; Portela, L.M.; Kleijn, C.R.; Kreutzer, M.T.; Van Steijn, V.

    2013-01-01

    The breakup of droplets due to creeping motion in a confined microchannel geometry is studied using three-dimensional numerical simulations. Analogously to unconfined droplets, there exist two distinct breakup phases: (i) a quasi-steady droplet deformation driven by the externally applied flow; and

  1. Modeling contact angle hysteresis of a liquid droplet sitting on a cosine wave-like pattern surface.

    Science.gov (United States)

    Promraksa, Arwut; Chen, Li-Jen

    2012-10-15

    A liquid droplet sitting on a hydrophobic surface with a cosine wave-like square-array pattern in the Wenzel state is simulated by using the Surface Evolver to determine the contact angle. For a fixed drop volume, multiple metastable states are obtained at two different surface roughnesses. Unusual and non-circular shape of the three-phase contact line of a liquid droplet sitting on the model surface is observed due to corrugation and distortion of the contact line by structure of the roughness. The contact angle varies along the contact line for each metastable state. The maximum and minimum contact angles among the multiple metastable states at a fixed viewing angle correspond to the advancing and the receding contact angles, respectively. It is interesting to observe that the advancing/receding contact angles (and contact angle hysteresis) are a function of viewing angle. In addition, the receding (or advancing) contact angles at different viewing angles are determined at different metastable states. The contact angle of minimum energy among the multiple metastable states is defined as the most stable (equilibrium) contact angle. The Wenzel model is not able to describe the contact angle along the three-phase contact line. The contact angle hysteresis at different drop volumes is determined. The number of the metastable states increases with increasing drop volume. Drop volume effect on the contact angles is also discussed. Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.

  2. Calculation and measurement of fog droplet size

    International Nuclear Information System (INIS)

    Laali, A.R.; Courant, J.J.; Kleitz, A.

    1991-01-01

    This paper outlines the elements involved in calculation and measurement of fog droplet size in steam turbines. The condensation calculations are performed for a 600 MW LP fossil fired, and for a 900 MW LP nuclear turbine. A simplified method based on classical condensation theory is used for these calculations. The fog droplet size measurement are carried out downstream of the last moving blades of these turbines in order to validate the program. The comparison between the results could lead to a better understanding of the condensation process in steam turbines. Some large droplet (re-entrained droplet) measurements are also taken using a microvideo probe

  3. Spontaneous droplet trampolining on rigid superhydrophobic surfaces

    Science.gov (United States)

    Schutzius, Thomas M.; Jung, Stefan; Maitra, Tanmoy; Graeber, Gustav; Köhme, Moritz; Poulikakos, Dimos

    2015-11-01

    Spontaneous removal of condensed matter from surfaces is exploited in nature and in a broad range of technologies to achieve self-cleaning, anti-icing and condensation control. But despite much progress, our understanding of the phenomena leading to such behaviour remains incomplete, which makes it challenging to rationally design surfaces that benefit from its manifestation. Here we show that water droplets resting on superhydrophobic textured surfaces in a low-pressure environment can self-remove through sudden spontaneous levitation and subsequent trampoline-like bouncing behaviour, in which sequential collisions with the surface accelerate the droplets. These collisions have restitution coefficients (ratios of relative speeds after and before collision) greater than unity despite complete rigidity of the surface, and thus seemingly violate the second law of thermodynamics. However, these restitution coefficients result from an overpressure beneath the droplet produced by fast droplet vaporization while substrate adhesion and surface texture restrict vapour flow. We also show that the high vaporization rates experienced by the droplets and the associated cooling can result in freezing from a supercooled state that triggers a sudden increase in vaporization, which in turn boosts the levitation process. This effect can spontaneously remove surface icing by lifting away icy drops the moment they freeze. Although these observations are relevant only to systems in a low-pressure environment, they show how surface texturing can produce droplet-surface interactions that prohibit liquid and freezing water-droplet retention on surfaces.

  4. Stochastic growth of cloud droplets by collisions during settling

    Science.gov (United States)

    Madival, Deepak G.

    2018-04-01

    In the last stage of droplet growth in clouds which leads to drizzle formation, larger droplets begin to settle under gravity and collide and coalesce with smaller droplets in their path. In this article, we shall deal with the simplified problem of a large drop settling amidst a population of identical smaller droplets. We present an expression for the probability that a given large drop suffers a given number of collisions, for a general statistically homogeneous distribution of droplets. We hope that our approach will serve as a valuable tool in dealing with droplet distribution in real clouds, which has been found to deviate from the idealized Poisson distribution due to mechanisms such as inertial clustering.

  5. Lipid droplets fusion in adipocyte differentiated 3T3-L1 cells: A Monte Carlo simulation

    Energy Technology Data Exchange (ETDEWEB)

    Boschi, Federico, E-mail: federico.boschi@univr.it [Department of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134 Verona (Italy); Department of Computer Science, University of Verona, Strada Le Grazie 15, 37134 Verona (Italy); Rizzatti, Vanni; Zamboni, Mauro [Department of Medicine, Geriatric Section, University of Verona, Piazzale Stefani 1, 37126 Verona (Italy); Sbarbati, Andrea [Department of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134 Verona (Italy)

    2014-02-15

    Several human worldwide diseases like obesity, type 2 diabetes, hepatic steatosis, atherosclerosis and other metabolic pathologies are related to the excessive accumulation of lipids in cells. Lipids accumulate in spherical cellular inclusions called lipid droplets (LDs) whose sizes range from fraction to one hundred of micrometers in adipocytes. It has been suggested that LDs can grow in size due to a fusion process by which a larger LD is obtained with spherical shape and volume equal to the sum of the progenitors’ ones. In this study, the size distribution of two populations of LDs was analyzed in immature and mature (5-days differentiated) 3T3-L1 adipocytes (first and second populations, respectively) after Oil Red O staining. A Monte Carlo simulation of interaction between LDs has been developed in order to quantify the size distribution and the number of fusion events needed to obtain the distribution of the second population size starting from the first one. Four models are presented here based on different kinds of interaction: a surface weighted interaction (R2 Model), a volume weighted interaction (R3 Model), a random interaction (Random model) and an interaction related to the place where the LDs are born (Nearest Model). The last two models mimic quite well the behavior found in the experimental data. This work represents a first step in developing numerical simulations of the LDs growth process. Due to the complex phenomena involving LDs (absorption, growth through additional neutral lipid deposition in existing droplets, de novo formation and catabolism) the study focuses on the fusion process. The results suggest that, to obtain the observed size distribution, a number of fusion events comparable with the number of LDs themselves is needed. Moreover the MC approach results a powerful tool for investigating the LDs growth process. Highlights: • We evaluated the role of the fusion process in the synthesis of the lipid droplets. • We compared the

  6. Lipid droplets fusion in adipocyte differentiated 3T3-L1 cells: A Monte Carlo simulation

    International Nuclear Information System (INIS)

    Boschi, Federico; Rizzatti, Vanni; Zamboni, Mauro; Sbarbati, Andrea

    2014-01-01

    Several human worldwide diseases like obesity, type 2 diabetes, hepatic steatosis, atherosclerosis and other metabolic pathologies are related to the excessive accumulation of lipids in cells. Lipids accumulate in spherical cellular inclusions called lipid droplets (LDs) whose sizes range from fraction to one hundred of micrometers in adipocytes. It has been suggested that LDs can grow in size due to a fusion process by which a larger LD is obtained with spherical shape and volume equal to the sum of the progenitors’ ones. In this study, the size distribution of two populations of LDs was analyzed in immature and mature (5-days differentiated) 3T3-L1 adipocytes (first and second populations, respectively) after Oil Red O staining. A Monte Carlo simulation of interaction between LDs has been developed in order to quantify the size distribution and the number of fusion events needed to obtain the distribution of the second population size starting from the first one. Four models are presented here based on different kinds of interaction: a surface weighted interaction (R2 Model), a volume weighted interaction (R3 Model), a random interaction (Random model) and an interaction related to the place where the LDs are born (Nearest Model). The last two models mimic quite well the behavior found in the experimental data. This work represents a first step in developing numerical simulations of the LDs growth process. Due to the complex phenomena involving LDs (absorption, growth through additional neutral lipid deposition in existing droplets, de novo formation and catabolism) the study focuses on the fusion process. The results suggest that, to obtain the observed size distribution, a number of fusion events comparable with the number of LDs themselves is needed. Moreover the MC approach results a powerful tool for investigating the LDs growth process. Highlights: • We evaluated the role of the fusion process in the synthesis of the lipid droplets. • We compared the

  7. Janus droplets: liquid marbles coated with dielectric/semiconductor particles.

    Science.gov (United States)

    Bormashenko, Edward; Bormashenko, Yelena; Pogreb, Roman; Gendelman, Oleg

    2011-01-04

    The manufacturing of water droplets wrapped with two different powders, carbon black (semiconductor) and polytetrafluoroethylene (dielectric), is presented. Droplets composed of two hemispheres (Janus droplets) characterized by various physical and chemical properties are reported first. Watermelon-like striped liquid marbles are reported. Janus droplets remained stable on solid and liquid supports and could be activated with an electric field.

  8. Droplet-based chemistry on a programmable micro-chip

    Science.gov (United States)

    Schwartz, Jon A.; Vykoukal, Jody V.; Gascoyne, Peter R. C.

    2009-01-01

    We describe the manipulation of aqueous droplets in an immiscible, low-permittivity suspending medium. Such droplets may serve as carriers for not only air- and water-borne samples, contaminants, chemical reagents, viral and gene products, and cells, but also the reagents to process and characterise these samples. We present proofs-of-concept for droplet manipulation through dielectrophoresis by: (1) moving droplets on a two-dimensional array of electrodes, (2) achieving dielectrically-activated droplet injection, (3) fusing and reacting droplets, and (4) conducting a basic biological assay through a combination of these steps. A long-term goal of this research is to provide a platform fluidic processor technology that can form the core of versatile, automated, micro-scale devices to perform chemical and biological assays at or near the point of care, which will increase the availability of modern medicine to people who do not have ready access to modern medical institutions, and decrease the cost and delays associated with that lack of access. PMID:15007434

  9. Snap evaporation of droplets on smooth topographies.

    Science.gov (United States)

    Wells, Gary G; Ruiz-Gutiérrez, Élfego; Le Lirzin, Youen; Nourry, Anthony; Orme, Bethany V; Pradas, Marc; Ledesma-Aguilar, Rodrigo

    2018-04-11

    Droplet evaporation on solid surfaces is important in many applications including printing, micro-patterning and cooling. While seemingly simple, the configuration of evaporating droplets on solids is difficult to predict and control. This is because evaporation typically proceeds as a "stick-slip" sequence-a combination of pinning and de-pinning events dominated by static friction or "pinning", caused by microscopic surface roughness. Here we show how smooth, pinning-free, solid surfaces of non-planar topography promote a different process called snap evaporation. During snap evaporation a droplet follows a reproducible sequence of configurations, consisting of a quasi-static phase-change controlled by mass diffusion interrupted by out-of-equilibrium snaps. Snaps are triggered by bifurcations of the equilibrium droplet shape mediated by the underlying non-planar solid. Because the evolution of droplets during snap evaporation is controlled by a smooth topography, and not by surface roughness, our ideas can inspire programmable surfaces that manage liquids in heat- and mass-transfer applications.

  10. In vitro characterization of perfluorocarbon droplets for focused ultrasound therapy

    Energy Technology Data Exchange (ETDEWEB)

    Schad, Kelly C; Hynynen, Kullervo, E-mail: khynynen@sri.utoronto.c [Imaging Research, Sunnybrook Health Sciences Centre, 2075 Bayview Ave, Toronto, Ontario M4N 3M5 (Canada); Department of Medical Biophysics, University of Toronto (Canada)

    2010-09-07

    Focused ultrasound therapy can be enhanced with microbubbles by thermal and cavitation effects. However, localization of treatment is difficult as bioeffects can occur outside of the target region. Spatial control of bubbles can be achieved by ultrasound-induced conversion of liquid perfluorocarbon droplets to gas bubbles. This study was undertaken to determine the acoustic parameters for bubble production by droplet conversion and how it depends on the acoustic conditions and droplet physical parameters. Lipid-encapsulated droplets containing dodecafluoropentane were manufactured with sizes ranging from 1.9 to 7.2 {mu}m in diameter and diluted to a concentration of 8 x 10{sup 6} droplets mL{sup -1}. The droplets were sonicated in vitro with a focused ultrasound transducer and varying frequency and exposure under flow conditions through an acoustically transparent vessel. The sonications were 10 ms in duration at frequencies of 0.578, 1.736 and 2.855 MHz. The pressure threshold for droplet conversion was measured with an active transducer operating in pulse-echo mode and simultaneous measurements of broadband acoustic emissions were performed with passive acoustic detection. The results show that droplets cannot be converted at low frequency without broadband emissions occurring. However, the pressure threshold for droplet conversion decreased with increasing frequency, exposure and droplet size. The pressure threshold for broadband emissions was independent of the droplet size and was 2.9, 4.4 and 5.3 MPa for 0.578, 1736 and 2.855 MHz, respectively. In summary, we have demonstrated that droplet conversion is feasible for clinically relevant sized droplets and acoustic exposures.

  11. In vitro characterization of perfluorocarbon droplets for focused ultrasound therapy

    International Nuclear Information System (INIS)

    Schad, Kelly C; Hynynen, Kullervo

    2010-01-01

    Focused ultrasound therapy can be enhanced with microbubbles by thermal and cavitation effects. However, localization of treatment is difficult as bioeffects can occur outside of the target region. Spatial control of bubbles can be achieved by ultrasound-induced conversion of liquid perfluorocarbon droplets to gas bubbles. This study was undertaken to determine the acoustic parameters for bubble production by droplet conversion and how it depends on the acoustic conditions and droplet physical parameters. Lipid-encapsulated droplets containing dodecafluoropentane were manufactured with sizes ranging from 1.9 to 7.2 μm in diameter and diluted to a concentration of 8 x 10 6 droplets mL -1 . The droplets were sonicated in vitro with a focused ultrasound transducer and varying frequency and exposure under flow conditions through an acoustically transparent vessel. The sonications were 10 ms in duration at frequencies of 0.578, 1.736 and 2.855 MHz. The pressure threshold for droplet conversion was measured with an active transducer operating in pulse-echo mode and simultaneous measurements of broadband acoustic emissions were performed with passive acoustic detection. The results show that droplets cannot be converted at low frequency without broadband emissions occurring. However, the pressure threshold for droplet conversion decreased with increasing frequency, exposure and droplet size. The pressure threshold for broadband emissions was independent of the droplet size and was 2.9, 4.4 and 5.3 MPa for 0.578, 1736 and 2.855 MHz, respectively. In summary, we have demonstrated that droplet conversion is feasible for clinically relevant sized droplets and acoustic exposures.

  12. In vitro characterization of perfluorocarbon droplets for focused ultrasound therapy

    Science.gov (United States)

    Schad, Kelly C.; Hynynen, Kullervo

    2010-09-01

    Focused ultrasound therapy can be enhanced with microbubbles by thermal and cavitation effects. However, localization of treatment is difficult as bioeffects can occur outside of the target region. Spatial control of bubbles can be achieved by ultrasound-induced conversion of liquid perfluorocarbon droplets to gas bubbles. This study was undertaken to determine the acoustic parameters for bubble production by droplet conversion and how it depends on the acoustic conditions and droplet physical parameters. Lipid-encapsulated droplets containing dodecafluoropentane were manufactured with sizes ranging from 1.9 to 7.2 µm in diameter and diluted to a concentration of 8 × 106 droplets mL-1. The droplets were sonicated in vitro with a focused ultrasound transducer and varying frequency and exposure under flow conditions through an acoustically transparent vessel. The sonications were 10 ms in duration at frequencies of 0.578, 1.736 and 2.855 MHz. The pressure threshold for droplet conversion was measured with an active transducer operating in pulse-echo mode and simultaneous measurements of broadband acoustic emissions were performed with passive acoustic detection. The results show that droplets cannot be converted at low frequency without broadband emissions occurring. However, the pressure threshold for droplet conversion decreased with increasing frequency, exposure and droplet size. The pressure threshold for broadband emissions was independent of the droplet size and was 2.9, 4.4 and 5.3 MPa for 0.578, 1736 and 2.855 MHz, respectively. In summary, we have demonstrated that droplet conversion is feasible for clinically relevant sized droplets and acoustic exposures.

  13. Differential solvation of intrinsically disordered linkers drives the formation of spatially organized droplets in ternary systems of linear multivalent proteins

    Science.gov (United States)

    Harmon, Tyler S.; Holehouse, Alex S.; Pappu, Rohit V.

    2018-04-01

    Intracellular biomolecular condensates are membraneless organelles that encompass large numbers of multivalent protein and nucleic acid molecules. The bodies assemble via a combination of liquid–liquid phase separation and gelation. A majority of condensates included multiple components and show multilayered organization as opposed to being well-mixed unitary liquids. Here, we put forward a simple thermodynamic framework to describe the emergence of spatially organized droplets in multicomponent systems comprising of linear multivalent polymers also known as associative polymers. These polymers, which mimic proteins and/or RNA have the architecture of domains or motifs known as stickers that are interspersed by flexible spacers known as linkers. Using a minimalist numerical model for a four-component system, we have identified features of linear multivalent molecules that are necessary and sufficient for generating spatially organized droplets. We show that differences in sequence-specific effective solvation volumes of disordered linkers between interaction domains enable the formation of spatially organized droplets. Molecules with linkers that are preferentially solvated are driven to the interface with the bulk solvent, whereas molecules that have linkers with negligible effective solvation volumes form cores in the core–shell architectures that emerge in the minimalist four-component systems. Our modeling has relevance for understanding the physical determinants of spatially organized membraneless organelles.

  14. Substrate curvature gradient drives rapid droplet motion.

    Science.gov (United States)

    Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui

    2014-07-11

    Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42  m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100  m/s on tapered surfaces.

  15. Numerical modeling of a vaporizing multicomponent droplet

    Science.gov (United States)

    Megaridis, C. M.; Sirignano, W. A.

    The fundamental processes governing the energy, mass, and momentum exchange between the liquid and gas phases of vaporizing, multicomponent liquid droplets have been investigated. The axisymmetric configuration under consideration consists of an isolated multicomponent droplet vaporizing in a convective environment. The model considers different volatilities of the liquid components, variable liquid properties due to variation of the species concentrations, and non-Fickian multicomponent gaseous diffusion. The bicomponent droplet model was employed to examine the commonly used assumptions of unity Lewis number in the liquid phase and Fickian gaseous diffusion. It is found that the droplet drag coefficients, the vaporization rates, and the related transfer numbers are not influenced by the above assumptions in a significant way.

  16. Numerical study on morphology and solidification characteristics of successive droplet depositions on a substrate

    Science.gov (United States)

    Adaikalanathan, Vimalan

    Successive droplet impingement finds extensive applications in additive manufacturing technologies such as 3D printing, Liquid Metal Jetting and Net Form Manufacturing. Deposition, deformation and solidification of droplets are the constitutive stages in the process which determine the final outcome. Detailed knowledge about the flow behaviour, phase transformation and free surface deformation is required to have a complete understanding and optimization of the process parameters. Experimental research in this field is only limited to imaging techniques and post solidification analysis which only provide superficial information while overlooking most of the governing phenomenon. Knowledge of the physics governing the fluid and thermal behaviours can be applied to study the process with real time data pertaining to flow field, temperature profiles and solidification. However, free surface tracking, surface tension modelling, non-isothermal solidification and convection dominant heat transfer pose mathematical challenges in the solution of the governing equations. Moreover, deposition of droplets on pre-solidified splats or non-flat surfaces requires accurate special attention. The objective of the present work is to model the successive droplet impacts and simultaneous solidification and deformation. The highly non-linear flow field governed by the Navier Stokes equation is solved using a Two Step Projection method. The surface tension effects are accounted for through a Continuum Surface Force technique. One of the crucial elements in the study is the interface tracking algorithm. A Coupled Level Set Volume of Fluid (CLSVOF) method is formulated to give an accurate orientation of the drastically deforming interface and also facilitates generation of multiple droplets in a fixed domain at a user defined frequency, thereby conserving computational resources. The phase change is modelled using an enthalpy formulation of the energy equation with an implicit source term

  17. A novel coarsening mechanism of droplets in immiscible fluid mixtures

    Science.gov (United States)

    Shimizu, Ryotaro; Tanaka, Hajime

    2015-06-01

    In our daily lives, after shaking a salad dressing, we see the coarsening of oil droplets suspended in vinegar. Such a demixing process is observed everywhere in nature and also of technological importance. For a case of high droplet density, domain coarsening proceeds with inter-droplet collisions and the resulting coalescence. This phenomenon has been explained primarily by the so-called Brownian-coagulation mechanism: stochastic thermal forces exerted by molecules induce random motion of individual droplets, causing accidental collisions and subsequent interface-tension-driven coalescence. Contrary to this, here we demonstrate that the droplet motion is not random, but hydrodynamically driven by the composition Marangoni force due to an interfacial tension gradient produced in each droplet as a consequence of composition correlation among droplets. This alters our physical understanding of droplet coarsening in immiscible liquid mixtures on a fundamental level.

  18. Thermophoretically driven water droplets on graphene and boron nitride surfaces

    Science.gov (United States)

    Rajegowda, Rakesh; Kannam, Sridhar Kumar; Hartkamp, Remco; Sathian, Sarith P.

    2018-05-01

    We investigate thermally driven water droplet transport on graphene and hexagonal boron nitride (h-BN) surfaces using molecular dynamics simulations. The two surfaces considered here have different wettabilities with a significant difference in the mode of droplet transport. The water droplet travels along a straighter path on the h-BN sheet than on graphene. The h-BN surface produced a higher driving force on the droplet than the graphene surface. The water droplet is found to move faster on h-BN surface compared to graphene surface. The instantaneous contact angle was monitored as a measure of droplet deformation during thermal transport. The characteristics of the droplet motion on both surfaces is determined through the moment scaling spectrum. The water droplet on h-BN surface showed the attributes of the super-diffusive process, whereas it was sub-diffusive on the graphene surface.

  19. Laser-induced fluorescence imaging of acetone inside evaporating and burning fuel droplets

    Science.gov (United States)

    Shringi, D. S.; Shaw, B. D.; Dwyer, H. A.

    2009-01-01

    Laser-induced fluorescence was used to visualize acetone fields inside individual droplets of pure acetone as well as droplets composed of methanol or 1-propanol initially mixed with acetone. Droplets were supported on a horizontal wire and two vaporization conditions were investigated: (1) slow evaporation in room air and (2) droplet combustion, which leads to substantially faster droplet surface regression rates. Acetone was preferentially gasified, causing its concentration in droplets to drop in time with resultant decreases in acetone fluorescence intensities. Slowly vaporizing droplets did not exhibit large spatial variations of fluorescence within droplets, indicating that these droplets were relatively well mixed. Ignition of droplets led to significant variations in fluorescence intensities within droplets, indicating that these droplets were not well mixed. Ignited droplets composed of mixtures of 1-propanol and acetone showed large time-varying changes in shapes for higher acetone concentrations, suggesting that bubble formation was occurring in these droplets.

  20. Foam droplet separation for nanoparticle synthesis

    International Nuclear Information System (INIS)

    Tyree, Corey A.; Allen, Jonathan O.

    2008-01-01

    A novel approach to nanoparticle synthesis was developed whereby foam bubble bursting produced aerosol droplets, an approach patterned after the marine foam aerosol cycle. The droplets were dried to remove solvent, leaving nanometer-sized particles composed of precursor material. Nanoparticles composed of sodium chloride (mean diameter, D-bar p ∼ 100 nm), phosphotungstic acid (D-bar p ∼ 55 nm), and bovine insulin (D p ∼ 5-30 nm) were synthesized. Foam droplet separation can be carried out at ambient temperature and pressure. The 'soft' nature of the process makes it compatible with a wide range of materials

  1. Heat exchanges between droplets and atmosphere

    International Nuclear Information System (INIS)

    Yadigaroglu, Georges.

    1975-01-01

    Data necessary for calculating the droplet cooling in wet cooling systems are surveyed. This cooling obeys the laws of simultaneous heat and mass transfer. Exchanges with a solid sphere moving inside a surrounding fluid medium are first examined. The corrections needed for taking into account various secondary effects (circulation in the droplet, lack of sphericity, oscillations, etc...) are then dealt with. Some data necessary for calculating the trajectories of the droplets and their behavior in a cooling system are included (diameter distribution, limit velocities, decay thresholds, etc...). Finally, calculation methods applying to spray systems, as well as wet towers broadly outlined [fr

  2. Frequency-dependent transient response of an oscillating electrically actuated droplet

    International Nuclear Information System (INIS)

    Dash, S; Kumari, N; Garimella, S V

    2012-01-01

    The transient response of a millimeter-sized sessile droplet under electrical actuation is experimentally investigated. Under dc actuation, the droplet spreading rate increases as the applied voltage is increased due to the higher electrical forces induced. At sufficiently high dc voltages, competition between the electrical actuation force, droplet inertia, the retarding surface tension force and contact line friction leads to droplet oscillation. The timescale for the droplet to attain its maximum wetted diameter during step actuation is analyzed. Systematic experiments are conducted over a frequency range of 5–200 Hz and actuation voltages of 40–80 V rms to determine the dependence of droplet oscillation on these parameters. The response of the droplet to different actuation frequencies and voltages is determined in terms of its contact angle and contact radius variation. The frequency of the driving force (equal to twice the frequency of the applied electrical signal) determines the mode of oscillation of the droplet which, together with its resonance characteristics, governs whether the droplet contact angle and contact radius vary in phase or out of phase with each other. In addition to the primary frequency response at the electrical forcing frequency, the droplet oscillation exhibits sub-harmonic oscillation at half of the forcing frequency that is attributed to the parametric nature of the electrical force acting on the triple contact line of the droplet. (paper)

  3. Short-range airborne transmission of expiratory droplets between two people

    DEFF Research Database (Denmark)

    Liu, Li; Li, Yuguo; Nielsen, Peter Vilhelm

    2017-01-01

    , ventilation, and breathing mode. Under the specific set of conditions studied, we found a substantial increase in airborne exposure to droplet nuclei exhaled by the source manikin when a susceptible manikin is within about 1.5 m of the source manikin, referred to as the proximity effect. The threshold...... distance of about 1.5 m distinguishes the two basic transmission processes of droplets and droplet nuclei, that is, short-range modes and the long-range airborne route. The short-range modes include both the conventional large droplet route and the newly defined short-range airborne transmission. We thus...... reveal that transmission occurring in close proximity to the source patient includes both droplet-borne (large droplet) and short-range airborne routes, in addition to the direct deposition of large droplets on other body surfaces. The mechanisms of the droplet-borne and short-range airborne routes...

  4. Transport of expiratory droplets in an aircraft cabin.

    Science.gov (United States)

    Gupta, Jitendra K; Lin, Chao-Hsin; Chen, Qingyan

    2011-02-01

    The droplets exhaled by an index patient with infectious disease such as influenza or tuberculosis may be the carriers of contagious agents. Indoor environments such as the airliner cabins may be susceptible to infection from such airborne contagious agents. The present investigation computed the transport of the droplets exhaled by the index patient seated in the middle of a seven-row, twin-aisle, fully occupied cabin using the CFD simulations. The droplets exhaled were from a single cough, a single breath, and a 15-s talk of the index patient. The expiratory droplets were tracked by using Lagrangian method, and their evaporation was modeled. It was found that the bulk airflow pattern in the cabin played the most important role on the droplet transport. The droplets were contained in the row before, at, and after the index patient within 30 s and dispersed uniformly to all the seven rows in 4 minutes. The total airborne droplet fraction reduced to 48, 32, 20, and 12% after they entered the cabin for 1, 2, 3, and 4 min, respectively, because of the ventilation from the environmental control system. It is critical to predict the risk of airborne infection to take appropriate measures to control and mitigate the risk. Most of the studies in past either assume a homogenous distribution of contaminants or use steady-state conditions. The present study instead provides information on the transient movement of the droplets exhaled by an index passenger in an aircraft cabin. These droplets may contain active contagious agents and can be potent enough to cause infection. The findings can be used by medical professionals to estimate the spatial and temporal distribution of risk of infection to various passengers in the cabin. © 2010 John Wiley & Sons A/S.

  5. Ultralocalized thermal reactions in subnanoliter droplets-in-air.

    Science.gov (United States)

    Salm, Eric; Guevara, Carlos Duarte; Dak, Piyush; Dorvel, Brian Ross; Reddy, Bobby; Alam, Muhammad Ashraf; Bashir, Rashid

    2013-02-26

    Miniaturized laboratory-on-chip systems promise rapid, sensitive, and multiplexed detection of biological samples for medical diagnostics, drug discovery, and high-throughput screening. Within miniaturized laboratory-on-chips, static and dynamic droplets of fluids in different immiscible media have been used as individual vessels to perform biochemical reactions and confine the products. Approaches to perform localized heating of these individual subnanoliter droplets can allow for new applications that require parallel, time-, and space-multiplex reactions on a single integrated circuit. Our method positions droplets on an array of individual silicon microwave heaters on chip to precisely control the temperature of droplets-in-air, allowing us to perform biochemical reactions, including DNA melting and detection of single base mismatches. We also demonstrate that ssDNA probe molecules can be placed on heaters in solution, dried, and then rehydrated by ssDNA target molecules in droplets for hybridization and detection. This platform enables many applications in droplets including hybridization of low copy number DNA molecules, lysing of single cells, interrogation of ligand-receptor interactions, and rapid temperature cycling for amplification of DNA molecules.

  6. Propagation of capillary waves and ejection of small droplets in rapid droplet spreading

    KAUST Repository

    Ding, Hang

    2012-03-12

    A new regime of droplet ejection following the slow deposition of drops onto a near-complete wetting solid substrate is identified in experiments and direct numerical simulations; a coalescence cascade subsequent to pinch-off is also observed for the first time. Results of numerical simulations indicate that the propagation of capillary waves that lead to pinch-off is closely related to the self-similar behaviour observed in the inviscid recoil of droplets, and that motions of the crests and troughs of capillary waves along the interface do not depend on the wettability and surface tension (or Ohnesorge number). The simulations also show that a self-similar theory for universal pinch-off can be used for the time evolution of the pinching neck. However, although good agreement is also found with the double-cone shape of the pinching neck for droplet ejection in drop deposition on a pool of the same liquid, substantial deviations are observed in such a comparison for droplet ejection in rapid drop spreading (including the newly identified regime). This deviation is shown to result from interference by the solid substrate, a rapid downwards acceleration of the top of the drop surface and the rapid spreading process. The experiments also confirm non-monotonic spreading behaviour observed previously only in numerical simulations, and suggest substantial inertial effects on the relation between an apparent contact angle and the dimensionless contact-line speed. © 2012 Cambridge University Press.

  7. Propagation of capillary waves and ejection of small droplets in rapid droplet spreading

    KAUST Repository

    Ding, Hang; Li, Erqiang; Zhang, F. H.; Sui, Yi; Spelt, Peter D M; Thoroddsen, Sigurdur T

    2012-01-01

    A new regime of droplet ejection following the slow deposition of drops onto a near-complete wetting solid substrate is identified in experiments and direct numerical simulations; a coalescence cascade subsequent to pinch-off is also observed for the first time. Results of numerical simulations indicate that the propagation of capillary waves that lead to pinch-off is closely related to the self-similar behaviour observed in the inviscid recoil of droplets, and that motions of the crests and troughs of capillary waves along the interface do not depend on the wettability and surface tension (or Ohnesorge number). The simulations also show that a self-similar theory for universal pinch-off can be used for the time evolution of the pinching neck. However, although good agreement is also found with the double-cone shape of the pinching neck for droplet ejection in drop deposition on a pool of the same liquid, substantial deviations are observed in such a comparison for droplet ejection in rapid drop spreading (including the newly identified regime). This deviation is shown to result from interference by the solid substrate, a rapid downwards acceleration of the top of the drop surface and the rapid spreading process. The experiments also confirm non-monotonic spreading behaviour observed previously only in numerical simulations, and suggest substantial inertial effects on the relation between an apparent contact angle and the dimensionless contact-line speed. © 2012 Cambridge University Press.

  8. Evaluation of droplet deposition in rod bundle

    International Nuclear Information System (INIS)

    Ji, W.; Gu, C.Y.; Anglart, H.

    1997-01-01

    Deposition model for droplets in gas droplet two-phase flow in rod bundle is developed in this work using the Lagrangian method. The model is evaluated in a 9-rod bundle geometry. The deposition coefficient in the bundle geometry are compared with that in round tube. The influences of the droplet size and gas mass flow rate on deposition coefficient are investigated. Furthermore, the droplet motion is studied in more detail by dividing the bundle channel into sub-channels. The results show that the overall deposition coefficient in the bundle geometry is close to that in the round tube with the diameter equal to the bundle hydraulic diameter. The calculated deposition coefficient is found to be higher for higher gas mass flux and smaller droplets. The study in the sub-channels show that the ratio between the local deposition coefficient for a sub-channel and the averaged value for the whole bundle is close to a constant value, deviations from the mean value for all the calculated cases being within the range of ±13%. (author)

  9. Splash Dynamics of Falling Surfactant-Laden Droplets

    Science.gov (United States)

    Sulaiman, Nur; Buitrago, Lewis; Pereyra, Eduardo

    2017-11-01

    Splashing dynamics is a common issue in oil and gas separation technology. In this study, droplet impact of various surfactant concentrations onto solid and liquid surfaces is studied experimentally using a high-speed imaging analysis. Although this area has been widely studied in the past, there is still not a good understanding of the role of surfactant over droplet impact and characterization of resulting splash dynamics. The experiments are conducted using tap water laden with anionic surfactant. The effects of system parameters on a single droplet impingement such as surfactant concentration (no surfactant, below, at and above critical micelle concentration), parent drop diameter (2-5mm), impact velocity and type of impact surface (thin and deep pool) are investigated. Image analysis technique is shown to be an effective technique for identification of coalescence to splashing transition. In addition, daughter droplets size distributions are analyzed qualitatively in the events of splashing. As expected, it is observed that the formation of secondary droplets is affected by the surfactant concentration. A summary of findings will be discussed.

  10. Sound Propagation in Saturated Gas-Vapor-Droplet Suspensions Considering the Effect of Transpiration on Droplet Evaporation

    Science.gov (United States)

    Kandula, Max

    2012-01-01

    The Sound attenuation and dispersion in saturated gas-vapor-droplet mixtures with evaporation has been investigated theoretically. The theory is based on an extension of the work of Davidson (1975) to accommodate the effects of transpiration on the linear particle relaxation processes of mass, momentum and energy transfer. It is shown that the inclusion of transpiration in the presence of mass transfer improves the agreement between the theory and the experimental data of Cole and Dobbins (1971) for sound attenuation in air-water fogs at low droplet mass concentrations. The results suggest that transpiration has an appreciable effect on both sound absorption and dispersion for both low and high droplet mass concentrations.

  11. Flow field induced particle accumulation inside droplets in rectangular channels.

    Science.gov (United States)

    Hein, Michael; Moskopp, Michael; Seemann, Ralf

    2015-07-07

    Particle concentration is a basic operation needed to perform washing steps or to improve subsequent analysis in many (bio)-chemical assays. In this article we present field free, hydrodynamic accumulation of particles and cells in droplets flowing within rectangular micro-channels. Depending on droplet velocity, particles either accumulate at the rear of the droplet or are dispersed over the entire droplet cross-section. We show that the observed particle accumulation behavior can be understood by a coupling of particle sedimentation to the internal flow field of the droplet. The changing accumulation patterns are explained by a qualitative change of the internal flow field. The topological change of the internal flow field, however, is explained by the evolution of the droplet shape with increasing droplet velocity altering the friction with the channel walls. In addition, we demonstrate that accumulated particles can be concentrated, removing excess dispersed phase by splitting the droplet at a simple channel junction.

  12. Droplet networks with incorporated protein diodes show collective properties

    Science.gov (United States)

    Maglia, Giovanni; Heron, Andrew J.; Hwang, William L.; Holden, Matthew A.; Mikhailova, Ellina; Li, Qiuhong; Cheley, Stephen; Bayley, Hagan

    2009-07-01

    Recently, we demonstrated that submicrolitre aqueous droplets submerged in an apolar liquid containing lipid can be tightly connected by means of lipid bilayers to form networks. Droplet interface bilayers have been used for rapid screening of membrane proteins and to form asymmetric bilayers with which to examine the fundamental properties of channels and pores. Networks, meanwhile, have been used to form microscale batteries and to detect light. Here, we develop an engineered protein pore with diode-like properties that can be incorporated into droplet interface bilayers in droplet networks to form devices with electrical properties including those of a current limiter, a half-wave rectifier and a full-wave rectifier. The droplet approach, which uses unsophisticated components (oil, lipid, salt water and a simple pore), can therefore be used to create multidroplet networks with collective properties that cannot be produced by droplet pairs.

  13. Three-dimensional parallelization of microfluidic droplet generators for a litre per hour volume production of single emulsions

    KAUST Repository

    Conchouso Gonzalez, David

    2014-01-01

    This paper looks at the design, fabrication and characterization of stackable microfluidic emulsion generators, with coefficients of variation as low as ~6% and with production rates as high as ~1 L h-1. This work reports the highest throughput reported in the literature for a microfluidic device with simultaneous operation of liquid-liquid droplet generators. The device was achieved by stacking several layers of 128 flow-focusing droplet generators, organized in a circular array. These layers are interconnected via through-holes and fed with designated fractal distribution networks. The proposed layers were milled on poly(methylmethacrylate) (PMMA) sheets and the stack was thermo-compression bonded to create a three-dimensional device with a high density of generators and an integrated hydraulic manifold. The effect of stacking multiple layers was studied and the results show that fabrication accuracy has a greater impact on the dispersity of the emulsion than the addition of more layers to the stack. Particle crystallization of drugs was also demonstrated as a possible application of this technology in industry. © 2014 the Partner Organisations.

  14. Designed pneumatic valve actuators for controlled droplet breakup and generation.

    Science.gov (United States)

    Choi, Jae-Hoon; Lee, Seung-Kon; Lim, Jong-Min; Yang, Seung-Man; Yi, Gi-Ra

    2010-02-21

    The dynamic breakup of emulsion droplets was demonstrated in double-layered microfluidic devices equipped with designed pneumatic actuators. Uniform emulsion droplets, produced by shearing at a T-junction, were broken into smaller droplets when they passed downstream through constrictions formed by a pneumatically actuated valve in the upper control layer. The valve-assisted droplet breakup was significantly affected by the shape and layout of the control valves on the emulsion flow channel. Interestingly, by actuating the pneumatic valve immediately above the T-junction, the sizes of the emulsion droplets were controlled precisely in a programmatic manner that produced arrays of uniform emulsion droplets in various sizes and dynamic patterns.

  15. Manipulation of microfluidic droplets by electrorheological fluid

    KAUST Repository

    Zhang, Menying

    2009-09-01

    Microfluidics, especially droplet microfluidics, attracts more and more researchers from diverse fields, because it requires fewer materials and less time, produces less waste and has the potential of highly integrated and computer-controlled reaction processes for chemistry and biology. Electrorheological fluid, especially giant electrorheological fluid (GERF), which is considered as a kind of smart material, has been applied to the microfluidic systems to achieve active and precise control of fluid by electrical signal. In this review article, we will introduce recent results of microfluidic droplet manipulation, GERF and some pertinent achievements by introducing GERF into microfluidic system: digital generation, manipulation of "smart droplets" and droplet manipulation by GERF. Once it is combined with real-time detection, integrated chip with multiple functions can be realized. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

  16. Droplets and sprays

    CERN Document Server

    Sazhin, Sergei

    2014-01-01

    Providing a clear and systematic description of droplets and spray dynamic models, this book maximises reader insight into the underlying physics of the processes involved, outlines the development of new physical and mathematical models, and broadens understanding of interactions between the complex physical processes which take place in sprays. Complementing approaches based on the direct application of computational fluid dynamics (CFD), Droplets and Sprays treats both theoretical and practical aspects of internal combustion engine process such as the direct injection of liquid fuel, subcritical heating and evaporation. Includes case studies that illustrate the approaches relevance to automotive applications,  it is also anticipated that the described models can find use in other areas such as in medicine and environmental science.

  17. Quantum Nanostructures by Droplet Epitaxy

    OpenAIRE

    Somsak Panyakeow

    2009-01-01

    Droplet epitaxy is an alternative growth technique for several quantum nanostructures. Indium droplets are distributed randomly on GaAs substrates at low temperatures (120-350'C). Under background pressure of group V elements, Arsenic and Phosphorous, InAs and InP nanostructures are created. Quantum rings with isotropic shape are obtained at low temperature range. When the growth thickness is increased, quantum rings are transformed to quantum dot rings. At high temperature range, anisotropic...

  18. MULTIPHASE DROPLET/SLUG BREAK-UP MECHANISM IN MICROFLUIDIC T-JUNCTIONS AT VARIOUS WEBER NUMBERS

    Directory of Open Access Journals (Sweden)

    Wan Leng (Dawn Leow

    2011-10-01

    Full Text Available Normal 0 false false false EN-MY X-NONE X-NONE The formation of immiscible liquid droplets, or slugs, in microchannels features the advantages of volume control and mixing enhancement over single-phase microflows. Although the applications of droplet-based microfluidics have been widely demonstrated, the fundamental physics governing droplet break-up remains an area of active research. This study defines an effective Weber (Weeff number that characterizes the interplay of interfacial tension, shear stress and channel pressure drop in driving slug formation in T-junction microchannel for a relative range of low, intermediate and high flow rates. The immiscible fluid system in this study consists of Tetradecane slug formation in Acetonitrile. The progressive deformation of slug interfaces during break-up events is observed. Experimental results indicate that, at a relatively low Weeff, clean slug break-up occurs at the intersection of the side and main channels. At intermediate Weeff, the connecting neck of the dispersed phase is stretched to a short and thin trail of laminar flow prior to breaking up a short distance downstream of the T-junction. At a relatively high Weeff, the connecting neck develops into a longer and thicker trail of laminar flow that breaks up further downstream of the main channel.

  19. AC electric field induced droplet deformation in a microfluidic T-junction.

    Science.gov (United States)

    Xi, Heng-Dong; Guo, Wei; Leniart, Michael; Chong, Zhuang Zhi; Tan, Say Hwa

    2016-08-02

    We present for the first time an experimental study on the droplet deformation induced by an AC electric field in droplet-based microfluidics. It is found that the deformation of the droplets becomes stronger with increasing electric field intensity and frequency. The measured electric field intensity dependence of the droplet deformation is consistent with an early theoretical prediction for stationary droplets. We also proposed a simple equivalent circuit model to account for the frequency dependence of the droplet deformation. The model well explains our experimental observations. In addition, we found that the droplets can be deformed repeatedly by applying an amplitude modulation (AM) signal.

  20. Control of droplet size in rain-zone in wet cooling tower

    Directory of Open Access Journals (Sweden)

    Vitkovicova Rut

    2018-01-01

    Full Text Available The performance of the wet cooling tower is significantly affected by the droplet size occurring in the rain zone. In order to effectively manage the size of these droplets, it was necessary to experimentally determine the effect of the fills of the cooling towers on droplets. Five types of cooling fillers were used for experimental measurements: 3 film fills and 2 splash fills - trickle and grid. Drop size measurements were performed using the LIF method. Histograms of droplets size were obtained from measured droplet sizes under each fill, and for each fill, the Sauter droplet diameter was then calculated. According to a theoretical analysis of a breakdown of droplets, the combinations of some fills and the effect of their surface treatment on the droplet diameter were then measured for comparison.

  1. Variable focus microscopy using a suspended water droplet

    International Nuclear Information System (INIS)

    Chowdhury, F A; Chau, K J

    2012-01-01

    We explore a low-technology methodology to dispense and shape water droplets for application as the magnifying element in a microscope using either reflection-mode or transmission-mode illumination. A water droplet is created at the end of a syringe and then coated with a thin layer of silicone oil to mitigate evaporation. By applying mechanical pressure to the water droplet using a metal tip, the shape of the droplet is tuned to yield focusing properties amenable for microscopy. Images captured using the microscope demonstrate micron-scale resolution, variable magnification and imaging quality comparable to that obtained by a conventional, laboratory-grade microscope. (paper)

  2. Numerical Study on Deformation and Interior Flow of a Droplet Suspended in Viscous Liquid under Steady Electric Fields

    Directory of Open Access Journals (Sweden)

    Zhentao Wang

    2014-07-01

    Full Text Available A model based on the volume of fluid (VOF method and leaky dielectric theory is established to predict the deformation and internal flow of the droplet suspended in another vicious fluid under the influence of the electric field. Through coupling with hydrodynamics and electrostatics, the rate of deformation and internal flow of the single droplet are simulated and obtained under the different operating parameters. The calculated results show that the direction of deformation and internal flow depends on the physical properties of fluids. The numerical results are compared with Taylor's theory and experimental results by Torza et al. When the rate of deformation is small, the numerical results are consistent with theory and experimental results, and when the rate is large the numerical results are consistent with experimental results but are different from Taylor's theory. In addition, fluid viscosity hardly affects the deformation rate and mainly dominates the deformation velocity. For high viscosity droplet spends more time to attain the steady state. The conductivity ratio and permittivity ratio of two different liquids affect the direction of deformation. When fluid electric properties change, the charge distribution at the interface is various, which leads to the droplet different deformation shapes.

  3. Nanoscale footprints of self-running gallium droplets on GaAs surface.

    Directory of Open Access Journals (Sweden)

    Jiang Wu

    Full Text Available In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001 surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems.

  4. Photophoretic trampoline—Interaction of single airborne absorbing droplets with light

    Science.gov (United States)

    Esseling, Michael; Rose, Patrick; Alpmann, Christina; Denz, Cornelia

    2012-09-01

    We present the light-induced manipulation of absorbing liquid droplets in air. Ink droplets from a printer cartridge are used to demonstrate that absorbing liquids—just like their solid counterparts—can interact with regions of high light intensity due to the photophoretic force. It is shown that droplets follow a quasi-ballistic trajectory after bouncing off a high intensity light sheet. We estimate the intensities necessary for this rebound of airborne droplets and change the droplet trajectories through a variation of the manipulating light field.

  5. Hydrodynamic clustering of droplets in turbulence

    Science.gov (United States)

    Kunnen, Rudie; Yavuz, Altug; van Heijst, Gertjan; Clercx, Herman

    2017-11-01

    Small, inertial particles are known to cluster in turbulent flows: particles are centrifuged out of eddies and gather in the strain-dominated regions. This so-called preferential concentration is reflected in the radial distribution function (RDF; a quantitative measure of clustering). We study clustering of water droplets in a loudspeaker-driven turbulence chamber. We track the motion of droplets in 3D and calculate the RDF. At moderate scales (a few Kolmogorov lengths) we find the typical power-law scaling of preferential concentration in the RDF. However, at even smaller scales (a few droplet diameters), we encounter a hitherto unobserved additional clustering. We postulate that the additional clustering is due to hydrodynamic interactions, an effect which is typically disregarded in modeling. Using a perturbative expansion of inertial effects in a Stokes-flow description of two interacting spheres, we obtain an expression for the RDF which indeed includes the additional clustering. The additional clustering enhances the collision probability of droplets, which enhances their growth rate due to coalescence. The additional clustering is thus an essential effect in precipitation modeling.

  6. Equilibrium Droplets on Deformable Substrates: Equilibrium Conditions.

    Science.gov (United States)

    Koursari, Nektaria; Ahmed, Gulraiz; Starov, Victor M

    2018-05-15

    Equilibrium conditions of droplets on deformable substrates are investigated, and it is proven using Jacobi's sufficient condition that the obtained solutions really provide equilibrium profiles of both the droplet and the deformed support. At the equilibrium, the excess free energy of the system should have a minimum value, which means that both necessary and sufficient conditions of the minimum should be fulfilled. Only in this case, the obtained profiles provide the minimum of the excess free energy. The necessary condition of the equilibrium means that the first variation of the excess free energy should vanish, and the second variation should be positive. Unfortunately, the mentioned two conditions are not the proof that the obtained profiles correspond to the minimum of the excess free energy and they could not be. It is necessary to check whether the sufficient condition of the equilibrium (Jacobi's condition) is satisfied. To the best of our knowledge Jacobi's condition has never been verified for any already published equilibrium profiles of both the droplet and the deformable substrate. A simple model of the equilibrium droplet on the deformable substrate is considered, and it is shown that the deduced profiles of the equilibrium droplet and deformable substrate satisfy the Jacobi's condition, that is, really provide the minimum to the excess free energy of the system. To simplify calculations, a simplified linear disjoining/conjoining pressure isotherm is adopted for the calculations. It is shown that both necessary and sufficient conditions for equilibrium are satisfied. For the first time, validity of the Jacobi's condition is verified. The latter proves that the developed model really provides (i) the minimum of the excess free energy of the system droplet/deformable substrate and (ii) equilibrium profiles of both the droplet and the deformable substrate.

  7. Mechanism and simulation of droplet coalescence in molten steel

    Science.gov (United States)

    Ni, Bing; Zhang, Tao; Ni, Hai-qi; Luo, Zhi-guo

    2017-11-01

    Droplet coalescence in liquid steel was carefully investigated through observations of the distribution pattern of inclusions in solidified steel samples. The process of droplet coalescence was slow, and the critical Weber number ( We) was used to evaluate the coalescence or separation of droplets. The relationship between the collision parameter and the critical We indicated whether slow coalescence or bouncing of droplets occurred. The critical We was 5.5, which means that the droplets gradually coalesce when We ≤ 5.5, whereas they bounce when We > 5.5. For the carbonate wire feeding into liquid steel, a mathematical model implementing a combined computational fluid dynamics (CFD)-discrete element method (DEM) approach was developed to simulate the movement and coalescence of variably sized droplets in a bottom-argon-blowing ladle. In the CFD model, the flow field was solved on the premise that the fluid was a continuous medium. Meanwhile, the droplets were dispersed in the DEM model, and the coalescence criterion of the particles was added to simulate the collision- coalescence process of the particles. The numerical simulation results and observations of inclusion coalescence in steel samples are consistent.

  8. A droplet entrainment model for horizontal segregated flows

    Energy Technology Data Exchange (ETDEWEB)

    Höhne, Thomas, E-mail: T.Hoehne@hzdr.de [Helmholtz-Zentrum Dresden-Rossendorf (HZDR) – Institute of Fluid Dynamics, P.O. Box 510119, D-01314 Dresden (Germany); Hänsch, Susann [Imperial College, Department of Mechanical Engineering, South Kensington Campus, London SW7 2AZ (United Kingdom)

    2015-05-15

    Highlights: • We further developed the flow morphology detection model AIAD. • An advanced droplet entrainment model was introduced. • The new approach is applied against HAWAC experiments. - Abstract: One limitation in simulating horizontal segregated flows is that there is no treatment of droplet formation mechanisms at wavy surfaces. For self-generating waves and slugs, the interfacial momentum exchange and the turbulence parameters have to be modeled correctly. Furthermore, understanding the mechanism of droplet entrainment for heat and mass transfer processes is of great importance in the chemical and nuclear industry. The development of general computational fluid dynamics models is an essential precondition for the application of CFD codes to the modeling of flow related phenomena. The new formulation for the interfacial drag at the free surface and turbulence parameters within the algebraic interfacial area density model (AIAD) represents one step toward a more physical description of free surface flows including less empiricism. The AIAD approach allows the use of different physical models depending on the local fluid morphology inside a macro-scale multi-fluid framework. A further step of improving the modeling of free interfaces lies within the consideration of droplet entrainment mechanisms. In this paper a new sub-grid entrainment model is proposed, which assumes that due to liquid turbulence the interface gets rough and wavy leading to the formation of droplets. Therefore, the droplet entrainment model requires the consideration of an additional droplet phase, which is described with an own set of balance equations in the spirit of the particle model. Two local key factors determine the rate of droplet entrainment: the liquid turbulent kinetic energy as well as the outward velocity gradient of the liquid relative to the interface motion. The new droplet entrainment approach is included into CFD simulations for attempting to reproduce existing

  9. High intensity laser interactions with sub-micron droplets

    International Nuclear Information System (INIS)

    Mountford, L.C.

    1999-01-01

    A high-density source of liquid ethanol droplets has been developed, characterised and used in laser interaction studies for the first time. Mie Scattering and attenuation measurements show that droplets with a radius of (0.5 ± 0.1) μm and atomic densities of 10 19 atoms/cm 3 can be produced, bridging the gap between clusters and macroscopic solids. Lower density (10 16 cm -3 ) sprays can also be produced and these are electrostatically split into smaller droplets with a radius of (0.3 ± 0.1) μm. This work has been accepted for publication in Review of Scientific Instruments. A range of high intensity interaction experiments have been carried out with this unique sub-micron source. The absolute yield of keV x-rays, generated using 527 nm, 2 ps pulses focused to ∼10 17 W/cm 2 , was measured for the first time. ∼7 μJ of x-rays with photon energies above 1 keV were produced, comparable to yields obtained from much higher Z Xenon clusters. At intensities ≤10 16 W/cm 2 the yield from droplets exceeds that from solid targets of similar Z. The droplet medium is debris free and self-renewing, providing a suitable x-ray source for lithographic techniques. Due to the spacing between the droplets, it was expected that the droplet plasma temperature would exceed that of a solid target plasma, which is typically limited by rapid heat conduction to <1 keV. Analysis of the x-ray data shows this to be true with a mean droplet plasma temperature of (2 ± 0.8) keV, and a number of measurements exceeding 5 keV (to appear in Applied Physics Letters). The absorption of high intensity laser pulses in the dense spray has been measured for the first time and this was found to be wavelength and polarisation independent and in excess of 60%. These first interaction measurements clearly indicate that there are significant differences between the laser heating of droplet, solid and cluster targets. (author)

  10. Statistical steady states in turbulent droplet condensation

    Science.gov (United States)

    Bec, Jeremie; Krstulovic, Giorgio; Siewert, Christoph

    2017-11-01

    We investigate the general problem of turbulent condensation. Using direct numerical simulations we show that the fluctuations of the supersaturation field offer different conditions for the growth of droplets which evolve in time due to turbulent transport and mixing. This leads to propose a Lagrangian stochastic model consisting of a set of integro-differential equations for the joint evolution of the squared radius and the supersaturation along droplet trajectories. The model has two parameters fixed by the total amount of water and the thermodynamic properties, as well as the Lagrangian integral timescale of the turbulent supersaturation. The model reproduces very well the droplet size distributions obtained from direct numerical simulations and their time evolution. A noticeable result is that, after a stage where the squared radius simply diffuses, the system converges exponentially fast to a statistical steady state independent of the initial conditions. The main mechanism involved in this convergence is a loss of memory induced by a significant number of droplets undergoing a complete evaporation before growing again. The statistical steady state is characterised by an exponential tail in the droplet mass distribution.

  11. Faraday Waves-Based Integrated Ultrasonic Micro-Droplet Generator and Applications.

    Science.gov (United States)

    Tsai, Chen S; Mao, Rong W; Tsai, Shirley C; Shahverdi, Kaveh; Zhu, Yun; Lin, Shih K; Hsu, Yu-Hsiang; Boss, Gerry; Brenner, Matt; Mahon, Sari; Smaldone, Gerald C

    2017-01-01

    An in-depth review on a new ultrasonic micro-droplet generator which utilizes megahertz (MHz) Faraday waves excited by silicon-based multiple Fourier horn ultrasonic nozzles (MFHUNs) and its potential applications is presented. The new droplet generator has demonstrated capability for producing micro droplets of controllable size and size distribution and desirable throughput at very low electrical drive power. For comparison, the serious deficiencies of current commercial droplet generators (nebulizers) and the other ultrasonic droplet generators explored in recent years are first discussed. The architecture, working principle, simulation, and design of the multiple Fourier horns (MFH) in resonance aimed at the amplified longitudinal vibration amplitude on the end face of nozzle tip, and the fabrication and characterization of the nozzles are then described in detail. Subsequently, a linear theory on the temporal instability of Faraday waves on a liquid layer resting on the planar end face of the MFHUN and the detailed experimental verifications are presented. The linear theory serves to elucidate the dynamics of droplet ejection from the free liquid surface and predict the vibration amplitude onset threshold for droplet ejection and the droplet diameters. A battery-run pocket-size clogging-free integrated micro droplet generator realized using the MFHUN is then described. The subsequent report on the successful nebulization of a variety of commercial pulmonary medicines against common diseases and on the experimental antidote solutions to cyanide poisoning using the new droplet generator serves to support its imminent application to inhalation drug delivery.

  12. Strange particle production from quark matter droplets

    International Nuclear Information System (INIS)

    Werner, K.; Hladik, M.

    1995-01-01

    We recently introduced new methods to study ultrarelativistic nuclear scattering by providing a link between the string model approach and a thermal description. The string model is used to provide information about fluctuations in energy density. Regions of high energy density are considered to be quark matter droplets and treated macroscopically. At SPS energies, we find mainly medium size droplets---with energies up to few tens of Gev. A key issue is the microcanonical treatment of individual quark matter droplets. Each droplet hadronizes instantaneously according to the available n-body phase space. Due to the huge number of possible hadron configurations, special Monte Carlo techniques have been developed to calculate this disintegration. We present results concerning the production of strange particles from such a hadronization as compared to string decay. copyright 1995 American Institute of Physics

  13. D:\\Archieve\\TJPR\\Volume 1 No 1\\goosen finalxxx5.wpd

    African Journals Online (AJOL)

    culture systems, modelling of electrostatic polymer droplet formation, and growth of plant somatic ..... critical volume for drop detachment resulting ... and collecting solution, V is the applied voltage, .... distribution with one peak around 50 mm.

  14. Electronically droplet energy harvesting using piezoelectric cantilevers

    KAUST Repository

    Al Ahmad, Mahmoud Al

    2012-01-01

    A report is presented on free falling droplet energy harvesting using piezoelectric cantilevers. The harvester incorporates a multimorph clamped-free cantilever which is composed of five layers of lead zirconate titanate piezoelectric thick films. During the impact, the droplet kinetic energy is transferred into the form of mechanical stress forcing the piezoelectric structure to vibrate. Experimental results show energy of 0.3 μJ per droplet. The scenario of moderate falling drop intensity, i.e. 230 drops per second, yields a total energy of 400 μJ. © 2012 The Institution of Engineering and Technology.

  15. Dynamic analysis of a liquid droplet and optimization of helical angles for vortex drainage gas recovery

    Directory of Open Access Journals (Sweden)

    Xiaodong Wu

    2016-10-01

    Full Text Available Downhole vortex drainage gas recovery is a new gas production technology. So far, however, the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured out. In this paper, the forces of liquid droplets in the swirling flow field of wellbores were analyzed on the basis of two-phase fluid dynamics theories. Then, the motion equations of fluid droplets along axial and radical directions were established. Magnitude comparison was performed on several typical acting forces, including Basset force, virtual mass force, Magnus force, Saffman force and Stokes force. Besides, the formula for calculating the optimal helical angle of vortex tools was established according to the principle that the vertical resultant force on fluid droplets should be the maximum. And afterwards, each acting force was comprehensively analyzed in terms of its origin, characteristics and direction based on the established force analysis model. Magnitude comparison indicates that the forces with less effect can be neglected, including virtual mass force, Basset force and convection volume force. Moreover, the vertically upward centrifugal force component occurs on the fluid droplets in swirling flow field instead of those in the conventional flow field of wellbores, which is favorable for the fluid droplets to move upward. The reliability of optimal helical angle calculation formula was verified by means of case analysis. It is demonstrated that with the decrease of well depth, the fluid-carrying capability of gas and the optimal helical angle increase. The research results in this paper have a guiding significance to the optimization design of downhole vortex tools and the field application of downhole vortex drainage gas recovery technology.

  16. Instability of expanding bacterial droplets.

    Science.gov (United States)

    Sokolov, Andrey; Rubio, Leonardo Dominguez; Brady, John F; Aranson, Igor S

    2018-04-03

    Suspensions of motile bacteria or synthetic microswimmers, termed active matter, manifest a remarkable propensity for self-organization, and formation of large-scale coherent structures. Most active matter research deals with almost homogeneous in space systems and little is known about the dynamics of strongly heterogeneous active matter. Here we report on experimental and theoretical studies on the expansion of highly concentrated bacterial droplets into an ambient bacteria-free fluid. The droplet is formed beneath a rapidly rotating solid macroscopic particle inserted in the suspension. We observe vigorous instability of the droplet reminiscent of a violent explosion. The phenomenon is explained in terms of continuum first-principle theory based on the swim pressure concept. Our findings provide insights into the dynamics of active matter with strong density gradients and significantly expand the scope of experimental and analytic tools for control and manipulation of active systems.

  17. The measurement of tiny dew droplets at the initial deposition stage and dew point using a phase-shift interference microscope

    Science.gov (United States)

    Shigeaki, Matsumoto

    2003-12-01

    The shape of a dew droplet deposited on the mirror surface of a copper plate was measured accurately using an interference microscope that employed a phase-shift technique. The microscope was constructed by adding a piezoelectric transducer to an interference microscope. A simple method that uses a conventional speaker horn and an optical fibre cable was used to depress any speckle noise. The shape of a dew droplet deposited at dew point on the plate surface with average roughness of 0.1 µm was measured with an accuracy of ± 3 nm. The mass of a tiny dew droplet could be determined from the volume of its shape and was of the order of 10-9 g. The total mass of a dew droplet deposited per unit area and the deposition velocity under a gentle wind were also obtained in a similar way. The total mass was of the order of 10-5 g cm-2 at the beginning of deposition and the deposition velocity ranged from 1 × 10-5 to 6 × 10-5 g cm-2 min-1 at room temperature.

  18. TRAJECTORY AND INCINERATION OF ROGUE DROPLETS IN A TURBULENT DIFFUSION FLAME

    Science.gov (United States)

    The trajectory and incineration efficiency of individual droplet streams of a fuel mixture injected into a swirling gas turbulent diffusion flame were measured as a function of droplet size, droplet velocity, interdroplet spacing, and droplet injection angle. Additional experimen...

  19. Study on factors affecting the droplet temperature in plasma MIG welding process

    Science.gov (United States)

    Mamat, Sarizam Bin; Tashiro, Shinichi; Tanaka, Manabu; Yusoff, Mahani

    2018-04-01

    In the present study, the mechanism to control droplet temperature in the plasma MIG welding was discussed based on the measurements of the droplet temperature for a wide range of MIG currents with different plasma electrode diameters. The measurements of the droplet temperatures were conducted using a two color temperature measurement method. The droplet temperatures in the plasma MIG welding were then compared with those in the conventional MIG welding. As a result, the droplet temperature in the plasma MIG welding was found to be reduced in comparison with the conventional MIG welding under the same MIG current. Especially when the small plasma electrode diameter was used, the decrease in the droplet temperature reached maximally 500 K. Also, for a particular WFS, the droplet temperatures in the plasma MIG welding were lower than those in the conventional MIG welding. It is suggested that the use of plasma contributes to reducing the local heat input into the base metal by the droplet. The presence of the plasma surrounding the wire is considered to increase the electron density in its vicinity, resulting in the arc attachment expanding upwards along the wire surface to disperse the MIG current. This dispersion of MIG current causes a decrease in current density on the droplet surface, lowering the droplet temperature. Furthermore, dispersed MIG current also weakens the electromagnetic pinch force acting on the neck of the wire above the droplet. This leads to a larger droplet diameter with increased surface area through lower frequency of droplet detachment to decrease the MIG current density on the droplet surface, as compared to the conventional MIG welding at the same MIG current. Thus, the lower droplet temperature is caused by the reduction of heat flux into the droplet. Consequently, the mechanism to control droplet temperature in the plasma MIG welding was clarified.

  20. Coding/decoding and reversibility of droplet trains in microfluidic networks.

    Science.gov (United States)

    Fuerstman, Michael J; Garstecki, Piotr; Whitesides, George M

    2007-02-09

    Droplets of one liquid suspended in a second, immiscible liquid move through a microfluidic device in which a channel splits into two branches that reconnect downstream. The droplets choose a path based on the number of droplets that occupy each branch. The interaction among droplets in the channels results in complex sequences of path selection. The linearity of the flow through the microchannels, however, ensures that the behavior of the system can be reversed. This reversibility makes it possible to encrypt and decrypt signals coded in the intervals between droplets. The encoding/decoding device is a functional microfluidic system that requires droplets to navigate a network in a precise manner without the use of valves, switches, or other means of external control.

  1. Bioreactor droplets from liposome-stabilized all-aqueous emulsions

    Science.gov (United States)

    Dewey, Daniel C.; Strulson, Christopher A.; Cacace, David N.; Bevilacqua, Philip C.; Keating, Christine D.

    2014-08-01

    Artificial bioreactors are desirable for in vitro biochemical studies and as protocells. A key challenge is maintaining a favourable internal environment while allowing substrate entry and product departure. We show that semipermeable, size-controlled bioreactors with aqueous, macromolecularly crowded interiors can be assembled by liposome stabilization of an all-aqueous emulsion. Dextran-rich aqueous droplets are dispersed in a continuous polyethylene glycol (PEG)-rich aqueous phase, with coalescence inhibited by adsorbed ~130-nm diameter liposomes. Fluorescence recovery after photobleaching and dynamic light scattering data indicate that the liposomes, which are PEGylated and negatively charged, remain intact at the interface for extended time. Inter-droplet repulsion provides electrostatic stabilization of the emulsion, with droplet coalescence prevented even for submonolayer interfacial coatings. RNA and DNA can enter and exit aqueous droplets by diffusion, with final concentrations dictated by partitioning. The capacity to serve as microscale bioreactors is established by demonstrating a ribozyme cleavage reaction within the liposome-coated droplets.

  2. Response of two-phase droplets to intense electromagnetic radiation

    Science.gov (United States)

    Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.

    1993-01-01

    The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii of 37, 55, and 80 microns) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.

  3. Supercritical droplet dynamics and emission in low speed cross-flows

    International Nuclear Information System (INIS)

    Chae, J. W.; Yang, H. S.; Yoon, W. S.

    2008-01-01

    Droplet dynamics and emission of a supercritical droplet in crossing gas stream are numerically investigated. Effects of ambient pressure and velocity of nitrogen gas on the dynamics of the supercritical oxygen droplet are parametrically examined. Unsteady conservative axisymmetric Navier-Stokes equations in curvilinear coordinates are preconditioned and solved by dual-time stepping method. A unified property evaluation scheme based on a fundamental equation of state and extended corresponding-state principle is established to deal with thermodynamic non-idealities and transport anomalies. At lower pressures and velocities of nitrogen cross flows, both the diffusion and the convection are important in determining the droplet dynamics. Relative flow motion causes a secondary breakup and cascading vortices, and the droplet lifetime is reduced with increasing in ambient pressure. At higher ambient pressures and velocities, however, the droplet dynamics become convection-controlled while the secondary breakup is hindered by reduced diffusivity of the oxygen. Gas-phase mixing depends on the convection and diffusion velocities in conjunction with corresponding droplet deformation and flow interaction. Supercritical droplet dynamics and emission is not similar with respect to the pressure and velocity of the ambient gas and thus provides no scale

  4. An experimental study on suspended sodium droplet combustion (2)

    International Nuclear Information System (INIS)

    Sato, Kenji

    2004-03-01

    As part of studies for phenomenological investigation of sodium droplet burning behavior, in our previous experimental studies for suspended single sodium droplet, behavior of ignition process and succeeding combustion, ignition delay time, and droplet temperature history had been investigated. In the present study, by using 4 mm diam. suspended sodium droplet, combustion experiments were performed for extended free-stream velocity range of dry air up to 200 cm/s, and for the initial droplet temperature T i =300degC and 400degC, and the effects of the free-stream velocity and initial droplet temperature on the ignition/burning behavior and ignition delay time were examined by using high speed video camera. The obtained experimental results are as follows: (1) Ignition phenomena of suspended spherical shape droplet were observed for all examined experimental conductions except the case of free-stream velocity U=200 cm/s at 300degC, where detachment of droplet from the support due to strained oxide film occurred. (2) The ignition delay time defined as the time to evolution of orange-light emitting zone or flame zone decreases with the increase of the free-stream velocity or of initial droplet temperature. Examples of typical ignition delay time are 0.68 s at U=20 cm/s, 0.52 s at U=100 cm/s, and 0.37 s at 200 cm/s for T i =400degC. (3) The orange-light emission at the moment of ignition occurs simultaneously over whole surface except the top region of the droplet. The intensity of the emission at the moment of ignition takes its maximum at the bottom region or upstream region of the droplet, and the emission intensity during the stable burning period increases with the increase of U. (4) When T i is 300degC, formation of temporal multiple short projections are observed before ignition for all examined free-stream velocities. The projections often do not disappear before ignition when the velocity is relatively high. (5) The layer or cloud composed of aerosol is formed

  5. Post-dryout heat transfer analysis model with droplet Lagrangian simulation

    International Nuclear Information System (INIS)

    Keizo Matsuura; Isao Kataoka; Kaichiro Mishima

    2005-01-01

    Post-dryout heat transfer analysis was carried out considering droplet behavior by using the Lagrangian simulation method. Post-dryout heat transfer is an important heat transfer mechanism in many industrial appliances. Especially in recent Japanese BWR licensing, the standard for assessing the integrity of fuel that has experienced boiling transition is being examined. Although post-dryout heat transfer analysis is important when predicting wall temperature, it is difficult to accurately predict the heat transfer coefficient in the post-dryout regime because of the many heat transfer paths and non-equilibrium status between droplet and vapor. Recently, an analysis model that deals with many heat transfer paths including droplet direct contact heat transfer was developed and its results showed good agreement with experimental results. The model also showed that heat transfer by droplet could not be neglected in the low mass flux condition. However, the model deals with droplet deposition behavior by experimental droplet deposition correlation, so it cannot estimate the effect of droplet flow on turbulent flow field and heat transfer. Therefore, in this study we deal with many droplets separately by using the Lagrangian simulation method and hence estimate the effect of droplet flow on the turbulent flow field. We analyzed post-dryout experimental results and found that they correlated well with the analysis results. (authors)

  6. Lipid droplets as ubiquitous fat storage organelles in C. elegans

    Directory of Open Access Journals (Sweden)

    Guo Fengli

    2010-12-01

    Full Text Available Abstract Background Lipid droplets are a class of eukaryotic cell organelles for storage of neutral fat such as triacylglycerol (TAG and cholesterol ester (CE. We and others have recently reported that lysosome-related organelles (LROs are not fat storage structures in the nematode C. elegans. We also reported the formation of enlarged lipid droplets in a class of peroxisomal fatty acid β-oxidation mutants. In the present study, we seek to provide further evidence on the organelle nature and biophysical properties of fat storage structures in wild-type and mutant C. elegans. Results In this study, we provide biochemical, histological and ultrastructural evidence of lipid droplets in wild-type and mutant C. elegans that lack lysosome related organelles (LROs. The formation of lipid droplets and the targeting of BODIPY fatty acid analogs to lipid droplets in live animals are not dependent on lysosomal trafficking or peroxisome dysfunction. However, the targeting of Nile Red to lipid droplets in live animals occurs only in mutants with defective peroxisomes. Nile Red labelled-lipid droplets are characterized by a fluorescence emission spectrum distinct from that of Nile Red labelled-LROs. Moreover, we show that the recently developed post-fix Nile Red staining method labels lipid droplets exclusively. Conclusions Our results demonstrate lipid droplets as ubiquitous fat storage organelles and provide a unified explanation for previous studies on fat labelling methods in C. elegans. These results have important applications to the studies of fat storage and lipid droplet regulation in the powerful genetic system, C. elegans.

  7. Faraday Waves-Based Integrated Ultrasonic Micro-Droplet Generator and Applications

    Directory of Open Access Journals (Sweden)

    Chen S. Tsai

    2017-02-01

    Full Text Available An in-depth review on a new ultrasonic micro-droplet generator which utilizes megahertz (MHz Faraday waves excited by silicon-based multiple Fourier horn ultrasonic nozzles (MFHUNs and its potential applications is presented. The new droplet generator has demonstrated capability for producing micro droplets of controllable size and size distribution and desirable throughput at very low electrical drive power. For comparison, the serious deficiencies of current commercial droplet generators (nebulizers and the other ultrasonic droplet generators explored in recent years are first discussed. The architecture, working principle, simulation, and design of the multiple Fourier horns (MFH in resonance aimed at the amplified longitudinal vibration amplitude on the end face of nozzle tip, and the fabrication and characterization of the nozzles are then described in detail. Subsequently, a linear theory on the temporal instability of Faraday waves on a liquid layer resting on the planar end face of the MFHUN and the detailed experimental verifications are presented. The linear theory serves to elucidate the dynamics of droplet ejection from the free liquid surface and predict the vibration amplitude onset threshold for droplet ejection and the droplet diameters. A battery-run pocket-size clogging-free integrated micro droplet generator realized using the MFHUN is then described. The subsequent report on the successful nebulization of a variety of commercial pulmonary medicines against common diseases and on the experimental antidote solutions to cyanide poisoning using the new droplet generator serves to support its imminent application to inhalation drug delivery.

  8. Fast Evaporation of Spreading Droplets of Colloidal Suspensions

    Science.gov (United States)

    Maki, Kara; Kumar, Satish

    2011-11-01

    When a coffee droplet dries on a countertop, a dark ring of coffee solute is left behind, a phenomenon often referred to as ``the coffee-ring effect.'' A closely related yet less-well-explored phenomenon is the formation of a layer of particles, or skin, at the surface of the droplet. In this work, we explore the behavior of a mathematical model that can qualitatively describe both phenomena. We consider a thin axisymmetric droplet of a colloidal suspension on a horizontal substrate undergoing spreading and rapid evaporation. The lubrication approximation is applied to simplify the mass and momentum conservation equations, and the colloidal particles are allowed to influence droplet rheology through their effect on the viscosity. By describing the transport of the colloidal particles with the full convection-diffusion equation, we are able to capture depthwise gradients in particle concentration and thus describe skin formation, a feature neglected in prior models of droplet evaporation. Whereas capillarity creates a flow that drives particles to the contact line to produce a coffee-ring, Marangoni flows can compete with this and promote skin formation. Increases in viscosity due to particle concentration slow down droplet dynamics, and can lead to a significant reduction in the spreading rate.

  9. Effect of Latent Heat Released by Freezing Droplets during Frost Wave Propagation.

    Science.gov (United States)

    Chavan, Shreyas; Park, Deokgeun; Singla, Nitish; Sokalski, Peter; Boyina, Kalyan; Miljkovic, Nenad

    2018-05-21

    Frost spreads on nonwetting surfaces during condensation frosting via an interdroplet frost wave. When a supercooled condensate water droplet freezes on a hydrophobic or superhydrophobic surface, neighboring droplets still in the liquid phase begin to evaporate. Two possible mechanisms govern the evaporation of neighboring water droplets: (1) The difference in saturation pressure of the water vapor surrounding the liquid and frozen droplets induces a vapor pressure gradient, and (2) the latent heat released by freezing droplets locally heats the substrate, leading to evaporation of nearby droplets. The relative significance of these two mechanisms is still not understood. Here, we study the significance of the latent heat released into the substrate by freezing droplets, and its effect on adjacent droplet evaporation, by studying the dynamics of individual water droplet freezing on aluminum-, copper-, and glass-based hydrophobic and superhydrophobic surfaces. The latent heat flux released into the substrate was calculated from the measured droplet sizes and the respective freezing times ( t f ), defined as the time from initial ice nucleation within the droplet to complete droplet freezing. To probe the effect of latent heat release, we performed three-dimensional transient finite element simulations showing that the transfer of latent heat to neighboring droplets is insignificant and accounts for a negligible fraction of evaporation during microscale frost wave propagation. Furthermore, we studied the effect of substrate thermal conductivity on the transfer of latent heat transfer to neighboring droplets by investigating the velocity of ice bridge formation. The velocity of the ice bridge was independent of the substrate thermal conductivity, indicating that adjacent droplet evaporation during condensation frosting is governed solely by vapor pressure gradients. This study not only provides key insights into the individual droplet freezing process but also

  10. A new approach for the calculation of falling droplets from a cylindrical glass capillary based on force balance and velocity

    Science.gov (United States)

    Hummel, Sebastian; Bogner, Martin; Haub, Michael; Saegebarth, Joachim; Sandmaier, Hermann

    2017-11-01

    This paper presents a new simple analytical method to estimate the properties of falling droplets without solving complex differential equations. The derivation starts from the balance of forces and uses Newton’s second law and the equations of motion to calculate the volume of growing and detaching droplets and the time between two successive droplets falling out of a thin cylindrical capillary of borosilicate glass. In this specific case the reservoir is located above the capillary and the hydrostatic pressure of the fluid level leads to drop formation times about one second. In the second part of this paper experimental results are presented to validate the introduced calculation method. It is shown that the new approach describes the measuring results within a deviation of ±6.2%. The third part of the paper sums up the advantages of the new approach and an outlook is given on how the research on this topic will be continued.

  11. METHANE GAS STABILIZES SUPERCOOLED ETHANE DROPLETS IN TITAN'S CLOUDS

    International Nuclear Information System (INIS)

    Wang, Chia C.; Lang, E. Kathrin; Signorell, Ruth

    2010-01-01

    Strong evidence for ethane clouds in various regions of Titan's atmosphere has recently been found. Ethane is usually assumed to exist as ice particles in these clouds, although the possible role of liquid and supercooled liquid ethane droplets has been recognized. Here, we report on infrared spectroscopic measurements of ethane aerosols performed in the laboratory under conditions mimicking Titan's lower atmosphere. The results clearly show that liquid ethane droplets are significantly stabilized by methane gas which is ubiquitous in Titan's nitrogen atmosphere-a phenomenon that does not have a counterpart for water droplets in Earth's atmosphere. Our data imply that supercooled ethane droplets are much more abundant in Titan's clouds than previously anticipated. Possibly, these liquid droplets are even more important for cloud processes and the formation of lakes than ethane ice particles.

  12. A new kind of droplet space distribution measuring method

    International Nuclear Information System (INIS)

    Ma Chao; Bo Hanliang

    2012-01-01

    A new kind of droplet space distribution measuring technique was introduced mainly, and the experimental device which was designed for the measuring the space distribution and traces of the flying film droplet produced by the bubble breaking up near the free surface of the water. This experiment was designed with a kind of water-sensitivity test paper (rice paper) which could record the position and size of the colored scattering droplets precisely. The rice papers were rolled into cylinders with different diameters by using tools. The bubbles broke up exactly in the center of the cylinder, and the space distribution and the traces of the droplets would be received by analysing all the positions of the droplets produced by the same size bubble on the rice papers. (authors)

  13. Role of cavitation in high-speed droplet impact problems

    Science.gov (United States)

    Kondo, Tomoki; Ando, Keita

    2014-11-01

    High-speed droplet impact is found in physical cleaning using liquid jets, but its mechanisms for particle removal from target surfaces are yet unclear. In this study, we explore the possibility of having cavitation inside the droplet. The pressure evolution within a droplet colliding with a flat surface of deformable materials is determined by multicomponent Euler equations. Dynamics of cavitation bubbles heterogeneously nucleated from preexisting nuclei are determined from Rayleigh-Plesset calculations according to the pressure evolution within the droplet in one-way-coupling manner. The simulation shows that cavitation indeed occurs due to tension that arises from the water hammer shock reflection at the droplet interface. The role of cavitation including pressure emission from its collapse is to be discussed based on the one-way-coupling computations.

  14. Drag Coefficient of Water Droplets Approaching the Leading Edge of an Airfoil

    Science.gov (United States)

    Vargas, Mario; Sor, Suthyvann; Magarino, Adelaida Garcia

    2013-01-01

    This work presents results of an experimental study on droplet deformation and breakup near the leading edge of an airfoil. The experiment was conducted in the rotating rig test cell at the Instituto Nacional de Tecnica Aeroespacial (INTA) in Madrid, Spain. An airfoil model was placed at the end of the rotating arm and a monosize droplet generator produced droplets that fell from above, perpendicular to the path of the airfoil. The interaction between the droplets and the airfoil was captured with high speed imaging and allowed observation of droplet deformation and breakup as the droplet approached the airfoil near the stagnation line. Image processing software was used to measure the position of the droplet centroid, equivalent diameter, perimeter, area, and the major and minor axes of an ellipse superimposed over the deforming droplet. The horizontal and vertical displacement of each droplet against time was also measured, and the velocity, acceleration, Weber number, Bond number, Reynolds number, and the drag coefficients were calculated along the path of the droplet to the beginning of breakup. Results are presented and discussed for drag coefficients of droplets with diameters in the range of 300 to 1800 micrometers, and airfoil velocities of 50, 70 and 90 meters/second. The effect of droplet oscillation on the drag coefficient is discussed.

  15. Diffusion and evaporation of a liquid droplet

    Science.gov (United States)

    Shukla, K. N.

    1980-06-01

    The process of evaporation and diffusion of a spherical liquid droplet in an atmosphere of noncondensable gas is studied theoretically. An equation for the shrinkage of the radius of the droplet is derived on the basis of continuity and momentum equations. Further, a conjugate problem consisting of the energy and mass balance for the gaseous environment is formulated. An approximation of thin thermal and diffusion boundary-layers is introduced to simplify the analysis. Results are presented for methanol-nitrogen, ammonia-nitrogen, and sodium-argon systems. It has been observed that the droplet of highly viscous fluid exhibits rapid contraction.

  16. The effect of coarse-droplet spraying with double flat fan air induction nozzle and spray volume adjustment model on the efficiency of fungicides and residues in processing tomato

    Directory of Open Access Journals (Sweden)

    Henryk Ratajkiewicz

    2018-04-01

    Full Text Available The study was conducted for the purpose of improving the application of fungicides against potato late blight (Phytophthora infestans (Mont. de Bary (PLB in processing tomato. The usability of coarse spray quality with double flat fan air induction IDKT12003 nozzle and the impact of fixed and variable spray volume and adjuvants during alternate application of azoxystrobin and chlorothalonil were analysed on the basis of plant infestation and fungicide residues. The variable spray volume was calculated based on the number of leaves on a plant. The study was conducted during three vegetation seasons. Spraying of plants with significantly flattened canopies during the peak of the fructification season using an IDKT12003 nozzle was as effective as in the case of fine spraying performed with an XR11003 nozzle and facilitated the increase of fungicides residue. In the case of plants with high-spreading canopy at the beginning of fructification, XR11003 nozzle favoured the reduction of PLB infestation. Both spray volume adjustment systems enabled the same level of protection of tomato against PLB, which could result from alternate application of systemic and contact fungicides. Polyalkyleneoxide modified heptamethyltrisiloxane adjuvant, which causes siginificant increase in wetting and droplet spreading, facilitated the reduction of tomato PLB infestation during the application of fungicides using an IDKT12003 nozzle.

  17. Field dependent shape variation of magnetic fluid droplets on magnetic dots

    International Nuclear Information System (INIS)

    Lee, Chiun-Peng; Yang, Shu-Ting; Wei, Zung-Hang

    2012-01-01

    The morphology of magnetic fluid droplets on magnetic thin film dots is studied experimentally, including the aspect ratio and the contact angle variation of the droplets. Under a uniform external magnetic field, the droplet's aspect ratio increases with the external field and with the diameter of the magnetic dot due to the concentrated magnetic flux inside the magnetic fluid droplet. Similar to the electrical wetting phenomenon, the induced magnetic dipoles in the magnetic film and in the magnetic fluid near the solid–liquid interface change the solid–liquid interfacial tension, and in consequence reduce the apparent contact angle of the magnetic fluid droplet. - Highlights: ► Morphology of ferrofluid droplets on magnetic thin film dots was studied experimentally. ► Aspect ratio of ferrofluid droplets was found to increase with increasing of magnetic field. ► Liquid–solid contact angle of ferrofluid droplets was found to vary with magnetic field. ► Relationship between magnetic field and the liquid–solid interfacial tension was modeled.

  18. Development of Single Optical Sensor Method for the Measurement Droplet Parameters

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Tae Ho; Ahn, Tae Hwan; Yun, Byong Jo [Pusan National University, Busan (Korea, Republic of); Bae, Byoung Uhn; Kim, Kyoung Doo [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    In this study, we tried to develop single optical fiber probe(S-TOP) sensor method to measure droplet parameters such as diameter, droplet fraction, and droplet velocity and so on. To calibrate and confirm the optical fiber sensor for those parameters, we conducted visualization experiments by using a high speed camera with the optical sensor. To evaluate the performance of the S-TOP accurately, we repeated calibration experiments at a given droplet flow condition. Figure. 3 shows the result of the calibration. In this graph, the x axis is the droplet velocity measured by visualization and the y axis is grd, D which is obtained from S-TOP. In this study, we have developed the single tip optical probe sensor to measure the droplet parameters. From the calibration experiments with high speed camera, we get the calibration curve for the droplet velocity. Additionally, the chord length distribution of droplets is measured by the optical probe.

  19. Development of Single Optical Sensor Method for the Measurement Droplet Parameters

    International Nuclear Information System (INIS)

    Kim, Tae Ho; Ahn, Tae Hwan; Yun, Byong Jo; Bae, Byoung Uhn; Kim, Kyoung Doo

    2016-01-01

    In this study, we tried to develop single optical fiber probe(S-TOP) sensor method to measure droplet parameters such as diameter, droplet fraction, and droplet velocity and so on. To calibrate and confirm the optical fiber sensor for those parameters, we conducted visualization experiments by using a high speed camera with the optical sensor. To evaluate the performance of the S-TOP accurately, we repeated calibration experiments at a given droplet flow condition. Figure. 3 shows the result of the calibration. In this graph, the x axis is the droplet velocity measured by visualization and the y axis is grd, D which is obtained from S-TOP. In this study, we have developed the single tip optical probe sensor to measure the droplet parameters. From the calibration experiments with high speed camera, we get the calibration curve for the droplet velocity. Additionally, the chord length distribution of droplets is measured by the optical probe.

  20. Assembly of silver nanowire ring induced by liquid droplet

    Science.gov (United States)

    Seong, Baekhoon; Park, Hyun Sung; Chae, Ilkyeong; Lee, Hyungdong; Wang, Xiaofeng; Jang, Hyung-Seok; Jung, Jaehyuck; Lee, Changgu; Lin, Liwei; Byun, Doyoung

    2017-11-01

    Several forces in the liquid droplet drive the nanomaterials to naturally form an assembled structure. During evaporation of a liquid droplet, nanomaterials can move to the rim of the droplet by convective flow and capillary flow, due to the difference in temperature between the top and contact line of the droplet. Here, we demonstrate a new, simple and scalable technology for the fabrication of ring-shaped Ag NWs by a spraying method. We experimentally identify the compressive force of the droplet driven by surface tension as the key mechanism for the self-assembly of ring structures. We investigated the progress of ring shape formation of Ag NWs according to the droplet size with theoretically calculated optimal conditions. As such, this self-assembly technique of making ring-shaped structures from Ag NWs could be applied to other nanomaterials. This work was supported by the New & Renewable Energy R&D program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) Grant funded by the Korea government Ministry of Trade, Industry and Energy. (No. 20163010071630).

  1. Droplet motion in microfluidic networks: Hydrodynamic interactions and pressure-drop measurements

    Science.gov (United States)

    Sessoms, D. A.; Belloul, M.; Engl, W.; Roche, M.; Courbin, L.; Panizza, P.

    2009-07-01

    We present experimental, numerical, and theoretical studies of droplet flows in hydrodynamic networks. Using both millifluidic and microfluidic devices, we study the partitioning of monodisperse droplets in an asymmetric loop. In both cases, we show that droplet traffic results from the hydrodynamic feedback due to the presence of droplets in the outlet channels. We develop a recently-introduced phenomenological model [W. Engl , Phys. Rev. Lett. 95, 208304 (2005)] and successfully confront its predictions to our experimental results. This approach offers a simple way to measure the excess hydrodynamic resistance of a channel filled with droplets. We discuss the traffic behavior and the variations in the corresponding hydrodynamic resistance length Ld and of the droplet mobility β , as a function of droplet interdistance and confinement for channels having circular or rectangular cross sections.

  2. Effect of solvent on the charging mechanisms of poly(ethylene glycol) in droplets

    Science.gov (United States)

    Soltani, Sepideh; Oh, Myong In; Consta, Styliani

    2015-03-01

    We examine the effect of solvent on the charging mechanisms of a macromolecule in a droplet by using molecular dynamics simulations. The droplet contains excess charge that is carried by sodium ions. To investigate the principles of the charging mechanisms of a macromolecule in a droplet, we simulate aqueous and methanol droplets that contain a poly(ethylene glycol) (PEG) molecule. We find that the solvent plays a critical role in the charging mechanism and in the manner that the sodiated PEG emerges from a droplet. In the aqueous droplets, the sodiated PEG is released from the droplet while it is being charged at a droplet charge state below the Rayleigh limit. The charging of PEG occurs on the surface of the droplet. In contrast to the aqueous droplets, in the methanol droplet, the sodiated PEG resides in the interior of the droplet and it may become charged at any location in the droplet, interior or surface. The sodiated PEG emerges from the droplet by drying-out of the solvent. Even though these two mechanisms appear to be phenomenologically similar to the widely accepted ion-evaporation and charge-residue mechanisms, they have fundamental differences from those. An integral part of the mechanism that the macromolecular ions emerge from droplets is the droplet morphology. Droplet morphologies give rise to different solvation interactions between the solvent and the macromolecule. In the water-sodiated PEG system, we find the extrusion of the PEG morphology, while in methanol-sodiated droplet, we find the "pearl-on-the-necklace" morphology and the extrusion of the sodiated PEG in the last stage of the desolvation process. These findings provide insight into the mechanisms that macromolecules acquire their charge in droplets produced in electrospray ionization experiments.

  3. Method for using magnetic particles in droplet microfluidics

    Science.gov (United States)

    Shah, Gaurav Jitendra (Inventor); Kim, Chang-Jin (Inventor)

    2012-01-01

    Methods of utilizing magnetic particles or beads (MBs) in droplet-based (or digital) microfluidics are disclosed. The methods may be used in enrichment or separation processes. A first method employs the droplet meniscus to assist in the magnetic collection and positioning of MBs during droplet microfluidic operations. The sweeping movement of the meniscus lifts the MBs off the solid surface and frees them from various surface forces acting on the MBs. A second method uses chemical additives to reduce the adhesion of MBs to surfaces. Both methods allow the MBs on a solid surface to be effectively moved by magnetic force. Droplets may be driven by various methods or techniques including, for example, electrowetting, electrostatic, electromechanical, electrophoretic, dielectrophoretic, electroosmotic, thermocapillary, surface acoustic, and pressure.

  4. Investigation on Shock Induced Stripping Breakup Process of A Liquid Droplet

    KAUST Repository

    Liu, Yao

    2017-03-02

    Stripping breakup process of a single liquid droplet under the impact of a planar shock wave is investigated both experimentally and numerically. The droplet breakup experiment is conducted in a horizontal shock tube and the evolution of the droplet is recorded by direct high-speed photography. The experimental images clearly illustrate the droplet interface evolution features from its early to relatively late stage. Compressible Euler equations are solved using an in-house inviscid upwind characteristic space-time conservation element and solution element (CE/SE) method coupled with the HLLC approximate Riemann solver. A reduced five-equation model is employed to demonstrate the air/liquid interface. Numerical results accurately reproduce the water column and axi-symmetric water droplet breakup processes in experiments. The present study confirms the validity of the present numerical method in solving the shock wave induced droplet breakup problem and elaborates the stripping breakup process numerically in a long period. Droplet inner flow pattern is depicted, based on which the drives of protrusions emerged on the droplet surface are clearly seen. The droplet deformation is proved to be determined by not only the outer air flow, but also the inner liquid flow.

  5. Investigation on Shock Induced Stripping Breakup Process of A Liquid Droplet

    KAUST Repository

    Liu, Yao; Wen, Chihyung; Shen, Hua; Guan, Ben

    2017-01-01

    Stripping breakup process of a single liquid droplet under the impact of a planar shock wave is investigated both experimentally and numerically. The droplet breakup experiment is conducted in a horizontal shock tube and the evolution of the droplet is recorded by direct high-speed photography. The experimental images clearly illustrate the droplet interface evolution features from its early to relatively late stage. Compressible Euler equations are solved using an in-house inviscid upwind characteristic space-time conservation element and solution element (CE/SE) method coupled with the HLLC approximate Riemann solver. A reduced five-equation model is employed to demonstrate the air/liquid interface. Numerical results accurately reproduce the water column and axi-symmetric water droplet breakup processes in experiments. The present study confirms the validity of the present numerical method in solving the shock wave induced droplet breakup problem and elaborates the stripping breakup process numerically in a long period. Droplet inner flow pattern is depicted, based on which the drives of protrusions emerged on the droplet surface are clearly seen. The droplet deformation is proved to be determined by not only the outer air flow, but also the inner liquid flow.

  6. Marangoni Convection in Evaporating Organic Liquid Droplets on a Nonwetting Substrate.

    Science.gov (United States)

    Chandramohan, Aditya; Dash, Susmita; Weibel, Justin A; Chen, Xuemei; Garimella, Suresh V

    2016-05-17

    We quantitatively characterize the flow field inside organic liquid droplets evaporating on a nonwetting substrate. A mushroom-structured surface yields the desired nonwetting behavior with methanol droplets, while use of a cooled substrate (5-15 °C) slows the rate of evaporation to allow quasi-static particle image velocimetry. Visualization reveals a toroidal vortex within the droplet that is characteristic of surface tension-driven flow; we demonstrate by means of a scaling analysis that this recirculating flow is Marangoni convection. The velocities in the droplet are on the order of 10-45 mm/s. Thus, unlike in the case of evaporation on wetting substrates where Marangoni convection can be ignored for the purpose of estimating the evaporation rate, advection due to the surface tension-driven flow plays a dominant role in the heat transfer within an evaporating droplet on a nonwetting substrate because of the large height-to-radius aspect ratio of the droplet. We formulate a reduced-order model that includes advective transport within the droplet for prediction of organic liquid droplet evaporation on a nonwetting substrate and confirm that the predicted temperature differential across the height of the droplet matches experiments.

  7. Droplet impact on superheated micro-structured surfaces

    NARCIS (Netherlands)

    Tran, Tuan; Staat, Erik-Jan; Susarrey Arce, A.; Foertsch, T.C.; van Houselt, Arie; Gardeniers, Johannes G.E.; Prosperetti, Andrea; Lohse, Detlef; Sun, Chao

    2013-01-01

    When a droplet impacts upon a surface heated above the liquid's boiling point, the droplet either comes into contact with the surface and boils immediately (contact boiling), or is supported by a developing vapor layer and bounces back (film boiling, or Leidenfrost state). We study the transition

  8. Experimental study on oxidation and combustion characteristics of sodium droplets

    International Nuclear Information System (INIS)

    Zhang Zhigang; Sun Shubin; Liu Chongchong; Tang Yexin

    2015-01-01

    In the operation of the sodium-cooled fast reactor, the accident caused by the leakage and combustion of liquid sodium is common and frequent. In this paper, the oxidation and combustion characteristics of sodium droplets were studied by carrying out the experiments of the oxidation and combustion under different conditions of initial temperatures (140-370℃) of the sodium droplets and oxygen concentrations (4%-21%). The oxidation and combustion behaviors were visualized by a set of combustion apparatus of sodium droplet and a high speed camera. The experiment results show that the columnar oxides grow longer as the initial temperature of sodium droplet and oxygen concentration become lower. Under the same oxygen concentration condition, the sodium droplet with the higher initial temperature is easier to ignite and burn. When the initial temperature of sodium droplet is below 200℃, it is very difficult to ignite. If there is a turbulence damaging the oxide layer on the surface, the sodium droplet will also burn gradually. When the initial temperature ranges from 140℃ to 370℃ and the oxygen fraction is equal to or higher than 12%, the sodium droplet could burn completely and the maximum combustion temperature could roughly reach 600-800℃. When the oxygen concentration is below 12%, the sodium droplet could not burn completely and the highest combustion temperature is below 600℃. The results are helpful to the research on the columnar flow and spray sodium fire. (authors)

  9. Droplet Impacting on Liquid Film: Evolution of Entrapped Air Layer

    Science.gov (United States)

    Tang, Xiaoyu; Saha, Abhishek; Law, Chung K.

    2014-11-01

    In this work we experimentally studied the dynamics of droplet impacting films of various thicknesses within a range of h / R <= 1 (h: film thickness; R: droplet radius). High speed imaging and color interferometry enabled the investigation of the evolution of the air layer trapped between two surfaces, which plays a critical role in determining the collision outcome. Globally, two distinct regimes of impaction outcome, namely bouncing and merging, are observed at low and high impact inertia, respectively. Impaction with high inertia depletes the air layer before the droplet significantly deforms, resulting in permanent merging. At low impact inertia, however, color interferometry shows the existence of three phases prior to bouncing. Upon impaction, droplet endures significant deformation trapping the air layer between the interfaces, hence increasing the resistance force. This phase is characterized by fast deformation of the air film, followed by a period of pseudo equilibrium, with minimal changes in the interfacial air-film profile. The droplet also lacks kinetic energy to penetrate further into the film, resulting in a temporary balance between the droplet weight and air-film pressure. The deformed droplet eventually relaxes towards spherical shape to destroy the equilibrium. Fast change occurs in air-layer and pressure distribution favoring the droplet bouncing.

  10. Aptamer-conjugated and drug-loaded acoustic droplets for ultrasound theranosis.

    Science.gov (United States)

    Wang, Chung-Hsin; Kang, Shih-Tsung; Lee, Ya-Hsuan; Luo, Yun-Ling; Huang, Yu-Fen; Yeh, Chih-Kuang

    2012-02-01

    Tumor therapy requires multi-functional treatment strategies with specific targeting of therapeutics to reduce general toxicity and increase efficacy. In this study we fabricated and functionally tested aptamer-conjugated and doxorubicin (DOX)-loaded acoustic droplets comprising cores of liquid perfluoropentane compound and lipid-based shell materials. Conjugation of sgc8c aptamers provided the ability to specifically target CCRF-CEM cells for both imaging and therapy. High-intensity focused ultrasound (HIFU) was introduced to trigger targeted acoustic droplet vaporization (ADV) which resulted in both mechanical cancer cell destruction by inertial cavitation and chemical treatment through localized drug release. HIFU insonation showed a 56.8% decrease in cell viability with aptamer-conjugated droplets, representing a 4.5-fold increase in comparison to non-conjugated droplets. In addition, the fully-vaporized droplets resulted in the highest DOX uptake by cancer cells, compared to non-vaporized or partially vaporized droplets. Optical studies clearly illustrated the transient changes that occurred upon ADV of droplet-targeted CEM cells, and B-mode ultrasound imaging revealed contrast enhancement by ADV in ultrasound images. In conclusion, our fabricated droplets functioned as a hybrid chemical and mechanical strategy for the specific destruction of cancer cells upon ultrasound-mediated ADV, while simultaneously providing ultrasound imaging capability. Copyright © 2011 Elsevier Ltd. All rights reserved.

  11. Operator formulation of the droplet model

    International Nuclear Information System (INIS)

    Lee, B.W.

    1987-01-01

    We study in detail the implications of the operator formulation of the droplet model. The picture of high-energy scattering that emerges from this model attributed the interaction between two colliding particles at high energies to an instantaneous, multiple exchange between two extended charge distributions. Thus the study of charge correlation functions becomes the most important problem in the droplet model. We find that in order for the elastic cross section to have a finite limit at infinite energy, the charge must be a conserved one. In quantum electrodynamics the charge in question is the electric charge. In hadronic physics, we conjecture, it is the baryonic charge. Various arguments for and implications of this hypothesis are presented. We study formal properties of the charge correlation functions that follow from microcausality, T, C, P invariances, and charge conservation. Perturbation expansion of the correlation functions is studied, and their cluster properties are deduced. A cluster expansion of the high-energy T matrix is developed, and the exponentiation of the interaction potential in this scheme is noted. The operator droplet model is put to the test of reproducing the high-energy limit of elastic scattering quantum electrodynamics found by Cheng and Wu in perturbation theory. We find that the droplet model reproduces exactly the results of Cheng and Wu as to the impact factor. In fact, the ''impact picture'' of Cheng and Wu is completely equivalent to the droplet model in the operator version. An appraisal is made of the possible limitation of the model. (author). 13 refs

  12. Droplet-Wall/Film Impact in IC Engine Applications

    Science.gov (United States)

    2017-08-14

    Report: Droplet-Wall/ Film Impact in IC Engine Applications (ARO Topic 1.4.1 under ARO’s Dr. Ralph A. Anthenien) The views, opinions and/or findings...Participants: RPPR Final Report as of 12-Oct-2017 Agreement Number: W911NF-16-1-0449 Organization: Princeton University Title: Droplet-Wall/ Film Impact...droplets impacting a wet surface under various film thickness, which plays a critical role in controlling the efficiency of applications such as those

  13. A Modeling of Compressible Droplets in a Fluid

    OpenAIRE

    Boudin, Laurent; Desvilletter, Laurent; Motte, Renaud

    2003-01-01

    In this work, we are interested in a complex fluid-kinetic model that aims to take into account the compressibility of the droplets of the spray. The ambient fluid is described by Euler-like equations, in which the transfer of momentum and energy form the droplets is taken into account, while the spray is represented by a probability density function satisfying a Vlasov-like equation. Implicit terms crop up because of the compressibility of the droplets. After having derived...

  14. Prediction of oil droplet size distribution in agitated aquatic environments

    International Nuclear Information System (INIS)

    Khelifa, A.; Lee, K.; Hill, P.S.

    2004-01-01

    Oil spilled at sea undergoes many transformations based on physical, biological and chemical processes. Vertical dispersion is the hydrodynamic mechanism controlled by turbulent mixing due to breaking waves, vertical velocity, density gradients and other environmental factors. Spilled oil is dispersed in the water column as small oil droplets. In order to estimate the mass of an oil slick in the water column, it is necessary to know how the droplets formed. Also, the vertical dispersion and fate of oil spilled in aquatic environments can be modelled if the droplet-size distribution of the oil droplets is known. An oil spill remediation strategy can then be implemented. This paper presented a newly developed Monte Carlo model to predict droplet-size distribution due to Brownian motion, turbulence and a differential settling at equilibrium. A kinematic model was integrated into the proposed model to simulate droplet breakage. The key physical input of the model is the maximum droplet size permissible in the simulation. Laboratory studies were found to be in good agreement with field studies. 26 refs., 1 tab., 5 figs

  15. Mechanism of Water Droplet Breakup Near the Leading Edge of an Airfoil

    Science.gov (United States)

    Vargas, Mario; Sor, Suthyvann; Magarino, Adelaida, Garcia

    2012-01-01

    This work presents results of an experimental study on droplet deformation and breakup near the leading edge of an airfoil. The experiment was conducted in the rotating rig test cell at the Instituto Nacional de Tecnica Aeroespacial (INTA) in Madrid, Spain. The airfoil model was placed at the end of the rotating arm and a monosize droplet generator produced droplets that fell from above, perpendicular to the path of the airfoil. The interaction between the droplets and the airfoil was captured with high speed imaging and allowed observation of droplet deformation and breakup as the droplet approached the airfoil near the stagnation line. Image processing software was used to measure the position of the droplet centroid, equivalent diameter, perimeter, area, and the major and minor axes of an ellipse superimposed over the deforming droplet. The horizontal and vertical displacement of each droplet against time was also measured, and the velocity, acceleration, Weber number, Bond number, Reynolds number, and the drag coefficients were calculated along the path of the droplet to the beginning of breakup. Droplet deformation is defined and studied against main parameters. The high speed imaging allowed observation of the actual mechanism of breakup and identification of the sequence of configurations from the initiation of the breakup to the disintegration of the droplet. Results and comparisons are presented for droplets of diameters in the range of 500 to 1800 microns, and airfoil velocities of 70 and 90 m/sec.

  16. A Computational Study of Internal Flows in a Heated Water-Oil Emulsion Droplet

    KAUST Repository

    Sim, Jaeheon

    2015-01-05

    The vaporization characteristics of water-oil emulsion droplets are investigated by high fidelity computational simulations. One of the key objectives is to identify the physical mechanism for the experimentally observed behavior that the component in the dispersed micro-droplets always vaporizes first, for both oil-in-water and water-in-oil emulsion droplets. The mechanism of this phenomenon has not been clearly understood. In this study, an Eulerian-Lagrangian method was implemented with a temperature-dependent surface tension model and a dynamic adaptive mesh refinement in order to effectively capture the thermo-capillary effect of a micro-droplet in an emulsion droplet efficiently. It is found that the temperature difference in an emulsion droplet creates a surface tension gradient along the micro-droplet surface, inducing surface movement. Subsequently, the outer shear flow and internal flow circulation inside the droplet, referred to as the Marangoni convection, are created. The present study confirms that the Marangoni effect can be sufficiently large to drive the micro-droplets to the emulsion droplet surface at higher temperature, for both water-in-oil and oil-and-water emulsion droplets. A further parametric study with different micro-droplet sizes and temperature gradients demonstrates that larger micro-droplets move faster with larger temperature gradient. The oil micro-droplet in oil-in-water emulsion droplets moves faster due to large temperature gradients by smaller thermal conductivity.

  17. Water droplet accumulation and motion in PEM (Proton Exchange Membrane) fuel cell mini-channels

    International Nuclear Information System (INIS)

    Carton, J.G.; Lawlor, V.; Olabi, A.G.; Hochenauer, C.; Zauner, G.

    2012-01-01

    Effective water management is one of the key strategies for improving low temperature PEM (Proton Exchange Membrane) fuel cell performance and durability. Phenomena such as membrane dehydration, catalyst layer flooding, mass transport and fluid flow regimes can be affected by the interaction, distribution and movement of water in flow plate channels. In this paper a literature review is completed in relation to PEM fuel cell water flooding. It is clear that droplet formation, movement and interaction with the GDL (Gas Diffusion Layer) have been studied extensively. However slug formation and droplet accumulation in the flow channels has not been analysed in detail. In this study, a CFD (Computational Fluid Dynamic) model and VOF (Volume of Fluid) method is used to simulate water droplet movement and slug formation in PEM fuel cell mini-channels. In addition, water slug visualisation is recorded in ex situ PEM fuel cell mini-channels. Observation and simulation results are discussed with relation to slug formation and the implications to PEM fuel cell performance. -- Highlights: ► Excess water in mini-channels from the collision and coalescence of droplets can directly form slugs in PEM fuel cells. ► Slugs can form at low flow rates so increasing the flow rate can reduce the size and frequency of slugs. ► One channel of a double serpentine mini-channel may become blocked due to the redistribution of airflow and pressure caused by slug formation. ► Correct GDL and mini-channel surface coatings are essential to reduce slug formation and stagnation. ► Having geometry changes (bends and steps) in the flow fields can disrupt slug movement and avoid channel blockages.

  18. Droplet behaviour in a Ranque-Hilsch vortex tube

    Energy Technology Data Exchange (ETDEWEB)

    Liew, R; Zeegers, J C H [Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Michalek, W R; Kuerten, J G M, E-mail: r.liew@tue.nl [Department of Mechanical Engineering, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands)

    2011-12-22

    The vortex tube is an apparatus by which compressed gas is separated into cold and warm streams. Although the apparatus is mostly used for cooling, the possibility to use the vortex tube as a device for removing non-desired condensable components from gas mixtures is investigated. To give first insight on how droplets behave in the vortex tube, a MATLAB model is written. The model tracks Lagrangian droplets in time and space according to the forces acting on the droplets. Phase interactions, i.e. evaporation or condensation, are modeled according to the kinetic approach for phase interactions. Liquid (water) concentrations are shown for two cases where the humidity at the inlet of the vortex tube is varied from 0% to 50%. It is clearly observed from the results that the concentration of liquid increases with increasing humidity. The higher this concentration is, the higher the probability that droplets collide with each other and form larger droplets which are swirled towards the wall to form an easy-to-separate liquid film.

  19. Droplet-Assisted Laser Direct Nanoscale Writing on Silicon

    Directory of Open Access Journals (Sweden)

    Yuan-Jen Chang

    2016-03-01

    Full Text Available Nano-structuring using laser direct writing technology has shown great potential for industrial applications. A novel application of water droplets to this technology is proposed in this paper. With a hydrophobic layer and a controlled substrate temperature, a layer of randomly distributed water droplets with a high contact angle is formed on the substrate. These liquid droplets can be used as lenses to enhance the laser intensity at the bottom of the droplets. As a result, nanoscale holes can be fabricated on the substrate by controlling the laser energy density. We successfully fabricated holes with a diameter of 600 nm at a substrate temperature of 12 ∘C and a power density of 1.2 × 108 W/cm2 in our experiments. We also found that the hole diameter was around a ninth of the water droplet diameter. Meanwhile, the machined holes are not affected much by the focal length of the lens, but a hole with less than 100 nm in diameter at the center was observed.

  20. Research into spectra transformation of cooling tower droplet drift

    International Nuclear Information System (INIS)

    Mandrykin, G.P.

    1990-01-01

    Empirical droplet-diameter distributions in a cooling tower and outside are well approximated by the Rosin-Rammler-Bennet two-parameter function. Fractional efficiency of eliminators is also approximated by the above function fairly well. The design formulas proposed are universal and allow evaluation of droplet spectra transformation as well as the efficiency of measures for preventing droplet emissions from cooling towers both at the design and operation stages. Estimates of cooling tower droplet emissions calculated by the formulas suggested may be recommended as input data applied to the solution of environmental pollution problems and their assessment

  1. Lattice-Boltzmann simulations of droplet evaporation

    KAUST Repository

    Ledesma-Aguilar, Rodrigo; Vella, Dominic; Yeomans, Julia M.

    2014-01-01

    © the Partner Organisations 2014. We study the utility and validity of lattice-Boltzmann (LB) simulations to explore droplet evaporation driven by a concentration gradient. Using a binary-fluid lattice-Boltzmann algorithm based on Cahn-Hilliard dynamics, we study the evaporation of planar films and 3D sessile droplets from smooth solid surfaces. Our results show that LB simulations accurately reproduce the classical regime of quasi-static dynamics. Beyond this limit, we show that the algorithm can be used to explore regimes where the evaporative and diffusive timescales are not widely separated, and to include the effect of boundaries of prescribed driving concentration. We illustrate the method by considering the evaporation of a droplet from a solid surface that is chemically patterned with hydrophilic and hydrophobic stripes. This journal is

  2. Lattice-Boltzmann simulations of droplet evaporation

    KAUST Repository

    Ledesma-Aguilar, Rodrigo

    2014-09-04

    © the Partner Organisations 2014. We study the utility and validity of lattice-Boltzmann (LB) simulations to explore droplet evaporation driven by a concentration gradient. Using a binary-fluid lattice-Boltzmann algorithm based on Cahn-Hilliard dynamics, we study the evaporation of planar films and 3D sessile droplets from smooth solid surfaces. Our results show that LB simulations accurately reproduce the classical regime of quasi-static dynamics. Beyond this limit, we show that the algorithm can be used to explore regimes where the evaporative and diffusive timescales are not widely separated, and to include the effect of boundaries of prescribed driving concentration. We illustrate the method by considering the evaporation of a droplet from a solid surface that is chemically patterned with hydrophilic and hydrophobic stripes. This journal is

  3. Experimental analysis of shape deformation of evaporating droplet using Legendre polynomials

    Energy Technology Data Exchange (ETDEWEB)

    Sanyal, Apratim [Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012 (India); Basu, Saptarshi, E-mail: sbasu@mecheng.iisc.ernet.in [Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012 (India); Kumar, Ranganathan [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States)

    2014-01-24

    Experiments involving heating of liquid droplets which are acoustically levitated, reveal specific modes of oscillations. For a given radiation flux, certain fluid droplets undergo distortion leading to catastrophic bag type breakup. The voltage of the acoustic levitator has been kept constant to operate at a nominal acoustic pressure intensity, throughout the experiments. Thus the droplet shape instabilities are primarily a consequence of droplet heating through vapor pressure, surface tension and viscosity. A novel approach is used by employing Legendre polynomials for the mode shape approximation to describe the thermally induced instabilities. The two dominant Legendre modes essentially reflect (a) the droplet size reduction due to evaporation, and (b) the deformation around the equilibrium shape. Dissipation and inter-coupling of modal energy lead to stable droplet shape while accumulation of the same ultimately results in droplet breakup.

  4. Experimental analysis of shape deformation of evaporating droplet using Legendre polynomials

    International Nuclear Information System (INIS)

    Sanyal, Apratim; Basu, Saptarshi; Kumar, Ranganathan

    2014-01-01

    Experiments involving heating of liquid droplets which are acoustically levitated, reveal specific modes of oscillations. For a given radiation flux, certain fluid droplets undergo distortion leading to catastrophic bag type breakup. The voltage of the acoustic levitator has been kept constant to operate at a nominal acoustic pressure intensity, throughout the experiments. Thus the droplet shape instabilities are primarily a consequence of droplet heating through vapor pressure, surface tension and viscosity. A novel approach is used by employing Legendre polynomials for the mode shape approximation to describe the thermally induced instabilities. The two dominant Legendre modes essentially reflect (a) the droplet size reduction due to evaporation, and (b) the deformation around the equilibrium shape. Dissipation and inter-coupling of modal energy lead to stable droplet shape while accumulation of the same ultimately results in droplet breakup.

  5. A theoretical study of the spheroidal droplet evaporation in forced convection

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jie, E-mail: leejay1986@163.com; Zhang, Jian

    2014-11-07

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet.

  6. A theoretical study of the spheroidal droplet evaporation in forced convection

    International Nuclear Information System (INIS)

    Li, Jie; Zhang, Jian

    2014-01-01

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet

  7. Grouping and trapping of evaporating droplets in an oscillating gas flow

    International Nuclear Information System (INIS)

    Katoshevski, David; Shakked, Tal; Sazhin, Sergei S.; Crua, Cyril; Heikal, Morgan R.

    2008-01-01

    A new approach to the analysis of droplet grouping in an oscillating gas flow is suggested. This is based on the investigation of droplet trajectories in the frame of reference moving with the phase velocity of the wave. Although the equations involved are relatively simple, the analysis shows distinctive characteristics of grouping and non-grouping cases. In the case of grouping, droplet trajectories converge to the points for which the ratio of flow velocity in this frame of reference and the amplitude of flow oscillations is less than 1, and the cosine of the arc sine of this ratio is positive. In the case of non-grouping, droplet trajectories in this frame of reference oscillate around the translational velocity close to the velocity of flow in the same frame of reference. The effect of droplet size on the grouping pattern is investigated. It has been pointed out that for the smaller droplets much more stable grouping is observed. The effect of droplet evaporation is studied in the limiting case when the contribution of the heat-up period can be ignored. It is shown that evaporation can lead to droplet grouping even in the case when the non-evaporating droplets are not grouped. This is related to the reduction in droplet diameter during the evaporation process. Coupling between gas and droplets is shown to decrease the grouping tendency. A qualitative agreement between predictions of the model and in-house experimental observations referring to Diesel engine sprays has been demonstrated

  8. Hot Surface Ignition of A Composite Fuel Droplet

    Directory of Open Access Journals (Sweden)

    Glushkov Dmitrii O.

    2015-01-01

    Full Text Available The present study examines the characteristics of conductive heating (up to ignition temperature of a composite fuel droplet based on coal, liquid petroleum products, and water. In this paper, we have established the difference between heat transfer from a heat source to a fuel droplet in case of conductive (hot surface and convective (hot gas heat supply. The Leidenfrost effect influences on heat transfer characteristics significantly due to the gas gap between a composite fuel droplet and a hot surface.

  9. Nanoparticle motion on the surface of drying droplets

    Science.gov (United States)

    Zhao, Mingfei; Yong, Xin

    2018-03-01

    Advances in solution-based printing and surface patterning techniques for additive manufacturing demand a clear understanding of particle dynamics in drying colloidal droplets and its relationship with deposit structure. Although the evaporation-driven deposition has been studied thoroughly for the particles dispersed in the bulk of the droplet, few investigations have focused on the particles strongly adsorbed to the droplet surface. We modeled the assembly and deposition of the surface-active particles in a drying sessile droplet with a pinned contact line by the multiphase lattice Boltzmann-Brownian dynamics method. The particle trajectory and its area density profile characterize the assembly dynamics and deposition pattern development during evaporation. While the bulk-dispersed particles continuously move to the contact line, forming the typical "coffee-ring" deposit, the interface-bound particles migrate first toward the apex and then to the contact line as the droplet dries out. To understand this unexpected behavior, we resolve the droplet velocity field both in the bulk and within the interfacial region. The simulation results agree well with the analytical solution for the Stokes flow inside an evaporating droplet. At different stages of evaporation, our study reveals that the competition between the tangential surface flow and the downward motion of the evaporating liquid-vapor interface governs the dynamics of the interface-bound particles. In particular, the interface displacement contributes to the particle motion toward the droplet apex in a short phase, while the outward advective flow prevails at the late stage of drying and carries the particles to the contact line. The final deposit of the surface-adsorbed particles exhibits a density enhancement at the center, in addition to a coffee ring. Despite its small influence on the final deposit in the present study, the distinct dynamics of surface-active particles due to the interfacial confinement

  10. Modeling of fuel vapor jet eruption induced by local droplet heating

    KAUST Repository

    Sim, Jaeheon

    2014-01-10

    The evaporation of a droplet by non-uniform heating is numerically investigated in order to understand the mechanism of the fuel-vapor jet eruption observed in the flame spread of a droplet array under microgravity condition. The phenomenon was believed to be mainly responsible for the enhanced flame spread rate through a droplet cloud at microgravity conditions. A modified Eulerian-Lagrangian method with a local phase change model is utilized to describe the interfacial dynamics between liquid droplet and surrounding air. It is found that the localized heating creates a temperature gradient along the droplet surface, induces the corresponding surface tension gradient, and thus develops an inner flow circulation commonly referred to as the Marangoni convection. Furthermore, the effect also produces a strong shear flow around the droplet surface, thereby pushing the fuel vapor toward the wake region of the droplet to form a vapor jet eruption. A parametric study clearly demonstrated that at realistic droplet combustion conditions the Marangoni effect is indeed responsible for the observed phenomena, in contrast to the results based on constant surface tension approximation

  11. Shape-Shifting Droplet Networks.

    Science.gov (United States)

    Zhang, T; Wan, Duanduan; Schwarz, J M; Bowick, M J

    2016-03-11

    We consider a three-dimensional network of aqueous droplets joined by single lipid bilayers to form a cohesive, tissuelike material. The droplets in these networks can be programed to have distinct osmolarities so that osmotic gradients generate internal stresses via local fluid flows to cause the network to change shape. We discover, using molecular dynamics simulations, a reversible folding-unfolding process by adding an osmotic interaction with the surrounding environment which necessarily evolves dynamically as the shape of the network changes. This discovery is the next important step towards osmotic robotics in this system. We also explore analytically and numerically how the networks become faceted via buckling and how quasi-one-dimensional networks become three dimensional.

  12. Droplet Traffic at a Simple Junction at Low Capillary Numbers

    Science.gov (United States)

    Engl, Wilfried; Roche, Matthieu; Colin, Annie; Panizza, Pascal; Ajdari, Armand

    2005-11-01

    We report that, when a train of confined droplets flowing through a channel reaches a junction, the droplets either are alternately distributed between the different outlets or all collect into the shortest one. We argue that this behavior is due to the hydrodynamic feedback of droplets in the different outlets on the selection process occurring at the junction. A “mean field” model, yielding semiquantitative results, offers a first guide to predict droplet traffic in branched networks.

  13. Cavitation-induced fragmentation of an acoustically-levitated droplet

    Science.gov (United States)

    Gonzalez Avila, Silvestre Roberto; Ohl, Claus-Dieter

    2015-12-01

    In this paper we investigate the initial sequence of events that lead to the fragmentation of a millimetre sized water droplets when interacting with a focused ns-laser pulse. The experimental results show complex processes that result from the reflection of an initial shock wave from plasma generation with the soft boundary of the levitating droplet; furthermore, when the reflected waves from the walls of the droplet refocus they leave behind a trail of microbubbles that later act as cavitation inception regions. Numerical simulations of a shock wave impacting and reflecting from a soft boundary are also reported; the simulated results show that the lowest pressure inside the droplet occurs at the equatorial plane. The results of the numerical model display good agreement with the experimental results both in time and in space.

  14. Cavitation-induced fragmentation of an acoustically-levitated droplet

    International Nuclear Information System (INIS)

    Avila, Silvestre Roberto Gonzalez; Ohl, Claus-Dieter

    2015-01-01

    In this paper we investigate the initial sequence of events that lead to the fragmentation of a millimetre sized water droplets when interacting with a focused ns-laser pulse. The experimental results show complex processes that result from the reflection of an initial shock wave from plasma generation with the soft boundary of the levitating droplet; furthermore, when the reflected waves from the walls of the droplet refocus they leave behind a trail of microbubbles that later act as cavitation inception regions. Numerical simulations of a shock wave impacting and reflecting from a soft boundary are also reported; the simulated results show that the lowest pressure inside the droplet occurs at the equatorial plane. The results of the numerical model display good agreement with the experimental results both in time and in space. (paper)

  15. Engineering Surfaces for Enhanced Nucleation and Droplet Removal During Dropwise Condensation

    Science.gov (United States)

    Dutta, Sanmitra; Khan, Sameera; Anand, Sushant

    2017-11-01

    Condensation plays critical role in numerous industrial applications, such as condensers, HVAC,etc In the most applications, fast formation (i.e. high nucleation) and subsequent removal of water droplets is critical for enhancing the efficiencies of their associated systems. Significant focus has been placed on the aspect of droplet removal from surfaces. This has led to, development of superhydrophobic surfaces with special textures on which droplets are self-removed after coalescence. However,because of their inherent low surface energy, nucleation energy barriers are also high on such surfaces. In contrast to conventional superhydrophobic surfaces, here we show that surfaces can be engineered such that the simultaneous benefits of high nucleation rates and fast droplet removal can be obtained during the condensation process.These benefits are obtained by impregnating a superhydrophobic surface with an oil that despite its defect-free interface provides low nucleation energy barrier during condensation. At the same time, the oil facilitates high droplet shedding rates by providing a lubricating layer below the droplets due to which droplets have negligible contact angle hysteresis. We provide a guide to choose oils that lead to enhanced nucleation, and provide experimental evidence supporting the proposed guide. We discuss the importance of different oil properties in affecting the droplet growth and subsequent removal of water droplets.

  16. Evolution, Development and Function of Vertebrate Cone Oil Droplets

    Directory of Open Access Journals (Sweden)

    Matthew B. Toomey

    2017-12-01

    Full Text Available To distinguish colors, the nervous system must compare the activity of distinct subtypes of photoreceptors that are maximally sensitive to different portions of the light spectrum. In vertebrates, a variety of adaptations have arisen to refine the spectral sensitivity of cone photoreceptors and improve color vision. In this review article, we focus on one such adaptation, the oil droplet, a unique optical organelle found within the inner segment of cone photoreceptors of a diverse array of vertebrate species, from fish to mammals. These droplets, which consist of neutral lipids and carotenoid pigments, are interposed in the path of light through the photoreceptor and modify the intensity and spectrum of light reaching the photosensitive outer segment. In the course of evolution, the optical function of oil droplets has been fine-tuned through changes in carotenoid content. Species active in dim light reduce or eliminate carotenoids to enhance sensitivity, whereas species active in bright light precisely modulate carotenoid double bond conjugation and concentration among cone subtypes to optimize color discrimination and color constancy. Cone oil droplets have sparked the curiosity of vision scientists for more than a century. Accordingly, we begin by briefly reviewing the history of research on oil droplets. We then discuss what is known about the developmental origins of oil droplets. Next, we describe recent advances in understanding the function of oil droplets based on biochemical and optical analyses. Finally, we survey the occurrence and properties of oil droplets across the diversity of vertebrate species and discuss what these patterns indicate about the evolutionary history and function of this intriguing organelle.

  17. Thermocapillary droplet actuation on structured solid surfaces

    Science.gov (United States)

    Karapetsas, George; Chamakos, Nikolaos T.; Papathanasiou, Athanasios G.

    2017-11-01

    The present work investigates, through 2D and 3D finite element simulations, the thermocapillary-driven flow inside a droplet which resides on a non-uniformly heated patterned surface. We employ a recently proposed sharp-interface scheme capable of efficiently modelling the flow over complicate surfaces and consider a wide range of substrate wettabilities, i.e. from hydrophilic to super-hydrophobic surfaces. Our simulations indicate that due to the presence of the solid structures and the induced effect of contact angle hysteresis, inherently predicted by our model, a critical thermal gradient arises beyond which droplet migration is possible, in line with previous experimental observations. The migration velocity as well as the direction of motion depends on the combined action of the net mechanical force along the contact line and the thermocapillary induced flow at the liquid-air interface. We also show that through a proper control and design of the substrate wettability, the contact angle hysteresis and the induced flow field it is possible to manipulate the droplet dynamics, e.g. controlling its motion along a predefined track or entrapping by a wetting defect a droplet based on its size as well as providing appropriate conditions for enhanced mixing inside the droplet. Funding from the European Research Council under the Europeans Community's Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement no. [240710] is acknowledged.

  18. Structural Transitions in Cholesteric Liquid Crystal Droplets

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ye; Bukusoglu, Emre; Martínez-González, José A.; Rahimi, Mohammad; Roberts, Tyler F.; Zhang, Rui; Wang, Xiaoguang; Abbott, Nicholas L.; de Pablo, Juan J.

    2016-07-26

    Confinement of cholesteric liquid crystals (ChLC) into droplets leads to a delicate interplay between elasticity, chirality, and surface energy. In this work, we rely on a combination of theory and experiments to understand the rich morphological behavior that arises from that balance. More specifically, a systematic study of micrometer-sized ChLC droplets is presented as a function of chirality and surface energy (or anchoring). With increasing chirality, a continuous transition is observed from a twisted bipolar structure to a radial spherical structure, all within a narrow range of chirality. During such a transition, a bent structure is predicted by simulations and confirmed by experimental observations. Simulations are also able to capture the dynamics of the quenching process observed in experiments. Consistent with published work, it is found that nanoparticles are attracted to defect regions on the surface of the droplets. For weak anchoring conditions at the nanoparticle surface, ChLC droplets adopt a morphology similar to that of the equilibrium helical phase observed for ChLCs in the bulk. As the anchoring strength increases, a planar bipolar structure arises, followed by a morphological transition to a bent structure. The influence of chirality and surface interactions are discussed in the context of the potential use of ChLC droplets as stimuli-responsive materials for reporting molecular adsorbates.

  19. Magnetically tunable oil droplet lens of deep-sea shrimp

    Science.gov (United States)

    Iwasaka, M.; Hirota, N.; Oba, Y.

    2018-05-01

    In this study, the tunable properties of a bio-lens from a deep-sea shrimp were investigated for the first time using magnetic fields. The skin of the shrimp exhibited a brilliantly colored reflection of incident white light. The light reflecting parts and the oil droplets in the shrimp's skin were observed in a glass slide sample cell using a digital microscope that operated in the bore of two superconducting magnets (maximum strengths of 5 and 13 T). In the ventral skin of the shrimp, which contained many oil droplets, some comparatively large oil droplets (50 to 150 μm in diameter) were present. A distinct response to magnetic fields was found in these large oil droplets. Further, the application of the magnetic fields to the sample cell caused a change in the size of the oil droplets. The phenomena observed in this work indicate that the oil droplets of deep sea shrimp can act as lenses in which the optical focusing can be modified via the application of external magnetic fields. The results of this study will make it possible to fabricate bio-inspired soft optical devices in future.

  20. Systems of mechanized and reactive droplets powered by multi-responsive surfactants

    Science.gov (United States)

    Yang, Zhijie; Wei, Jingjing; Sobolev, Yaroslav I.; Grzybowski, Bartosz A.

    2018-01-01

    Although ‘active’ surfactants, which are responsive to individual external stimuli such as temperature, electric or magnetic fields, light, redox processes or chemical agents, are well known, it would be interesting to combine several of these properties within one surfactant species. Such multi-responsive surfactants could provide ways of manipulating individual droplets and possibly assembling them into larger systems of dynamic reactors. Here we describe surfactants based on functionalized nanoparticle dimers that combine all of these and several other characteristics. These surfactants and therefore the droplets that they cover are simultaneously addressable by magnetic, optical and electric fields. As a result, the surfactant-covered droplets can be assembled into various hierarchical structures, including dynamic ones, in which light powers the rapid rotation of the droplets. Such rotating droplets can transfer mechanical torques to their non-nearest neighbours, thus acting like systems of mechanical gears. Furthermore, droplets of different types can be merged by applying electric fields and, owing to interfacial jamming, can form complex, non-spherical, ‘patchy’ structures with different surface regions covered with different surfactants. In systems of droplets that carry different chemicals, combinations of multiple stimuli can be used to control the orientations of the droplets, inter-droplet transport, mixing of contents and, ultimately, sequences of chemical reactions. Overall, the multi-responsive active surfactants that we describe provide an unprecedented level of flexibility with which liquid droplets can be manipulated, assembled and reacted.

  1. Rayleigh Instability-Assisted Satellite Droplets Elimination in Inkjet Printing.

    Science.gov (United States)

    Yang, Qiang; Li, Huizeng; Li, Mingzhu; Li, Yanan; Chen, Shuoran; Bao, Bin; Song, Yanlin

    2017-11-29

    Elimination of satellite droplets in inkjet printing has long been desired for high-resolution and precision printing of functional materials and tissues. Generally, the strategy to suppress satellite droplets is to control ink properties, such as viscosity or surface tension, to assist ink filaments in retracting into one drop. However, this strategy brings new restrictions to the ink, such as ink viscosity, surface tension, and concentration. Here, we report an alternative strategy that the satellite droplets are eliminated by enhancing Rayleigh instability of filament at the break point to accelerate pinch-off of the droplet from the nozzle. A superhydrophobic and ultralow adhesive nozzle with cone morphology exhibits the capability to eliminate satellite droplets by cutting the ink filament at breakup point effectively. As a result, the nozzles with different sizes (10-80 μm) are able to print more inks (1 printing electronics and biotechnologies.

  2. Dynamic interactions of Leidenfrost droplets on liquid metal surface

    Science.gov (United States)

    Ding, Yujie; Liu, Jing

    2016-09-01

    Leidenfrost dynamic interaction effects of the isopentane droplets on the surface of heated liquid metal were disclosed. Unlike conventional rigid metal, such conductive and deformable liquid metal surface enables the levitating droplets to demonstrate rather abundant and complex dynamics. The Leidenfrost droplets at different diameters present diverse morphologies and behaviors like rotation and oscillation. Depending on the distance between the evaporating droplets, they attract and repulse each other through the curved surfaces beneath them and their vapor flows. With high boiling point up to 2000 °C, liquid metal offers a unique platform for testing the evaporating properties of a wide variety of liquid even solid.

  3. Mechanism of Supercooled Water Droplet Breakup near the Leading Edge of an Airfoil

    Science.gov (United States)

    Veras-Alba, Belen; Palacios, Jose; Vargas, Mario; Ruggeri, Charles; Bartkus, Tadas P.

    2017-01-01

    This work presents the results of an experimental study on supercooled droplet deformation and breakup near the leading edge of an airfoil. The results are compared to prior room temperature droplet deformation results to explore the effects of droplet supercooling. The experiments were conducted in the Adverse Environment Rotor Test Stand (AERTS) at The Pennsylvania State University. An airfoil model placed at the end of the rotor blades mounted onto the hub in the AERTS chamber was moved at speeds ranging between 50 and 80 m/sec. The temperature of the chamber was set at -20°C. A monotonic droplet generator was used to produce droplets that fell from above, perpendicular to the path of the airfoil. The supercooled state of the droplets was determined by measurement of the temperature of the drops at various locations below the droplet generator exit. A temperature prediction code was also used to estimate the temperature of the droplets based on vertical velocity and the distance traveled by droplets from the droplet generator to the airfoil stagnation line. High speed imaging was employed to observe the interaction between the droplets and the airfoil. The high speed imaging provided droplet deformation information as the droplet approached the airfoil near the stagnation line. A tracking software program was used to measure the horizontal and vertical displacement of the droplet against time. It was demonstrated that to compare the effects of water supercooling on droplet deformation, the ratio of the slip velocity and the initial droplet velocity must be equal. A case with equal slip velocity to initial velocity ratios was selected for room temperature and supercooled droplet conditions. The airfoil velocity was 60 m/s and the slip velocity for both sets of data was 40 m/s. In these cases, the deformation of the weakly supercooled and warm droplets did not present different trends. The similar behavior for both environmental conditions indicates that water

  4. Numerical simulation of droplet formation regimes and sizes in microfluidic T-junction devices

    Science.gov (United States)

    Nekouei, Mehdi; Vanapalli, Siva

    2014-11-01

    The T-junction geometry has been widely used for producing monodisperse droplets in microfluidic devices. Droplet formation regimes and sizes are expected to depend on a variety of conditions including flow rates, capillary number, channel geometry and viscosity ratio. Experiments have investigated drop production at a T-junction in a narrow control parameter space and developed analytical models for specific operating regimes. In this study, we take advantage of numerical simulations based on volume-of-fluid method to explore this broad parameter space systematically, and contrast our results with prior experimental data. We find our simulations predict well the regimes of squeezing, dripping and jetting. We also observe that our drop size data is in good agreement with three different experimental reports. Although our results match experimental data, the analytical models do not agree with each other since they are based on specific operating conditions. We use numerical simulations to elucidate the missing components in the physics of drop formation at a T-junction, with an attempt to reconcile existing analytical models.

  5. Droplet rotation model apply in steam uniform flow and gravitational field

    International Nuclear Information System (INIS)

    Zhang Jinyi; Bo Hanliang; Sun Yuliang; Wang Dazhong

    2012-01-01

    The mechanism droplet movement behavior and the qualitative description of droplet trajectory in the steam uniform flow field in the gravitational field were researched with droplet rotation model. According to the mechanism of gravitational field and uniform flow fields, the effects on droplets movement were analyzed and the importance of lift forces was also discussed. Finally, a general trajectory and mechanism of the droplets movement was derived which lays the groundwork for the qualitative analysis of the single-drop model and could be general enough to be used in many applications. (authors)

  6. Printing microstructures in a polymer matrix using a ferrofluid droplet

    International Nuclear Information System (INIS)

    Abdel Fattah, Abdel Rahman; Ghosh, Suvojit; Puri, Ishwar K.

    2016-01-01

    We print complex curvilinear microstructures in an elastomer matrix using a ferrofluid droplet as the print head. A magnetic field moves the droplet along a prescribed path in liquid polydimethylsiloxane (PDMS). The droplet sheds magnetic nanoparticle (MNP) clusters in its wake, forming printed features. The PDMS is subsequently heated so that it crosslinks, which preserves the printed features in the elastomer matrix. The competition between magnetic and drag forces experienced by the ferrofluid droplet and its trailing MNPs highlight design criteria for successful printing, which are experimentally confirmed. The method promises new applications, such as flexible 3D circuitry. - Highlights: • Magnetically guided miscible ferrofluid droplets print 3D patterns in a polymer. • Printing mechanism depends on the dynamics between the fluid and magnetic forces. • Droplet size influences the width of the printed trail. • The Colloidal distribution of the ferrofluid is important for pattern integrity. • Particle trajectories and trails are simulated and validated through experiments.

  7. Droplet Impact on a Heated Surface under a Depressurized Environment

    Science.gov (United States)

    Hatakenaka, Ryuta; Tagawa, Yoshiyuki

    2016-11-01

    Behavior of a water droplet of the diameter 1-3mm impacting on a heated surface under depressurized environment (100kPa -1kPa) has been studied. A syringe pump for droplet generation and a heated plate are set into a transparent acrylic vacuum chamber. The internal pressure of the chamber is automatically controlled at a target pressure with a rotary pump, a pressure transducer, and an electrical valve. A silicon wafer of the thickness 0.28 mm is mounted on the heater plate, whose temperature is directly measured by attaching a thermocouple on the backside. The droplet behavior is captured using a high-speed camera in a direction perpendicular to droplet velocity. Some unique behaviors of droplet are observed by decreasing the environmental pressure, which are considered to be due to two basic elements: Enhancement of evaporation due to the lowered saturation temperature, and shortage of pneumatic spring effect between the droplet and heated wall due to the lowered pressure of the air.

  8. Printing microstructures in a polymer matrix using a ferrofluid droplet

    Energy Technology Data Exchange (ETDEWEB)

    Abdel Fattah, Abdel Rahman [Department of Mechanical Engineering, Hamilton, Ontario (Canada); Ghosh, Suvojit [Department of Engineering Physics, McMaster University, Hamilton, Ontario (Canada); Puri, Ishwar K. [Department of Mechanical Engineering, Hamilton, Ontario (Canada); Department of Engineering Physics, McMaster University, Hamilton, Ontario (Canada)

    2016-03-01

    We print complex curvilinear microstructures in an elastomer matrix using a ferrofluid droplet as the print head. A magnetic field moves the droplet along a prescribed path in liquid polydimethylsiloxane (PDMS). The droplet sheds magnetic nanoparticle (MNP) clusters in its wake, forming printed features. The PDMS is subsequently heated so that it crosslinks, which preserves the printed features in the elastomer matrix. The competition between magnetic and drag forces experienced by the ferrofluid droplet and its trailing MNPs highlight design criteria for successful printing, which are experimentally confirmed. The method promises new applications, such as flexible 3D circuitry. - Highlights: • Magnetically guided miscible ferrofluid droplets print 3D patterns in a polymer. • Printing mechanism depends on the dynamics between the fluid and magnetic forces. • Droplet size influences the width of the printed trail. • The Colloidal distribution of the ferrofluid is important for pattern integrity. • Particle trajectories and trails are simulated and validated through experiments.

  9. Metabolite profiling of microfluidic cell culture conditions for droplet based screening

    DEFF Research Database (Denmark)

    Björk, Sara M.; Sjoström, Staffan L.; Svahn, Helene Andersson

    2015-01-01

    We investigate the impact of droplet culture conditions on cell metabolic state by determining key metabolite concentrations in S. cerevisiae cultures in different microfluidic droplet culture formats. Control of culture conditions is critical for single cell/clone screening in droplets......, such as directed evolution of yeast, as cell metabolic state directly affects production yields from cell factories. Here, we analyze glucose, pyruvate, ethanol, and glycerol, central metabolites in yeast glucose dissimilation to establish culture formats for screening of respiring as well as fermenting yeast...... limited cultures, whereas the metabolite profiles of cells cultured in the alternative wide tube droplet incubation format resemble those from aerobic culture. Furthermore, we demonstrate retained droplet stability and size in the new better oxygenated droplet incubation format....

  10. Numerical and experimental studies of droplet-gas flow

    Energy Technology Data Exchange (ETDEWEB)

    Joesang, Aage Ingebret

    2002-07-01

    This thesis considers droplet-gas flow by the use of numerical methods and experimental verification. A commercial vane separator was studied both numerical and by experiment. In addition some efforts are put into the numerical analysis of cyclones. The experimental part contains detailed measurements of the flow field between a pair of vanes in a vane separator and droplet size measurements. LDA (Laser Doppler Anemometry) was used to measure the velocity in two dimensions and corresponding turbulence quantities. The results from the LDA measurements are considered to be of high quality and are compared to numerical results obtained from a CFD (Computational Fluid Dynamics) analysis. The simulation showed good agreement between the numerical and experimental results. Combinations of different turbulence models; the standard k-epsilon model and the Reynold Stress Mode, different schemes; first order and higher order scheme and different near wall treatment of the turbulence; the Law of the wall and the Two-Layer Zonal model were used in the simulations. The Reynold Stress Model together with a higher order scheme performed rather poorly. The recirculation in parts of the separator was overpredicted in this case. For the other cases the overall predictions are satisfactory. PDA (Phase Doppler Anemometry) measurements were used to study the changes in the droplet size distribution through the vane separator. The PDA measurements show that smaller droplets are found at the outlet than present at the inlet. In the literature there exists different mechanisms for explaining the re-entrainment and generation of new droplets. The re-entrainments mechanisms are divided into four groups where droplet-droplet interaction, droplet break-up, splashing of impinging droplet and re-entrainment from the film are defined as the groups of re-entrainment mechanisms. Models for these groups are found in the literature and these models are tested for re-entrainment using the operational

  11. Computational/experimental studies of isolated, single component droplet combustion

    Science.gov (United States)

    Dryer, Frederick L.

    1993-01-01

    Isolated droplet combustion processes have been the subject of extensive experimental and theoretical investigations for nearly 40 years. The gross features of droplet burning are qualitatively embodied by simple theories and are relatively well understood. However, there remain significant aspects of droplet burning, particularly its dynamics, for which additional basic knowledge is needed for thorough interpretations and quantitative explanations of transient phenomena. Spherically-symmetric droplet combustion, which can only be approximated under conditions of both low Reynolds and Grashof numbers, represents the simplest geometrical configuration in which to study the coupled chemical/transport processes inherent within non-premixed flames. The research summarized here, concerns recent results on isolated, single component, droplet combustion under microgravity conditions, a program pursued jointly with F.A. Williams of the University of California, San Diego. The overall program involves developing and applying experimental methods to study the burning of isolated, single component droplets, in various atmospheres, primarily at atmospheric pressure and below, in both drop towers and aboard space-based platforms such as the Space Shuttle or Space Station. Both computational methods and asymptotic methods, the latter pursued mainly at UCSD, are used in developing the experimental test matrix, in analyzing results, and for extending theoretical understanding. Methanol, and the normal alkanes, n-heptane, and n-decane, have been selected as test fuels to study time-dependent droplet burning phenomena. The following sections summarizes the Princeton efforts on this program, describe work in progress, and briefly delineate future research directions.

  12. Bioprinting: Functional droplet networks

    Science.gov (United States)

    Durmus, Naside Gozde; Tasoglu, Savas; Demirci, Utkan

    2013-06-01

    Tissue-mimicking printed networks of droplets separated by lipid bilayers that can be functionalized with membrane proteins are able to spontaneously fold and transmit electrical currents along predefined paths.

  13. Encapsulation of emulsion droplets by organo–silica shells

    NARCIS (Netherlands)

    Zoldesi, C.; Steegstra, Patrick; Imhof, Arnout

    2007-01-01

    Surfactant-stabilized emulsion droplets were used as templates for the synthesis of hollow colloidal particles. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysiloxane monomer, in the presence of surfactant: sodium dodecyl sulphate (SDS, anionic)

  14. Annealing temperature effect on self-assembled Au droplets on Si (111).

    Science.gov (United States)

    Sui, Mao; Li, Ming-Yu; Kim, Eun-Soo; Lee, Jihoon

    2013-12-13

    We investigate the effect of annealing temperature on self-assembled Au droplets on Si (111). The annealing temperature is systematically varied while fixing other growth parameters such as deposition amount and annealing duration clearly to observe the annealing temperature effect. Self-assembled Au droplets are fabricated by annealing from 50°C to 850°C with 2-nm Au deposition for 30 s. With increased annealing temperatures, Au droplets show gradually increased height and diameter while the density of droplets progressively decreases. Self-assembled Au droplets with fine uniformity can be fabricated between 550°C and 800°C. While Au droplets become much larger with increased deposition amount, the extended annealing duration only mildly affects droplet size and density. The results are systematically analyzed with cross-sectional line profiles, Fourier filter transform power spectra, height histogram, surface area ratio, and size and density plots. This study can provide an aid point for the fabrication of nanowires on Si (111).

  15. Continuous growth of cloud droplets in cumulus cloud

    International Nuclear Information System (INIS)

    Gotoh, Toshiyuki; Suehiro, Tamotsu; Saito, Izumi

    2016-01-01

    A new method to seamlessly simulate the continuous growth of droplets advected by turbulent flow inside a cumulus cloud was developed from first principle. A cubic box ascending with a mean updraft inside a cumulus cloud was introduced and the updraft velocity was self-consistently determined in such a way that the mean turbulent velocity within the box vanished. All the degrees of freedom of the cloud droplets and turbulence fields were numerically integrated. The box ascended quickly inside the cumulus cloud due to the updraft and the mean radius of the droplets grew from 10 to 24 μ m for about 10 min. The turbulent flow tended to slow down the time evolutions of the updraft velocity, the box altitude and the mean cloud droplet radius. The size distribution of the cloud droplets in the updraft case was narrower than in the absence of the updraft. It was also found that the wavenumeber spectra of the variances of the temperature and water vapor mixing ratio were nearly constant in the low wavenumber range. The future development of the new method was argued. (paper)

  16. DNS of droplet motion in a turbulent flow

    Science.gov (United States)

    Rosso, Michele; Elghobashi, S.

    2013-11-01

    The objective of our research is to study the multi-way interactions between turbulence and vaporizing liquid droplets by performing direct numerical simulations (DNS). The freely-moving droplets are fully resolved in 3D space and time and all the relevant scales of the turbulent motion are simultaneously resolved down to the smallest length- and time-scales. Our DNS solve the unsteady three-dimensional Navier-Stokes and continuity equations throughout the whole computational domain, including the interior of the liquid droplets. The droplet surface motion and deformation are captured accurately by using the Level Set method. The pressure jump condition, density and viscosity discontinuities across the interface as well as surface tension are accounted for. Here, we present only the results of the first stage of our research which considers the effects of turbulence on the shape change of an initially spherical liquid droplet, at density ratio (of liquid to carrier fluid) of 1000, moving in isotropic turbulent flow. We validate our results via comparison with available expe. This research has been supported by NSF-CBET Award 0933085 and NSF PRAC (Petascale Computing Resource Allocation) Award.

  17. Comparison between sprinkler irrigation and natural rainfall based on droplet diameter

    Energy Technology Data Exchange (ETDEWEB)

    Ge, M.S.; Wu, P.; Zhu, D.; Ames, D.P.

    2016-11-01

    An indoor experiment was conducted to analyze the movement characteristics of different sized droplets and their influence on water application rate distribution and kinetic energy distribution. Radial droplets emitted from a Nelson D3000 sprinkler nozzle under 66.3, 84.8, and 103.3 kPa were measured in terms of droplet velocity, landing angle, and droplet kinetic energy and results were compared to natural rainfall characteristics. Results indicate that sprinkler irrigation droplet landing velocity for all sizes of droplets is not related to nozzle pressure and the values of landing velocity are very close to that of natural rainfall. The velocity horizontal component increases with radial distance while the velocity vertical component decreases with radial distance. Additionally, landing angle of all droplet sizes decreases with radial distance. The kinetic energy is decomposed into vertical component and horizontal component due to the oblique angles of droplet impact on the surface soil, and this may aggravate soil erosion. Therefore the actual oblique angle of impact should be considered in actual field conditions and measures should be taken for remediation of soil erosion if necessary. (Author)

  18. Transport mechanism of an initially spherical droplet on a combined hydrophilic/hydrophobic surface

    Energy Technology Data Exchange (ETDEWEB)

    Myong, Hyon Kook; Kwon, Young Hoo [Dept. of Mechanical Engineering, Kookmin University, Seoul (Korea, Republic of)

    2015-11-15

    Fluid transport is a key issue in the development of microfluidic systems. Recently, Myong (2014) has proposed a new concept for droplet transport without external power sources, and numerically validated the results for a hypothetical 2D shape, initially having a hemicylindrical droplet shape. Myong and Kwon (2015) have also examined the transport mechanism for an actual water droplet, initially having a 3D hemispherical shape, on a horizontal hydrophilic/hydrophobic surface, based on the numerical results of the time evolution of the droplet shape, as well as the total kinetic, gravitational, pressure and surface free energies inside the droplet. In this study, a 3D numerical analysis of an initially spherical droplet is carried out to establish a new concept for droplet transport. Further, the transport mechanism of an actual water droplet is examined in detail from the viewpoint of the capillarity force imbalance through the numerical results of droplet shape and various energies inside the droplet.

  19. Droplet deposition above a quench front during reflood after a large break LOCA

    International Nuclear Information System (INIS)

    Lee, R.

    1982-01-01

    Droplet deposition or migration towards the wall in a dispersed flow has been the subject of many investigations due to its industrial applications such as combustion of sprays of liquid fuel, evaporators, spray cooling, nuclear reactors, etc. Dispersed flow is characterized by high void and hence low droplet concentration and the theoretical study of droplet deposition is the treatment of a single droplet trajectory in the dispersed. As the droplet is travelling towards the wall, whether it will eventually be deposited on the wall or not, will be determined by the competing forces acting on it and by the boundary layer it is traversing through towards the wall. The mechanism of droplet deposition will be examined. The prediction of the boundary layer thickness will take into account the droplet size and density difference between the fluid and the droplet. Given the condition above the quench front, the minimum lateral velocity required for droplet deposition could be determined as a function of droplet diameter

  20. Response of Superheated Droplet Detector (SDD) and Bubble Detector (BD) to interrupted irradiations

    Energy Technology Data Exchange (ETDEWEB)

    Mondal, Prasanna Kumar, E-mail: prasanna_ind_82@yahoo.com; Sarkar, Rupa, E-mail: sarkar_rupa2003@yahoo.com; Chatterjee, Barun Kumar, E-mail: barun_k_chatterjee@yahoo.com

    2017-06-11

    Superheated droplet detectors (SDD) and bubble detectors (BD) are suspensions of micron-sized superheated liquid droplets in inert medium. The metastable droplets can vaporise upon interaction with ionising radiation generating visible bubbles. In this work, we investigated the response of SDD and BD to interrupted neutron irradiations. We observed that the droplet vaporisation rates for SDD and BD are different in nature. The unusual increase in droplet vaporisation rate observed when the SDD is exposed to neutrons after few minutes of radiation-off period is absent for BD. - Highlights: • Superheated droplet detectors (SDD) and bubble detectors (BD) are suspensions of superheated liquid droplets in inert medium. • The bubble nucleation in superheated droplets can be induced by ionising radiation. • The droplet vaporisation rate for SDD is non-monotonic when it is irradiated periodically to neutrons. • For BD the droplet vaporisation rate decrease monotonically when it is irradiated periodically to neutrons.

  1. Recent Advances In Science Support For Isolated Droplet Combustion Experiments

    Science.gov (United States)

    Dryer, F. L.; Kazakov, A.; Urban, B. D.; Kroenlein, K.

    2003-01-01

    In a joint program involving Prof. F.A. Williams of the University of California, San Diego and Dr. V. Nayagam of the National Center for Microgravity Research, the combustion characteristics of isolated liquid fuel droplets of n-heptane, n-decane, methanol, methanol-water, ethanol and ethanol-water having initial diameters between about 1 mm and 6 mm continues to be investigated. The objectives of the work are to improve fundamental knowledge of droplet combustion dynamics for pure fuels and fuel-water mixtures through microgravity experiments and theoretical analyses. The Princeton contributions support the engineering design, data analysis, and data interpretation requirements for the study of initially single component, spherically symmetric, isolated droplet combustion studies through experiments and numerical modeling. UCSD contributions are described in a companion communication in this conference. The Princeton effort also addresses the analyses of Fiber Supported Droplet Combustion (FSDC) experiments conducted with the above fuels and collaborative work with others who are investigating droplet combustion in the presence of steady convection. A thorough interpretation of droplet burning behavior for n-heptane and n-decane over a relatively wide range of conditions also involves the influences of sooting on the combustion behavior, and this particular aspect on isolated burning of droplets is under consideration in a collaborative program underway with Drexel University. This collaboration is addressed in another communication at this conference. The one-dimensional, time-dependent, numerical modeling approach that we have continued to evolve for analyzing isolated, quiescent droplet combustion data has been further applied to investigate several facets of isolated droplet burning of simple alcohols, n-heptane, and n-decane. Some of the new results are described below.

  2. Model of a liquid droplet impinging on a high-temperature solid surface

    International Nuclear Information System (INIS)

    Gulikov, A.V.; Berlin, I.I.; Karpyshev, A.V.

    2004-01-01

    The model of the collision of the liquid droplet, vertically falling on the heated solid surface, is presented. The wall temperature is predeterminated so that the droplet interaction with the wall proceeds through the gas interlayer (T≥400 Deg C). The droplet liquid is incompressible, nonviscous. The droplet surface is assigned as free one. The pressure is composed of two components. The first component is the surface tension. The record component is the steam pressure between the droplet and the wall. The liquid motion inside the droplet is assumed to be potential, axisymmetric. The calculation of the droplet collision are carried out with application of the above model. The obtained results are compared with the data of other authors [ru

  3. Droplet activation, separation, and compositional analysis: laboratory studies and atmospheric measurements

    Science.gov (United States)

    Hiranuma, N.; Kohn, M.; Pekour, M. S.; Nelson, D. A.; Shilling, J. E.; Cziczo, D. J.

    2011-10-01

    Droplets produced in a cloud condensation nuclei chamber (CCNC) as a function of supersaturation have been separated from unactivated aerosol particles using counterflow virtual impaction. Residual material after droplets were evaporated was chemically analyzed with an Aerodyne Aerosol Mass Spectrometer (AMS) and the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Experiments were initially conducted to verify activation conditions for monodisperse ammonium sulfate particles and to determine the resulting droplet size distribution as a function of supersaturation. Based on the observed droplet size, the counterflow virtual impactor cut-size was set to differentiate droplets from unactivated interstitial particles. Validation experiments were then performed to verify that only droplets with sufficient size passed through the counterflow virtual impactor for subsequent analysis. A two-component external mixture of monodisperse particles was also exposed to a supersaturation which would activate one of the types (hygroscopic salts) but not the other (polystyrene latex spheres or adipic acid). The mass spectrum observed after separation indicated only the former, validating separation of droplets from unactivated particles. Results from ambient measurements using this technique and AMS analysis were inconclusive, showing little chemical differentiation between ambient aerosol and activated droplet residuals, largely due to low signal levels. When employing as single particle mass spectrometer for compositional analysis, however, we observed enhancement of sulfate in droplet residuals.

  4. Dynamic behaviour of natural oil droplets through the water column in deep-water environment: the case of the Lower Congo Basin

    Science.gov (United States)

    Jatiault, R.; Dhont, D.; Loncke, L.; Durrieu De Madron, X.; Dubucq, D.; Channelliere, C.; Bourrin, F.

    2017-12-01

    Key words: Hydrocarbon seepage, Oil Slick, Lower Congo Basin, Underwater deflection, Deep-water Pockmark, Ascent speedThe space-borne imagery provides a significant means to locate active oil seeps and to estimate the expelled volume in the marine environment. The analysis of numerous overlapping satellite images revealed an abundant volume of 4400 m3 of oil naturally reaching the sea surface per year, expelled from more than a hundred seep sites through the Lower Congo Basin. The active seepage area is located in the distal compressional province of the basin where salt napes and squeezed diapirs. The integration of current data was used to link accurately sea surface manifestations of natural oil leakages with active fluid flow features on the seafloor. A mooring with ADCPs (Acoustic Doppler Current Profilers) distributed throughout the water column provided an efficient calibration tool to evaluate the horizontal deflection of oil droplets. Using a Eulerian propagation model that considered a range of probable ascent speeds, we estimated the oil migration pathways through the water column using two different approaches. The first approach consisted in simulating the backwards trajectory of oil droplets using sea surface oil slicks locations and concomitant current measurements. The second method analyzed the spatial spreading of the surfacing signatures of natural oil slicks based on 21 years of satellite observations. The location of the surfacing points of oil droplets at the sea surface is restricted to a circle of 2.5 km radius around the release point at the seafloor. Both approaches provided a range of ascent speeds of oil droplets between 3 to 8 cm.s-1. The low deflection values validate the near-vertical links between the average surfacing area of oil slicks at the sea surface with specific seafloor disturbances (i.e. pockmarks or mounds) known to expel fluids.

  5. Experiments on melt droplets falling into a water pool

    Energy Technology Data Exchange (ETDEWEB)

    Okkonen, T.; Sehgal, B.R. [Royal Inst. of Tech., Stockholm (Sweden). Div. of Nuclear Power Safety

    1998-01-01

    This paper presents experimental data and analysis related to melt droplets falling into a water pool. A binary CaO-B{sub 2}O{sub 3} melt mixture is used to study the influence of melt superheat and water subcooling on droplet deformation and fragmentation. For the conditions studied (We {<=} 1000), the surface tension of the melt droplet and the film boiling stability greatly affect the fragmentation behaviour. If the melt temperature is between the liquidus and solidus point (mushy zone) or if the film boiling is stable due to a relatively low subcooling, the droplet deformation and fragmentation are mitigated. This behaviour can be related to the effective Weber number (We) of the melt droplet upon entry into the water pool. Similar phenomena can be expected also for interactions of corium (UO{sub 2}-ZrO{sub 2}) and water, which are characterized by a potentially fast transformation of melt into the mushy zone and by particularly stable film boiling. (author)

  6. Composition measurements of binary mixture droplets by rainbow refractometry.

    Science.gov (United States)

    Wilms, J; Weigand, B

    2007-04-10

    So far, refractive index measurements by rainbow refractometry have been used to determine the temperature of single droplets and ensembles of droplets. Rainbow refractometry is, for the first time, to the best of our knowledge, applied to measure composition histories of evaporating, binary mixture droplets. An evaluation method is presented that makes use of Airy theory and the simultaneous size measurement by Mie scattering imaging. The method further includes an empirical correction function for a certain diameter and refractive index range. The measurement uncertainty was investigated by numerical simulations with Lorenz-Mie theory. For the experiments, an optical levitation setup was used allowing for long measurement periods. Temperature measurements of single-component droplets at different temperature levels are shown to demonstrate the accuracy of rainbow refractometry. Measurements of size and composition histories of binary mixture droplets are presented for two different mixtures. Experimental results show good agreement with numerical results using a rapid-mixing model.

  7. Composition measurements of binary mixture droplets by rainbow refractometry

    International Nuclear Information System (INIS)

    Wilms, J.; Weigand, B.

    2007-01-01

    So far, refractive index measurements by rainbow refractometry have been used to determine the temperature of single droplets and ensembles of droplets. Rainbow refractometry is, for the first time, to the best of our knowledge, applied to measure composition histories of evaporating, binary mixture droplets. An evaluation method is presented that makes use of Airy theory and the simultaneous size measurement by Mie scattering imaging. The method further includes an empirical correction function for a certain diameter and refractive index range. The measurement uncertainty was investigated by numerical simulations with Lorenz-Mie theory. For the experiments, an optical levitation setup was used allowing for long measurement periods. Temperature measurements of single-component droplets at different temperature levels are shown to demonstrate the accuracy of rainbow refractometry. Measurements of size and composition histories of binary mixture droplets are presented for two different mixtures. Experimental results show good agreement with numerical results using a rapid-mixing model

  8. On the origin of surface imposed anisotropic growth of salicylic and acetylsalicylic acids crystals during droplet evaporation

    OpenAIRE

    Przybyłek, Maciej; Cysewski, Piotr; Pawelec, Maciej; Ziółkowska, Dorota; Kobierski, Mirosław

    2018-01-01

    In this paper droplet evaporative crystallization of salicylic acid (SA) and acetylsalicylic acid (ASA) crystals on different surfaces, such as glass, polyvinyl alcohol (PVA), and paraffin was studied. The obtained crystals were analyzed using powder X-ray diffraction (PXRD) technique. In order to better understand the effect of the surface on evaporative crystallization, crystals deposited on glass were scraped off. Moreover, evaporative crystallization of a large volume of solution was perf...

  9. Amalgamation of Chlamydia pneumoniae inclusions with lipid droplets in foam cells in human atherosclerotic plaque.

    Science.gov (United States)

    Bobryshev, Yuri V; Killingsworth, Murray C; Tran, Dihn; Lord, Reginald

    2008-07-01

    Chlamydia pneumoniae (Chlamydophila pneumoniae) infect macrophages and accelerates foam cell formation in in vitro experiments, but whether this might occur in human atherosclerosis is unknown. In the present study, we examined 17 carotid artery segments, obtained by endarterectomy, in which the presence of C. pneumoniae was confirmed by both polymerase chain reaction and immunohistochemistry. Electron microscopy demonstrated the presence of structures with the appearance of elementary, reticulate and aberrant bodies of C. pneumoniae in the cytoplasm of macrophage foam cells. The volume of the cytoplasm that was free from vacuoles and lipid droplets in C. pneumoniae-infected foam cells was dramatically reduced, and a phenomenon of the amalgamation of C. pneumoniae inclusions with lipid droplets was detected. Double immunohistochemistry showed that C. pneumoniae-infected foam cells contained a large number of oxidized low-density lipoproteins. The observations provide support to the hypothesis that C. pneumoniae could affect foam cell formation in human atherosclerosis.

  10. Simulation of water vapor condensation on LOX droplet surface using liquid nitrogen

    Science.gov (United States)

    Powell, Eugene A.

    1988-01-01

    The formation of ice or water layers on liquid oxygen (LOX) droplets in the Space Shuttle Main Engine (SSME) environment was investigated. Formulation of such ice/water layers is indicated by phase-equilibrium considerations under conditions of high partial pressure of water vapor (steam) and low LOX droplet temperature prevailing in the SSME preburner or main chamber. An experimental investigation was begun using liquid nitrogen as a LOX simulant. A monodisperse liquid nitrogen droplet generator was developed which uses an acoustic driver to force the stream of liquid emerging from a capillary tube to break up into a stream of regularly space uniformly sized spherical droplets. The atmospheric pressure liquid nitrogen in the droplet generator reservoir was cooled below its boiling point to prevent two phase flow from occurring in the capillary tube. An existing steam chamber was modified for injection of liquid nitrogen droplets into atmospheric pressure superheated steam. The droplets were imaged using a stroboscopic video system and a laser shadowgraphy system. Several tests were conducted in which liquid nitrogen droplets were injected into the steam chamber. Under conditions of periodic droplet formation, images of 600 micron diameter liquid nitrogen droplets were obtained with the stroboscopic video systems.

  11. Development of advanced diagnostics for characterization of burning droplets in microgravity

    Science.gov (United States)

    Sankar, Subramanian; Buermann, Dale H.; Bachalo, William D.

    1995-01-01

    Diagnostic techniques currently used for microgravity research are generally not as advanced as those used in earth based gravity experiments. Diagnostic techniques for measuring the instantaneous radial temperature profile (or temperature gradients) within the burning droplet do not exist. Over the past few years, Aerometrics has been researching and developing a rainbow thermometric technique for measuring the droplet temperatures of burning droplets. This technique has recently been integrated with the phase Doppler interferometric technique to yield a diagnostic instrument that can be used to simultaneously measure the size, velocity, and temperature of burning droplets in complex spray flames. Also, the rainbow thermometric technique has been recently integrated with a point-diffraction interferometric technique for measuring the instantaneous gas phase temperature field surrounding a burning droplet. These research programs, apart from being very successful, have also helped us identify other innovative techniques for the characterization of burning droplets. For example, new techniques have been identified for measuring the instantaneous regression rate of burning droplets. Also, there is the possibility of extracting the instantaneous radial temperature distribution or the temperature gradients within a droplet during transient heating. What is important is that these diagnostic techniques have the potential for making use of inexpensive, light-weight, and rugged devices such as diode lasers and linear CCD arrays. As a result, they can be easily packaged for incorporation into microgravity drop-test and flight-test facilities. Furthermore, with the use of linear CCD arrays, data rates as high as 10-100 kHz can be easily achieved. This data rate is orders of magnitude higher than what is currently achievable. In this research and development program, a compact and rugged diagnostic system will be developed that can be used to measure instantaneous fuel

  12. Video-microscopy of NCAP films: the observation of LC droplets in real time

    Science.gov (United States)

    Reamey, Robert H.; Montoya, Wayne; Wong, Abraham

    1992-06-01

    We have used video-microscopy to observe the behavior of liquid crystal (LC) droplets within nematic droplet-polymer films (NCAP) as the droplets respond to an applied electric field. The textures observed at intermediate fields yielded information about the process of liquid crystal orientation dynamics within droplets. The nematic droplet-polymer films had low LC content (less than 1 percent) to allow the observation of individual droplets in a 2 - 6 micrometers size range. The aqueous emulsification technique was used to prepare the films as it allows the straightforward preparation of low LC content films with a controlled droplet size range. Standard electro-optical (E-O) tests were also performed on the films, allowing us to correlate single droplet behavior with that of the film as a whole. Hysteresis measured in E-O tests was visually confirmed by droplet orientation dynamics; a film which had high hysteresis in E-O tests exhibited distinctly different LC orientations within the droplet when ramped up in voltage than when ramped down in voltage. Ramping the applied voltage to well above saturation resulted in some droplets becoming `stuck'' in a new droplet structure which can be made to revert back to bipolar with high voltage pulses or with heat.

  13. Quantitative measurement of zinc secretion from pancreatic islets with high temporal resolution using droplet-based microfluidics.

    Science.gov (United States)

    Easley, Christopher J; Rocheleau, Jonathan V; Head, W Steven; Piston, David W

    2009-11-01

    We assayed glucose-stimulated insulin secretion (GSIS) from live, murine islets of Langerhans in microfluidic devices by the downstream formation of aqueous droplets. Zinc ions, which are cosecreted with insulin from beta-cells, were quantitatively measured from single islets with high temporal resolution using a fluorescent indicator, FluoZin-3. Real-time storage of secretions into droplets (volume of 0.470 +/- 0.009 nL) effectively preserves the temporal chemical information, allowing reconstruction of the secretory time record. The use of passive flow control within the device removes the need for syringe pumps, requiring only a single hand-held syringe. Under stimulatory glucose levels (11 mM), bursts of zinc as high as approximately 800 fg islet(-1) min(-1) were measured. Treatment with diazoxide effectively blocked zinc secretion, as expected. High temporal resolution reveals two major classes of oscillations in secreted zinc, with predominate periods at approximately 20-40 s and approximately 5-10 min. The more rapid oscillation periods match closely with those of intraislet calcium oscillations, while the slower oscillations are consistent with insulin pulses typically measured in bulk islet experiments or in the bloodstream. This droplet sampling technique should be widely applicable to time-resolved cellular secretion measurements, either in real-time or for postprocessing.

  14. Recent Advances in Controlling the Depositing Morphologies of Inkjet Droplets.

    Science.gov (United States)

    Sun, Jiazhen; Bao, Bin; He, Min; Zhou, Haihua; Song, Yanlin

    2015-12-30

    Inkjet printing has been widely used in functional material patterning for fabrication of optical/electrical devices. The depositing morphologies of inkjet droplets are critical to the resolution and performance of resulted functional patterns. This review summarizes various strategies to control the depositing morphologies of inkjet droplets, including suppressing and utilizing coffee-ring effect, employing liquid substrates, developing patterned substrates and controlling droplets coalescence. Moreover, the remaining challenges in controlling inkjet droplets are presented, and the broad research and application prospects of controlling nanomaterial patterning by inkjet printing are proposed.

  15. Evaluation of StereoPIV Measurement of Droplet Velocity in an Effervescent Spray

    Directory of Open Access Journals (Sweden)

    Sina Ghaemi

    2010-06-01

    Full Text Available Particle image velocimetry (PIV is a well known technique for measuring the instantaneous velocity field of flows. However, error may be introduced when measuring the velocity field of sprays using this technique when the spray droplets are used as the seed particles. In this study, the effect of droplet number density, droplet velocity profile, and droplet size distribution of a spray produced by an effervescent atomizer on velocity measurement using a StereoPIV has been investigated. A shadowgraph-particle tracking velocimetry (S-PTV system provided measurement of droplet size and velocity for comparison. This investigation demonstrated that the StereoPIV under-estimates velocity at near-field dense spray region where measurement accuracy is limited by multi-scattering of the laser sheet. In the dilute far-field region of the spray, StereoPIV measurement is mostly in agreement with velocity of the droplet size-class which is close to the mean diameter based on droplet number frequency times droplet cross sectional area.

  16. Drop size distribution measured by imaging: determination of the measurement volume by the calibration of the point spread function

    International Nuclear Information System (INIS)

    Fdida, Nicolas; Blaisot, Jean-Bernard

    2010-01-01

    Measurement of drop size distributions in a spray depends on the definition of the control volume for drop counting. For image-based techniques, this implies the definition of a depth-of-field (DOF) criterion. A sizing procedure based on an imaging model and associated with a calibration procedure is presented. Relations between image parameters and object properties are used to provide a measure of the size of the droplets, whatever the distance from the in-focus plane. A DOF criterion independent of the size of the drops and based on the determination of the width of the point spread function (PSF) is proposed. It allows to extend the measurement volume to defocused droplets and, due to the calibration of the PSF, to clearly define the depth of the measurement volume. Calibrated opaque discs, calibrated pinholes and an optical edge are used for this calibration. A comparison of the technique with a phase Doppler particle analyser and a laser diffraction granulometer is performed on an application to an industrial spray. Good agreement is found between the techniques when particular care is given to the sampling of droplets. The determination of the measurement volume is used to determine the drop concentration in the spray and the maximum drop concentration that imaging can support

  17. Theoretical analysis for the optical deformation of emulsion droplets.

    Science.gov (United States)

    Tapp, David; Taylor, Jonathan M; Lubansky, Alex S; Bain, Colin D; Chakrabarti, Buddhapriya

    2014-02-24

    We propose a theoretical framework to predict the three-dimensional shapes of optically deformed micron-sized emulsion droplets with ultra-low interfacial tension. The resulting shape and size of the droplet arises out of a balance between the interfacial tension and optical forces. Using an approximation of the laser field as a Gaussian beam, working within the Rayleigh-Gans regime and assuming isotropic surface energy at the oil-water interface, we numerically solve the resulting shape equations to elucidate the three-dimensional droplet geometry. We obtain a plethora of shapes as a function of the number of optical tweezers, their laser powers and positions, surface tension, initial droplet size and geometry. Experimentally, two-dimensional droplet silhouettes have been imaged from above, but their full side-on view has not been observed and reported for current optical configurations. This experimental limitation points to ambiguity in differentiating between droplets having the same two-dimensional projection but with disparate three-dimensional shapes. Our model elucidates and quantifies this difference for the first time. We also provide a dimensionless number that indicates the shape transformation (ellipsoidal to dumbbell) at a value ≈ 1.0, obtained by balancing interfacial tension and laser forces, substantiated using a data collapse.

  18. Numerical study of droplet impact and rebound on superhydrophobic surface

    Science.gov (United States)

    Cai, Xuan; Wu, Yanchen; Woerner, Martin; Frohnapfel, Bettina

    2017-11-01

    Droplet impact and rebound on superhydrophobic surface is an important process in many applications; among them are developing self-cleaning or anti-icing materials and limiting liquid film formation of Diesel Exhaust Fluid (DEF) in exhaust gas pipe. In the latter field, rebound of DEF droplet from wall is desired as an effective mean for avoiding or reducing unwanted solid deposition. Our goal is to numerically study influence of surface wettability on DEF droplet impact and rebound behavior. A phase-field method is chosen, which was implemented in OpenFOAM by us and validated for wetting-related interfacial flow problems. In the present contribution we first numerically reproduce relevant experimental studies in literature, to validate the code for droplet impact and rebound problem. There we study droplet-surface contact time, maximum/instantaneous spreading factor and droplet shape evolution. Our numerical results show good agreement with experimental data. Next we investigate for DEF droplets the effects of diameter, impact velocity and surface wettability on rebound behavior and jumping height. Based on Weber number and equilibrium contact angle, two regimes are identified. We show that surface wettability is a deciding factor for achieving rebound event. This work is supported by Foundation ``Friedrich-und-Elisabeth Boysen Stiftung fuer Forschung und Innovation'' (BOY-127-TP1).

  19. Simulation and modeling of turbulent non isothermal vapor-droplet dispersed flow

    International Nuclear Information System (INIS)

    Baalbaki, Daoud

    2011-01-01

    One of the reference accident that may occur in PWR (Pressurized Water Reactor) is LOCA (Loss of Coolant Accident). The LOCA is studied to design some emergency systems implemented in the basic nuclear installations. The LOCA corresponds to the break of a pipe in the primary loop. This accident is associated with a loss of pressure which leads to the vaporization of the water in the reactor core and then to the rise of the temperature of the assemblies. In this study, we focus on the area of vapor-droplet flow, where the cooling effectiveness of such a mixture is a major concern. The droplets act as heat sinks for the vapor and control the vapor temperature profile which, in turn, determines the wall heat transfer rate. Our general objective is to ameliorate the modeling of the vapor-droplet flow (i.e. at CFD scale). Particularly the estimation of the radial distribution of the droplets. The volume fraction distribution of the two phases depends on the size and dispersion of the droplets in the flow. The size of the droplets is controlled by the rupture and coalescence mechanisms and the interfacial mass transfer (evaporation/condensation). The distribution of the droplets is controlled by the transfer of momentum between the two phases. Our study focuses particularly on the latter point. We are restricted to flows where the liquid water flows under the form of non-deformable spherical droplets that do not interact with each other. Both phases are treated by a two-fluid approach Euler-Euler. In chapter 2, a description of two-phase flow model is presented, using separate mass, momentum, and energy equations for the two phases. These separate balance equations are obtained in an averaging process starting from the local instantaneous conservation equations of the individual phases. During the averaging process, important information on local flow processes are lost and, consequently, additional correlations are needed in order to close the system of equations. The

  20. Chemotactic droplet swimmers in complex geometries

    Science.gov (United States)

    Jin, Chenyu; Hokmabad, Babak V.; Baldwin, Kyle A.; Maass, Corinna C.

    2018-02-01

    Chemotaxis1 and auto-chemotaxis are key mechanisms in the dynamics of micro-organisms, e.g. in the acquisition of nutrients and in the communication between individuals, influencing the collective behaviour. However, chemical signalling and the natural environment of biological swimmers are generally complex, making them hard to access analytically. We present a well-controlled, tunable artificial model to study chemotaxis and autochemotaxis in complex geometries, using microfluidic assays of self-propelling oil droplets in an aqueous surfactant solution (Herminghaus et al 2014 Soft Matter 10 7008-22 Krüger et al 2016 Phys. Rev. Lett. 117). Droplets propel via interfacial Marangoni stresses powered by micellar solubilisation. Moreover, filled micelles act as a chemical repellent by diffusive phoretic gradient forces. We have studied these chemotactic effects in a series of microfluidic geometries, as published in Jin et al (2017 Proc. Natl Acad. Sci. 114 5089-94): first, droplets are guided along the shortest path through a maze by surfactant diffusing into the maze from the exit. Second, we let auto-chemotactic droplet swimmers pass through bifurcating microfluidic channels and record anticorrelations between the branch choices of consecutive droplets. We present an analytical Langevin model matching the experimental data. In a previously unpublished experiment, pillar arrays of variable sizes and shapes provide a convex wall interacting with the swimmer and, in the case of attachment, bending its trajectory and forcing it to revert to its own trail. We observe different behaviours based on the interplay of wall curvature and negative autochemotaxis, i.e. no attachment for highly curved interfaces, stable trapping at large pillars, and a narrow transition region where negative autochemotaxis makes the swimmers detach after a single orbit.

  1. "V-junction": a novel structure for high-speed generation of bespoke droplet flows.

    Science.gov (United States)

    Ding, Yun; Casadevall i Solvas, Xavier; deMello, Andrew

    2015-01-21

    We present the use of microfluidic "V-junctions" as a droplet generation strategy that incorporates enhanced performance characteristics when compared to more traditional "T-junction" formats. This includes the ability to generate target-sized droplets from the very first one, efficient switching between multiple input samples, the production of a wide range of droplet sizes (and size gradients) and the facile generation of droplets with residence time gradients. Additionally, the use of V-junction droplet generators enables the suspension and subsequent resumption of droplet flows at times defined by the user. The high degree of operational flexibility allows a wide range of droplet sizes, payloads, spacings and generation frequencies to be obtained, which in turn provides for an enhanced design space for droplet-based experimentation. We show that the V-junction retains the simplicity of operation associated with T-junction formats, whilst offering functionalities normally associated with droplet-on-demand technologies.

  2. Investigation of Effective Parameters of Drop-on-Demand Droplet Generator

    Directory of Open Access Journals (Sweden)

    Mojtaba Ghodsi

    2017-06-01

    Full Text Available This article presents a design and development of a drop-on-demand (DOD droplets generator. This generator uses molten metal as a liquid and can be used in fabrication, prototyping and any kind of printing with solder droplets. This setup consists of a vibrator solenoid with tunable frequency to produce a semi-spherical shape of molten metal, close to the surface of fabrication. This design also has a nozzle with micro-size orifice, a rod for transmitting force and a heater to melt the metal and keep it in superheat temperature. This DOD can produce droplets in different sizes (less than 550 µm by controlling the vibration frequency of solenoid. This ability together with the accuracy of the droplets in positioning (the error is less than ±20 µm for 1.5 mm amplitude can be used in different applications.  Moreover, in this paper, the impact of initial position of the head and temperature on the average diameter of droplets and the impact of the frequency on the shape of the droplets have been tested and discussed

  3. Multi-scale simulations of droplets in generic time-dependent flows

    Science.gov (United States)

    Milan, Felix; Biferale, Luca; Sbragaglia, Mauro; Toschi, Federico

    2017-11-01

    We study the deformation and dynamics of droplets in time-dependent flows using a diffuse interface model for two immiscible fluids. The numerical simulations are at first benchmarked against analytical results of steady droplet deformation, and further extended to the more interesting case of time-dependent flows. The results of these time-dependent numerical simulations are compared against analytical models available in the literature, which assume the droplet shape to be an ellipsoid at all times, with time-dependent major and minor axis. In particular we investigate the time-dependent deformation of a confined droplet in an oscillating Couette flow for the entire capillary range until droplet break-up. In this way these multi component simulations prove to be a useful tool to establish from ``first principles'' the dynamics of droplets in complex flows involving multiple scales. European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 642069. & European Research Council under the European Community's Seventh Framework Program, ERC Grant Agreement No 339032.

  4. Vitrification and levitation of a liquid droplet on liquid nitrogen.

    Science.gov (United States)

    Song, Young S; Adler, Douglas; Xu, Feng; Kayaalp, Emre; Nureddin, Aida; Anchan, Raymond M; Maas, Richard L; Demirci, Utkan

    2010-03-09

    The vitrification of a liquid occurs when ice crystal formation is prevented in the cryogenic environment through ultrarapid cooling. In general, vitrification entails a large temperature difference between the liquid and its surrounding medium. In our droplet vitrification experiments, we observed that such vitrification events are accompanied by a Leidenfrost phenomenon, which impedes the heat transfer to cool the liquid, when the liquid droplet comes into direct contact with liquid nitrogen. This is distinct from the more generally observed Leidenfrost phenomenon that occurs when a liquid droplet is self-vaporized on a hot plate. In the case of rapid cooling, the phase transition from liquid to vitrified solid (i.e., vitrification) and the levitation of droplets on liquid nitrogen (i.e., Leidenfrost phenomenon) take place simultaneously. Here, we investigate these two simultaneous physical events by using a theoretical model containing three dimensionless parameters (i.e., Stefan, Biot, and Fourier numbers). We explain theoretically and observe experimentally a threshold droplet radius during the vitrification of a cryoprotectant droplet in the presence of the Leidenfrost effect.

  5. Design and construction of hydrogen pellet injector by droplet-method

    International Nuclear Information System (INIS)

    Noda, Etsuo; Iida, Yoshiyuki; Sekiguchi, Tadashi; Suemori, Nobuo; Imaizumi, Hideki.

    1984-01-01

    A hydrogen pellet injector by a droplet-method has been constructed and studied, in order to realize a hydrogen-isotope pellet injector for refueling into nuclear fusion reactors, which can inject pellets into plasma repetitively. Preliminary experiments with oxygen gas, instead of hydrogen gas, has been systematically carried out. Assuming the liquid concerned as viscous fluid, theoretical predictions about droplet-diameter, its ejected velocity and optimum frequency of ejecting-nozzle vibration for stable droplet production has been made, and it is found that theoretical results are in good agreement with experimental ones. It is found that the stable droplet train can be obtained when the value of Reynolds number is in the range of 1,100--1,300. In the hydrogen experiments based upon the oxygen results, the production of a stable hydrogen liquid-droplet train, their self-solidification and transfer into a vacuum space through an orifice (with the diameter of 1 mm) have been successfully realized, by maintaining the gas pressure around the droplets at 45--50 Torr. (author)

  6. Ultrahigh throughput microfluidic platform for in-air production of microscale droplets

    Science.gov (United States)

    Tirandazi, Pooyan; Healy, John; Hidrovo, Carlos H.

    2017-11-01

    In-air droplet formation inside microfluidic networks is an alternative technique to the conventional in-liquid systems for creating uniform, microscale droplets. Recent works have highlighted and quantified the use of a gaseous continuous phase for controlled generation of droplets in the Dripping regime in planar structures. Here we demonstrate a new class of non-planar droplet-based systems which rely on controlled breakup of a liquid microjet within a high speed flow of air inside a confined microfluidic flow-focusing PDMS channel. We investigate the physics of confined gas-liquid flows and the effect of geometry on the behavior of a liquid water jet in a gaseous flow. Droplet breakup in the Jetting regime is studied both numerically and experimentally and the results are compared. We show droplet production capability at rates higher than 100 KHz with droplets ranging from 15-30 μm in diameter and a polydispersity index of less than 15%. This work represents an important investigation into the Jetting regime in confined microchannels. The ability to control jet behavior, generation rate, and droplet size in gas-liquid microflows will further expand the potential applications of this system for high throughput operations in material synthesis and biochemical analysis. We acknowledge funding support from NSF CAREER Award Grant CBET-1522841.

  7. Evaporation and discharge dynamics of highly charged multicomponent droplets generated by electrospray ionization.

    Science.gov (United States)

    Grimm, Ronald L; Beauchamp, J L

    2010-01-28

    We investigate the Rayleigh discharge and evaporation dynamics of highly charged two-component droplets consisting principally of methanol with 2-methoxyethanol, tert-butanol, or m-nitrobenzyl alcohol. A phase Doppler anemometer (PDA) characterizes droplets generated by electrospray ionization (ESI) according to size, velocity, and charge as they move through a uniform electric field within an ion mobility spectrometer (IMS). Repeated field reversals result in droplet "ping-pong" through the PDA. This generates individual droplet histories of solvent evaporation behavior and the dynamics of charge loss to progeny droplets during Rayleigh discharge events. On average, methanol droplets discharge at 127% their Rayleigh limit of charge, q(R), and release 25% of the net charge. Charge loss from methanol/2-methoxyethanol droplets behaves similarly to pure 2-methoxyethanol droplets which release approximately 28% of their net charge. Binary methanol droplets containing up to 50% tert-butanol discharge at a lower percent q(R) than pure methanol and release a greater fraction of their net charge. Mixed 99% methanol/1% m-nitrobenzyl alcohol droplets possess discharge characteristics similar to those of methanol. However, droplets of methanol containing 2% m-nitrobenzyl evaporate down to a fixed size and charge that remains constant with no observable discharges. Quasi-steady-state evaporation models accurately describe observed evaporation phenomena in which methanol/tert-butanol droplets evaporate at a rate similar to that of pure methanol and methanol/2-methoxyethanol droplets evaporate at a rate similar to that of 2-methoxyethanol. We compare these results to previous Rayleigh discharge experiments and discuss the implications for binary solvents in electrospray mass spectrometry (ESI-MS) and field-induced droplet ionization mass spectrometry (FIDI-MS).

  8. Droplet bubbling evaporatively cools a blowfly.

    Science.gov (United States)

    Gomes, Guilherme; Köberle, Roland; Von Zuben, Claudio J; Andrade, Denis V

    2018-04-19

    Terrestrial animals often use evaporative cooling to lower body temperature. Evaporation can occur from humid body surfaces or from fluids interfaced to the environment through a number of different mechanisms, such as sweating or panting. In Diptera, some flies move tidally a droplet of fluid out and then back in the buccopharyngeal cavity for a repeated number of cycles before eventually ingesting it. This is referred to as the bubbling behaviour. The droplet fluid consists of a mix of liquids from the ingested food, enzymes from the salivary glands, and antimicrobials, associated to the crop organ system, with evidence pointing to a role in liquid meal dehydration. Herein, we demonstrate that the bubbling behaviour also serves as an effective thermoregulatory mechanism to lower body temperature by means of evaporative cooling. In the blowfly, Chrysomya megacephala, infrared imaging revealed that as the droplet is extruded, evaporation lowers the fluid´s temperature, which, upon its re-ingestion, lowers the blowfly's body temperature. This effect is most prominent at the cephalic region, less in the thorax, and then in the abdomen. Bubbling frequency increases with ambient temperature, while its cooling efficiency decreases at high air humidities. Heat transfer calculations show that droplet cooling depends on a special heat-exchange dynamic, which result in the exponential activation of the cooling effect.

  9. Modeling the evaporation of sessile multi-component droplets

    NARCIS (Netherlands)

    Diddens, C.; Kuerten, Johannes G.M.; van der Geld, C.W.M.; Wijshoff, H.M.A.

    2017-01-01

    We extended a mathematical model for the drying of sessile droplets, based on the lubrication approximation, to binary mixture droplets. This extension is relevant for e.g. inkjet printing applications, where ink consisting of several components are used. The extension involves the generalization of

  10. Liquid crystal droplet formation and anchoring dynamics in a microfluidic device

    Science.gov (United States)

    Steinhaus, Ben; Shen, Amy; Feng, James; Link, Darren

    2004-11-01

    Liquid crystal drops dispersed in a continuous phase of silicon oil are generated with a narrow distribution in droplet size in microfluidic devices both above and below the nematic to isotropic transition temperature. For these two cases, we observe not only the different LC droplet generation and coalescence dynamics, but also distinct droplet morphology. Our experiments show that the nematic liquid crystalline order is important for the LC droplet formation and anchoring dynamics.

  11. Sectorial oscillation of acoustically levitated nanoparticle-coated droplet

    Science.gov (United States)

    Zang, Duyang; Chen, Zhen; Geng, Xingguo

    2016-01-01

    We have investigated the dynamics of a third mode sectorial oscillation of nanoparticle-coated droplets using acoustic levitation in combination with active modulation. The presence of nanoparticles at the droplet surface changes its oscillation amplitude and frequency. A model linking the interfacial rheology and oscillation dynamics has been proposed in which the compression modulus ɛ of the particle layer is introduced into the analysis. The ɛ obtained with the model is in good agreement with that obtained by the Wilhelmy plate approach, highlighting the important role of interfacial rheological properties in the sectorial oscillation of droplets.

  12. In Situ Raman Spectroscopic Observations of Gas-Saturated Rising Oil droplets: Simulation with Decane as an Oil-Equivalent Substitute

    Science.gov (United States)

    Peltzer, E. T.; Walz, P. M.; Brewer, P. G.

    2016-02-01

    Oil droplets rising from the sea floor, whether from seeps or well leakage, contain very large quantities of dissolved gas that profoundly affects their density and critical oil-water interfacial characteristics. The primary dissolved gas is methane which may be up to 30% of the molar volume. This can create a hydrate skin as the methane gas is shed from the oil as it rises through the water column, thus decreasing in pressure and increasing in temperature, and steadily changing the rising droplet buoyancy. We have explored this phenomenon by executing controlled ROV based experiments with a "bubble cup" technique in which a small volume of gas saturated decane (saturated with pure methane, a mix of methane and nitrogen , or a mix of methane and CO2) is interrogated by laser Raman spectroscopy. The use of decane as an oil "substitute" is required since natural oil samples are highly fluorescent due to the presence of polycyclic aromatic hydrocarbons. We have devised Matlab techniques for extracting the spectroscopic dissolved methane signal from the thicket of decane peaks that surround it. We have directly observed the rate at which gases are lost from the "oil" per unit area at depths in the water column that are both within and outside the hydrate forming phase boundary. We have compared the behavior of both a non-hydrate forming dissolved gas (nitrogen) with CO2 where the hydrate phase boundary is at significantly shallower depth. The results indicate complex interfacial behavior and physical chemistry. We did not observe direct gas bubble formation on the decane outer surface but did observe gas bubble formation within the oil droplets as they rose through the water column. Because there are significant energy barriers for homogeneous bubble formation within the decane phase, we took this as evidence of significant gas super-saturation within the oil droplet. The gas loss rates increased significantly in all cases when the hydrate phase boundary was crossed.

  13. Measurement of airborne droplets by the magnesium oxide method

    Energy Technology Data Exchange (ETDEWEB)

    May, K R

    1950-01-01

    A complete calibration has been made for the first time of the method of detecting and measuring airborne droplets whereby the permanent impressions made when they strike a layer of magnesium oxide smoked on a glass slide are measured microscopically. A size range of 200 to 10 microns and a wide range of liquids and impact velocities were investigated, and it was found that the ratio of true drop size to impression size is constant at 0.86 for droplets greater than 20 microns of any liquid. The method fails below 10 microns. The calibration was made against an absolute method of droplet measurement, also against the so-called focal-length method. Droplets of any desired size were generated by a uniform spray apparatus.

  14. Surface characterization of polymethylmetacrylate bombarded by charged water droplets

    International Nuclear Information System (INIS)

    Hiraoka, Kenzo; Takaishi, Riou; Asakawa, Daiki; Sakai, Yuji; Iijima, Yoshitoki

    2009-01-01

    The electrospray droplet impact (EDI), in which the charged electrospray water droplets are introduced in vacuum, accelerated, and allowed to impact the sample, is applied to polymethylmetacrylate (PMMA). The secondary ions generated were measured by an orthogonal time-of-flight mass spectrometer. In EDI mass spectra for PMMA, fragment ions originating from PMMA could not be detected. This is due to the fact that the proton affinities of fragments formed from PMMA are smaller than those from acetic acid contained in the charged droplet. The x-ray photoelectron spectroscopy spectra of PMMA irradiated by water droplets did not change with prolonged cluster irradiation, i.e., EDI is capable of shallow surface etching for PMMA with a little damage of the sample underneath the surface.

  15. Analysis of slippery droplet on tilted plate by development of optical correction method

    Science.gov (United States)

    Ko, Han Seo; Gim, Yeonghyeon; Choi, Sung Ho; Jang, Dong Kyu; Sohn, Dong Kee

    2017-11-01

    Because of distortion effects on a surface of a sessile droplet, the inner flow field of the droplet is measured by a PIV (particle image velocimetry) method with low reliability. In order to solve this problem, many researchers have studied and developed the optical correction method. However, the method cannot be applied for various cases such as the tilted droplet or other asymmetric shaped droplets since most methods were considered only for the axisymmetric shaped droplets. For the optical correction of the asymmetric shaped droplet, the surface function was calculated by the three-dimensional reconstruction using the ellipse curve fitting method. Also, the optical correction using the surface function was verified by the numerical simulation. Then, the developed method was applied to reconstruct the inner flow field of the droplet on the tilted plate. The colloidal droplet of water on the tilted surface was used, and the distorted effect on the surface of the droplet was calculated. Using the obtained results and the PIV method, the corrected flow field for the inner and interface parts of the droplet was reconstructed. Consequently, the error caused by the distortion effect of the velocity vector located on the apex of the droplet was removed. National Research Foundation (NRF) of Korea, (2016R1A2B4011087).

  16. Electrical actuation of electrically conducting and insulating droplets using ac and dc voltages

    International Nuclear Information System (INIS)

    Kumari, N; Bahadur, V; Garimella, S V

    2008-01-01

    Electrical actuation of liquid droplets at the microscale offers promising applications in the fields of microfluidics and lab-on-chip devices. Much prior research has targeted the electrical actuation of electrically conducting liquid droplets using dc voltages (classical electrowetting). Electrical actuation of conducting droplets using ac voltages and the actuation of insulating droplets (using dc or ac voltages) has remained relatively unexplored. This paper utilizes an energy-minimization-based analytical framework to study the electrical actuation of a liquid droplet (electrically conducting or insulating) under ac actuation. It is shown that the electromechanical regimes of classical electrowetting, electrowetting under ac actuation and insulating droplet actuation can be extracted from the generic electromechanical actuation framework, depending on the electrical properties of the droplet, the underlying dielectric layer and the frequency of the actuation voltage. This paper also presents experiments which quantify the influence of the ac frequency and the electrical properties of the droplet on its velocity under electrical actuation. The velocities of droplets moving between two parallel plates under ac actuation are experimentally measured; these velocities are then related to the actuation force on the droplet which is predicted by the electromechanical model developed in this work. It is seen that the droplet velocities are strongly dependent on the frequency of the ac actuation voltage; the cut-off ac frequency, above which the droplet fails to actuate, is experimentally determined and related to the electrical conductivity of the liquid. This paper then analyzes and directly compares the various electromechanical regimes for the actuation of droplets in microfluidic applications

  17. Dynamic Wetting Behavior of Vibrated Droplets on a Micropillared Surface

    Directory of Open Access Journals (Sweden)

    Zhi-hai Jia

    2016-01-01

    Full Text Available The dynamical wetting behavior has been observed under vertical vibration of a water droplet placed on a micropillared surface. The wetting transition takes place under the different processes. In compression process, the droplet is transited from Cassie state to Wenzel state. The droplet undergoes a Wenzel-Cassie wetting transition in restoring process and the droplet bounces off from the surface in bouncing process. Meanwhile, the wetting and dewetting models during vibration are proposed. The wetting transition is confirmed by the model calculation. This study has potential to be used to control the wetting state.

  18. In situ droplet size and speed determination in a fluid-bed granulator.

    Science.gov (United States)

    Ehlers, Henrik; Larjo, Jussi; Antikainen, Osmo; Räikkönen, Heikki; Heinämäki, Jyrki; Yliruusi, Jouko

    2010-05-31

    The droplet size affects the final product in fluid-bed granulation and coating. In the present study, spray characteristics of aqueous granulation liquid (purified water) were determined in situ in a fluid-bed granulator. Droplets were produced by a pneumatic nozzle. Diode laser stroboscopy (DLS) was used for droplet detection and particle tracking velocimetry (PTV) was used for determination of droplet size and speed. Increased atomization pressure decreased the droplet size and the effect was most strongly visible in the 90% size fractile. The droplets seemed to undergo coalescence after which only slight evaporation occurred. Furthermore, the droplets were subjected to a strong turbulence at the event of atomization, after which the turbulence reached a minimum value in the lower halve of the chamber. The turbulence increased as speed and droplet size decreased due to the effects of the fluidizing air. The DLS and PTV system used was found to be a useful and rapid tool in determining spray characteristics and in monitoring and predicting nozzle performance. Copyright (c) 2010 Elsevier B.V. All rights reserved.

  19. Probing droplets on superhydrophobic surfaces by synchrotron radiation scattering techniques

    KAUST Repository

    Accardo, Angelo

    2014-06-10

    Droplets on artificially structured superhydrophobic surfaces represent quasi contact-free sample environments which can be probed by X-ray microbeams and nanobeams in the absence of obstructing walls. This review will discuss basic surface wettability concepts and introduce the technology of structuring surfaces. Quasi contact-free droplets are compared with contact-free droplets; processes related to deposition and evaporation on solid surfaces are discussed. Droplet coalescence based on the electrowetting effect allows the probing of short-time mixing and reaction processes. The review will show for several materials of biological interest that structural processes related to conformational changes, nucleation and assembly during droplet evaporation can be spatially and temporally resolved by raster-scan diffraction techniques. Orientational ordering of anisotropic materials deposited during solidification at pinning sites facilitates the interpretation of structural data. 2014 International Union of Crystallography.

  20. An interfacial mechanism for cloud droplet formation on organic aerosols.

    Science.gov (United States)

    Ruehl, Christopher R; Davies, James F; Wilson, Kevin R

    2016-03-25

    Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depression by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation. Copyright © 2016, American Association for the Advancement of Science.

  1. Probing droplets on superhydrophobic surfaces by synchrotron radiation scattering techniques

    KAUST Repository

    Accardo, Angelo; Di Fabrizio, Enzo M.; Limongi, Tania; Marinaro, Giovanni; Riekel, Christian

    2014-01-01

    Droplets on artificially structured superhydrophobic surfaces represent quasi contact-free sample environments which can be probed by X-ray microbeams and nanobeams in the absence of obstructing walls. This review will discuss basic surface wettability concepts and introduce the technology of structuring surfaces. Quasi contact-free droplets are compared with contact-free droplets; processes related to deposition and evaporation on solid surfaces are discussed. Droplet coalescence based on the electrowetting effect allows the probing of short-time mixing and reaction processes. The review will show for several materials of biological interest that structural processes related to conformational changes, nucleation and assembly during droplet evaporation can be spatially and temporally resolved by raster-scan diffraction techniques. Orientational ordering of anisotropic materials deposited during solidification at pinning sites facilitates the interpretation of structural data. 2014 International Union of Crystallography.

  2. Downstream pressure and elastic wall reflection of droplet flow in a T-junction microchannel

    Science.gov (United States)

    Pang, Yan; Liu, Zhaomiao; Zhao, Fuwang

    2016-08-01

    This paper discusses pressure variation on a wall during the process of liquid flow and droplet formation in a T-junction microchannel. Relevant pressure in the channel, deformation of the elastic wall, and responses of the droplet generation are analyzed using a numerical method. The pressure difference between the continuous and dispersed phases can indicate the droplet-generation period. The pressure along the channel of the droplet flow is affected by the position of droplets, droplet-generation period, and droplet escape from the outlet. The varying pressures along the channel cause a nonuniform deformation of the wall when they are elastic. The deformation is a vibration and has the same period as the droplet generation arising from the process of droplet formation.

  3. Study of flow behaviors of droplet merging and splitting in microchannels using Micro-PIV measurement

    Science.gov (United States)

    Li, Yi; Liu, Zhaomiao

    2017-01-01

    Droplet merging and splitting are important droplet manipulations in droplet-based microfluidics. However, the fundamental flow behaviors of droplets were not systematically studied. Hence, we designed two different microstructures to achieve droplet merging and splitting respectively, and quantitatively compared different flow dynamics in different microstructures for droplet merging and splitting via micro-particle image velocimetry (micro-PIV) experiments. Some flow phenomena of droplets different from previous studies were observed during merging and splitting using a high-speed microscope. It was also found the obtained instantaneous velocity vector fields of droplets have significant influence on the droplets merging and splitting. For droplet merging, the probability of droplets coalescence (η) in a microgroove is higher (50% T-junction microchannel (15% < η < 50%), and the highest coalescence efficiency (η = 92%) comes at the two-phase flow ratio e of 0.42 in the microgroove. Moreover, compared with a cylinder obstacle, Y-junction bifurcation can split droplets more effectively and the droplet flow during splitting is steadier. The results can provide better understanding of droplet behaviors and are useful for the design and applications of droplet-based microfluidics. PMID:28890680

  4. Study of flow behaviors of droplet merging and splitting in microchannels using Micro-PIV measurement.

    Science.gov (United States)

    Shen, Feng; Li, Yi; Liu, Zhaomiao; Li, XiuJun

    2017-04-01

    Droplet merging and splitting are important droplet manipulations in droplet-based microfluidics. However, the fundamental flow behaviors of droplets were not systematically studied. Hence, we designed two different microstructures to achieve droplet merging and splitting respectively, and quantitatively compared different flow dynamics in different microstructures for droplet merging and splitting via micro-particle image velocimetry (micro-PIV) experiments. Some flow phenomena of droplets different from previous studies were observed during merging and splitting using a high-speed microscope. It was also found the obtained instantaneous velocity vector fields of droplets have significant influence on the droplets merging and splitting. For droplet merging, the probability of droplets coalescence ( η ) in a microgroove is higher (50% < η < 92%) than that in a T-junction microchannel (15% < η < 50%), and the highest coalescence efficiency ( η = 92%) comes at the two-phase flow ratio e of 0.42 in the microgroove. Moreover, compared with a cylinder obstacle, Y-junction bifurcation can split droplets more effectively and the droplet flow during splitting is steadier. The results can provide better understanding of droplet behaviors and are useful for the design and applications of droplet-based microfluidics.

  5. Droplet Traffic Control at a simple T junction

    Science.gov (United States)

    Panizza, Pascal; Engl, Wilfried; Colin, Annie; Ajdari, Armand

    2006-03-01

    A basic yet essential element of every traffic flow control is the effect of a junction where the flow is separated into several streams. How do pedestrians, vehicles or blood cells divide when they reach a junction? How does the outcome depend on their density? Similar fundamental questions hold for much simpler systems: in this paper, we have studied the behaviour of periodic trains of water droplets flowing in oil through a channel as they reach a simple, locally symmetric, T junction. Depending on their dilution, we observe that the droplets are either alternately partitioned between both outlets or sorted exclusively into the shortest one. We show that this surprising behaviour results from the hydrodynamic feed-back of drops in the two outlets on the selection process occurring at the junction. Our results offer a first guide for the design and modelling of droplet traffic in complex branched networks, a necessary step towards parallelized droplet-based ``lab-on-chip'' devices.

  6. Insights into Evaporative Droplet Dynamics in the High-Wind Atmospheric Boundary Layer

    Science.gov (United States)

    Peng, T.; Richter, D. H.

    2017-12-01

    Sea-spray droplets ejected into the air-sea boundary layer take part in a series of complex transport processes. To model the air-sea exchange of heat and moisture under high-wind conditions, it is important yet challenging to understand influences of evaporative droplets in the atmospheric boundary layer. We implement a high-resolution Eulerian-Lagrangian algorithm with droplets laden in a turbulent open-channel flow to reveal the dynamic and thermodynamic characteristics of evaporating sea spray. Our past numerical simulations demonstrated an overall weak modification to the total heat flux by evaporative droplets. This is due to redistributed sensible and latent heat fluxes from relatively small droplets that respond rapidly to the ambient environment or the limited residence time of larger droplets. However, droplets with a slower thermodynamic response to the environment indicate a potential to enhance the total heat flux, but this is dependent on concentration and suspension time. In the current study, we focus on correlations between the residence time and thermodynamic statistics of droplets in order to better understand how best to parameterize in large-scale models. In addition, we focus in detail on the different scales of turbulence to further characterize the range of influence that evaporating droplets have on the surrounding fluid.

  7. Ignition of a Droplet of Composite Liquid Fuel in a Vortex Combustion Chamber

    Science.gov (United States)

    Valiullin, T. R.; Vershinina, K. Yu; Glushkov, D. O.; Strizhak, P. A.

    2017-11-01

    Experimental study results of a droplet ignition and combustion were obtained for coal-water slurry containing petrochemicals (CWSP) prepared from coal processing waste, low-grade coal and waste petroleum products. A comparative analysis of process characteristics were carried out in different conditions of fuel droplet interaction with heated air flow: droplet soars in air flow in a vortex combustion chamber, droplet soars in ascending air flow in a cone-shaped combustion chamber, and droplet is placed in a thermocouple junction and motionless in air flow. The size (initial radii) of CWSP droplet was varied in the range of 0.5-1.5 mm. The ignition delay time of fuel was determined by the intensity of the visible glow in the vicinity of the droplet during CWSP combustion. It was established (under similar conditions) that ignition delay time of CWSP droplets in the combustion chamber is lower in 2-3.5 times than similar characteristic in conditions of motionless droplet placed in a thermocouple junction. The average value of ignition delay time of CWSP droplet is 3-12 s in conditions of oxidizer temperature is 600-850 K. Obtained experimental results were explained by the influence of heat and mass transfer processes in the droplet vicinity on ignition characteristics in different conditions of CWSP droplet interaction with heated air flow. Experimental results are of interest for the development of combustion technology of promising fuel for thermal power engineering.

  8. Fundamentals of magnet-actuated droplet manipulation on an open hydrophobic surface†

    Science.gov (United States)

    Long, Zhicheng; Shetty, Abhishek M.; Solomon, Michael J.; Larson, Ronald G.

    2010-01-01

    We systematically investigate droplet movement, coalescence, and splitting on an open hydrophobic surface. These processes are actuated by magnetic beads internalized in an oil-coated aqueous droplet using an external magnet. Results are organized into an ‘operating diagram’ that describes regions of droplet stable motion, breakage, and release from the magnet. The results are explained theoretically with a simple model that balances magnetic, friction, and capillary-induced drag forces and includes the effects of particle type, droplet size, surrounding oil layer, surface tension, and viscosity. Finally, we discuss the implications of the results for the design of magnet-actuated droplet systems for applications such as nucleic acid purification, immunoassay and drug delivery. PMID:19458864

  9. Droplet Image Super Resolution Based on Sparse Representation and Kernel Regression

    Science.gov (United States)

    Zou, Zhenzhen; Luo, Xinghong; Yu, Qiang

    2018-05-01

    Microgravity and containerless conditions, which are produced via electrostatic levitation combined with a drop tube, are important when studying the intrinsic properties of new metastable materials. Generally, temperature and image sensors can be used to measure the changes of sample temperature, morphology and volume. Then, the specific heat, surface tension, viscosity changes and sample density can be obtained. Considering that the falling speed of the material sample droplet is approximately 31.3 m/s when it reaches the bottom of a 50-meter-high drop tube, a high-speed camera with a collection rate of up to 106 frames/s is required to image the falling droplet. However, at the high-speed mode, very few pixels, approximately 48-120, will be obtained in each exposure time, which results in low image quality. Super-resolution image reconstruction is an algorithm that provides finer details than the sampling grid of a given imaging device by increasing the number of pixels per unit area in the image. In this work, we demonstrate the application of single image-resolution reconstruction in the microgravity and electrostatic levitation for the first time. Here, using the image super-resolution method based on sparse representation, a low-resolution droplet image can be reconstructed. Employed Yang's related dictionary model, high- and low-resolution image patches were combined with dictionary training, and high- and low-resolution-related dictionaries were obtained. The online double-sparse dictionary training algorithm was used in the study of related dictionaries and overcome the shortcomings of the traditional training algorithm with small image patch. During the stage of image reconstruction, the algorithm of kernel regression is added, which effectively overcomes the shortcomings of the Yang image's edge blurs.

  10. Development of droplets‐based microfluidic systems for single­‐cell high‐throughput screening

    DEFF Research Database (Denmark)

    Chen, Jun; Jensen, Thomas Glasdam; Godina, Alexei

    2014-01-01

    High-throughput screening (HTS) plays an important role in the development of microbial cell factories. One of the most popular approaches is to use microplates combined with the application of robotics, liquid handling and sophisticated detection methods. However, these workstations require large...... investment, and a logarithmic increase to screen large combinatorial libraries over the decades also makes it gradually out of depth. Here, we are trying to develop a feasible high‐throughput system that uses microfluidics to compartmentalize a single cell for propagation and analysis in monodisperse...... picoliter aqueous droplets surround by an immiscible fluorinated oil phase. Our aim is to use this system to facilitate the screening process for both the biotechnology and food industry....

  11. Models of lipid droplets growth and fission in adipocyte cells

    Energy Technology Data Exchange (ETDEWEB)

    Boschi, Federico, E-mail: federico.boschi@univr.it [Department of Computer Science, University of Verona, Strada Le Grazie 15, 37134 Verona (Italy); Rizzatti, Vanni; Zamboni, Mauro [Department of Medicine, Geriatric Section, University of Verona, Piazzale Stefani 1, 37126 Verona (Italy); Sbarbati, Andrea [Department of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134 Verona (Italy)

    2015-08-15

    Lipid droplets (LD) are spherical cellular inclusion devoted to lipids storage. It is well known that excessive accumulation of lipids leads to several human worldwide diseases like obesity, type 2 diabetes, hepatic steatosis and atherosclerosis. LDs' size range from fraction to one hundred of micrometers in adipocytes and is related to the lipid content, but their growth is still a puzzling question. It has been suggested that LDs can grow in size due to the fusion process by which a larger LD is obtained by the merging of two smaller LDs, but these events seems to be rare and difficult to be observed. Many other processes are thought to be involved in the number and growth of LDs, like the de novo formation and the growth through additional neutral lipid deposition in pre-existing droplets. Moreover the number and size of LDs are influenced by the catabolism and the absorption or interaction with other organelles. The comprehension of these processes could help in the confinement of the pathologies related to lipid accumulation. In this study the LDs' size distribution, number and the total volume of immature (n=12), mature (n=12, 10-days differentiated) and lipolytic (n=12) 3T3-L1 adipocytes were considered. More than 11,000 LDs were measured in the 36 cells after Oil Red O staining. In a previous work Monte Carlo simulations were used to mimic the fusion process alone between LDs. We found that, considering the fusion as the only process acting on the LDs, the size distribution in mature adipocytes can be obtained with numerical simulation starting from the size distribution in immature cells provided a very high rate of fusion events. In this paper Monte Carlo simulations were developed to mimic the interaction between LDs taking into account many other processes in addition to fusion (de novo formation and the growth through additional neutral lipid deposition in pre-existing droplets) in order to reproduce the LDs growth and we also simulated the

  12. Models of lipid droplets growth and fission in adipocyte cells

    International Nuclear Information System (INIS)

    Boschi, Federico; Rizzatti, Vanni; Zamboni, Mauro; Sbarbati, Andrea

    2015-01-01

    Lipid droplets (LD) are spherical cellular inclusion devoted to lipids storage. It is well known that excessive accumulation of lipids leads to several human worldwide diseases like obesity, type 2 diabetes, hepatic steatosis and atherosclerosis. LDs' size range from fraction to one hundred of micrometers in adipocytes and is related to the lipid content, but their growth is still a puzzling question. It has been suggested that LDs can grow in size due to the fusion process by which a larger LD is obtained by the merging of two smaller LDs, but these events seems to be rare and difficult to be observed. Many other processes are thought to be involved in the number and growth of LDs, like the de novo formation and the growth through additional neutral lipid deposition in pre-existing droplets. Moreover the number and size of LDs are influenced by the catabolism and the absorption or interaction with other organelles. The comprehension of these processes could help in the confinement of the pathologies related to lipid accumulation. In this study the LDs' size distribution, number and the total volume of immature (n=12), mature (n=12, 10-days differentiated) and lipolytic (n=12) 3T3-L1 adipocytes were considered. More than 11,000 LDs were measured in the 36 cells after Oil Red O staining. In a previous work Monte Carlo simulations were used to mimic the fusion process alone between LDs. We found that, considering the fusion as the only process acting on the LDs, the size distribution in mature adipocytes can be obtained with numerical simulation starting from the size distribution in immature cells provided a very high rate of fusion events. In this paper Monte Carlo simulations were developed to mimic the interaction between LDs taking into account many other processes in addition to fusion (de novo formation and the growth through additional neutral lipid deposition in pre-existing droplets) in order to reproduce the LDs growth and we also simulated the

  13. Preferential nucleation, guiding, and blocking of self-propelled droplets by dislocations

    Science.gov (United States)

    Kanjanachuchai, Songphol; Wongpinij, Thipusa; Kijamnajsuk, Suphakan; Himwas, Chalermchai; Panyakeow, Somsak; Photongkam, Pat

    2018-04-01

    Lattice-mismatched layers of GaAs/InGaAs are grown on GaAs(001) using molecular beam epitaxy and subsequently heated in vacuum while the surface is imaged in situ using low-energy electron microscopy, in order to study (i) the nucleation of group-III droplets formed as a result of noncongruent sublimation and (ii) the dynamics of these self-propelled droplets as they navigate the surface. It is found that the interfacial misfit dislocation network not only influences the nucleation sites of droplets, but also exerts unusual steering power over their subsequent motion. Atypical droplet flow patterns including 90° and 180° turns are found. The directions of these dislocations-guided droplets are qualitatively explained in terms of in-plane and out-of-plane stress fields associated with the buried dislocations and the driving forces due to chemical potential and stress gradients typical of Marangoni flow. The findings would benefit processes and devices that employ droplets as catalysts or active structures such as droplet epitaxy of quantum nanostructures, vapor-liquid-solid growth of nanowires, or the fabrication of self-integrated circuits.

  14. On the relevance of droplet sedimentation in stratocumulus-top mixing

    Science.gov (United States)

    Mellado, Juan Pedro; de Lozar, Alberto

    2017-11-01

    The interaction between droplet sedimentation, turbulent mixing, evaporative cooling, and radiative cooling at the top of stratocumulus clouds has been studied using direct numerical simulations. This interaction is important to determine the mixing rate of the cloud and dry air above it, which eventually determines the cloud lifetime. By investigating the entrainment-rate equation, which is an analytical relationship between the contributions to cloud-top entrainment from the phenomena indicated above, we have found that the reduction of entrainment velocity by droplet sedimentation can be 2 to 3 times larger than previously conjectured. The reason is twofold. First, the reduction of evaporative cooling as droplets fall out of the inversion is stronger than previously observed in large-eddy simulations, where excessive mixing by turbulence models and numerical artifacts may have partially masked this effect of sedimentation on entrainment. Second, there is a non-negligible direct contribution from mass loading, as falling droplets leave behind more buoyant air in the inversion. This contribution is proportional to the fifth moment of the droplet-size distribution, which provides further evidence for the need to better understand the evolution of the droplet-size distribution.

  15. Collective oscillations and coupled modes in confined microfluidic droplet arrays

    Science.gov (United States)

    Schiller, Ulf D.; Fleury, Jean-Baptiste; Seemann, Ralf; Gompper, Gerhard

    Microfluidic droplets have a wide range of applications ranging from analytic assays in cellular biology to controlled mixing in chemical engineering. Ensembles of microfluidic droplets are interesting model systems for non-equilibrium many-body phenomena. When flowing in a microchannel, trains of droplets can form microfluidic crystals whose dynamics are governed by long-range hydrodynamic interactions and boundary effects. In this contribution, excitation mechanisms for collective waves in dense and confined microfluidic droplet arrays are investigated by experiments and computer simulations. We demonstrate that distinct modes can be excited by creating specific `defect' patterns in flowing droplet trains. While longitudinal modes exhibit a short-lived cascade of pairs of laterally displacing droplets, transversely excited modes form propagating waves that behave like microfluidic phonons. We show that the confinement induces a coupling between longitudinal and transverse modes. We also investigate the life time of the collective oscillations and discuss possible mechanisms for the onset of instabilities. Our results demonstrate that microfluidic phonons can exhibit effects beyond the linear theory, which can be studied particularly well in dense and confined systems. This work was supported by Deutsche Forschungsgemeinschaft under Grant No. SE 1118/4.

  16. EVAPORATIVE DROPLETS IN ONE-COMPONENT FLUIDS DRIVEN BY THERMAL GRADIENTS ON SOLID SUBSTRATES

    KAUST Repository

    Xu, Xinpeng; Qian, Tiezheng

    2013-01-01

    A continuum hydrodynamic model is presented for one-component liquid-gas flows on nonisothermal solid substrates. Numerical simulations are carried out for evaporative droplets moving on substrates with thermal gradients. For droplets in one-component fluids on heated/cooled substrates, the free liquid-gas interfaces are nearly isothermal. Consequently, a thermal singularity occurs at the contact line while the Marangoni effect due to interfacial temperature variation is suppressed. Through evaporation/condensation near the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. Due to this effect, droplets will move toward the cold end on substrates with thermal gradients. The droplet migration velocity is found to be proportional to the change of substrate temperature across the droplet. It follows that for two droplets of different sizes on a substrate with temperature gradient, the larger droplet moves faster and will catch up with the smaller droplet ahead. As soon as they touch, they coalesce rapidly into an even larger droplet that will move even faster. © 2013 World Scientific Publishing Company.

  17. EVAPORATIVE DROPLETS IN ONE-COMPONENT FLUIDS DRIVEN BY THERMAL GRADIENTS ON SOLID SUBSTRATES

    KAUST Repository

    Xu, Xinpeng

    2013-03-20

    A continuum hydrodynamic model is presented for one-component liquid-gas flows on nonisothermal solid substrates. Numerical simulations are carried out for evaporative droplets moving on substrates with thermal gradients. For droplets in one-component fluids on heated/cooled substrates, the free liquid-gas interfaces are nearly isothermal. Consequently, a thermal singularity occurs at the contact line while the Marangoni effect due to interfacial temperature variation is suppressed. Through evaporation/condensation near the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. Due to this effect, droplets will move toward the cold end on substrates with thermal gradients. The droplet migration velocity is found to be proportional to the change of substrate temperature across the droplet. It follows that for two droplets of different sizes on a substrate with temperature gradient, the larger droplet moves faster and will catch up with the smaller droplet ahead. As soon as they touch, they coalesce rapidly into an even larger droplet that will move even faster. © 2013 World Scientific Publishing Company.

  18. Theoretical study of liquid droplet dispersion in a venturi scrubber.

    Science.gov (United States)

    Fathikalajahi, J; Talaie, M R; Taheri, M

    1995-03-01

    The droplet concentration distribution in an atomizing scrubber was calculated based on droplet eddy diffusion by a three-dimensional dispersion model. This model is also capable of predicting the liquid flowing on the wall. The theoretical distribution of droplet concentration agrees well with experimental data given by Viswanathan et al. for droplet concentration distribution in a venturi-type scrubber. The results obtained by the model show a non-uniform distribution of drops over the cross section of the scrubber, as noted by the experimental data. While the maximum of droplet concentration distribution may depend on many operating parameters of the scrubber, the results of this study show that the highest uniformity of drop distribution will be reached when penetration length is approximately equal to one-fourth of the depth of the scrubber. The results of this study can be applied to evaluate the removal efficiency of a venturi scrubber.

  19. Towards a high throughput droplet-based agglutination assay

    KAUST Repository

    Kodzius, Rimantas; Castro, David; Foulds, Ian G.

    2013-01-01

    This work demonstrates the detection method for a high throughput droplet based agglutination assay system. Using simple hydrodynamic forces to mix and aggregate functionalized microbeads we avoid the need to use magnetic assistance or mixing structures. The concentration of our target molecules was estimated by agglutination strength, obtained through optical image analysis. Agglutination in droplets was performed with flow rates of 150 µl/min and occurred in under a minute, with potential to perform high-throughput measurements. The lowest target concentration detected in droplet microfluidics was 0.17 nM, which is three orders of magnitude more sensitive than a conventional card based agglutination assay.

  20. Towards a high throughput droplet-based agglutination assay

    KAUST Repository

    Kodzius, Rimantas

    2013-10-22

    This work demonstrates the detection method for a high throughput droplet based agglutination assay system. Using simple hydrodynamic forces to mix and aggregate functionalized microbeads we avoid the need to use magnetic assistance or mixing structures. The concentration of our target molecules was estimated by agglutination strength, obtained through optical image analysis. Agglutination in droplets was performed with flow rates of 150 µl/min and occurred in under a minute, with potential to perform high-throughput measurements. The lowest target concentration detected in droplet microfluidics was 0.17 nM, which is three orders of magnitude more sensitive than a conventional card based agglutination assay.