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Sample records for ethanol droplet flames

  1. Structure and extinction of laminar ethanol/air spray flames

    Energy Technology Data Exchange (ETDEWEB)

    Gutheil, E. [Heidelberg Univ. (DE). Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen (IWR)

    2001-07-01

    The paper presents the structure and extinction of both mono- and bidisperse ethanol/air spray flames in the counterflow configuration. A similarity transformation for monodisperse spray flames is extended to polydisperse spray flames, and the resulting one-dimensional formulation accesses the use of detailed chemical reaction mechanisms as well as detailed transport. For the ethanol/air system, 38 species and 337 elementary reactions are used. At high strain, the droplets cross the gas stagnation plane, reverse and return towards their injector. For this situation, the width of the chemical reaction zone of bidisperse and monodisperse sprays with the Sauter mean radius is almost the same. However, the droplet oscillation causes the spray flame of the bidisperse spray to strongly increase the total spray flame thickness. For the injection velocity of the spray studied here, the droplets returning to their injector hit the boundary of the computational domain as strain is increased whereas the monodisperse spray flame extinguishs at a considerably higher value of gas strain rate. Thus, the extinction behavior of the bidisperse spray flame is not represented by the monodisperse spray flame with the Sauter mean radius. The model is also suitable to predict pollutant formation. (orig.)

  2. Aspects of Cool-Flame Supported Droplet Combustion in Microgravity

    Science.gov (United States)

    Nayagam, Vedha; Dietrich, Daniel L.; Williams, Forman A.

    2015-01-01

    Droplet combustion experiments performed on board the International Space Station have shown that normal-alkane fuels with negative temperature coefficient (NTC) chemistry can support quasi-steady, low-temperature combustion without any visible flame. Here we review the results for n-decane, n-heptane, and n-octane droplets burning in carbon dioxidehelium diluted environments at different pressures and initial droplet sizes. Experimental results for cool-flame burning rates, flame standoff ratios, and extinction diameters are compared against simplified theoretical models of the phenomenon. A simplified quasi-steady model based on the partial-burning regime of Lin predicts the burning rate, and flame standoff ratio reasonably well for all three normal alkanes. The second-stage cool-flame burning and extinction following the first-stage hot-flame combustion, however, shows a small dependence on the initial droplet size, thus deviating from the quasi-steady results. An asymptotic model that estimates the oxygen depletion by the hot flame and its influence on cool-flame burning rates is shown to correct the quasi-steady results and provide a better comparison with the measured burning-rate results.This work was supported by the NASA Space Life and Physical Sciences Research and Applications Program and the International Space Station Program.

  3. Numerical Analysis of Multicomponent Suspension Droplets in High-Velocity Flame Spray Process

    Science.gov (United States)

    Gozali, Ebrahim; Mahrukh, Mahrukh; Gu, Sai; Kamnis, Spyros

    2014-08-01

    The liquid feedstock or suspension as a different mixture of liquid fuel ethanol and water is numerically studied in high-velocity suspension flame spray (HVSFS) process, and the results are compared for homogenous liquid feedstock of ethanol and water. The effects of mixture on droplet aerodynamic breakup, evaporation, combustion, and gas dynamics of HVSFS process are thoroughly investigated. The exact location where the particle heating is initiated (above the carrier liquid boiling point) can be controlled by increasing the water content in the mixture. In this way, the particle inflight time in the high-temperature gas regions can be adjusted avoiding adverse effects from surface chemical transformations. The mixture is modeled as a multicomponent droplet, and a convection/diffusion model, which takes into account the convective flow of evaporating material from droplet surface, is used to simulate the suspension evaporation. The model consists of several sub-models that include premixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling of multicomponent droplet breakup and evaporation, as well as heat and mass transfer between liquid droplets and gas phase.

  4. Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment

    Science.gov (United States)

    Williams, Forman A.; Nayagam, Vedha; Choi, Mun Y.; Dryer, Frederick L.; Shaw, Benjamin D.

    2009-01-01

    Multi-User Droplet Combustion Apparatus Flame Extinguishment Experiment (MDCA-FLEX) will assess the effectiveness of fire suppressants in microgravity and quantify the effect of different possible crew exploration atmospheres on fire suppression. The goal of this research is to provide definition and direction for large scale fire suppression tests and selection of the fire suppressant for next generation crew exploration vehicles.

  5. 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

  6. Spontaneous Ignition of Hydrothermal Flames in Supercritical Ethanol Water Solutions

    Science.gov (United States)

    Hicks, Michael C.; Hegde, Uday G.; Kojima, Jun J.

    2017-01-01

    Results are reported from recent tests where hydrothermal flames spontaneously ignited in a Supercritical Water Oxidation (SCWO) Test Cell. Hydrothermal flames are generally categorized as flames that occur when appropriate concentrations of fuel and oxidizer are present in supercritical water (SCW); i.e., water at conditions above its critical point (218 atm and 374 C). A co-flow injector was used to inject fuel, comprising an aqueous solution of 30-vol to 50-vol ethanol, and air into a reactor held at constant pressure and filled with supercritical water at approximately 240 atm and 425 C. Hydrothermal flames auto-ignited and quickly stabilized as either laminar or turbulent diffusion flames, depending on the injection velocities and test cell conditions. Two orthogonal views, one of which provided a backlit shadowgraphic image, provided visual observations. Optical emission measurements of the steady state flame were made over a spectral range spanning the ultraviolet (UV) to the near infrared (NIR) using a high-resolution, high-dynamic-range spectrometer. Depending on the fuel air flow ratios varying degrees of sooting were observed and are qualitatively compared using light absorption comparisons from backlit images.

  7. Experimental investigation of evaporation enhancement for water droplet containing solid particles in flaming combustion area

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    Glushkov Dmitrii O.

    2016-01-01

    Full Text Available The experimental study of integral characteristics of extinguishing liquid (water droplet evaporation in flaming combustion area has been held. Optical methods of two-phase and heterogeneous mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging” have been used for heat and mass transfer process investigation. It was established that small-size solid particles (for example, carbon particles in droplet structure can enhance water evaporation in flame area. It was shown that the rate of evaporation process depends on concentration and sizes of solid particles in a water droplet. The correlations have been determined between the sizes of solid particles and water droplets for maximum efficiency of fire extinguishing. The physical aspects of the problem have been discussed.

  8. Flame Shapes of Fuel Droplet Could in High Temperature Gaseous Environment under Micro-gravity

    Science.gov (United States)

    Enomoto, Hiroshi; Nagata, Hitoshi; Segawa, Daisuke; Kadota, Toshikazu

    In order to investigate the spray combustion mechanism, a new methodology (Fine Wire Sustaining method) was established. Fine wires of 14µm in diameter were used to sustain the droplets. Any arrangement of the droplets could be performed with this method. In this study, 33 fuel droplets arranged in symmetrically were subjected to the quiescent high temperature air in an electric furnace. The temperature of the environment air was about 1000K. Fuel was n-eicosane and the mean droplet diameter was 0.58mm. The standard deviation of the droplet diameter was 0.02mm. A high-speed video camera of 250ftp was provided to observe the auto-ignition and flames of fuel droplet clouds. The experiments were done at atmospheric pressure using the JAMIC drop shaft that provides 10 seconds of effective period of time for the micro-gravity. As the results, the time histories of the diameter of the particle flames had maximum and that of the diameter of the group flame had the minimum.

  9. Temperature measurements by oh lif and chemiluminescence kinetic modeling for ethanol flames

    OpenAIRE

    Marques,Carla S. T.; Leila R. dos Santos; Sbampato,Maria E.; Barreta, Luiz G.; Alberto M. dos Santos

    2009-01-01

    OH LIF-thermometry was applied to premixed ethanol flames at atmospheric pressure in a burner for three flame conditions. Flame temperatures were simulated from energy equation with PREMIX code of CHEMKIN software package for comparison. A kinetic modeling based on a model validated through chemiluminescence measurements and on a set of reactions for nitrogen chemistry was evaluated. Marinov's mechanism was also tested. Sensitivity analysis was performed for fuel-rich flame condition with ...

  10. Octagon to Square Wetting Area Transition of Water-Ethanol Droplets on a Micropyramid Substrate by Increasing Ethanol Concentration.

    Science.gov (United States)

    Feng, Huicheng; Chong, Karen Siew-Ling; Ong, Kian-Soo; Duan, Fei

    2017-02-07

    The wettability and evaporation of water-ethanol binary droplets on the substrate with micropyramid cavities are studied by controlling the initial ethanol concentrations. The droplets form octagonal initial wetting areas on the substrate. As the ethanol concentration increases, the side ratio of the initial wetting octagon increases from 1.5 at 0% ethanol concentration to 3.5 at 30% ethanol concentration. The increasing side ratio indicates that the wetting area transforms from an octagon to a square if we consider the octagon to be a square with its four corners cut. The droplets experience a pinning-depinning transition during evaporation. The pure water sessile droplet evaporation demonstrates three stages from the constant contact line (CCL) stage, and then the constant contact angle (CCA) stage, to the mixed stage. An additional mixed stage is found between the CCL and CCA stages in the evaporation of water-ethanol binary droplets due to the anisotropic depinning along the two different axes of symmetry of the octagonal wetting area. Droplet depinning occurs earlier on the patterned surface as the ethanol concentration increases.

  11. Temperature measurements by oh lif and chemiluminescence kinetic modeling for ethanol flames

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    Carla S. T. Marques

    2009-01-01

    Full Text Available OH LIF-thermometry was applied to premixed ethanol flames at atmospheric pressure in a burner for three flame conditions. Flame temperatures were simulated from energy equation with PREMIX code of CHEMKIN software package for comparison. A kinetic modeling based on a model validated through chemiluminescence measurements and on a set of reactions for nitrogen chemistry was evaluated. Marinov's mechanism was also tested. Sensitivity analysis was performed for fuel-rich flame condition with Φ = 1.34. Simulated temperatures from both reaction mechanisms evaluated were higher than experimental values. However, the proposed kinetic modeling resulted in temperature profiles qualitatively very close to the experimental.

  12. Monitoring the buckling threshold of drying colloidal droplets using water-ethanol mixtures.

    Science.gov (United States)

    Marty, G; Tsapis, N

    2008-10-01

    We visualize the drying of droplets of colloids suspended in a mixture of two miscible solvents, namely water and ethanol. After a period of isotropic shrinkage, droplets suddenly buckle like elastic shells. For a fixed colloid solid fraction, the buckling threshold evolves as a function of ethanol content, due to changes of the solvent mixture physical properties, such as viscosity and evaporation rate. A simplified model predicting the qualitative behavior of the buckling threshold as a function of the initial ethanol mass fraction has been developed that fits well experimental results.

  13. Making a Low-Cost Soda Can Ethanol Burner for Out-of-Laboratory Flame Test Demonstrations and Experiments

    Science.gov (United States)

    Yu, Henson L. Lee; Domingo, Perfecto N., Jr.; Yanza, Elliard Roswell S.; Guidote, Armando M., Jr.

    2015-01-01

    This article demonstrates how to make a low-cost ethanol burner utilizing soda cans. It burns with a light blue flame suitable for out-of-laboratory flame test demonstrations where interference from a yellow flame needs to be avoided.

  14. Lipid Droplet Accumulation and Impaired Fat Efflux in Polarized Hepatic Cells: Consequences of Ethanol Metabolism

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    Benita L. McVicker

    2012-01-01

    Full Text Available Steatosis, an early manifestation in alcoholic liver disease, is associated with the accumulation of hepatocellular lipid droplets (LDs. However, the role ethanol metabolism has in LD formation and turnover remains undefined. Here, we assessed LD dynamics following ethanol and oleic acid treatment to ethanol-metabolizing WIF-B cells (a hybrid of human fibroblasts (WI 38 and Fao rat hepatoma cells. An OA dose-dependent increase in triglyceride and stained lipids was identified which doubled (P<0.05 in the presence of ethanol. This effect was blunted with the inclusion of an alcohol metabolism inhibitor. The ethanol/ OA combination also induced adipophilin, LD coat protein involved in the attenuation of lipolysis. Additionally, ethanol treatment resulted in a significant reduction in lipid efflux. These data demonstrate that the metabolism of ethanol in hepatic cells is related to LD accumulation, impaired fat efflux, and enhancements in LD-associated proteins. These alterations in LD dynamics may contribute to ethanol-mediated defects in hepatocellular LD regulation and the formation of steatosis.

  15. Numerical and experimental studies of ethanol flames and autoignition theory for higher alkanes

    Science.gov (United States)

    Saxena, Priyank

    In order to enhance the fuel efficiency of an engine and to control pollutant formation, an improved understanding of the combustion chemistry of the fuels at a fundamental level is paramount. This knowledge can be gained by developing detailed reaction mechanisms of the fuels for various combustion processes and by studying combustion analytically employing reduced-chemistry descriptions. There is a need for small detailed reaction mechanisms for alkane and alcohol fuels with reduced uncertainties in their combustion chemistry that are computationally cheaper in multidimensional CFD calculations. Detailed mechanisms are the starting points in identifying reduced-chemistry descriptions of combustion processes to study problems analytically. This research includes numerical, experimental and analytical studies. The first part of the dissertation consists of numerical and experimental studies of ethanol flames. Although ethanol has gained popularity as a possible low-pollution source of renewable energy, significant uncertainties remain in its combustion chemistry. To begin to address ethanol combustion, first a relatively small detailed reaction mechanism, commonly known as the San Diego Mech, is developed for the combustion of hydrogen, carbon monoxide, formaldehyde, methane, methanol, ethane, ethylene, and acetylene, in air or oxygen-inert mixtures. This mechanism is tested for autoignition, premixed-flame burning velocities, and structures and extinction of diffusion flames and of partially premixed flames of many of these fuels. The reduction in uncertainties in the combustion chemistry can best be achieved by consistently updating a reaction mechanism with reaction rate data for the elementary steps based on newer studies in literature and by testing it against as many experimental conditions as available. The results of such a testing for abovementioned fuels are reported here along with the modifications of reaction-rate parameters of the most important

  16. Analysis of Completely Prevaporized Spray Flames with Water/Octane Core/Shell Structured Droplets

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    Chung-Yao Hsuan

    2015-01-01

    Full Text Available A series of studies on laminar flame propagation in off-stoichiometric dilute sprays of monodispersed inert or fuel drops had been investigated by large activation energy asymptotics. The present study extends previous theoretical model to consider water/octane core/shell structured drops instead of single-phase drops. The core/shell structured drops are composed of core fluid (water encased by a layer of shell fluid (n-octane. In this study, we only deal with the case that core/shell structured drops are vaporized completely just at flame location. Namely, the discussions of this paper are restricted to the completely prevaporized mode. By varying parameters of core water radius, core-to-shell ratio, the amount of liquid loading, and the stoichiometric ratio (lean or rich burning, we examine the gasification of core water and shell fuel of core/shell structured drops upstream of the bulk flame and its relation to the internal heat transfer. The effects of drop radius, core-to-shell ratio, liquid loading, and overall heat loss or gain on flame propagation flux are reported and discussed.

  17. Improvement of Flame-made ZnO Nanoparticulate Thick Film Morphology for Ethanol Sensing

    Science.gov (United States)

    Liewhiran, Chaikarn; Phanichphantandast, Sukon

    2007-01-01

    ZnO nanoparticles were produced by flame spray pyrolysis using zinc naphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particles properties were analyzed by XRD, BET. The ZnO particle size and morphology was observed by SEM and HR-TEM revealing spheroidal, hexagonal, and rod-like morphologies. The crystallite sizes of ZnO spheroidal and hexagonal particles ranged from 10-20 nm. ZnO nanorods were ranged from 10-20 nm in width and 20-50 nm in length. Sensing films were produced by mixing the nanoparticles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed onto Al2O3 substrates interdigitated with Au electrodes. The morphology of the sensing films was analyzed by optical microscopy and SEM analysis. Cracking of the sensing films during annealing process was improved by varying the heating conditions. The gas sensing of ethanol (25-250 ppm) was studied at 400 °C in dry air containing SiC as the fluidized particles. The oxidation of ethanol on the surface of the semiconductor was confirmed by mass spectroscopy (MS). The effect of micro-cracks was quantitatively accounted for as a provider of extra exposed edges. The sensitivity decreased notably with increasing crack of sensing films. It can be observed that crack widths were reduced with decreasing heating rates. Crack-free of thick (5 μm) ZnO films evidently showed higher sensor signal and faster response times (within seconds) than cracked sensor. The sensor signal increased and the response time decreased with increasing ethanol concentration.

  18. Improvement of Flame-made ZnO Nanoparticulate Thick Film Morphology for Ethanol Sensing

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    Sukon Phanichphant

    2007-05-01

    Full Text Available ZnO nanoparticles were produced by flame spray pyrolysis using zinc naphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%. The particles properties were analyzed by XRD, BET. The ZnO particle size and morphology was observed by SEM and HR-TEM revealing spheroidal, hexagonal, and rod-like morphologies. The crystallite sizes of ZnO spheroidal and hexagonal particles ranged from 10-20 nm. ZnO nanorods were ranged from 10-20 nm in width and 20-50 nm in length. Sensing films were produced by mixing the nanoparticles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed onto Al2O3 substrates interdigitated with Au electrodes. The morphology of the sensing films was analyzed by optical microscopy and SEM analysis. Cracking of the sensing films during annealing process was improved by varying the heating conditions. The gas sensing of ethanol (25-250 ppm was studied at 400 °C in dry air containing SiC as the fluidized particles. The oxidation of ethanol on the surface of the semiconductor was confirmed by mass spectroscopy (MS. The effect of micro-cracks was quantitatively accounted for as a provider of extra exposed edges. The sensitivity decreased notably with increasing crack of sensing films. It can be observed that crack widths were reduced with decreasing heating rates. Crack-free of thick (5 μm ZnO films evidently showed higher sensor signal and faster response times (within seconds than cracked sensor. The sensor signal increased and the response time decreased with increasing ethanol concentration.

  19. Ethanol analysis by headspace gas chromatography with simultaneous flame-ionization and mass spectrometry detection.

    Science.gov (United States)

    Tiscione, Nicholas B; Alford, Ilene; Yeatman, Dustin Tate; Shan, Xiaoqin

    2011-09-01

    Ethanol is the most frequently identified compound in forensic toxicology. Although confirmation involving mass spectrometry is desirable, relatively few methods have been published to date. A novel technique utilizing a Dean's Switch to simultaneously quantitate and confirm ethyl alcohol by flame-ionization (FID) and mass spectrometric (MS) detection after headspace sampling and gas chromatographic separation is presented. Using 100 μL of sample, the limits of detection and quantitation were 0.005 and 0.010 g/dL, respectively. The zero-order linear range (r(2) > 0.990) was determined to span the concentrations of 0.010 to 1.000 g/dL. The coefficient of variation of replicate analyses was less than 3.1%. Quantitative accuracy was within ±8%, ±6%, ±3%, and ±1.5% at concentrations of 0.010, 0.025, 0.080, and 0.300 g/dL, respectively. In addition, 1,1-difluoroethane was validated for qualitative identification by this method. The validated FID-MS method provides a procedure for the quantitation of ethyl alcohol in blood by FID with simultaneous confirmation by MS and can also be utilized as an identification method for inhalants such as 1,1-difluoroethane.

  20. Simultaneous determination of methanol, acetaldehyde, acetone, and ethanol in human blood by gas chromatography with flame ionization detection.

    Science.gov (United States)

    Schlatter, J; Chiadmi, F; Gandon, V; Chariot, P

    2014-01-01

    Methanol, acetaldehyde, acetone, and ethanol, which are commonly used as biomarkers of several diseases, in acute intoxications, and forensic settings, can be detected and quantified in biological fluids. Gas chromatography (GC)-mass spectrometry techniques are complex, require highly trained personnel and expensive materials. Gas chromatographic determinations of ethanol, methanol, and acetone have been reported in one study with suboptimal accuracy. Our objective was to improve the assessment of these compounds in human blood using GC with flame ionization detection. An amount of 50 µl of blood was diluted with 300 µl of sterile water, 40 µl of 10% sodium tungstate, and 20 µl of 1% sulphuric acid. After centrifugation, 1 µl of the supernatant was injected into the gas chromatograph. We used a dimethylpolysiloxane capillary column of 30 m × 0.25 mm × 0.25 µm. We observed linear correlations from 7.5 to 240 mg/l for methanol, acetaldehyde, and acetone and from 75 to 2400 mg/l for ethanol. Precision at concentrations 15, 60, and 120 mg/l for methanol, acetaldehyde, and acetone and 150, 600, and 1200 mg/ml for ethanol were 0.8-6.9%. Ranges of accuracy were 94.7-98.9% for methanol, 91.2-97.4% for acetaldehyde, 96.1-98.7% for acetone, and 105.5-111.6% for ethanol. Limits of detection were 0.80 mg/l for methanol, 0.61 mg/l for acetaldehyde, 0.58 mg/l for acetone, and 0.53 mg/l for ethanol. This method is suitable for routine clinical and forensic practices.

  1. Combustion dynamics of low vapour pressure nanofuel droplets

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    Pandey, Khushboo; Chattopadhyay, Kamanio; Basu, Saptarshi

    2017-07-01

    Multiscale combustion dynamics, shape oscillations, secondary atomization, and precipitate formation have been elucidated for low vapour pressure nanofuel [n-dodecane seeded with alumina nanoparticles (NPs)] droplets. Dilute nanoparticle loading rates (0.1%-1%) have been considered. Contrary to our previous studies of ethanol-water blend (high vapour pressure fuel), pure dodecane droplets do not exhibit internal boiling after ignition. However, variation in surface tension due to temperature causes shape deformations for pure dodecane droplets. In the case of nanofuels, intense heat release from the enveloping flame leads to the formation of micron-size aggregates (of alumina NPS) which serve as nucleation sites promoting heterogeneous boiling. Three boiling regimes (A, B, and C) have been identified with varying bubble dynamics. We have deciphered key mechanisms responsible for the growth, transport, and rupture of the bubbles. Bubble rupture causes ejections of liquid droplets termed as secondary atomization. Ejection of small bubbles (mode 1) resembles the classical vapour bubble collapse mechanism near a flat free surface. However, large bubbles induce severe shape deformations as well as bulk oscillations. Rupture of large bubbles results in high speed liquid jet formation which undergoes Rayleigh-Plateau tip break-up. Both modes contribute towards direct fuel transfer from the droplet surface to flame envelope bypassing diffusion limitations. Combustion lifetime of nanofuel droplets consequently has two stages: stage I (where bubble dynamics are dominant) and stage II (formation of gelatinous mass due to continuous fuel depletion; NP agglomeration). In the present work, variation of flame dynamics and spatio-temporal heat release (HR) have been analysed using high speed OH* chemiluminescence imaging. Fluctuations in droplet shape and flame heat release are found to be well correlated. Droplet flame is bifurcated in two zones (I and II). Flame response is

  2. Speciation of Tl(III and Tl(I in hair samples by dispersive liquid–liquid microextraction based on solidification of floating organic droplet prior to flame atomic absorption spectrometry determination

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    S.Z. Mohammadi

    2016-11-01

    Full Text Available Dispersive liquid–liquid microextraction based on solidification of floating organic droplet was successfully used as a sample preparation method prior to flame atomic absorption determination of trace amounts of Tl(III and Tl(I in hair samples. In the proposed method, 1-(2-pyridylazo-2-naphthol, 1-dodecanol and ethanol were used as chelating agent, extraction and dispersive solvent, respectively. Several factors that may be affected in the extraction process, such as type and volume of extraction and disperser solvents, pH, salting out effect, ionic strength and extraction time were studied. Under the optimal conditions, linearity was maintained between 6.0 and 900.0 ng mL−1 for Tl(III. The relative standard deviation for seven replicate determinations of 0.2 μg mL−1 Tl(III was 2.5%. The detection limit based on 3Sb for Tl(III in the original solution was 2.1 ng mL−1. The proposed method has been applied for the determination of trace amounts of thallium in hair samples and satisfactory results were obtained.

  3. Fiber-Supported Droplet Combustion Experiment-2

    Science.gov (United States)

    Colantonio, Renato O.

    1998-01-01

    A major portion of the energy produced in the world today comes from the burning of liquid hydrocarbon fuels in the form of droplets. Understanding the fundamental physical processes involved in droplet combustion is not only important in energy production but also in propulsion, in the mitigation of combustion-generated pollution, and in the control of the fire hazards associated with handling liquid combustibles. Microgravity makes spherically symmetric combustion possible, allowing investigators to easily validate their droplet models without the complicating effects of gravity. The Fiber-Supported Droplet Combustion (FSDC-2) investigation was conducted in the Microgravity Glovebox facility of the shuttles' Spacelab during the reflight of the Microgravity Science Laboratory (MSL- 1R) on STS-94 in July 1997. FSDC-2 studied fundamental phenomena related to liquid fuel droplet combustion in air. Pure fuels and mixtures of fuels were burned as isolated single and duo droplets with and without forced air convection. FSDC-2 is sponsored by the NASA Lewis Research Center, whose researchers are working in cooperation with several investigators from industry and academia. The rate at which a droplet burns is important in many commercial applications. The classical theory of droplet burning assumes that, for an isolated, spherically symmetric, single-fuel droplet, the gas-phase combustion processes are much faster than the droplet surface regression rate and that the liquid phase is at a uniform temperature equal to the boiling point. Recent, more advanced models predict that both the liquid and gas phases are unsteady during a substantial portion of the droplet's burning history, thus affecting the instantaneous and average burning rates, and that flame radiation is a dominant mechanism that can extinguish flames in a microgravity environment. FSDC-2 has provided well-defined, symmetric droplet burning data including radiative emissions to validate these theoretical

  4. Highly Stretchable, Ultrasensitive, and Wearable Strain Sensors Based on Facilely Prepared Reduced Graphene Oxide Woven Fabrics in an Ethanol Flame.

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    Yin, Biao; Wen, Yanwei; Hong, Tao; Xie, Zhongshuai; Yuan, Guoliang; Ji, Qingmin; Jia, Hongbing

    2017-09-20

    The recent booming development of wearable electronics urgently calls for high-performance flexible strain sensors. To date, it is still a challenge to manufacture flexible strain sensors with superb sensitivity and a large workable strain range simultaneously. Herein, a facile, quick, cost-effective, and scalable strategy is adopted to fabricate novel strain sensors based on reduced graphene oxide woven fabrics (GWF). By pyrolyzing commercial cotton bandages coated with graphene oxide (GO) sheets in an ethanol flame, the reduction of GO and the pyrolysis of the cotton bandage template can be synchronously completed in tens of seconds. Due to the unique hierarchical structure of the GWF, the strain sensor based on GWF exhibits large stretchability (57% strain) with high sensitivity, inconspicuous drift, and durability. The GWF strain sensor is successfully used to monitor full-range (both subtle and vigorous) human activities or physical vibrational signals of the local environment. The present work offers an effective strategy to rapidly prepare low-cost flexible strain sensors with potential applications in the fields of wearable electronics, artificial intelligence devices, and so forth.

  5. Temperature and Concentration Traces of Spray Flows During Motion in a Flame

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    Antonov Dmitry V.

    2016-01-01

    Full Text Available Heat and mass transfer models are developed on the base of experimental data and using Ansys Fluent software. These models allow prediction of the temperature and concentration traces of droplets. Transfer mechanisms of water droplets from different flames of flammable liquid (ethanol, kerosene И benzine with temperature gases 450–850 К are analyzed. The paper considers aerosol flows with droplets sizes of 0.04–0.4 mm and concentration of 3.8·10-5 –10.3·10-5 m3 of droplets/m3 of gas. The maximum gas temperature reduction in the trace of a moving liquid is ranged from 850 K to 600 K. The times of keeping the low temperature of the gas-vapor mixture in the droplets trace are from 13 s to 25 s relative to the initial gas temperature.

  6. Influence of Thickness on Ethanol Sensing Characteristics of Doctor-bladed Thick Film from Flame-made ZnO Nanoparticles

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    Sukon Phanichphant

    2007-02-01

    Full Text Available ZnO nanoparticles were produced by flame spray pyrolysis (FSP using zincnaphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%. The particleproperties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced bymixing the particles into an organic paste composed of terpineol and ethyl cellulose as avehicle binder and were fabricated by doctor-blade technique with various thicknesses (5,10, 15 μm. The morphology of the sensing films was analyzed by SEM and EDS analyses.The gas sensing characteristics to ethanol (25-250 ppm were evaluated as a function of filmthickness at 400°C in dry air. The relationship between thickness and ethanol sensingcharacteristics of ZnO thick film on Al2O3 substrate interdigitated with Au electrodes wereinvestigated. The effects of film thickness, as well as the cracking phenomenon, though,many cracks were observed for thicker sensing films. Crack widths increased withincreasing film thickness. The film thickness, cracking and ethanol concentration havesignificant effect on the sensing characteristics. The sensing characteristics with variousthicknesses were compared, showing the tendency of the sensitivity to ethanol decreasedwith increasing film thickness and response time. The relationship between gas sensingproperties and film thickness was discussed on the basis of diffusively and reactivity of thegases inside the oxide films. The thinnest sensing film (5 μm showed the highest sensitivityand the fastest response time (within seconds.

  7. Influence of Thickness on Ethanol Sensing Characteristics of Doctor-bladed Thick Film from Flame-made ZnO Nanoparticles

    Science.gov (United States)

    Liewhiran, Chaikarn; Phanichphant, Sukon

    2007-01-01

    ZnO nanoparticles were produced by flame spray pyrolysis (FSP) using zinc naphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particle properties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced by mixing the particles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder and were fabricated by doctor-blade technique with various thicknesses (5, 10, 15 μm). The morphology of the sensing films was analyzed by SEM and EDS analyses. The gas sensing characteristics to ethanol (25-250 ppm) were evaluated as a function of film thickness at 400°C in dry air. The relationship between thickness and ethanol sensing characteristics of ZnO thick film on Al2O3 substrate interdigitated with Au electrodes were investigated. The effects of film thickness, as well as the cracking phenomenon, though, many cracks were observed for thicker sensing films. Crack widths increased with increasing film thickness. The film thickness, cracking and ethanol concentration have significant effect on the sensing characteristics. The sensing characteristics with various thicknesses were compared, showing the tendency of the sensitivity to ethanol decreased with increasing film thickness and response time. The relationship between gas sensing properties and film thickness was discussed on the basis of diffusively and reactivity of the gases inside the oxide films. The thinnest sensing film (5 μm) showed the highest sensitivity and the fastest response time (within seconds).

  8. Effects of Palladium Loading on the Response of Thick Film Flame-made ZnO Gas Sensor for Detection of Ethanol Vapor

    Directory of Open Access Journals (Sweden)

    Sukon Phanichphant

    2007-07-01

    Full Text Available ZnO nanoparticles doped with 0-5 mol% Pd were successfully produced in asingle step by flame spray pyrolysis (FSP using zinc naphthenate and palladium (IIacetylacetonate dissolved in toluene-acetonitrile (80:20 vol% as precursors. The effect ofPd loading on the ethanol gas sensing performance of the ZnO nanoparticles and thecrystalline sizes were investigated. The particle properties were analyzed by XRD, BET,AFM, SEM (EDS line scan mode, TEM, STEM, EDS, and CO-pulse chemisorptionmeasurements. A trend of an increase in specific surface area of samples and a decrease inthe dBET with increasing Pd concentrations was noted. ZnO nanoparticles were observed asparticles presenting clear spheroidal, hexagonal and rod-like morphologies. The sizes ofZnO spheroidal and hexagonal particle crystallites were in the 10-20 nm range. ZnOnanorods were in the range of 10-20 nm in width and 20-50 nm in length. The size of Pdnanoparticles increased and Pd-dispersion% decreased with increasing Pd concentrations.The sensing films were produced by mixing the particles into an organic paste composedof terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed ontoAl2O3 substrates interdigitated with Au electrodes. The film morphology was analyzed bySEM and EDS analyses. The gas sensing of ethanol (25-250 ppm was studied in dry air at400°C. The oxidation of ethanol on the sensing surface of the semiconductor wasconfirmed by MS. A well-dispersed of 1 mol%Pd/ZnO films showed the highest sensitivityand the fastest response time (within seconds.

  9. Effects of Palladium Loading on the Response of a Thick Film Flame-made ZnO Gas Sensor for Detection of Ethanol Vapor

    Science.gov (United States)

    Liewhiran, Chaikarn; Phanichphant, Sukon

    2007-01-01

    ZnO nanoparticles doped with 0-5 mol% Pd were successfully produced in a single step by flame spray pyrolysis (FSP) using zinc naphthenate and palladium (II) acetylacetonate dissolved in toluene-acetonitrile (80:20 vol%) as precursors. The effect of Pd loading on the ethanol gas sensing performance of the ZnO nanoparticles and the crystalline sizes were investigated. The particle properties were analyzed by XRD, BET, AFM, SEM (EDS line scan mode), TEM, STEM, EDS, and CO-pulse chemisorption measurements. A trend of an increase in specific surface area of samples and a decrease in the dBET with increasing Pd concentrations was noted. ZnO nanoparticles were observed as particles presenting clear spheroidal, hexagonal and rod-like morphologies. The sizes of ZnO spheroidal and hexagonal particle crystallites were in the 10-20 nm range. ZnO nanorods were in the range of 10-20 nm in width and 20-50 nm in length. The size of Pd nanoparticles increased and Pd-dispersion% decreased with increasing Pd concentrations. The sensing films were produced by mixing the particles into an organic paste composed of terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed onto Al2O3 substrates interdigitated with Au electrodes. The film morphology was analyzed by SEM and EDS analyses. The gas sensing of ethanol (25-250 ppm) was studied in dry air at 400°C. The oxidation of ethanol on the sensing surface of the semiconductor was confirmed by MS. A well-dispersed of 1 mol%Pd/ZnO films showed the highest sensitivity and the fastest response time (within seconds).

  10. Dynamics of Droplet Collision and Flamefront Motion

    National Research Council Canada - National Science Library

    Law, Chung K

    2005-01-01

    ... of air bubbles entrained upon coalescence of the colliding droplets. (3) The dynamics of droplet-film collision, especially on the influence of the film thickness in effecting droplet bouncing versus absorption. (4) The dynamics of flame motion when it is subjected to the combined hydrodynamic and body-force instabilities and freestream vortical motion.

  11. FLAME DENITRATION AND REDUCTION OF URANIUM NITRATE TO URANIUM DIOXIDE

    Science.gov (United States)

    Hedley, W.H.; Roehrs, R.J.; Henderson, C.M.

    1962-06-26

    A process is given for converting uranyl nitrate solution to uranium dioxide. The process comprises spraying fine droplets of aqueous uranyl nitrate solution into a hightemperature hydrocarbon flame, said flame being deficient in oxygen approximately 30%, retaining the feed in the flame for a sufficient length of time to reduce the nitrate to the dioxide, and recovering uranium dioxide. (AEC)

  12. combination of flame atomic absorption spectrometry with ligandless

    African Journals Online (AJOL)

    Preferred Customer

    separation and flame atomic absorption spectrometry determination of trace amount of lead(II) ion. In the proposed approach 1,2-dicholorobenzene and ethanol were used as extraction .... in ethanol was added to it. The final solution was aspirated directly into the flame of AAS. The extraction scheme of Pb(II) ion is shown in.

  13. Dancing Droplets

    Science.gov (United States)

    Cira, Nate; Prakash, Manu

    2013-11-01

    Inspired by the observation of intricate and beautifully dynamic patterns generated by food coloring on corona treated glass slides, we have investigated the behavior of propylene glycol and water droplets on clean glass surfaces. These droplets exhibit a range of interesting behaviors including long distance attraction or repulsion, and chasing/fleeing upon contact. We present explanations for each of these behaviors, and propose a detailed model for the long distance interactions based on vapor facilitated coupling. Finally we use our understanding to create several novel devices which: passively sort droplets by surface tension, spontaneously align droplets, drive droplets in circles, and cause droplets to bounce on a vertical surface. The simplicity of this system lends it particularly well to application as a toy model for physical systems with force fields and biological systems such as chemotaxis and motility.

  14. Swimming Droplets

    Science.gov (United States)

    Maass, Corinna C.; Krüger, Carsten; Herminghaus, Stephan; Bahr, Christian

    2016-03-01

    Swimming droplets are artificial microswimmers based on liquid droplets that show self-propelled motion when immersed in a second liquid. These systems are of tremendous interest as experimental models for the study of collective dynamics far from thermal equilibrium. For biological systems, such as bacterial colonies, plankton, or fish swarms, swimming droplets can provide a vital link between simulations and real life. We review the experimental systems and discuss the mechanisms of self-propulsion. Most systems are based on surfactant-stabilized droplets, the surfactant layer of which is modified in a way that leads to a steady Marangoni stress resulting in an autonomous motion of the droplet. The modification of the surfactant layer is caused either by the advection of a chemical reactant or by a solubilization process. Some types of swimming droplets possess a very simple design and long active periods, rendering them promising model systems for future studies of collective behavior.

  15. Numerical Simulations of Acoustically Driven, Burning Droplets

    Science.gov (United States)

    Kim, Heon-Chang; Karagozian, Ann R.; Smith, Owen I.

    1999-11-01

    The burning characteristics of fuel droplets exposed to external acoustical excitation within a microgravity environment are investigated numerically. The issue of acoustic excitation of flames in microgravity is especially pertinent to understanding the behavior of accidental fires which could occur in spacecraft crew quarters and which could be affected by pressure perturbations as result from ventilation fans or engine vibrations. Combustion of methanol fuel droplets is considered here using a full chemical reaction mechanism.(Marchese, A.J., et al., 26th Symp. (Int.) on Comb., p. 1209, 1997) The droplet and surrounding diffusion flame are situated within a cylindrical acoustic waveguide where standing waves are generated with varying frequency and amplitude. Applied sound pressure levels are limited at present to magnitudes for which the droplet shape remains spherical. A third order accurate, essentially-non-oscillatory (ENO) numerical scheme is employed to accurately resolve the spatial and temporal evolution of the flame front. Acoustically excited vs. non-excited external conditions for the burning droplet in microgravity are compared, and the effects of acoustic frequency, sound pressure level, and relative position of the droplet with respect to pressure and velocity nodes are explored.

  16. Dancing Droplets

    CERN Document Server

    Cira, Nate J

    2013-01-01

    Inspired by the observation of intricate and beautifully dynamic patterns generated by food coloring on clean glass slides, we have investigated the behavior of propylene glycol and water droplets on high energy surfaces. In this fluid dynamics video we show a range of interesting behaviors including long distance attraction, and chasing/fleeing upon contact. We present explanations for each of these behaviors including a mechanism for the long distance interactions based on vapor facilitated coupling. Finally we use our understanding to create several novel devices which: spontaneously align droplets, drive droplets in circles, cause droplets to bounce on a vertical surface, and passively sort droplets by surface tension. The simplicity of this system lends it particularly well to application as a toy model for physical systems with force fields and biological systems such as chemotaxis and motility.

  17. Flame Length

    Data.gov (United States)

    Earth Data Analysis Center, University of New Mexico — Flame length was modeled using FlamMap, an interagency fire behavior mapping and analysis program that computes potential fire behavior characteristics. The tool...

  18. 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

  19. 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

  20. Flames in vortices & tulip-flame inversion

    Science.gov (United States)

    Dold, J. W.

    This article summarises two areas of research regarding the propagation of flames in flows which involve significant fluid-dynamical motion [1]-[3]. The major difference between the two is that in the first study the fluid motion is present before the arrival of any flame and remains unaffected by the flame [1, 2] while, in the second study it is the flame that is responsible for all of the fluid dynamical effects [3]. It is currently very difficult to study flame-motion in which the medium is both highly disturbed before the arrival of a flame and is further influenced by the passage of the flame.

  1. Dancing Droplets

    OpenAIRE

    Cira, Nate J.; Prakash, Manu

    2013-01-01

    Inspired by the observation of intricate and beautifully dynamic patterns generated by food coloring on clean glass slides, we have investigated the behavior of propylene glycol and water droplets on high energy surfaces. In this fluid dynamics video we show a range of interesting behaviors including long distance attraction, and chasing/fleeing upon contact. We present explanations for each of these behaviors including a mechanism for the long distance interactions based on vapor facilitated...

  2. Phase diagram for droplet impact on superheated surfaces

    NARCIS (Netherlands)

    Staat, Erik-Jan; Tran, Tuan; Geerdink, B.M.; Riboux, G.; Sun, Chao; Gordillo, J.M.; Lohse, Detlef

    2015-01-01

    We experimentally determine the phase diagram for impacting ethanol droplets on a smooth, sapphire surface in the parameter space of Weber number We versus surface temperature T. We observe two transitions, namely the one towards splashing (disintegration of the droplet) with increasing We, and the

  3. Definition of an experiment on combustion of two droplets in microgravity

    Energy Technology Data Exchange (ETDEWEB)

    Naja, G.

    1986-01-01

    This paper deals with the improvement of droplet combustion models - the key to the proper working of rocket engines. The result of the present study is a very simple criterion defining the threshold of interaction between the flames of two droplets. Microgravity experiments will be the only way to check this theoretical result. 5 references.

  4. Laminar Flame Speeds of Gasoline Surrogates Measured with the Flat Flame Method

    KAUST Repository

    Liao, Y.-H.

    2016-01-27

    © 2016 American Chemical Society. The adiabatic, laminar flame speeds of gasoline surrogates at atmospheric pressure over a range of equivalence ratios of = 0.8-1.3 and unburned gas temperatures of 298-400 K are measured with the flat flame method, which produces a one-dimensional flat flame free of stretch. Surrogates used in the current work are the primary reference fuels (PRFs, mixtures of n-heptane and isooctane), the toluene reference fuels (TRFs, mixtures of toluene and PRFs), and the ethanol reference fuels (ERFs, mixtures of ethanol and PRFs). In general, there is good agreement between the present work and the literature data for single-component fuel and PRF mixtures. Surrogates of TRF mixtures are found to exhibit comparable flame speeds to a real gasoline, while there is discrepancy observed between isooctane and gasoline. Moreover, the laminar flame speeds of TRF mixtures with similar fractions of n-heptane are found to be insensitive to the quantity of toluene in the mixture. Mixtures of ERFs exhibit comparable flame speeds to those of TRFs with similar mole fractions of n-heptane and isooctane.

  5. Electric field effects on droplet burning

    Science.gov (United States)

    Patyal, Advitya; Kyritsis, Dimitrios; Matalon, Moshe

    2015-11-01

    The effects of an externally applied electric field are studied on the burning characteristics of a spherically symmetric fuel drop including the structure, mass burning rate and extinction characteristics of the diffusion flame. A reduced three-step chemical kinetic mechanism that reflects the chemi-ionization process for general hydrocarbon fuels has been proposed to capture the production and destruction of ions inside the flame zone. Due to the imposed symmetry, the effect of the ionic wind is simply to modify the pressure field. Our study thus focuses exclusively on the effects of Ohmic heating and kinetic effects on the burning process. Two distinguished limits of weak and strong field are identified, highlighting the relative strength of the internal charge barrier compared to the externally applied field, and numerically simulated. For both limits, significantly different charged species distributions are observed. An increase in the mass burning rate is noticed with increasing field in either limit with negligible change in the flame temperature. Increasing external voltages pushes the flame away from the droplet and causes a strengthening of the flame with a reduction in the extinction Damkhöler number.

  6. 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......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...

  7. Droplet-based microfluidics.

    Science.gov (United States)

    Sharma, Sanjiv; Srisa-Art, Monpichar; Scott, Steven; Asthana, Amit; Cass, Anthony

    2013-01-01

    Droplet-based microfluidics or digital microfluidics is a subclass of microfluidic devices, wherein droplets are generated using active or passive methods. The active method for generation of droplets involves the use of an external factor such as an electric field for droplet generation. Two techniques that fall in this category are dielectrophoresis (DEP) and electrowetting on dielectric (EWOD). In passive methods, the droplet generation depends on the geometry and dimensions of the device. T-junction and flow focusing methods are examples of passive methods used for generation of droplets. In this chapter the methods used for droplet generation, mixing of contents of droplets, and the manipulation of droplets are described in brief. A review of the applications of digital microfluidics with emphasis on the last decade is presented.

  8. Flame structure of methane inverse diffusion flame

    KAUST Repository

    Elbaz, Ayman M.

    2014-07-01

    This paper presents high speed images of OH-PLIF at 10. kHz simultaneously with 2D PIV (particle image velocimetry) measurements collected along the entire length of an inverse diffusion flame with circumferentially arranged methane fuel jets. For a fixed fuel flow rate, the central air jet Re was varied, leading to four air to fuel velocity ratios, namely Vr = 20.7, 29, 37.4 and 49.8. A double flame structure could be observed composed of a lower fuel entrainment region and an upper mixing and intense combustion region. The entrainment region was enveloped by an early OH layer, and then merged through a very thin OH neck to an annular OH layer located at the shear layer of the air jet. The two branches of this annular OH layer broaden as they moved downstream and eventfully merged together. Three types of events were observed common to all flames: breaks, closures and growing kernels. In upstream regions of the flames, the breaks were counterbalanced by flame closures. These breaks in OH signal were found to occur at locations where locally high velocity flows were impinging on the flame. As the Vr increased to 37.4, the OH layers became discontinuous over the downstream region of the flame, and these regions of low or no OH moved upstream. With further increases in Vr, these OH pockets act as flame kernels, growing as they moved downstream, and became the main mechanism for flame re-ignition. Along the flame length, the direction of the two dimensional principle compressive strain rate axis exhibited a preferred orientation of approximately 45° with respect to the flow direction. Moreover, the OH zones were associated with elongated regions of high vorticity. © 2013 Elsevier Inc.

  9. Emulsion Droplet Combustion in Microgravity: Water/Heptane Emulsions

    Science.gov (United States)

    Avedisian, C. Thomas

    1997-01-01

    This presentation reviews a series of experiments to further examine parametric effects on sooting processes of droplet flames in microgravity. The particular focus is on a fuel droplet emulsified with water, specifically emulsions of n-heptane as the fuel-phase and water as the dispersed phase. Water was selected as the additive because of its anticipated effect on soot formation, and the heptane fuel phase was chosen to theoretically reduce the likelihood of microexplosions because its boiling point is nearly the same as that of water: 100 C for water and 98 C for heptane. The water content was varied while the initial droplet diameter was kept within a small range. The experiments were carried out in microgravity to reduce the effects of buoyancy and to promote spherical symmetry in the burning process. Spherically symmetric droplet burning is a convenient starting point for analysis, but experimental data are difficult to obtain for this situation as evidenced by the fact that no quantitative data have been reported on unsupported emulsion droplet combustion in a convection-free environment. The present study improves upon past work carried out on emulsion droplet combustion in microgravity which employed emulsion droplets suspended from a fiber. The fiber can be instrusive to the emulsion droplet burning process as it can promote coalescence of the dispersed water phase and heterogeneous nucleation on the fiber. Prior work has shown that the presence of water in liquid hydrocarbons can have both beneficial and detrimental effects on the combustion process. Water is known to reduce soot formation and radiation heat transfer to combustor walls Gollahalli (1979) reduce flame temperatures and thereby NOx emissions, and encourage secondary droplet atomization or microexplosion. Water also tends to retard ignition and and promote early extinction. The former effect restricted the range of water volume fractions as discussed below.

  10. Charged slurry droplet research

    Science.gov (United States)

    Kelly, A. J.

    1989-02-01

    Rayleigh Bursting, wherein critically charged droplets explosively expel a number of micron sized sibling droplets, enhances atomization and combustion of all liquid fuels. Droplet surface charge is retained during evaporation, permitting multiple Rayleigh Bursts to occur. Moreover, the charge is available for the deagglomeration of residual particulate flocs from slurry droplet evaporation. To fill gaps in our knowledge of these processes, an experimental program involving the use of a charged droplet levitator and a Quadrupole Mass Spectrometer, High Speed Electrometer (QMS/HSE) has been undertaken to observe the disruption and to measure quantitatively the debris. A charged droplet levitator based on a new video frame grabber technology to image transient events, is described. Sibling droplet size is ten microns or less and is close to, if not coincident with, the predicted phase transition in droplet charging level. The research effort has focused on the exploration of this transition and its implications.

  11. Vortex formation in coalescence of droplets with a reservoir using molecular dynamics simulations.

    Science.gov (United States)

    Taherian, Fereshte; Marcon, Valentina; Bonaccurso, Elmar; van der Vegt, Nico F A

    2016-10-01

    The flow patterns generated by the coalescence of aqueous ethanol droplets with a water reservoir are investigated using molecular dynamics simulations. The influence of surface tension gradient, which leads to the spreading of the droplet along the liquid-vapor interface of the reservoir, is studied by changing the ethanol concentration of the droplet. The internal circulation (vortex strength) of the droplet and the reservoir are analyzed separately. Simulation results reveal the formation of swirling flows within the droplet at early times when the radius of the coalescence neck due to the capillary forces increases rapidly with time. The vortex strength is found to be higher at lower concentrations of ethanol (higher liquid-vapor surface tension of the droplet), where the driving force for the contact line movement (capillary force) is stronger. The circulation diminishes by moving the center of mass of the droplet toward the reservoir. The lower surface tension of the droplet compared to the reservoir leads to surface tension gradient driven flow, which transports the droplet molecules along the liquid-vapor interface of the reservoir. Such a flow motion results in the generation of convective flows in the underlying water, which forms swirling flows within the reservoir. Therefore, the vortex strength of the reservoir is higher at higher ethanol concentrations of the droplet. The reservoir circulation decays to zero as soon as the ethanol concentration becomes homogeneous along the interface of the pool. The time evolution of circulation within the droplet and the reservoir are correlated with the center of mass motion of the droplet toward the surface, the time variation of the precursor film radius and the dynamic surface tension of the reservoir. Copyright © 2016 Elsevier Inc. All rights reserved.

  12. Droplet Combustion Experiments Aboard the International Space Station

    Science.gov (United States)

    Dietrich, Daniel L.; Nayagam, Vedha; Hicks, Michael C.; Ferkul, Paul V.; Dryer, Frederick L.; Farouk, Tanvir; Shaw, Benjamin D.; Suh, Hyun Kyu; Choi, Mun Y.; Liu, Yu Cheng; Avedisian, C. Thomas; Williams, Forman A.

    2014-10-01

    This paper summarizes the first results from isolated droplet combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial droplet droplet diameters between 1.5 and 5.0 m m, ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 a t m and ambient environments containing oxygen and nitrogen diluted with both carbon dioxide and helium. The experiments show both radiative and diffusive extinction. For both fuels, the flames exhibited pre-extinction flame oscillations during radiative extinction with a frequency of approximately 1 H z. The results revealed that as the ambient oxygen mole fraction was reduced, the diffusive-extinction droplet diameter increased and the radiative-extinction droplet diameter decreased. In between these two limiting extinction conditions, quasi-steady combustion was observed. Another important measurement that is related to spacecraft fire safety is the limiting oxygen index (LOI), the oxygen concentration below which quasi-steady combustion cannot be supported. This is also the ambient oxygen mole fraction for which the radiative and diffusive extinction diameters become equal. For oxygen/nitrogen mixtures, the LOI is 0.12 and 0.15 for methanol and heptane, respectively. The LOI increases to approximately 0.14 (0.14 O 2/0.56 N 2/0.30 C O 2) and 0.17 (0.17 O 2/0.63 N 2/0.20 C O 2) for methanol and heptane, respectively, for ambient environments that simulated dispersing an inert-gas suppressant (carbon dioxide) into a nominally air (1.0 a t m) ambient environment. The LOI is approximately 0.14 and 0.15 for methanol and heptane, respectively, when helium is dispersed into air at 1 atm. The experiments also showed unique burning behavior for large heptane droplets. After the

  13. Cool Flame Quenching

    Science.gov (United States)

    Pearlman, Howard; Chapek, Richard

    2001-01-01

    Cool flame quenching distances are generally presumed to be larger than those associated with hot flames, because the quenching distance scales with the inverse of the flame propagation speed, and cool flame propagation speeds are often times slower than those associated with hot flames. To date, this presumption has never been put to a rigorous test, because unstirred, non-isothermal cool flame studies on Earth are complicated by natural convection. Moreover, the critical Peclet number (Pe) for quenching of cool flames has never been established and may not be the same as that associated with wall quenching due to conduction heat loss in hot flames, Pe approx. = 40-60. The objectives of this ground-based study are to: (1) better understand the role of conduction heat loss and species diffusion on cool flame quenching (i.e., Lewis number effects), (2) determine cool flame quenching distances (i.e, critical Peclet number, Pe) for different experimental parameters and vessel surface pretreatments, and (3) understand the mechanisms that govern the quenching distances in premixtures that support cool flames as well as hot flames induced by spark-ignition. Objective (3) poses a unique fire safety hazard if conditions exist where cool flame quenching distances are smaller than those associated with hot flames. For example, a significant, yet unexplored risk, can occur if a multi-stage ignition (a cool flame that transitions to a hot flame) occurs in a vessel size that is smaller than that associated with the hot quenching distance. To accomplish the above objectives, a variety of hydrocarbon-air mixtures will be tested in a static reactor at elevated temperature in the laboratory (1g). In addition, reactions with chemical induction times that are sufficiently short will be tested aboard NASA's KC-135 microgravity (mu-g) aircraft. The mu-g results will be compared to a numerical model that includes species diffusion, heat conduction, and a skeletal kinetic mechanism

  14. Droplet Mobility Manipulation on Porous Media Using Backpressure.

    Science.gov (United States)

    Vourdas, N; Pashos, G; Kokkoris, G; Boudouvis, A G; Stathopoulos, V N

    2016-05-31

    Wetting phenomena on hydrophobic surfaces are strongly related to the volume and pressure of gas pockets residing at the solid-liquid interface. In this study, we explore the underlying mechanisms of droplet actuation and mobility manipulation when backpressure is applied through a porous medium under a sessile pinned droplet. Reversible transitions between the initially sticky state and the slippery states are thus incited by modulating the backpressure. The sliding angles of deionized (DI) water and ethanol in DI water droplets of various volumes are presented to quantify the effect of the backpressure on the droplet mobility. For a 50 μL water droplet, the sliding angle decreases from 45 to 0° when the backpressure increases to ca. 0.60 bar. Significantly smaller backpressure levels are required for lower surface energy liquids. We shed light on the droplet actuation and movement mechanisms by means of simulations encompassing the momentum conservation and the continuity equations along with the Cahn-Hilliard phase-field equations in a 2D computational domain. The droplet actuation mechanism entails depinning of the receding contact line and movement by means of forward wave propagation reaching the front of the droplet. Eventually, the droplet skips forward. The contact line depinning is also corroborated by analytical calculations based on the governing vertical force balance, properly modified to incorporate the effect of the backpressure.

  15. How coalescing droplets jump.

    Science.gov (United States)

    Enright, Ryan; Miljkovic, Nenad; Sprittles, James; Nolan, Kevin; Mitchell, Robert; Wang, Evelyn N

    2014-10-28

    Surface engineering at the nanoscale is a rapidly developing field that promises to impact a range of applications including energy production, water desalination, self-cleaning and anti-icing surfaces, thermal management of electronics, microfluidic platforms, and environmental pollution control. As the area advances, more detailed insights of dynamic wetting interactions on these surfaces are needed. In particular, the coalescence of two or more droplets on ultra-low adhesion surfaces leads to droplet jumping. Here we show, through detailed measurements of jumping droplets during water condensation coupled with numerical simulations of binary droplet coalescence, that this process is fundamentally inefficient with only a small fraction of the available excess surface energy (≲ 6%) convertible into translational kinetic energy. These findings clarify the role of internal fluid dynamics during the jumping droplet coalescence process and underpin the development of systems that can harness jumping droplets for a wide range of applications.

  16. Droplets As Liquid Robots.

    Science.gov (United States)

    Čejková, Jitka; Banno, Taisuke; Hanczyc, Martin M; Štěpánek, František

    2017-01-01

    Liquid droplets are very simple objects present in our everyday life. They are extremely important for many natural phenomena as well as for a broad variety of industrial processes. The conventional research areas in which the droplets are studied include physical chemistry, fluid mechanics, chemical engineering, materials science, and micro- and nanotechnology. Typical studies include phenomena such as condensation and droplet formation, evaporation of droplets, or wetting of surfaces. The present article reviews the recent literature that employs droplets as animated soft matter. It is argued that droplets can be considered as liquid robots possessing some characteristics of living systems, and such properties can be applied to unconventional computing through maze solving or operation in logic gates. In particular, the lifelike properties and behavior of liquid robots, namely (i) movement, (ii) self-division, and (iii) group dynamics, will be discussed.

  17. The amazing bouncing droplet

    OpenAIRE

    Terwagne, Denis; Dorbolo, Stéphane; Vandewalle, Nicolas; Gilet, Tristan

    2008-01-01

    When a low viscosity oil droplet is laid onto the surface of a high viscosity oil liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inhibited by injecting fresh air under the droplet. This can happen when the surface of the bath oscillates vertically. In this case the droplet basically bounces on the interface [1, 2]. We observe that the conditions for bouncing depends on the frequency, more precisely we observe resonance whe...

  18. Water droplets also swim!

    Science.gov (United States)

    van der Linden, Marjolein; Izri, Ziane; Michelin, Sébastien; Dauchot, Olivier

    2015-03-01

    Recently there has been a surge of interest in producing artificial swimmers. One possible path is to produce self-propelling droplets in a liquid phase. The self-propulsion often relies on complex mechanisms at the droplet interface, involving chemical reactions and the adsorption-desorption kinetics of the surfactant. Here, we report the spontaneous swimming of droplets in a very simple system: water droplets immersed in an oil-surfactant medium. The swimmers consist of pure water, with no additional chemical species inside: water droplets also swim! The swimming is very robust: the droplets are able to transport cargo such as large colloids, salt crystals, and even cells. In this talk we discuss the origin of the spontaneous motion. Water from the droplet is solubilized by the reverse micellar solution, creating a concentration gradient of swollen reverse micelles around each droplet. By generalizing a recently proposed instability mechanism, we explain how spontaneous motion emerges in this system at sufficiently large Péclet number. Our water droplets in an oil-surfactant medium constitute the first experimental realization of spontaneous motion of isotropic particles driven by this instability mechanism.

  19. Droplet impaction on solid surfaces exposed to impinging jet fires

    Energy Technology Data Exchange (ETDEWEB)

    Kazemi, Zia

    2005-12-15

    The thermal response of hot surfaces exposed to impinging jet fire and subsequent impacting water droplets is investigated. The research was done mainly experimentally by utilizing three different concepts. This included experiments on a laboratory scale steel plate and large outdoor fire tests with a quadratic steel channel and steel plates. Besides the horizontal jet flame itself was characterized in a comprehensive study. As a comparative study, the last three types of the experiment were additionally modeled by the CFD-code Kameleon FireEx for validation of results. The purpose of the experiments done on bench scale steel plate (L x W x T : 300 x 200 x 8 mm) was mainly to map data on wetting temperature, water droplet size, droplet impingement angle, and droplet velocity prior to large scale jet fire tests. The droplet release angle normal to hot surface gives best cooling effect, when the surface is oriented in upright position. The partial wetting begins at about 165 degrees C. When the surface is positioned in horizontal plane, the droplet of about 5 mm in diameter wets the hot surface partially at around 240-250 degrees C within an impaction distance of 20 cm. At about 150 degrees C, the droplet is entirely attached to the surface with almost zero contact angle, and cools down the solid at a critical heat flux equivalent to 1750 kW/m{sup 2}. The cooling effectiveness is about 8 % with a Weber number of 68. Although in the event of horizontal channel (L x W x T : 1000 x 200 x 8 mm) water droplets were not applied, however, the knowledge gained with jet fire tests gave valuable information about temperature progress in solids (steels and insulation) and their response to impinging jet fire during long duration experiments. The temperature of the insulated area of the channel keeps 200 degrees C below that of the exposed surface, as long as the insulation material remained intact. Upon long test fire durations, the insulation either burns or degrades despite

  20. Unsteady Flame Embedding

    KAUST Repository

    El-Asrag, Hossam A.

    2011-01-01

    Direct simulation of all the length and time scales relevant to practical combustion processes is computationally prohibitive. When combustion processes are driven by reaction and transport phenomena occurring at the unresolved scales of a numerical simulation, one must introduce a dynamic subgrid model that accounts for the multiscale nature of the problem using information available on a resolvable grid. Here, we discuss a model that captures unsteady flow-flame interactions- including extinction, re-ignition, and history effects-via embedded simulations at the subgrid level. The model efficiently accounts for subgrid flame structure and incorporates detailed chemistry and transport, allowing more accurate prediction of the stretch effect and the heat release. In this chapter we first review the work done in the past thirty years to develop the flame embedding concept. Next we present a formulation for the same concept that is compatible with Large Eddy Simulation in the flamelet regimes. The unsteady flame embedding approach (UFE) treats the flame as an ensemble of locally one-dimensional flames, similar to the flamelet approach. However, a set of elemental one-dimensional flames is used to describe the turbulent flame structure directly at the subgrid level. The calculations employ a one-dimensional unsteady flame model that incorporates unsteady strain rate, curvature, and mixture boundary conditions imposed by the resolved scales. The model is used for closure of the subgrid terms in the context of large eddy simulation. Direct numerical simulation (DNS) data from a flame-vortex interaction problem is used for comparison. © Springer Science+Business Media B.V. 2011.

  1. 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

  2. Ethanol poisoning

    Science.gov (United States)

    ... this page: //medlineplus.gov/ency/article/002644.htm Ethanol poisoning To use the sharing features on this page, please enable JavaScript. Ethanol poisoning is caused by drinking too much alcohol. ...

  3. Flame Shapes of Nonbuoyant Laminar Jet Diffusion Flames

    Science.gov (United States)

    Xu, F.; Dai, Z.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z. G. (Technical Monitor)

    2001-01-01

    The shapes (flame-sheet and luminous-flame boundaries) of steady nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue CO2 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet exit Reynolds number of 3-54, initial air/fuel velocity ratios of 0-9 and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at micro-gravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smokepoint conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smokepoint conditions. Flame-shape predictions were based on simplified analyses using the boundary layer approximations along with empirical parameters to distinguish flame-sheet and luminous flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions due to the presence of luminous soot particles in the fuel-lean region of the flames.

  4. Flame Shapes of Nonbuoyant Laminar Jet Diffusion Flames. Appendix K

    Science.gov (United States)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    The shapes (flame-sheet and luminous-flame boundaries) of steady nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue C02 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet exit Reynolds number of 3-54, initial air/fuel velocity ratios of 0-9 and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at micro-gravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smoke-point conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smoke-point conditions. Flame-shape predictions were based on simplified analyses using the boundary layer approximations along with empirical parameters to distinguish flame-sheet and luminous-flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions due to the presence of luminous soot particles in the fuel-lean region of the flames.

  5. 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...

  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. Ethanol Basics

    Energy Technology Data Exchange (ETDEWEB)

    None

    2015-01-30

    Ethanol is a widely-used, domestically-produced renewable fuel made from corn and other plant materials. More than 96% of gasoline sold in the United States contains ethanol. Learn more about this alternative fuel in the Ethanol Basics Fact Sheet, produced by the U.S. Department of Energy's Clean Cities program.

  8. Compound Droplets on Fibers.

    Science.gov (United States)

    Weyer, Floriane; Ben Said, Marouen; Hötzer, Johannes; Berghoff, Marco; Dreesen, Laurent; Nestler, Britta; Vandewalle, Nicolas

    2015-07-21

    Droplets on fibers have been extensively studied in the recent years. Although the equilibrium shapes of simple droplets on fibers are well established, the situation becomes more complex for compound fluidic systems. Through experimental and numerical investigations, we show herein that compound droplets can be formed on fibers and that they adopt specific geometries. We focus on the various contact lines formed at the meeting of the different phases and we study their equilibrium state. It appears that, depending on the surface tensions, the triple contact lines can remain separate or merge together and form quadruple lines. The nature of the contact lines influences the behavior of the compound droplets on fibers. Indeed, both experimental and numerical results show that, during the detachment process, depending on whether the contact lines are triple or quadruple, the characteristic length is the inner droplet radius or the fiber radius.

  9. Enhancing Throughput of Combinatorial Droplet Devices via Droplet Bifurcation, Parallelized Droplet Fusion, and Parallelized Detection

    National Research Council Canada - National Science Library

    Kuangwen Hsieh; Helena C Zec; Polly C Ma; Tushar D Rane; Tza-Huei Wang

    2015-01-01

      Combinatorial droplet microfluidic devices with programmable microfluidic valves have recently emerged as a viable approach for performing multiplexed experiments in microfluidic droplets...

  10. Microphysics of Astrophysical Flames

    Science.gov (United States)

    Dursi, L. J.; Zingale, M.; Caceres, A.; Calder, A. C.; Timmes, F. X.; Truran, J. W.; Rosner, R.; Lamb, D. Q.; Brown, E.; Ricker, P.; Fryxell, B.; Olson, K.; Riley, K.; Siegel, A.; Vladimirova, N.

    2003-03-01

    Type Ia supernovae are thought to begin with a deflagration phase, where burning occurs as a subsonic flame which accelerates and possibly undergoes a transition to a supersonic detonation. Both the acceleration and possible transition will depend on the microphysics of astrophysical flames, and their interaction with a turbulent flow in degenerate material. Here we present recent progress in studying the interactions of astrophysical flames and curvature and strain at the FLASH center; in particular, we discuss quantitative measurements of the effects of strain on burning rate of these flames, and implications for instability growth and quenching. This work was supported by the DOE ASCI/Alliances program at the University of Chicago under grant No. B341495 and the Scientific through Advanced Computing (SciDAC) program of the DOE, grant number DE-FC02-01ER41176 to the Supernova Science Center/UCSC.

  11. Effect of viscosity on droplet-droplet collisional interaction

    NARCIS (Netherlands)

    Finotello, Giulia; Padding, J.T.; Deen, Niels G.; Jongsma, Alfred; Innings, Fredrik; Kuipers, J.A.M.

    2017-01-01

    A complete knowledge of the effect of droplet viscosity on droplet-droplet collision outcomes is essential for industrial processes such as spray drying. When droplets with dispersed solids are dried, the apparent viscosity of the dispersed phase increases by many orders of magnitude, which

  12. Supercritical microgravity droplet vaporization

    Science.gov (United States)

    Hartfield, J.; Curtis, E.; Farrell, P.

    1990-01-01

    Supercritical droplet vaporization is an important issue in many combustion systems, such as liquid fueled rockets and compression-ignition (diesel) engines. In order to study the details of droplet behavior at these conditions, an experiment was designed to provide a gas phase environment which is above the critical pressure and critical temperature of a single liquid droplet. In general, the droplet begins as a cold droplet in the hot, high pressure environment. In order to eliminate disruptions to the droplet by convective motion in the gas, forced and natural convection gas motion are required to be small. Implementation of this requirement for forced convection is straightforward, while reduction of natural convection is achieved by reduction in the g-level for the experiment. The resulting experiment consists of a rig which can stably position a droplet without restraint in a high-pressure, high temperature gas field in microgravity. The microgravity field is currently achieved by dropping the device in the NASA Lewis 2.2 second drop tower. The performance of the experimental device and results to date are presented.

  13. Waveguides for walking droplets

    CERN Document Server

    Filoux, Boris; Schlagheck, Peter; Vandewalle, Nicolas

    2015-01-01

    When gently placing a droplet onto a vertically vibrated bath, a drop can bounce permanently. Upon increasing the forcing acceleration, the droplet is propelled by the wave it generates and becomes a walker with a well defined speed. We investigate the confinement of a walker in different rectangular cavities, used as waveguides for the Faraday waves emitted by successive droplet bounces. By studying the walker velocities, we discover that 1d confinement is optimal for narrow channels. We also propose an analogy with waveguide models based on the observation of the Faraday instability within the channels.

  14. Some Physics Inside Drying Droplets

    Indian Academy of Sciences (India)

    IAS Admin

    Spreading of a droplet placed on a solid surface (sessile droplet) depends on the wetting properties of the liquid on that surface. Depending upon the wetting nature, a droplet can fully or partially spread over a solid sur- face. In the case of total wetting, the droplet spreads completely on the surface. On the other hand, in par-.

  15. Dynamics of Water Absorption and Evaporation During Methanol Droplet Combustion in Microgravity

    Science.gov (United States)

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

    2012-01-01

    The combustion of methanol droplets is profoundly influenced by the absorption and evaporation of water, generated in the gas phase as a part of the combustion products. Initially there is a water-absorption period of combustion during which the latent heat of condensation of water vapor, released into the droplet, enhances its burning rate, whereas later there is a water-evaporation period, during which the water vapor reduces the flame temperature suffciently to extinguish the flame. Recent methanol droplet-combustion experiments in ambient environments diluted with carbon dioxide, conducted in the Combustion Integrated Rack on the International Space Station (ISS), as a part of the FLEX project, provided a method to delineate the water-absorption period from the water-evaporation period using video images of flame intensity. These were obtained using an ultra-violet camera that captures the OH* radical emission at 310 nm wavelength and a color camera that captures visible flame emission. These results are compared with results of ground-based tests in the Zero Gravity Facility at the NASA Glenn Research Center which employed smaller droplets in argon-diluted environments. A simplified theoretical model developed earlier correlates the transition time at which water absorption ends and evaporation starts. The model results are shown to agree reasonably well with experiment.

  16. 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.

  17. Universal fluid droplet ejector

    Science.gov (United States)

    Lee, Eric R.; Perl, Martin L.

    1999-08-24

    A droplet generator comprises a fluid reservoir having a side wall made of glass or quartz, and an end cap made from a silicon plate. The end cap contains a micromachined aperture through which the fluid is ejected. The side wall is thermally fused to the end cap, and no adhesive is necessary. This means that the fluid only comes into contact with the side wall and the end cap, both of which are chemically inert. Amplitudes of drive pulses received by reservoir determine the horizontal displacements of droplets relative to the ejection aperture. The drive pulses are varied such that the dropper generates a two-dimensional array of vertically-falling droplets. Vertical and horizontal interdroplet spacings may be varied in real time. Applications include droplet analysis experiments such as Millikan fractional charge searches and aerosol characterization, as well as material deposition applications.

  18. Butschli Dynamic Droplet System

    DEFF Research Database (Denmark)

    Armstrong, R.; Hanczyc, M.

    2013-01-01

    of a technology with living properties. Otto Butschli first described the system in 1898, when he used alkaline water droplets in olive oil to initiate a saponification reaction. This simple recipe produced structures that moved and exhibited characteristics that resembled, at least superficially, the amoeba. We......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...... to the oil phase), qualify this system as an example of living technology. The analysis of the Butschli droplets suggests that a set of conditions may precede the emergence of lifelike characteristics and exemplifies the richness of this rudimentary chemical system, not only for artificial life...

  19. Precise, contactless measurements of the surface tension of picolitre aerosol droplets.

    Science.gov (United States)

    Bzdek, Bryan R; Power, Rory M; Simpson, Stephen H; Reid, Jonathan P; Royall, C Patrick

    2016-01-01

    The surface composition and surface tension of aqueous droplets can influence key aerosol characteristics and processes including the critical supersaturation required for activation to form cloud droplets in the atmosphere. Despite its fundamental importance, surface tension measurements on droplets represent a considerable challenge owing to their small volumes. In this work, we utilize holographic optical tweezers to study the damped surface oscillations of a suspended droplet (surface tension and viscosity of droplets containing only 1-4 pL of material. An advantage of performing the measurement in aerosol is that supersaturated solute states (common in atmospheric aerosol) may be accessed. For pairs of droplets starting at their equilibrium surface composition, surface tensions and viscosities are consistent with bulk equilibrium values, indicating that droplet surfaces respond to changes in surface area on microsecond timescales and suggesting that equilibrium values can be assumed for growing atmospheric droplets. Furthermore, droplet surfaces are shown to be rapidly modified by trace species thereby altering their surface tension. This equilibration of droplet surface tension to the local environmental conditions is illustrated for unknown contaminants in laboratory air and also for droplets exposed to gas passing through a water-ethanol solution. This approach enables precise measurements of surface tension and viscosity over long time periods, properties that currently are poorly constrained.

  20. Ionic liquid ultrasound assisted dispersive liquid-liquid microextraction method for preconcentration of trace amounts of rhodium prior to flame atomic absorption spectrometry determination

    Energy Technology Data Exchange (ETDEWEB)

    Molaakbari, Elaheh [Chemistry Department, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Young Research Society, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Mostafavi, Ali, E-mail: mostafavi.ali@gmail.com [Chemistry Department, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Afzali, Daryoush [Environment and Nanochemistry Department, Research Institute of Environmental Science, International Center for Science, High Technology and Environmental Science, Kerman (Iran, Islamic Republic of); Mineral Industries Research Center, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of)

    2011-01-30

    In this article, we consider ionic liquid based ultrasound-assisted dispersive liquid-liquid microextraction of trace amounts of rhodium from aqueous samples and show that this is a fast and reliable sample pre-treatment for the determination of rhodium ions by flame atomic absorption spectrometry. The Rh(III) was transferred into its complex with 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol as a chelating agent, and an ultrasonic bath with the ionic liquid, 1-octyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide at room temperature was used to extract the analyte. The centrifuged rhodium complex was then enriched in the form of ionic liquid droplets and prior to its analysis by flame atomic absorption spectrometry, 300 {mu}L ethanol was added to the ionic liquid-rich phase. Finally, the influence of various parameters on the recovery of Rh(III) was optimized. Under optimum conditions, the calibration graph was linear in the range of 4.0-500.0 ng mL{sup -1}, the detection limit was 0.37 ng mL{sup -1} (3S{sub b}/m, n = 7) and the relative standard deviation was {+-}1.63% (n = 7, C = 200 ng mL{sup -1}). The results show that ionic liquid based ultrasound assisted dispersive liquid-liquid microextraction, combined with flame atomic absorption spectrometry, is a rapid, simple, sensitive and efficient analytical method for the separation and determination of trace amounts of Rh(III) ions with minimum organic solvent consumption.

  1. 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....

  2. Dynamics of a Water Droplet over a Sessile Oil Droplet: Compound Droplets Satisfying a Neumann Condition.

    Science.gov (United States)

    Iqbal, R; Dhiman, S; Sen, A K; Shen, Amy Q

    2017-06-13

    We report the dynamics of compound droplets with a denser liquid (water) droplet over a less dense sessile droplet (mineral oil) that satisfies the Neumann condition. For a fixed size of an oil droplet, depending on the size of the water droplet, either it attains the axisymmetric position or tends to migrate toward the edge of the oil droplet. For a water droplet-to-oil droplet at volume ratio V w /V o ≥ 0.05, stable axisymmetric configuration is achieved; for V w /V o droplet is observed. The stability and migration of water droplets of size above and below critical size, respectively, are explained using the force balance at the three-phase contact line and film tension. The larger and smaller droplets that initially attain the axisymmetric position or some radial position, respectively, evaporate continuously and thus migrate toward the edge of the oil droplet. The radial location and migration of the water droplets of different initial sizes with respect to time are studied. Experiments with water droplets on a flat oil-air interface did not show migration, which signified the role of the curved oil-air interface for droplet migration. Finally, coalescence of water droplets of size above the critical size at the axisymmetric position is demonstrated. Our compound droplet studies could be beneficial for applications involving droplet transport where contamination due to direct contact and pinning of droplets on solid surfaces is of concern. Migration and coalescence of water droplets on curved oil-air interfaces could open new frontiers in chemical and biological applications including multiphase processing and biological interaction of cells and atmospheric chemistry.

  3. High-throughput detection of ethanol-producing cyanobacteria in a microdroplet platform.

    Science.gov (United States)

    Abalde-Cela, Sara; Gould, Anna; Liu, Xin; Kazamia, Elena; Smith, Alison G; Abell, Chris

    2015-05-06

    Ethanol production by microorganisms is an important renewable energy source. Most processes involve fermentation of sugars from plant feedstock, but there is increasing interest in direct ethanol production by photosynthetic organisms. To facilitate this, a high-throughput screening technique for the detection of ethanol is required. Here, a method for the quantitative detection of ethanol in a microdroplet-based platform is described that can be used for screening cyanobacterial strains to identify those with the highest ethanol productivity levels. The detection of ethanol by enzymatic assay was optimized both in bulk and in microdroplets. In parallel, the encapsulation of engineered ethanol-producing cyanobacteria in microdroplets and their growth dynamics in microdroplet reservoirs were demonstrated. The combination of modular microdroplet operations including droplet generation for cyanobacteria encapsulation, droplet re-injection and pico-injection, and laser-induced fluorescence, were used to create this new platform to screen genetically engineered strains of cyanobacteria with different levels of ethanol production.

  4. Ethanol fermentation

    Energy Technology Data Exchange (ETDEWEB)

    1981-01-01

    The inulin of chicory slices was hydrolyzed enzymically and fermented to ethanol. Maximum ethanol yield was achieved with fermentation combined with saccharification, using cellulase and inulinase for saccharification. The fermenting organism was Saccharomyces cerevisiae. Kluyveromyces fragilis, containing endogenous inulinase, was also used, but with lower yield.

  5. Flaming on YouTube

    NARCIS (Netherlands)

    Moor, Peter J.; Heuvelman, A.; Verleur, R.

    2010-01-01

    In this explorative study, flaming on YouTube was studied using surveys of YouTube users. Flaming is defined as displaying hostility by insulting, swearing or using otherwise offensive language. Three general conclusions were drawn. First, although many users said that they themselves do not flame,

  6. Direct numerical simulation of two-phases turbulent combustion: application to study of propagation and structure of flames; Simulation numerique directe de la combustion turbulente diphasique: application a l'etude de la propagation et de la structure des flammes

    Energy Technology Data Exchange (ETDEWEB)

    Canneviere, K.

    2003-12-15

    This work is devoted to the study of the propagation and the structure of two-phases turbulent flames. To this end, Direct Numerical Simulations (DNS) are used. First, numerical systems for two-phases flow simulations is presented along with a specific chemical model. Then, a study of laminar spray flames is carried out. An analytical study related to the dynamics of evaporation of droplets is first proposed where the influence on the equivalence ratio of the ratio between the heating delay of the droplet and the evaporation delay is detailed. The simulation of a propagating flame through a cloud of droplets is carried out and a pulsating behavior is highlighted. A study of these flames according to the topology of liquid fuel enabled us to characterize a double flame structure composed of a premixed flame and a diffusion flame. Our last study is devoted to spray turbulent flames. Two-phase combustion of turbulent jets has been simulated. By varying the spray injection parameters (density, equivalence ratio), a database has been generated. This database allowed us to describe local and global flame regimes appearing in the combustion of sprays. They have been categorized in four main structures: open and closed external regime, group combustion and mixed combustion. Eventually, a combustion diagram has been developed. It involves the spray vaporization time, the mean inter-space between droplets or group of droplets and eventually the injected equivalence ratio. (author)

  7. Droplet Microfluidic Technique for the Study of Fermentation

    Directory of Open Access Journals (Sweden)

    Krzysztof Churski

    2015-10-01

    Full Text Available We demonstrate a technique that uses microdroplets for culturing and selecting bacterial cultures in a model biotechnological application. We propose an assay for determination of ethanol concentration that provides increased dynamic range and is compatible with droplet microfluidic screening technologies. The assay comprises two enzymes—alcohol oxidase (AOX and horseradish peroxidase (HRP—and a colorimetric readout system of phenol-4-sulfonic acid (PSA and 4-aminoantipyrine (4-AAP. The microdroplet method provides high repeatability (a relative error of measured ethanol concentration < 5%, high specificity for ethanol, low consumption of reagents and wide dynamic range (1–70 g·L-1 compared to existing assays. We report the use of this method in a screen of ethanol generation efficiency of Zymomonas mobilis (strain 3881 against the concentration of glucose in the culture media.

  8. 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

  9. "Magic Eraser" Flame Tests

    Science.gov (United States)

    Landis, Arthur M.; Davies, Malonne I.; Landis, Linda

    2009-01-01

    Cleaning erasers are used to support methanol-fueled flame tests. This safe demonstration technique requires only small quantities of materials, provides clean colors for up to 45 seconds, and can be used in the classroom or the auditorium. (Contains 1 note.)

  10. Chip-based droplet sorting

    Science.gov (United States)

    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.

  11. 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.

  12. Chip-based droplet sorting

    Science.gov (United States)

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

    2014-07-01

    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.

  13. Extended lattice Boltzmann scheme for droplet combustion.

    Science.gov (United States)

    Ashna, Mostafa; Rahimian, Mohammad Hassan; Fakhari, Abbas

    2017-05-01

    The available lattice Boltzmann (LB) models for combustion or phase change are focused on either single-phase flow combustion or two-phase flow with evaporation assuming a constant density for both liquid and gas phases. To pave the way towards simulation of spray combustion, we propose a two-phase LB method for modeling combustion of liquid fuel droplets. We develop an LB scheme to model phase change and combustion by taking into account the density variation in the gas phase and accounting for the chemical reaction based on the Cahn-Hilliard free-energy approach. Evaporation of liquid fuel is modeled by adding a source term, which is due to the divergence of the velocity field being nontrivial, in the continuity equation. The low-Mach-number approximation in the governing Navier-Stokes and energy equations is used to incorporate source terms due to heat release from chemical reactions, density variation, and nonluminous radiative heat loss. Additionally, the conservation equation for chemical species is formulated by including a source term due to chemical reaction. To validate the model, we consider the combustion of n-heptane and n-butanol droplets in stagnant air using overall single-step reactions. The diameter history and flame standoff ratio obtained from the proposed LB method are found to be in good agreement with available numerical and experimental data. The present LB scheme is believed to be a promising approach for modeling spray combustion.

  14. Enhanced Jumping-Droplet Departure.

    Science.gov (United States)

    Kim, Moon-Kyung; Cha, Hyeongyun; Birbarah, Patrick; Chavan, Shreyas; Zhong, Chen; Xu, Yuehan; Miljkovic, Nenad

    2015-12-15

    Water vapor condensation on superhydrophobic surfaces has received much attention in recent years because of its ability to shed water droplets at length scales 3 decades smaller than the capillary length (∼1 mm) via coalescence-induced droplet jumping. Jumping-droplet condensation has been demonstrated to enhance heat transfer, anti-icing, and self-cleaning efficiency and is governed by the theoretical inertial-capillary scaled jumping speed (U). When two droplets coalesce, the experimentally measured jumping speed (Uexp) is fundamentally limited by the internal fluid dynamics during the coalescence process (Uexp 2) coalescence as an avenue to break the two-droplet speed limit. Using side-view and top-view high-speed imaging to study more than 1000 jumping events on a copper oxide nanostructured superhydrophobic surface, we verify that droplet jumping occurs as a result of three fundamentally different mechanisms: (1) coalescence between two droplets, (2) coalescence among more than two droplets (multidroplet), and (3) coalescence between one or more droplets on the surface and a returning droplet that has already departed (multihop). We measured droplet-jumping speeds for a wide range of droplet radii (5-50 μm) and demonstrated that while the two-droplet capillary-to-inertial energy conversion mechanism is not identical to that of multidroplet jumping, speeds above the theoretical two-droplet limit (>0.23U) can be achieved. However, we discovered that multihop coalescence resulted in drastically reduced jumping speeds (≪0.23U) due to adverse momentum contributions from returning droplets. To quantify the impact of enhanced jumping speed on heat-transfer performance, we developed a condensation critical heat flux model to show that modest jumping speed enhancements of 50% using multidroplet jumping can enhance performance by up to 40%. Our results provide a starting point for the design of enhanced-performance jumping-droplet surfaces for industrial

  15. 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...

  16. 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.

  17. Impact of blood droplets

    NARCIS (Netherlands)

    Laan, N.

    2015-01-01

    Within Bloodstain Pattern Analysis, forensic experts commonly use the stringing method, based on a straight line approximation of the blood droplets trajectories to determine where the source of a bloodstain pattern was. However, by ignoring gravity, large errors may arise when inferring the

  18. Flame Retardant Epoxy Resins

    Science.gov (United States)

    Thompson, C. M.; Smith, J. G., Jr.; Connell, J. W.; Hergenrother, P. M.; Lyon, R. E.

    2004-01-01

    As part of a program to develop fire resistant exterior composite structures for future subsonic commercial aircraft, flame retardant epoxy resins are under investigation. Epoxies and their curing agents (aromatic diamines) containing phosphorus were synthesized and used to prepare epoxy formulations. Phosphorus was incorporated within the backbone of the epoxy resin and not used as an additive. The resulting cured epoxies were characterized by thermogravimetric analysis, propane torch test, elemental analysis and microscale combustion calorimetry. Several formulations showed excellent flame retardation with phosphorous contents as low as 1.5% by weight. The fracture toughness of plaques of several cured formulations was determined on single-edge notched bend specimens. The chemistry and properties of these new epoxy formulations are discussed.

  19. Antimony: a flame fighter

    Science.gov (United States)

    Wintzer, Niki E.; Guberman, David E.

    2015-01-01

    Antimony is a brittle, silvery-white semimetal that conducts heat poorly. The chemical compound antimony trioxide (Sb2O3) is widely used in plastics, rubbers, paints, and textiles, including industrial safety suits and some children’s clothing, to make them resistant to the spread of flames. Also, sodium antimonate (NaSbO3) is used during manufacturing of high-quality glass, which is found in cellular phones.

  20. On the formation of nitrogen oxides during the combustion of partially pre-vaporized droplets

    Energy Technology Data Exchange (ETDEWEB)

    Moesl, Klaus Georg

    2012-12-12

    achieved. The degree of droplet vaporization has an effect on flame stabilization around the droplet and on NOx formation. More than half of the droplet mass needs to be pre-vaporized, before the required technical effort leads to a significant reduction of the overall NO{sub x} emissions. In the ignition model, the NO{sub x} production rate turns out to be very sensitive against the ignition position. Thus, it is important to adjust the model parameters carefully to obtain realistic emission results.

  1. Effect of viscosity on droplet-droplet collisional interaction

    Science.gov (United States)

    Finotello, Giulia; Padding, Johan T.; Deen, Niels G.; Jongsma, Alfred; Innings, Fredrik; Kuipers, J. A. M.

    2017-06-01

    A complete knowledge of the effect of droplet viscosity on droplet-droplet collision outcomes is essential for industrial processes such as spray drying. When droplets with dispersed solids are dried, the apparent viscosity of the dispersed phase increases by many orders of magnitude, which drastically changes the outcome of a droplet-droplet collision. However, the effect of viscosity on the droplet collision regime boundaries demarcating coalescence and reflexive and stretching separation is still not entirely understood and a general model for collision outcome boundaries is not available. In this work, the effect of viscosity on the droplet-droplet collision outcome is studied using direct numerical simulations employing the volume of fluid method. The role of viscous energy dissipation is analysed in collisions of droplets with different sizes and different physical properties. From the simulations results, a general phenomenological model depending on the capillary number (Ca, accounting for viscosity), the impact parameter (B), the Weber number (We), and the size ratio (Δ) is proposed.

  2. Saw palmetto ethanol extract inhibits adipocyte differentiation.

    Science.gov (United States)

    Villaverde, Nicole; Galvis, Adriana; Marcano, Adriana; Priestap, Horacio A; Bennett, Bradley C; Barbieri, M Alejandro

    2013-07-01

    The fruits of saw palmetto have been used for the treatment of a variety of urinary and reproductive system problems. In this study we investigated whether the fruit extracts affect in vitro adipogenesis. Saw palmetto ethanol extract inhibited the lipid droplet accumulation by induction media in a dose-dependent manner, and it also attenuated the protein expressions of C-EBPα and PPARγ. Phosphorylation of Erk1/2 and Akt1 were also decreased by saw palmetto ethanol extract. This report suggests that saw palmetto extracts selectively affect the adipocyte differentiation through the modulation of several key factors that play a critical role during adipogenesis.

  3. 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.

  4. Electric Fields for Flame Extinguishment

    Science.gov (United States)

    1993-03-01

    ethylene-air and methane-air flames, the application of a DC field of 0.5 kV/cm increased the burning velocity by close to a factor of two. Salamandra and...flame surface area and thus the velocity, but Jaggers and von Engel also saw physical perturbations in flame fronts with no electric field. Salamandra ...Conductivity in Propane-Air Flames by Using Rydberg State Stark Spectroscopy," Proc. Combustion Inst., Fall (1990). 12. Salamandra , G.D., and Mairov, N.I

  5. Hovering UFO Droplets

    CERN Document Server

    Anand, Sushant; Dhiman, Rajeev; Smith, J David; Varanasi, Kripa K

    2012-01-01

    This fluid dynamics video is an entry for the Gallery of Fluid Motion of the 65th Annual Meeting of the APS-DFD. This video shows behavior of condensing droplets on a lubricant impregnated surface and a comparison with a superhydrophobic surface. On impregnated surfaces, drops appear like UFOs hovering over a surface. The videos were recorded in an Environmental SEM and a specially built condensation rig.

  6. High-Voltage Droplet Dispenser

    Science.gov (United States)

    Eichenberg, Dennis J.

    2003-01-01

    An apparatus that is extremely effective in dispensing a wide range of droplets has been developed. This droplet dispenser is unique in that it utilizes a droplet bias voltage, as well as an ionization pulse, to release a droplet. Apparatuses that deploy individual droplets have been used in many applications, including, notably, study of combustion of liquid fuels. Experiments on isolated droplets are useful in that they enable the study of droplet phenomena under well-controlled and simplified conditions. In this apparatus, a syringe dispenses a known value of liquid, which emerges from, and hangs onto, the outer end of a flat-tipped, stainless steel needle. Somewhat below the needle tip and droplet is a ring electrode. A bias high voltage, followed by a high-voltage pulse, is applied so as to attract the droplet sufficiently to pull it off the needle. The voltages are such that the droplet and needle are negatively charged and the ring electrode is positively charged.

  7. Experimental Study of Nonane and Nonane/Hexanol Fuel Droplet Combustion in Microgravity

    Science.gov (United States)

    Avedisian, C. T.; Callahan, B. J.

    1999-01-01

    In this presentation we review experiments carried out on nonane droplets, and a nonane/hexanol droplet, burning in microgravity to promote spherical symmetry. The nonane/hexanol combination was selected for the following reasons: 1) the spherically symmetric burning history of nonane and nonane/hexanol mixtures has not been previously studied; 2) measurements of the burning history of pure nonane droplets in air extend the existing data base of spherical droplet flames of soot-producing fuels which are useful for testing detailed chemical kinetic models of the spherically symmetric droplet burning process; 3) nonane and hexanol have almost identical boiling points so heterogeneous nucleation on a support fiber is unlikely; 4) hexanol does not have a strong propensity for water vapor absorption; 5) hexanol produces less soot than nonane so that mixtures of nonane and hexanol should show an effect of composition on soot formation. The far-field gas was atmospheric pressure air at room temperature. The evolution of droplet diameter was measured using high speed cine photography of spark-ignited droplets within a confined volume in a drop tower. The importance of soot formation during droplet combustion is derived from the fact that soot is the basic component of the particulate emission process that occurs in spray combustion. The complexity of soot formation motivates a one-dimensional transport condition which is advantageous for modeling. Recent numerical studies of droplet combustion have assumed spherical symmetry when incorporating such aspects as detailed chemistry and radiation, though soot formation itself has not yet been included in any droplet combustion modeling effort. If radiation is not important as would be the case for'small' droplets (i.e., droplets with initial diameters less than about ]mm), soot formation can lead to a nonlinear burning process and a time-varying burning rate, (non-linear burning of a non-sooting fuel like methanol is due to

  8. Interfacial phenomena in droplet evaporation and nanoparticle-cell systems

    Science.gov (United States)

    Fang, Xiaohua

    2005-11-01

    The factors affecting droplet evaporation are discussed. It is found that the droplet morphology at a specific temperature is controlled by the physical properties of the liquid itself, such as the molecular weight, density, diffusion coefficient in air, and heat of vaporization. Two processes are included in droplet evaporation: (1) diffusion of liquid molecules into the air (diffusion part) and (2) flow of the liquid molecules from inside the droplet to the free outer shell liquid layer within the liquid-vapor interface (energy part). The diffusion part remains steady during drying and was not sensitive to the variation of temperature. The energy part, however, was an active factor and determined the differences in drop evaporation behaviors. A model is developed to measure the solubility parameters of the solvents via droplet evaporation. Droplets were deposited on Octadecyltrichlorosilane (OTS) covered silicon surfaces and the contact angle and overall drop morphology are observed using a KSV contact angle goniometer as a function of time. OTS is considered a non-absorbing surface for the solvents examined and does not affect the accuracy of the measured results. This method allows determination of the attraction forces between solvent molecules in the condensed phases. The solubility parameter values of droplets containing pure water, methanol, ethanol and butanol are measured. The test results are independent of the droplet size. The evaporation kinetics of droplets containing DNA is studied. Simultaneously, the DNA re-distribution and adsorption kinetics are measured by confocal microscopy. The DNA droplets are stained with ethidium bromide solution and deposited on OTS covered silicon surfaces. The results showed that the drying behavior depended on the DNA concentration. During drying, DNA relocation inside of the drop affects the internal forces of the liquid. A ring is formed at the air/solid/liquid interface. The absorbed amount of DNA was obtained by

  9. Cellulosic ethanol

    DEFF Research Database (Denmark)

    Lindedam, Jane; Bruun, Sander; Jørgensen, Henning

    2010-01-01

    Background Variations in sugar yield due to genotypic qualities of feedstock are largely undescribed for pilot-scale ethanol processing. Our objectives were to compare glucose and xylose yield (conversion and total sugar yield) from straw of five winter wheat cultivars at three enzyme loadings (2...

  10. Flame Resistant Foam

    Science.gov (United States)

    1984-01-01

    Solimide manufactured by Imi-Tech Corporation, is a lightweight fire resistant material produced under a manufacturing process that allows it to be uniformly foamed. Can be produced in a variety of densities and structural configurations and remains resilient under exposure to temperatures ranging from minus 300 to plus 500 degrees Fahrenheit. Is resistant to open flame and generates virtually no smoke or toxic by-products. Used in aircraft for its superior damping characteristics, lighter weight and fire barrier properties, it's also applicable to ships and surface transportation systems such as transit cars, trains, buses and automobiles.

  11. Chemo-Sensitive Running Droplet

    OpenAIRE

    Sumino, Yutaka; Nagayama, Masaharu; Kitahata, Hiroyuki; Nomura, Shin-ichiro M.; Magome, Nobuyuki; Mori, Yoshihito; Yoshikawa, Kenichi

    2005-01-01

    Chemical control of the spontaneous motion of a reactive oil droplet moving on a glass substrate under an aqueous phase is reported. Experimental results show that the self-motion of an oil droplet is confined on an acid-treated glass surface. The transient behavior of oil-droplet motion is also observed with a high-speed video camera. A mathematical model that incorporates the effect of the glass surface charge is built based on the experimental observation of oil-droplet motion. A numerical...

  12. Gelled MMH hypergolic droplet investigation

    Science.gov (United States)

    Solomon, Yair

    Gelled propellants are promising candidates for certain future rocket applications, offering potential improvements in performance and/or safety over conventional liquid and solid systems. In particular, gelled hypergolic propellants can eliminate some handling difficulties by reducing leakage hazard. Before such systems can be developed, however, a fundamental understanding of combustion of the gel droplet is required. This study addresses the combustion behavior of monomethyl hydrazine (MMH) droplet gelled with both hydroxypropyl cellulose (HPC) and fumed silica in an environment of gaseous nitrogen dioxide. All MMH/HPC gel droplets displayed swelling and jetting that are typical to hydrocarbon gels with an organic gelling agent. Burning rates were measured for droplet diameters from 1.8 to 3.2 mm at three ambient pressures of 1.72, 2.06 and 2.89 bar. It was found that the droplet burning rate is dependent on the droplet diameter similarly to liquid MMH. Over the investigated pressure range, no dependence of burning rate on pressure was found. The combustion of MMH/HPC gel was compared to MMH/tetraglyme to examine the influence the type of gelling agent. Droplets of MMH and liquid tetraglyme showed increasing swelling frequencies and volume fluctuations during combustion while the MMH and HPC droplets exhibited a more constant burning history. The MMH/Silica gels showed a different combustion mechanism with the formation of a rigid silica structure, micro-explosions, and up to a 50% reduction in droplet volume during combustion.

  13. Dynamics and structure of stretched flames

    Energy Technology Data Exchange (ETDEWEB)

    Law, C.K. [Princeton Univ., NJ (United States)

    1993-12-01

    This program aims to gain fundamental understanding on the structure, geometry, and dynamics of laminar premixed flames, and relate these understanding to the practical issues of flame extinction and stabilization. The underlying fundamental interest here is the recent recognition that the response of premixed flames can be profoundly affected by flame stretch, as manifested by flow nonuniformity, flame curvature, and flame/flow unsteadiness. As such, many of the existing understanding on the behavior of premixed flames need to be qualitatively revised. The research program consists of three major thrusts: (1) detailed experimental and computational mapping of the structure of aerodynamically-strained planar flames, with emphasis on the effects of heat loss, nonequidiffusion, and finite residence time on the flame thickness, extent of incomplete reaction, and the state of extinction. (2) Analytical study of the geometry and dynamics of stretch-affected wrinkled flame sheets in simple configurations, as exemplified by the Bunsen flame and the spatially-periodic flame, with emphasis on the effects of nonlinear stretch, the phenomena of flame cusping, smoothing, and tip opening, and their implications on the structure and burning rate of turbulent flames. (3) Stabilization and blowoff of two-dimensional inverted premixed and stabilization and determining the criteria governing flame blowoff. The research is synergistically conducted through the use of laser-based diagnostics, computational simulation of the flame structure with detailed chemistry and transport, and mathematical analysis of the flame dynamics.

  14. Turbulent Flame Speed and Self Similarity of Expanding Premixed Flames

    Science.gov (United States)

    Chaudhuri, Swetaprovo; Wu, Fujia; Zhu, Delin; Law, Chung

    2011-11-01

    In this study we present experimental turbulent flame speed data measured in constant-pressure expanding turbulent flames, propagating in nearly homogenous isotropic turbulence, in a dual-chamber, fan-stirred vessel. The cold flow is characterized by high speed particle image velocimetry while the flame propagation rate is obtained by tracking high speed Schlieren images of unity Lewis number methane-air flames over wide ranges of pressure and turbulence intensity. It is found that the normalized turbulent flame speed as a function of the average radius scales as a turbulent Reynolds number to the one-half power, where the average radius is the length scale and thermal diffusivity is the transport property, thus showing self-similar propagation. Utilizing this dependence it is found that the turbulent flame speeds from expanding flames and those from Bunsen geometries can be scaled by a single parameter: the turbulent Reynolds number utilizing recent theoretical results obtained by spectral closure of the G equation, after correcting for gas expansion effects.

  15. Vaporization of perfluorocarbon droplets using optical irradiation

    National Research Council Canada - National Science Library

    Strohm, Eric; Rui, Min; Gorelikov, Ivan; Matsuura, Naomi; Kolios, Michael

    2011-01-01

    .... Droplet vaporization has been previously demonstrated using acoustic methods. We propose using laser irradiation as a means to induce PFC droplet vaporization using a method we term optical droplet vaporization (ODV...

  16. Ethanol dehydration

    Directory of Open Access Journals (Sweden)

    Ana María Uyazán

    2010-04-01

    Full Text Available This review outlines ethanol dehydration processes and their most important characteristics. It also deals with the main operating variables and some criteria used in designing the separation scheme. A differentiation is made between processes involving liquid steam balance in separation operations and those doing it by screening the difference in molecule size. The last part presents a comparison between the three main industrial processes, stressing their stengths and weaknesses from the operational, energy consumption and industrial services points of view.

  17. Ethanol dehydration

    Directory of Open Access Journals (Sweden)

    Ana María Uyazán

    2004-09-01

    Full Text Available This review outlines ethanol dehydration processes and their most important characteristics. It also deals with the main operating variables and some criteria used in designing the separation scheme. A differentiation is made between processes involving liquid steam balance in separation operations and those doing it by screening the difference in molecule size. The last part presents a comparison between the three main industrial processes, stressing their stengths and weaknesses from the operational, energy consumption and industrial services points of view.

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

    Science.gov (United States)

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

    2017-08-01

    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.

  19. 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.

  20. 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.

  1. Premixed flame propagation in vertical tubes

    CERN Document Server

    Kazakov, Kirill A

    2015-01-01

    Analytical treatment of premixed flame propagation in vertical tubes with smooth walls is given. Using the on-shell flame description, equations describing quasi-steady flame with a small but finite front thickness are obtained and solved numerically. It is found that near the limits of inflammability, solutions describing upward flame propagation come in pairs having close propagation speeds, and that the effect of gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a theory of partial flame propagation driven by the gravitational field is developed. A complete explanation is given of the intricate observed behavior of limit flames, including dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction. The role of the finite front-thickness effects is discussed in detail. Also, various mechanisms governing flame acceleration in smooth tubes are ide...

  2. Flame spraying of polymers

    Energy Technology Data Exchange (ETDEWEB)

    Varacalle, D.J. Jr.; Zeek, D.P. [Idaho National Engineering Lab., Idaho Falls, ID (United States); Couch, K.W.; Benson, D.M. [Protech Laboratory Corp., Cincinnati, OH (United States); Kirk, S.M. [3M Co., St. Paul, MN (United States)

    1997-08-01

    Statistical design-of-experiment studies of the thermal spraying of polymer powders are presented. Studies of the subsonic combustion (i.e., Flame) process were conducted in order to determine the quality and economics of polyester and urethane coatings. Thermally sprayed polymer coatings are of interest to several industries for anticorrosion applications, including the chemical, automotive, and aircraft industries. In this study, the coating design has been optimized for a site-specific application using Taguchi-type fractional-factorial experiments. Optimized coating designs are presented for the two powder systems. A substantial range of thermal processing conditions and their effect on the resultant polymer coatings is presented. The coatings were characterized by optical metallography, hardness testing, tensile testing, and compositional analysis. Characterization of the coatings yielded the thickness, bond strength, Knoop microhardness, roughness, deposition efficiency, and porosity. Confirmation testing was accomplished to verify the coating designs.

  3. Effect of the Ethanol Injection Moment During Compression Stroke on the Combustion of Ethanol - Diesel Dual Direct Injection Engine

    Science.gov (United States)

    Liang, Yu; Zhou, Liying; Huang, Haomin; Xu, Mingfei; Guo, Mei; Chen, Xin

    2018-01-01

    A set of GDI system is installed on a F188 single-cylinder, air-cooled and direct injection diesel engine, which is used for ethanol injection, with the injection time controlled by the crank angle signal collected by AVL angle encoder. The injection of ethanol amounts to half of the thermal equivalent of an original diesel fuel. A 3D combustion model is established for the ethanol - diesel dual direct injection engine. Diesel was injected from the original fuel injection system, with a fuel supply advance angle of 20°CA. The ethanol was injected into the cylinder during compression process. Diesel injection began after the completion of ethanol injection. Ethanol injection starting point of 240°CA, 260°CA, 280°CA, 300°CA and 319.4°CA were simulated and analyzed. Due to the different timing of ethanol injection, the ignition of the ethanol mixture when diesel fires, results in non-uniform ignition distribution and flame propagation rate, since the distribution and concentration gradients of the ethanol mixture in the cylinder are different, thus affecting the combustion process. The results show that, when ethanol is injected at 319.4°CA, the combustion heat release rate and the pressure rise rate during the initial stage are the highest. Also, the maximum combustion pressure, with a relatively advance phase, is the highest. In case of later initial ethanol injection, the average temperature in the cylinder during the initial combustion period will have a faster rise. In case of initial injection at 319.4°CA, the average temperature in the cylinder is the highest, followed by 240°CA ethanol injection. In the post-combustion stage, the earlier ethanol injection will result in higher average temperature in the cylinder and more complete fuel combustion. The injection of ethanol at 319.4°CA produces earlier and highest NOX emissions.

  4. Electrical Aspects of Impinging Flames

    Science.gov (United States)

    Chien, Yu-Chien

    This dissertation examines the use of electric fields as one mechanism for controlling combustion as flames are partially extinguished when impinging on nearby surfaces. Electrical aspects of flames, specifically, the production of chemi-ions in hydrocarbon flames and the use of convective flows driven by these ions, have been investigated in a wide range of applications in prior work but despite this fairly comprehensive effort to study electrical aspects of combustion, relatively little research has focused on electrical phenomena near flame extinguishment, nor for flames near impingement surfaces. Electrical impinging flames have complex properties under global influences of ion-driven winds and flow field disturbances from the impingement surface. Challenges of measurements when an electric field is applied in the system have limited an understanding of changes to the flame behavior and species concentrations caused by the field. This research initially characterizes the ability of high voltage power supplies to respond on sufficiently short time scales to permit real time electrical flame actuation. The study then characterizes the influence of an electric field on the impinging flame shape, ion current and flow field of the thermal plume associated with the flame. The more significant further examinations can be separated into two parts: 1) the potential for using electric fields to control the release of carbon monoxide (CO) from surface-impinging flames, and 2) an investigation of controlling electrically the heat transfer to a plate on which the flame impinges. Carbon monoxide (CO) results from the incomplete oxidation of hydrocarbon fuels and, while CO can be desirable in some syngas processes, it is usually a dangerous emission from forest fires, gas heaters, gas stoves, or furnaces where insufficient oxygen in the core reaction does not fully oxidize the fuel to carbon dioxide and water. Determining how carbon monoxide is released and how heat transfer

  5. Leidenfrost levitation: beyond droplets.

    Science.gov (United States)

    Hashmi, Ali; Xu, Yuhao; Coder, Benjamin; Osborne, Paul A; Spafford, Jonathon; Michael, Grant E; Yu, Gan; Xu, Jie

    2012-01-01

    Friction is a major inhibitor in almost every mechanical system. Enlightened by the Leidenfrost effect - a droplet can be levitated by its own vapor layer on a sufficiently hot surface - we demonstrate for the first time that a small cart can also be levitated by Leidenfrost vapor. The levitated cart can carry certain amount of load and move frictionlessly over the hot surface. The maximum load that the cart can carry is experimentally tested over a range of surface temperatures. We show that the levitated cart can be propelled not only by gravitational force over a slanted flat surface, but also self-propelled over a ratchet shaped horizontal surface. In the end, we experimentally tested water consumption rate for sustaining the levitated cart, and compared the results to theoretical calculations. If perfected, this frictionless Leidenfrost cart could be used in numerous engineering applications where relative motion exists between surfaces.

  6. Detailed finite element method modeling of evaporating multi-component droplets

    Energy Technology Data Exchange (ETDEWEB)

    Diddens, Christian, E-mail: C.Diddens@tue.nl

    2017-07-01

    The evaporation of sessile multi-component droplets is modeled with an axisymmetic finite element method. The model comprises the coupled processes of mixture evaporation, multi-component flow with composition-dependent fluid properties and thermal effects. Based on representative examples of water–glycerol and water–ethanol droplets, regular and chaotic examples of solutal Marangoni flows are discussed. Furthermore, the relevance of the substrate thickness for the evaporative cooling of volatile binary mixture droplets is pointed out. It is shown how the evaporation of the more volatile component can drastically decrease the interface temperature, so that ambient vapor of the less volatile component condenses on the droplet. Finally, results of this model are compared with corresponding results of a lubrication theory model, showing that the application of lubrication theory can cause considerable errors even for moderate contact angles of 40°. - Graphical abstract:.

  7. Influence of ethanol and EGR on laminar burning behaviors of FACE-C gasoline and its surrogate

    KAUST Repository

    Mannaa, Ossama Abde El Hamid

    2017-10-31

    Laminar burning velocities of FACE-C gasoline and a surrogate comprised of toluene primary reference fuels (TPRFs) were investigated under the effects of EGR dilution and ethanol blending. Measurements were conducted in a spherical constant volume combustion chamber for a range of equivalence ratios from 0.8 to 1.6 at initial temperatures and pressures up to 383 K and 0.6 MPa, respectively. These measurements highlighted the effects of real combustion residuals at mole fractions up to 0.3 and various volumetric percentages of ethanol blending. For both studied fuels, significant reductions in stretched and un-stretched flame speeds were observed for mixtures laden with real combustion residuals. Blends with less than 50% ethanol showed a minimal enhancement in the flame speed. By combining both EGR and ethanol blending, the flame speed reduction by EGR can be compensated for with ethanol addition. For example, up to 10% of EGR requires 60% ethanol blending to maintain the same flame speed. Flame stability enhancement by EGR addition was also quantified through the determination of the Markstein length.

  8. Development and Validation of a Method for Alcohol Analysis in Brain Tissue by Headspace Gas Chromatography with Flame Ionization Detector

    OpenAIRE

    Chun, Hao-Jung; Poklis, Justin L.; Poklis, Alphonse; Wolf, Carl E.

    2016-01-01

    Ethanol is the most widely used and abused drug. While blood is the preferred specimen for analysis, tissue specimens such as brain serve as alternative specimens for alcohol analysis in post-mortem cases where blood is unavailable or contaminated. A method was developed using headspace gas chromatography with flame ionization detection (HS-GC-FID) for the detection and quantification of ethanol, acetone, isopropanol, methanol and n-propanol in brain tissue specimens. Unfixed volatile-free br...

  9. Dynamic Characterization of Candle Flame

    Directory of Open Access Journals (Sweden)

    Suvojit Ghosh

    2010-09-01

    Full Text Available The present work focuses on studying the flickering of a candle placed in a hollow cylindrical glass tube. Variations in flame area and intensity have been studied as the oscillating parameters of the flame with a camera and a Photomultiplier tube (PMT, and results have been found to be indicative of the presence of some well defined peaks in the amplitude spectrum of the flame intensity. Tests have been carried out with a range of candle diameters for the same glass tube giving similar results. Fluctuations in fractal dimension of the flame structure have also been studied in the course of the work. The time series data generated by processing camera images and also the PMT voltage output has been studied for existence of periodicity in the signal recorded. The correlation dimension has been determined for a number of experiments to characterize the dynamics of the signal.

  10. 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.

  11. Bacterial encountering with oil droplet

    Science.gov (United States)

    Sheng, Jian; Molaei, Mehdi

    2014-11-01

    Encountering of microorganisms with rising oil droplets in aqueous environments is the first and one of the critical steps in the biodegradation of crude oil. Several factors such as droplet sizes, rising velocity, surfactant, and motility of bacteria are expected to affect the encounter rate. We establish well controlled microfluidic devices by applying layer-by-layer technique that allows us to produce horizontal micro droplets with different sizes. The encounter rates of passive particles, motile and non-motile bacteria with these droplets are measured by high speed microscopy. The effects of mobility and motility of these particles on encounter rates are assessed quantitatively. Meanwhile, we visualize reorientation of the particle due to flow filed around the oil droplet. Results show that the motile bacteria have higher probabilities to interact with an oil droplet compare to the passive particles. Ongoing analyses focus on the effect of shear rates, angular dispersion, curvatures of streamlines, and the swimming velocity of bacteria. The ratios of the encounter area to the entire droplet surface at various flow regimes will also been measured. GoMRI.

  12. Ultrasonic Levitation for Liquid Droplet

    Science.gov (United States)

    Otsuka, Tetsuro; Nakane, Tomoo

    2002-05-01

    Ultrasonic levitation in a gravity field was tested using a viscous liquid at a frequency range from 20 kHz to 28 kHz. Red ink and glycerin droplets havingdiameters in the range of 3 mm to 5 mm were placed at a node of a standing wave. As a result, the droplets were not only flattened like a disk, but also found to contain fine air bubbles. Additionally, the droplets continuously changed their location moving from node to node while maintaining a constant volume.

  13. 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

  14. Thermophoresis of water droplets inside carbon nanotubes

    DEFF Research Database (Denmark)

    Zambrano, Harvey; Walther, Jens Honore; Oyarzua, Elton

    2016-01-01

    for nanodevice fabrication. Thermal gradients have been proposed as mechanism to drive particles, fullerenes and droplets inside CNTs. Here, by conducting Molecular Dynamics (MD) simulations, we study thermophoresis of water droplets inside CNTs. We systematically change the size of the droplets, the axial...... simulations to determine the friction and thermophoretic forces acting on the droplet....

  15. Enabling Droplet Functionality on Anisotropic Ratchet Conveyors

    Directory of Open Access Journals (Sweden)

    Hal R. Holmes

    2017-12-01

    Full Text Available Anisotropic ratchet conveyors (ARCs are a recently developed microfluidic platform that transports liquid droplets through a passive, microfabricated surface pattern and applied orthogonal vibrations. In this work, three new functionalities are presented for controlling droplet transport on the ARC system. These devices can pause droplet transport (ARC gate, decide between two pathways of droplet transport (ARC switch, and pass droplets between transport tracks (ARC delivery junction. All devices function solely through the modification of pinning forces acting on the transported droplet and are the first reported devices that can selectively control droplet timing and directionality without active (e.g., thermal, electrical, or magnetic surface components.

  16. 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 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.

  17. Mechanistic aspects of ionic reactions in flames

    DEFF Research Database (Denmark)

    Egsgaard, H.; Carlsen, L.

    1993-01-01

    Some fundamentals of the ion chemistry of flames are summarized. Mechanistic aspects of ionic reactions in flames have been studied using a VG PlasmaQuad, the ICP-system being substituted by a simple quartz burner. Simple hydrocarbon flames as well as sulfur-containing flames have been investigated....... The simple hydrocarbon flames are dominated by a series of hydrocarbonic ions and, to a minor extent, protonated oxo-compounds. The introduction of sulfur to the flames leads to significant changes in the ion composition, as sulfur-containing species become dominant. The ability of the technique to study...

  18. Sintering of polydisperse viscous droplets

    Science.gov (United States)

    Wadsworth, Fabian B.; Vasseur, Jérémie; Llewellin, Edward W.; Dingwell, Donald B.

    2017-03-01

    Sintering—or coalescence—of compacts of viscous droplets is driven by the interfacial tension between the droplets and the interstitial gas phase. The process, which occurs in a range of industrial and natural settings, such as the manufacture of ceramics and the welding of volcanic ash, causes the compact to densify, to become stronger, and to become less permeable. We investigate the role of droplet polydispersivity in sintering dynamics by conducting experiments in which populations of glass spheres with different size distributions are heated to temperatures above the glass transition interval. We quantify the progress of sintering by tracking changes in porosity with time. The sintering dynamics is modeled by treating the system as a random distribution of interstitial gas bubbles shrinking under the action of interfacial tension only. We identify the scaling between the polydispersivity of the initial droplets and the dynamics of bulk densification. The framework that we develop allows the sintering dynamics of arbitrary polydisperse populations of droplets to be predicted if the initial droplet (or particle) size distribution is known.

  19. Biofuel effect on flame propagation and soot formation in a DISI engine

    Science.gov (United States)

    Irimescu, A.; Merola, S. S.; Di Iorio, S.; Vaglieco, B. M.

    2017-10-01

    The use of biofuels, especially in transportation and industrial processes, is seen as one of the most effective solutions to promote the reduction of greenhouse gases and pollutant emissions, as well as to lighten the dependence from petro-fuel producers. Biofuels are defined as a wide range of energy sources derived from biomass. In this category, alcohols produced through fermentation, such as ethanol and butanol, are considered some of the most suitable alternatives for transportation purposes. The benefits of bio-ethanol addition to gasoline have always been recognized for practical reasons. Apart from the variety of sources which it can be produced from, ethanol can raise the octane rating, given its improved anti-knock characteristics, allowing the use of higher compression ratios and higher thermal efficiency. However, ethanol’s high latent heat of vaporization can cause problems during cold-start due to poor evaporation. On the other hand, in hot climates ethanol fuelling can result in adverse effects such as vapour lock. Butanol can be considered as an emergent alternative fuel. Normal butanol has several well-known advantages when compared to ethanol, including increased energy content, greater miscibility with transportation fuels, and lower propensity for water absorption. Despite of these pros, the costs of n-butanol production are higher due to lower yields compared to ethanol. Moreover, vaporization remains a critical aspect of this biofuel. Understanding the effect of biofuels on in-cylinder combustion processes is a key-point for the optimization of fuel flexibility and achieving lower CO2 emissions. To this aim, a combined thermodynamic and optical investigation was performed on a direct injection spark ignition engine fuelled with ethanol, butanol and gasoline. Fuels were compared by fixing the injection and spark ignition strategies. Thermodynamic measurements were coupled with optical investigations based on cycle resolved flame

  20. Selective droplet coalescence using microfluidic systems.

    Science.gov (United States)

    Mazutis, Linas; Griffiths, Andrew D

    2012-04-24

    We report a microfluidic approach, which allows selective and controlled 1 : 1, 2 : 1 or 3 : 1 droplet fusion. A surfactant-stabilized droplet with an interfacial surfactant coverage, Γ, of >98% will fuse spontaneously with a second droplet when Γ of the latter droplet is droplet is ~66%, the two droplets will not fuse, unless they have previously been brought into contact for critical time τ. Therefore, controlling the number of droplets in contact for time τ allows precise control over the number of fused droplets. We have demonstrated efficient (proportion of droplets coalesced p(c) = 1.0, n > 1000) and selective 1 : 1, 2 : 1 or 3 : 1 droplet fusion (proportion of correctly fused droplets p(s) > 0.99, n > 1000). Coalescence in this regime is induced by hydrodynamic flow causing interface separation and is efficient at different Ca numbers and using different dispersed phases, continuous phases and surfactants. However, when Γ of the second droplet is ~96% coalescence is no longer observed. Droplet-based microfluidic systems, in which each droplet functions as an independent microreactor, are proving a promising tool for a wide range of ultrahigh-throughput applications in biology and chemistry. The addition of new reagents to pre-formed droplets is critical to many of these applications and we believe the system described here is a simple and flexible method to do so, as well as a new tool to study interfacial stability phenomena.

  1. Role of the outer-edge flame on flame extinction in nitrogen-diluted non-premixed counterflow flames with finite burner diameters

    KAUST Repository

    Chung, Yong Ho

    2013-03-01

    This study of nitrogen-diluted non-premixed counterflow flames with finite burner diameters investigates the important role of the outer-edge flame on flame extinction through experimental and numerical analyses. It explores flame stability diagrams mapping the flame extinction response of nitrogen-diluted non-premixed counterflow flames to varying global strain rates in terms of burner diameter, burner gap, and velocity ratio. A critical nitrogen mole fraction exists beyond which the flame cannot be sustained; the critical nitrogen mole fraction versus global strain rate curves have C-shapes for various burner diameters, burner gaps, and velocity ratios. At sufficiently high strain-rate flames, these curves collapse into one curve; therefore, the flames follow the one-dimensional flame response of a typical diffusion flame. Low strain-rate flames are significantly affected by radial conductive heat loss, and therefore flame length. Three flame extinction modes are identified: flame extinction through shrinkage of the outer-edge flame with or without oscillations at the outer-edge flame prior to the extinction, and flame extinction through a flame hole at the flame center. The extinction modes are significantly affected by the behavior of the outer-edge flame. Detailed explanations are provided based on the measured flame-surface temperature and numerical evaluation of the fractional contribution of each term in the energy equation. Radial conductive heat loss at the flame edge to ambience is the main mechanism of extinction through shrinkage of the outer-edge flame in low strain-rate flames. Reduction of the burner diameter can extend the flame extinction mode by shrinking the outer-edge flame in higher strain-rate flames. © 2012 Elsevier Ltd. All rights reserved.

  2. Flame Retardants Used in Flexible Polyurethane Foam

    Science.gov (United States)

    The partnership project on flame retardants in furniture seeks to update the health and environmental profiles of flame-retardant chemicals that meet fire safety standards for upholstered consumer products with polyurethane foam

  3. Stabilization and structure of N-heptane flame on CWJ-spray burner with kHZ SPIV and OH-PLIF

    KAUST Repository

    Mansour, Morkous S.

    2015-08-31

    A curved wall-jet (CWJ) burner was employed to stabilize turbulent spray flames that utilized a Coanda effect by supplying air as annular-inward jet over a curved surface, surrounding an axisymmetric solid cone fuel spray. The stabilization characteristics and structure of n-heptane/air turbulent flames were investigated with varying fuel and air flow rates and the position of pressure atomizer (L). High-speed planar laser-induced fluorescence (PLIF) of OH radicals delineated reaction zone contours and simultaneously stereoscopic particle image velocimetry (SPIV) quantified the flow field features, involving turbulent mixing within spray, ambient air entrainment and flame-turbulence interaction. High turbulent rms velocities were generated within the recirculation zone, which improved the flame stabilization. OH fluorescence signals revealed a double flame structure near the stabilization edge of lifted flame that consisted of inner partially premixed flame and outer diffusion flame front. The inner reaction zone is highly wrinkled and folded due to significant turbulent mixing between the annular-air jet and the fuel vapor generated from droplets along the contact interface of this air jet with the fuel spray. Larger droplets, having higher momentum are able to penetrate the inner reaction zone and then vaporized in the low-speed hot region bounded by these reaction zones; this supports the outer diffusion flame. Frequent local extinctions in the inner reaction zone were observed at low air flow rate. As flow rate increases, the inner zone is more resistant to local extinction despite of its high wrinkling and corrugation degree. However, the outer reaction zone exhibits stable and mildly wrinkled features irrespective of air flow rate. The liftoff height increases with the air mass flow rate but decreases with L.

  4. 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.

  5. Physical and Chemical Processes in Turbulent Flames

    Science.gov (United States)

    2015-06-23

    used a constant-pressure, fan -stirred combustion chamber to investigate the propagation of a spherically expanding flame (Fig. 1.1). Chambers based...radius, closer to the fans . However during flame expansion, the mean radial flow adjacent to the flame is radially outward in nature shown by the...AFRL-OSR-VA-TR-2015-0136 Physical and Chemical Processes in Turbulent Flames Chung Law TRUSTEES OF PRINCETON UNIVERSITY Final Report 06/23/2015

  6. A computational study of droplet evaporation with fuel vapor jet ejection induced by localized heat sources

    KAUST Repository

    Sim, Jaeheon

    2015-05-12

    Droplet evaporation by a localized heat source under microgravity conditions was numerically investigated in an attempt to understand the mechanism of the fuel vapor jet ejection, which was observed experimentally during the flame spread through a droplet array. An Eulerian-Lagrangian method was implemented with a temperature-dependent surface tension model and a local phase change model in order to effectively capture the interfacial dynamics between liquid droplet and surrounding air. It was found that the surface tension gradient caused by the temperature variation within the droplet creates a thermo-capillary effect, known as the Marangoni effect, creating an internal flow circulation and outer shear flow which drives the fuel vapor into a tail jet. A parametric study demonstrated that the Marangoni effect is indeed significant at realistic droplet combustion conditions, resulting in a higher evaporation constant. A modified Marangoni number was derived in order to represent the surface force characteristics. The results at different pressure conditions indicated that the nonmonotonic response of the evaporation rate to pressure may also be attributed to the Marangoni effect.

  7. Acoustic power measurements of oscillating flames

    NARCIS (Netherlands)

    Valk, M.

    1981-01-01

    The acoustic power of an oscillating flame is measured. A turbulent premixed propane/air flame is situated near a pressure antinode of a standing wave in a laboratory combustion chamber. This standing wave is generated by a piston. The fluctuating heat release of the flame will supply acoustic power

  8. Hysteresis and transition in swirling nonpremixed flames

    NARCIS (Netherlands)

    Tummers, M.J.; Hübner, A.W.; van Veen, E.H.; Hanjalic, K.; van der Meer, Theodorus H.

    2009-01-01

    Strongly swirling nonpremixed flames are known to exhibit a hysteresis when transiting from an attached long, sooty, yellow flame to a short lifted blue flame, and vice versa. The upward transition (by increasing the air and fuel flow rates) corresponds to a vortex breakdown, i.e. an abrupt change

  9. Environmental Considerations for Flame Resistant Textiles

    Science.gov (United States)

    Virtually all common textiles will ignite and burn. There are mandatory and voluntary cigarette and open-flame ignition regulations to address unreasonable fire risks associated with textile products that require them to be treated with and/or contain flame retardant chemicals to make them flame res...

  10. 30 CFR 14.20 - Flame resistance.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Flame resistance. 14.20 Section 14.20 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR TESTING, EVALUATION, AND APPROVAL OF... § 14.20 Flame resistance. Conveyor belts for use in underground coal mines must be flame-resistant and...

  11. Experimental characterization of methane inverse diffusion flame

    KAUST Repository

    Elbaz, Ayman M.

    2014-06-26

    This article presents 10-kHz images of OH-PLIF simultaneously with 2-D PIV measurements in an inverse methane diffusion flame. Under a constant fuel flow rate, the central air jet Re was varied, leading to air to fuel velocity ratio, Vr, to vary from 8.3 to 66.5. Starting from Vr = 20.7, the flame is commonly characterized by three distinct zones. The length of the lower fuel entrainment region is inversely proportional to Vr. The flames investigated resemble a string shear layer confining this zone, and converging into the second distinct region, the flame neck zone. The third region is the rest of the flame, which spreads in a jet-like manner. The inverse diffusion flames exhibit varying degrees of partial premixing, depending upon on the velocity ratio Vr, and this region of partial premixing evolves into a well-mixed reaction zone along the flame centerline. The OH distribution correlated with the changes in the mean characteristics of the flow through reduction in the local Reynolds number due to heat release. The existence of a flame suppresses or laminarizes the turbulence at early axial locations and promotes fluctuations at the flame tip for flames with Vr < 49.8. In addition, the flame jet width can be correlated to the OH distribution. In upstream regions of the flames, the breaks in OH are counterbalanced by flame closures and are governed by edge flame propagation. These local extinctions were found to occur at locations where large flow structures were impinging on the flame and are associated with a locally higher strain rate or correlated to the local high strain rates at the flame hole edges without this flow impinging. Another contributor to re-ignition was found to be growing flame kernels. As the flames approach global blow-off, these kernels become the main mechanism for re-ignition further downstream of the flames. At low Vr, laminarization within the early regions of the flame provides an effective shield, preventing the jet flow from

  12. A Characterization Of Alcohol Fuel Vapor For Wavelength Modulation Spectroscopy Applied To Microgravity Flame Spread

    Science.gov (United States)

    Kulis, Michael J.; Perry, David S.; Miller, Fletcher; Piltch, Nancy

    2003-01-01

    A diode laser diagnostic is being developed for use in an ongoing investigation of flame spread in microgravity at NASA Glenn Research Center. Flame spread rates through non-homogenous gas mixtures are significantly different in a microgravity environment because of buoyancy and possibly hydrostatic pressure effects. These effects contribute to the fuel vapor concentration ahead of the flame being altered so that flame spread is more rapid in microgravity. This paper describes spectral transmission measurements made through mixtures of alcohol, water vapor, and nitrogen in a gas cell that was designed and built to allow measurements at temperatures up to 500 C. The alcohols considered are methanol, ethanol, and n-propanol. The basic technique of wavelength modulation spectroscopy for gas species measurements in microgravity was developed by Silver et al. For this technique to be applicable, one must carefully choose the spectral features over which the diode laser is modulated to provide good sensitivity and minimize interference from other molecular lines such as those in water. Because the methanol spectrum was not known with sufficient resolution in the wavelength region of interest, our first task was to perform high-resolution transmission measurements with an FTIR spectrometer for methanol vapor in nitrogen, followed recently by ethanol and n-propanol. A computer program was written to generate synthesized data to mimic that expected from the experiment using the laser diode, and results from that simulation are also presented.

  13. Low Reynolds Number Droplet Combustion In CO2 Enriched Atmospheres In Microgravity

    Science.gov (United States)

    Hicks, M. C.

    2003-01-01

    The effect of radiative feedback from the gas phase in micro-gravity combustion processes has been of increasing concern because of the implications in the selection and evaluation of appropriate fire suppressants. The use of CO2, an optically thick gas in the infrared region of the electromagnetic spectrum, has garnered widespread acceptance as an effective fire suppressant for most ground based applications. Since buoyant forces often dominate the flow field in 1-g environments the temperature field between the flame front and the fuel surface is not significantly affected by gas phase radiative absorption and re-emission as these hot gases are quickly swept downstream. However, in reduced gravity environments where buoyant-driven convective flows are negligible and where low-speed forced convective flows may be present at levels where gas phase radiation becomes important, then changes in environment that enhance gas phase radiative effects need to be better understood. This is particularly true in assessments of flammability limits and selection of appropriate fire suppressants for future space applications. In recognition of this, a ground-based investigation has been established that uses a droplet combustion configuration to systematically study the effects of enhanced gas phase radiation on droplet burn rates, flame structure, and radiative output from the flame zone.

  14. Structures of laminar spray flames in the counterflow configuration; Strukturen laminarer Sprayflammen in der Gegenstromkonfiguration

    Energy Technology Data Exchange (ETDEWEB)

    Gutheil, E.; Sirignano, W.A.

    1995-12-31

    Structures of mono-dispersed methanol sprays in the counterflow configuration, were examined where detailed transport and a detailed reaction mechanism was taken into account with 23 species and 168 elementary reactions. It was found that the structure of spray flames, in contrast to gas flames at fixed temperature and composition of the incoming flow and the pressure, depends not only on the rate of expansion, but also on the speed of entry of the droplets. This can alter the structure of the spray flame considerably. It was also shown that the outer flame structure with low expansion can be described sufficiently accurately by the entry mechanism. If the initial droplet radius is increased form 25 {mu}m to 50 {mu}m, this leads to an increase of the flame temperature with a simultaneous increase of mass fracture of gaseous methanol. It was found that the spray flame with the largest initial radius of the droplets is extinguished with low expansion. In future, the computer code will be made more efficient by implementing an adaptive grid; n-heptane and n-octane sprays will also be examined. Measured results are available for the fuel n-heptane, which can be compared with the calculations. The boundary conditions in the code of a potential flow in piston flow must be changed for this purpose. (orig.) [Deutsch] Es wurden Strukturen von monodispersen Methanolsprays in der Gegenstromkonfiguration untersucht, dabei wurde detaillierter Transport und ein detaillierter Reaktionsmechanismus mit 23 Spezies und 168 Elementarreaktionen beruecksichtigt. Es zeigt sich, dass die Struktur von Sprayflammen im Gegensatz zu Gasflammen bei fester Temperatur und Zusammensetzung der Eingangsstroeme sowie des Drucks nicht nur von der Streckungsrate, sondern auch von der Eintrittsgeschwindigkeit der Troepfchen abhaengt. Diese kann die Struktur der Sprayflamme wesentlich veraendern. Weiterhin wurde gezeigt, dass die aeussere Flammenstruktur bei geringer Streckung hinreichend genau mit

  15. Droplet evaporation and combustion in a liquid-gas multiphase system

    Science.gov (United States)

    Muradoglu, Metin; Irfan, Muhammad

    2017-11-01

    Droplet evaporation and combustion in a liquid-gas multiphase system are studied computationally using a front-tracking method. One field formulation is used to solve the flow, energy and species equations with suitable jump conditions. Both phases are assumed to be incompressible; however, the divergence-free velocity field condition is modified to account for the phase change at the interface. Both temperature and species gradient driven phase change processes are simulated. Extensive validation studies are performed using the benchmark cases: The Stefan and the sucking interface problems, d2 law and wet bulb temperature comparison with the psychrometric chart values. The phase change solver is then extended to incorporate the burning process following the evaporation as a first step towards the development of a computational framework for spray combustion. We used detailed chemistry, variable transport properties and ideal gas behaviour for a n-heptane droplet combustion; the chemical kinetics being handled by the CHEMKIN. An operator-splitting approach is used to advance temperature and species mass fraction in time. The numerical results of the droplet burning rate, flame temperature and flame standoff ratio show good agreement with the experimental and previous numeric.

  16. Experimental and Numerical Study of Spacecraft Contamination Problems Associated With Gas and Gas-Droplet Thruster Plume Flows

    Science.gov (United States)

    2006-04-17

    sources of contamination of the surface of space vehicles are jets of their control thrusters, containing products of poor combustion (droplets... Etanol , 4861 Е Experimental Points Approximating Curve Fig. 2.16. Calibration dependence of optical radiation intensity for ethanol vapors -6

  17. The VLT FLAMES Tarantula Survey

    NARCIS (Netherlands)

    Evans, C.; Taylor, W.; Sana, H.; Hénault-Brunet, V.; Bagnoli, T.; Bastian, N.; Bestenlehner, J.; Bonanos, A.; Bressert, E.; Brott, I.; Campbell, M.; Cantiello, M.; Carraro, G.; Clark, S.; Costa, E.; Crowther, P.; de Koter, A.; de Mink, S.; Doran, E.; Dufton, P.; Dunstall, P.; Garcia, M.; Gieles, M.; Gräfener, G.; Herrero, A.; Howarth, I.; Izzard, R.; Köhler, K.; Langer, N.; Lennon, D.; Maíz Apellániz, J.; Markova, N.; Najarro, P.; Puls, J.; Ramirez, O.; Sabín-Sanjulián, C.; Simón-Díaz, S.; Smartt, S.; Stroud, V.; van Loon, J.; Vink, J.S.; Walborn, N.

    2011-01-01

    We introduce the VLT FLAMES Tarantula Survey, an ESO Large Programme from which we have obtained optical spectroscopy of over 800 massive stars in the spectacular 30 Doradus region of the Large Magellanic Cloud. A key feature is the use of multi-epoch observations to provide strong constraints on

  18. Cars Spectroscopy of Propellant Flames

    Science.gov (United States)

    1983-11-01

    Propellant Flames," Fast Reactions in Energetic Systems, D. Capellos and R. F. Walker, ed., Reidel, Boston, MA, 1981, pp 473-434. 2. L. E. Harris and M. E...Beardell Y. Carignon J. Fendell K, Aron E. Petro DRStfC-LCE-(D), R. Walker P. Marinkas C. Capellos S. Buluou F. Gilbert Dover, tU 07801 Afmtnistrator

  19. Theory of Colored Flame Production

    Science.gov (United States)

    1964-03-20

    cal/mole, UnO electron volt per molecule is equivalent to 23.US3 kilocalories per gram mole. At ++ ~2000Oý, it is estimatted that molecules with a...because halides stimulate alkali metal compound folaltion, the halogens must be classed as negativo enhancement agents in flames containing alkali

  20. Combustion Characterization of Individual Bio-oil Droplets

    DEFF Research Database (Denmark)

    Hansen, Brian Brun; Jensen, Peter Arendt

    2015-01-01

    Single droplet combustion characteristics has been investigated for bio-oil slurries, containing biomass residue, and compared to conventional fuels for pulverized burners, such as fuel oil (start up) and wood chips (solid biomass fuel). The investigated fuels ignition delays and pyrolysis behavi...... and thereby decreased flame stability. Most promising were oil or diesel (not palm oil) containing slurries (1 and 5) with heating values in the range of 15 MJ/kg.......Single droplet combustion characteristics has been investigated for bio-oil slurries, containing biomass residue, and compared to conventional fuels for pulverized burners, such as fuel oil (start up) and wood chips (solid biomass fuel). The investigated fuels ignition delays and pyrolysis behavior...... was tested in a single particle reactor at conditions relevant for suspension firing (A: 1200 °C, 5.5 % O2; B: 1200 °C, 2.9 % O2 and C: 990 °C, 5.5 % O2). The slurries were tested to optimize the bio-oil composition for use as an alternative power plant start-up fuel. Pyrolysis times for 5 mg bio-oil samples...

  1. Single droplet experimentation on spray drying:evaporation of sessile droplets deposited on a flat surface

    NARCIS (Netherlands)

    Perdana, J.A.; Fox, M.B.; Schutyser, M.A.I.; Boom, R.M.

    2010-01-01

    Abstract: Individually dispensed droplets were dried on a flat surface to mimic the drying of single droplets during spray drying. A robust dispensing process is presented that generates small droplets (dp>150 µm). A predictive model based on Bernoulli’s law accurately describes droplet size with

  2. 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

  3. Investigation of Droplet Atomization and Evaporation in Solution Precursor Plasma Spray Coating

    Directory of Open Access Journals (Sweden)

    Hongbing Xiong

    2017-11-01

    Full Text Available Solution precursor plasma spray (SPPS is a novel and promising technique in producing nanostructured coatings. This technique involves complex heat, mass and momentum transfer among the liquid feedstock, droplets, plasma jet and the coating material. Nevertheless, the droplet atomization and evaporation in the plasma jet is one of the most essential parts to obtain the desired coating architecture. In the present work, a three-dimensional two-way-coupled Eulerian-Lagrangian code is used to simulate the interactions between the solution precursor and plasma. In order to obtain a more realistic understanding regarding droplet atomization and vaporization, the flash-boiling effect is modeled by an improved vaporization model. This model could provide accurate details for the droplet pyrolysis and help to optimize the solution precursor plasma spray process. We show that the fragmentation of the liquid stock and its vaporization mainly dominate the spraying details and can be decisive to the coating quality. We further investigate their role in SPPS and separately probe their inner link with the flow field relating to the distinctive area when droplets are flying through the thermal flow field. Our studies reveal that ethanol droplets, compared to those of water, show a superior characteristics in SPPS, owing to the low boiling point and low surface tension, conducive to the evaporation and atomization of droplets. In addition, the mixture of the plasma gas with hydrogen breaks the droplets more thoroughly compared to the pure plasma. The numerical results were compared and found to agree well with previous experimental and simulation work.

  4. A flame particle tracking analysis of turbulence–chemistry interaction in hydrogen–air premixed flames

    KAUST Repository

    Uranakara, Harshavardhana A.

    2015-11-21

    Interactions of turbulence, molecular transport, and energy transport, coupled with chemistry play a crucial role in the evolution of flame surface geometry, propagation, annihilation, and local extinction/re-ignition characteristics of intensely turbulent premixed flames. This study seeks to understand how these interactions affect flame surface annihilation of lean hydrogen–air premixed turbulent flames. Direct numerical simulations (DNSs) are conducted at different parametric conditions with a detailed reaction mechanism and transport properties for hydrogen–air flames. Flame particle tracking (FPT) technique is used to follow specific flame surface segments. An analytical expression for the local displacement flame speed (Sd) of a temperature isosurface is considered, and the contributions of transport, chemistry, and kinematics on the displacement flame speed at different turbulence-flame interaction conditions are identified. In general, the displacement flame speed for the flame particles is found to increase with time for all conditions considered. This is because, eventually all flame surfaces and their resident flame particles approach annihilation by reactant island formation at the end of stretching and folding processes induced by turbulence. Statistics of principal curvature evolving in time, obtained using FPT, suggest that these islands are ellipsoidal on average enclosing fresh reactants. Further examinations show that the increase in Sd is caused by the increased negative curvature of the flame surface and eventual homogenization of temperature gradients as these reactant islands shrink due to flame propagation and turbulent mixing. Finally, the evolution of the normalized, averaged, displacement flame speed vs. stretch Karlovitz number are found to collapse on a narrow band, suggesting that a unified description of flame speed dependence on stretch rate may be possible in the Lagrangian description.

  5. Vaporization of perfluorocarbon droplets using optical irradiation.

    Science.gov (United States)

    Strohm, Eric; Rui, Min; Gorelikov, Ivan; Matsuura, Naomi; Kolios, Michael

    2011-06-01

    Micron-sized liquid perfluorocarbon (PFC) droplets are currently being investigated as activatable agents for medical imaging and cancer therapy. After injection into the bloodstream, superheated PFC droplets can be vaporized to a gas phase for ultrasound imaging, or for cancer therapy via targeted drug delivery and vessel occlusion. Droplet vaporization has been previously demonstrated using acoustic methods. We propose using laser irradiation as a means to induce PFC droplet vaporization using a method we term optical droplet vaporization (ODV). In order to facilitate ODV of PFC droplets which have negligible absorption in the infrared spectrum, optical absorbing nanoparticles were incorporated into the droplet. In this study, micron-sized PFC droplets loaded with silica-coated lead sulfide (PbS) nanoparticles were evaluated using a 1064 nm laser and ultra-high frequency photoacoustic ultrasound (at 200 and 375 MHz). The photoacoustic response was proportional to nanoparticle loading and successful optical droplet vaporization of individual PFC droplets was confirmed using photoacoustic, acoustic, and optical measurements. A minimum laser fluence of 1.4 J/cm(2) was required to vaporize the droplets. The vaporization of PFC droplets via laser irradiation can lead to the activation of PFC agents in tissues previously not accessible using standard ultrasound-based techniques.

  6. Particle manipulation methods in droplet microfluidics.

    Science.gov (United States)

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

    2017-11-30

    This Feature article describes the different particle manipulation techniques available in the droplet microfluidics tool-box 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. Sophisticated compound droplets on fiber networks

    Science.gov (United States)

    Weyer, Floriane; Lismont, Marjorie; Dreesen, Laurent; Vandewalle, Nicolas

    2015-11-01

    Droplets on fibers are part of our everyday lives. Indeed, many phenomena involve drops and fibers such as the formation of dew droplets on a spiderweb, the trapping of water droplets on cactus spines or the dyeing of cotton or wool fibers. Therefore, this topic has been widely studied in the recent years and it appears that droplets on fibers can be the starting point for an open digital microfluidics. We study the behavior of soapy water droplets on a fiber array. When a droplet slides along a vertical fiber and encounters a horizontal fiber, it can either stick there or continue its way. In the latter case, the droplet releases a tiny residue. We study the volume of these residues depending on the geometry of the node. By using this technique, a large number of small droplets can be trapped at the nodes of a fiber array. These residues can be encapsulated and collected by an oil droplet in order to create a multicompound droplet. Moreover, by using optical fibers, we can provoke and detect the fluorescence of the inner droplets. Fibers provide therefore an original way to study compound droplets and multiple reactions. F. Weyer is financially supported by an FNRS grant. This work is also supported by the FRFC 2.4504.12.

  8. 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.

  9. Droplets, Bubbles and Ultrasound Interactions

    NARCIS (Netherlands)

    Shpak, O.; Verweij, M.; de Jong, N.; Versluis, Michel; Escoffre, J.M.; Bouakaz, A.

    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

  10. Salt stains from evaporating droplets

    NARCIS (Netherlands)

    Shahidzadeh, N.; Schut, M.F.L.; Desarnaud, J.; Prat, M.; Bonn, D.

    2015-01-01

    The study of the behavior of sessile droplets on solid substrates is not only associated with common everyday phenomena, such as the coffee stain effect, limescale deposits on our bathroom walls, but also very important in many applications such as purification of pharmaceuticals, deicing of

  11. 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: http://www.ias.ac.in/article/fulltext/reso/019/02/0123-0134 ...

  12. Mechanism of Candle Flame Oscillation: Detection of Descending Flow above the Candle Flame

    Science.gov (United States)

    Nagamine, Yuko; Otaka, Koki; Zuiki, Hiroyuki; Miike, Hidetoshi; Osa, Atsushi

    2017-07-01

    When several candles are bundled together, the size of the combined candle flame oscillates. We carried out observational experiments to understand the mechanism of this oscillation. These were optical imaging, shadow graph imaging, temperature imaging around the oscillating candle flame, and image analysis to obtain the quantitative velocity distribution of the air flow above the candle flame. The experiments detected the descending air flow to the candle flame from the upper area, and showed that the descending air flow is involved with the candle flame oscillation. According to the results, we propose a new mechanism of the candle flame oscillation using the analogy of the cumulonimbus cloud in meteorology.

  13. Combustion Characteristics of Hydrocarbon Droplets Induced by Photoignition of Aluminum Nanoparticles (Conference Paper with Briefing Charts)

    Science.gov (United States)

    2017-04-23

    average values of K, while Fischer−Tropsch Jet fuel (FT) has the highest. Also, the burning rate constant for ethanol was the same for both PI and...hardly visible. The frame rate was 1,000 fps and the exposure time was ~ 0.98 ms. The values of ignition delays obtained through the application of PI ...droplets has been achieved through photoignition ( PI ) utilizing sub milligram of aluminum nanoparticles (Al NPs). For diesel fuel, a reliable ignition

  14. Methanol Droplet Extinction in Oxygen/Carbon-dioxide/Nitrogen Mixtures in Microgravity: Results from the International Space Station Experiments

    Science.gov (United States)

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

    2012-01-01

    Motivated by the need to understand the flammability limits of condensed-phase fuels in microgravity, isolated single droplet combustion experiments were carried out in the Combustion Integrated Rack Facility onboard the International Space Station. Experimental observations of methanol droplet combustion and extinction in oxygen/carbon-dioxide/nitrogen mixtures at 0.7 and 1 atmospheric pressure in quiescent microgravity environment are reported for initial droplet diameters varying between 2 mm to 4 mm in this study.The ambient oxygen concentration was systematically lowered from test to test so as to approach the limiting oxygen index (LOI) at fixed ambient pressure. At one atmosphere pressure, ignition and some burning were observed for an oxygen concentration of 13% with the rest being nitrogen. In addition, measured droplet burning rates, flame stand-off ratios, and extinction diameters are presented for varying concentrations of oxygen and diluents. Simplified theoretical models are presented to explain the observed variations in extinction diameter and flame stand-off ratios.

  15. Study on Heat Transfer and Flow Characteristic Under Phase-Change Process of an Acoustically Levitated Droplet

    Science.gov (United States)

    Shitanishi, Kuniharu; Hasegawa, Koji; Kaneko, Akiko; Abe, Yutaka

    2014-11-01

    Acoustic levitation is one of the levitation technique which is expected to be used for analytical chemistry and manufacturing new materials. Thus, it is important to gather the knowledge about acoustically levitated droplet. The purpose of this study is to investigate the heat transfer and flow behavior under phase change process of an acoustically levitated droplet. The following results were obtained from experiments. Evaporation process and external flow structure of the levitated droplet is visualized by a high speed camera and it is found that they differ by the type of fluid. Toroidal vortices are observed near the surface of the ethanol solution droplet. Heat transfer coefficient is estimated from the volume change and temperature gradient. It is substantially higher than that estimated by the existing experimental correlation.

  16. Ethanol Basics (Fact Sheet)

    Energy Technology Data Exchange (ETDEWEB)

    2015-01-01

    Ethanol is a widely-used, domestically-produced renewable fuel made from corn and other plant materials. More than 96% of gasoline sold in the United States contains ethanol. Learn more about this alternative fuel in the Ethanol Basics Fact Sheet, produced by the U.S. Department of Energy's Clean Cities program.

  17. Laminar Flame Characteristics of C1–C5 Primary Alcohol-Isooctane Blends at Elevated Temperature

    Directory of Open Access Journals (Sweden)

    Qianqian Li

    2016-06-01

    Full Text Available The laminar combustion characteristics of blends of isooctane and C1–C5 primary alcohols (i.e., methanol, ethanol, n-propanol, n-butanol and n-pentanol were investigated using the spherical expanding flame methodology in a constant volume chamber at various equivalence ratios and volume fractions of alcohol. The stretch effect was removed using the nonlinear methodology. The results indicate that the laminar flame speeds of alcohol-isooctane blends increase monotonously with the increasing volume fraction of alcohol. Among the five alcohols, the addition of methanol is identified to be the most effective in enhancing laminar flame speed. The addition of ethanol results in an approximately equivalent laminar flame speed enhancement rate as those of n-propanol, n-butanol and n-pentanol at ratios of 0.8 and 1.5, and a higher rate at 1.0 and 1.2. An empirical correlation is provided to describe the laminar flame speed variation with the volume fraction of alcohol. Meanwhile, the laminar flame speed increases with the mass content of oxygen in the fuel blends. At the equivalence ratio of 0.8 and fixed oxygen content, similar laminar flame speeds are observed with different alcohols blended into isooctane. Nevertheless, with the increase of equivalence ratio, heavier alcohol-isooctane blends tend to exhibit higher values. Markstein lengths of alcohol-isooctane blends decrease with the addition of alcohol into isooctane at 0.8, 1.0 and 1.2, however they increase at 1.5. This is consistent with the behavior deduced from the Schlieren images.

  18. Thermophoresis of water droplets inside carbon nanotubes

    Science.gov (United States)

    Zambrano, Harvey; Walther, Jh; Oyarzua, Elton; Rojano, Andres

    2016-11-01

    Carbon Nanotubes (CNTs) offer unique possibilities as fluid conduits with applications ranging from lab on a chip devices to encapsulation media for drug delivery. CNTs feature high mechanical strength, chemical and thermal stability and biocompatibility therefore they are promising candidates for nanodevice fabrication. Thermal gradients have been proposed as mechanism to drive particles, fullerenes and droplets inside CNTs. Here, by conducting Molecular Dynamics (MD) simulations, we study thermophoresis of water droplets inside CNTs. We systematically change the size of the droplets, the axial thermal gradient and CNT chirality. We find that the droplet motion in the armchair CNTs exhibits two clearly delimited stages, a regime wherein the droplet is accelerated and subsequently, a regime wherein the droplet moves with constant velocity. Inside the zig zag CNTs, the droplet accelerates during a very short time and then it moves with constant velocity. We compute the net force during the droplet acceleration and find a correlation between the droplet acceleration and the magnitude of the thermal gradient without any dependence on the droplet size. Moreover, we conduct velocity constrained MD simulations to determine the friction and thermophoretic forces acting on the droplet. We acknowledge partial funding from FONDECYT through the Project No. 11130559 and from VRID Universidad de Concepcion.

  19. Droplet lasers: a review of current progress

    Science.gov (United States)

    McGloin, D.

    2017-05-01

    It is perhaps surprising that something as fragile as a microscopic droplet could possibly form a laser. In this article we will review some of the underpinning physics as to how this might be possible, and then examine the state of the art in the field. The technology to create and manipulate droplets will be examined, as will the different classes of droplet lasers. We discuss the rapidly developing fields of droplet biolasers, liquid crystal laser droplets and explore how droplet lasers could give rise to new bio and chemical sensing and analysis. The challenges that droplet lasers face in becoming robust devices, either as sensors or as photonic components in the lab on chip devices, is assessed.

  20. 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.

  1. Heat and mass transfer in flames

    Science.gov (United States)

    Faeth, G. M.

    1986-01-01

    Heat- and mass-transfer processes in turbulent diffusion flames are discussed, considering turbulent mixing and the structure of single-phase flames, drop processes in spray flames, and nonluminous and luminous flame radiation. Interactions between turbulence and other phenomena are emphasized, concentrating on past work of the author and his associates. The conserved-scalar formalism, along with the laminar-flamelet approximation, is shown to provide reasonable estimates of the structure of gas flames, with modest levels of empiricism. Extending this approach to spray flames has highlighted the importance of drop/turbulence interactions; e.g., turbulent dispersion of drops, modification of turbulence by drops, etc. Stochastic methods being developed to treat these phenomena are yielding encouraging results.

  2. Transitional Gas Jet Diffusion Flames in Microgravity

    Science.gov (United States)

    Agrawal, Ajay K.; Alammar, Khalid; Gollahalli, S. R.; Griffin, DeVon (Technical Monitor)

    2000-01-01

    Drop tower experiments were performed to identify buoyancy effects in transitional hydrogen gas jet diffusion flames. Quantitative rainbow schlieren deflectometry was utilized to optically visualize the flame and to measure oxygen concentration in the laminar portion of the flame. Test conditions consisted of atmospheric pressure flames burning in quiescent air. Fuel from a 0.3mm inside diameter tube injector was issued at jet exit Reynolds numbers (Re) of 1300 to 1700. Helium mole percentage in the fuel was varied from 0 to 40%. Significant effects of buoyancy were observed in near field of the flame even-though the fuel jets were momentum-dominated. Results show an increase of breakpoint length in microgravity. Data suggest that transitional flames in earth-gravity at Re<1300 might become laminar in microgravity.

  3. Flame assisted synthesis of catalytic ceramic membranes

    DEFF Research Database (Denmark)

    Johansen, Johnny; Mosleh, Majid; Johannessen, Tue

    2004-01-01

    technology it is possible to make supported catalysts, composite metal oxides, catalytically active surfaces, and porous ceramic membranes. Membrane layers can be formed by using a porous substrate tube (or surface) as a nano-particle filter. The aerosol gas from the flame is led through a porous substrate......Membranes consisting of one or more metal oxides can be synthesized by flame pyrolysis. The general principle behind flame pyrolysis is the decomposition and oxidation of evaporated organo-metallic precursors in a flame, thereby forming metal oxide monomers. Because of the extreme supersaturation...... created in the flame, the monomers will nucleate homogeneously and agglomerate to form aggregates of large ensembles of monomers. The aggregates will then sinter together to form single particles. If the flame temperature and the residence time are sufficiently high, the formed oxide particles...

  4. 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.

  5. Advances in Turbulent Combustion Dynamics Simulations in Bluff-Body Stabilized Flames-Body Stabilized Flames

    Science.gov (United States)

    2015-11-30

    improved Linear Eddy Model approach is applied to predict the flame properties inside the Volvo rig and it is shown to over-predict the flame...work, the improved Linear Eddy Model approach is applied to predict the flame properties inside the Volvo rig and it is shown to over-predict the flame...39 4.1 Volvo Rig Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 4.2 Simulation Description

  6. Quantum Nanostructures by Droplet Epitaxy

    Directory of Open Access Journals (Sweden)

    Somsak Panyakeow

    2009-02-01

    Full Text Available 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 strain gives rise to quantum rings with square holes and non-uniform ring stripe. Regrowth of quantum dots on these anisotropic quantum rings, Quadra-Quantum Dots (QQDs could be realized. Potential applications of these quantum nanostructures are also discussed.

  7. Pole solutions for flame front propagation

    CERN Document Server

    Kupervasser, Oleg

    2015-01-01

    This book deals with solving mathematically the unsteady flame propagation equations. New original mathematical methods for solving complex non-linear equations and investigating their properties are presented. Pole solutions for flame front propagation are developed. Premixed flames and filtration combustion have remarkable properties: the complex nonlinear integro-differential equations for these problems have exact analytical solutions described by the motion of poles in a complex plane. Instead of complex equations, a finite set of ordinary differential equations is applied. These solutions help to investigate analytically and numerically properties of the flame front propagation equations.

  8. Experimental Investigation Evaporation of Liquid Mixture Droplets during Depressurization into Air Stream

    Science.gov (United States)

    Liu, L.; Bi, Q. C.; Terekhov, Victor I.; Shishkin, Nikolay E.

    2010-03-01

    The objective of this study is to develop experimental method to study the evaporation process of liquid mixture droplets during depressurization and into air stream. During the experiment, a droplet was suspended on a thermocouple; an infrared thermal imager was used to measure the droplet surface temperature transition. Saltwater droplets were used to investigate the evaporation process during depressurization, and volatile liquid mixtures of ethanol, methanol and acetone in water were applied to experimentally research the evaporation into air stream. According to the results, the composition and concentration has a complex influence on the evaporation rate and the temperature transition. With an increase in the share of more volatile component, the evaporation rate increases. While, a higher salt concentration in water results in a lower evaporation rate. The shape variation of saltwater droplet also depends on the mass concentration in solution, whether it is higher or lower than the eutectic point (22.4%). The results provide important insight into the complex heat and mass transfer of liquid mixture during evaporation.

  9. Droplet based cavities and lasers

    DEFF Research Database (Denmark)

    Mølhave, Kristian; Kristensen, Anders; Mortensen, Asger

    2009-01-01

    The self-organized and molecularly smooth surface on liquid microdroplets makes them attractive as optical cavities with very high quality factors. This chapter describes the basic theory of optical modes in spherical droplets. The mechanical properties including vibrational excitation are also...... described, and their implications for microdroplet resonator technology are discussed. Optofluidic implementations of microdroplet resonators are reviewed with emphasis on the basic optomechanical properties....

  10. Recent developments in droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Mano, Takaaki; Jo, Masafumi; Kuroda, Takashi; Abbarchi, Marco; Noda, Takeshi [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Sakoda, Kazuaki [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan and Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan)

    2014-05-15

    The droplet epitaxy allows for self-assembly of lattice-matched GaAs quantum dots (QDs) with high quality and high uniformity. In this article, we show our efforts to realize the GaAs QDs with excellent optical properties. After the optimization of the several growth processes, we achieved current-injection lasing in the GaAs QDs. In addition, formation of further advanced nanostructure is presented.

  11. Flame Retardation Modification of Paper-Based PVC Wallcoverings

    National Research Council Canada - National Science Library

    Lin, Hui; Yang, Haiyang; Xiao, He; Cao, Shilin; Huang, Liulian; Chen, Lihui; Li, Jian

    2016-01-01

    The flame-retarded paper-based polyvinyl chloride (PVC) wallcoverings were successfully prepared, using plant fiber paper as base material and adding inorganic flame retardants and flame-retarded plasticizer as additives...

  12. Vortices catapult droplets in atomization

    Science.gov (United States)

    Jerome, J. John Soundar; Marty, Sylvain; Matas, Jean-Philippe; Zaleski, Stéphane; Hoepffner, Jérôme

    2013-11-01

    A droplet ejection mechanism in planar two-phase mixing layers is examined. Any disturbance on the gas-liquid interface grows into a Kelvin-Helmholtz wave, and the wave crest forms a thin liquid film that flaps as the wave grows downstream. Increasing the gas speed, it is observed that the film breaks up into droplets which are eventually thrown into the gas stream at large angles. In a flow where most of the momentum is in the horizontal direction, it is surprising to observe these large ejection angles. Our experiments and simulations show that a recirculation region grows downstream of the wave and leads to vortex shedding similar to the wake of a backward-facing step. The ejection mechanism results from the interaction between the liquid film and the vortex shedding sequence: a recirculation zone appears in the wake of the wave and a liquid film emerges from the wave crest; the recirculation region detaches into a vortex and the gas flow over the wave momentarily reattaches due to the departure of the vortex; this reattached flow pushes the liquid film down; by now, a new recirculation vortex is being created in the wake of the wave—just where the liquid film is now located; the liquid film is blown up from below by the newly formed recirculation vortex in a manner similar to a bag-breakup event; the resulting droplets are catapulted by the recirculation vortex.

  13. Compound droplet manipulations on fiber arrays

    Science.gov (United States)

    Weyer, Floriane; Lismont, Marjorie; Dreesen, Laurent; Vandewalle, Nicolas

    2014-11-01

    Recent works demonstrated that fibers are the basis of an open digital microfluidics. Indeed, various processes such as droplet motion, fragmentation, trapping, releasing, mixing and encapsulation can be constructed on fiber arrays. However, addressing a large number of tiny droplets resulting from the mixing of several liquid components is still a challenge. Here we show that it is possible to manipulate tiny droplets reaching a high level of complexity. Wetting droplets are known to glide along vertical fibers. When a droplet reaches an horizontal fiber, it sticks at the crossing if capillary overcomes gravity. Otherwise, the droplet continues its way, crosses the node and leaves a tiny residue. Therefore, a vertical fiber decorated with a series of horizontal fibers will retain residual droplets at the successive nodes. An oil droplet, sliding on the vertical fiber, is able to collect the residues. Thus a multicompound droplet is created. The volume of the residual droplets has been studied and seems to be related to the diameters of both vertical and horizontal fibers. Moreover, the conditions under which the residues are released have been investigated in order to understand the formation of such a fluidic object. F. Weyer is financially supported by an FNRS grant. This work is also supported by the FRFC 2.4504.12.

  14. 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

  15. Model flames in the Boussinesq limit: The effects of feedback

    Science.gov (United States)

    Vladimirova, N.; Rosner, R.

    2003-06-01

    We have studied the fully nonlinear behavior of premixed flames in a gravitationally stratified medium, subject to the Boussinesq approximation. The key results include the establishment of criteria for when such flames propagate as simple planar flames, elucidation of scaling laws for the effective flame speed, and a study of the stability properties of these flames. The simplicity of some of our scaling results suggests that analytical work may further advance our understandings of buoyant flames.

  16. [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.

  17. Flame dynamics of a meso-scale heat recirculating combustor

    Energy Technology Data Exchange (ETDEWEB)

    Vijayan, V.; Gupta, A.K. [Department of Mechanical Engineering, University of Maryland, College Park, MD 20742 (United States)

    2010-12-15

    The dynamics of premixed propane-air flame in a meso-scale ceramic combustor has been examined here. The flame characteristics in the combustor were examined by measuring the acoustic emissions and preheat temperatures together with high-speed cinematography. For the small-scale combustor, the volume to surface area ratio is small and hence the walls have significant effect on the global flame structure, flame location and flame dynamics. In addition to the flame-wall thermal coupling there is a coupling between flame and acoustics in the case of confined flames. Flame-wall thermal interactions lead to low frequency flame fluctuations ({proportional_to}100 Hz) depending upon the thermal response of the wall. However, the flame-acoustic interactions can result in a wide range of flame fluctuations ranging from few hundred Hz to few kHz. Wall temperature distribution is one of the factors that control the amount of reactant preheating which in turn effects the location of flame stabilization. Acoustic emission signals and high-speed flame imaging confirmed that for the present case flame-acoustic interactions have more significant effect on flame dynamics. Based on the acoustic emissions, five different flame regimes have been identified; whistling/harmonic mode, rich instability mode, lean instability mode, silent mode and pulsating flame mode. (author)

  18. Tulip flames: changes in shape of premixed flames propagating in closed tubes

    Science.gov (United States)

    Dunn-Rankin, D.; Sawyer, R. F.

    The experimental results that are the subject of this communication provide high-speed schlieren images of the closed-tube flame shape that has come to be known as the tulip flame. The schlieren images, along with in-chamber pressure records, help demonstrate the effects of chamber length, equivalence ratio, and igniter geometry on formation of the tulip flame. The pressure/time records show distinct features which correlate with flame shape changes during the transition to tulip. The measurements indicate that the basic tulip flame formation is a robust phenomenon that depends on little except the overall geometry of the combustion vessel.

  19. Nanoscale guiding and shaping of indium droplets

    Science.gov (United States)

    DÄ browski, Maciej; Dai, Yanan; Hocevar, Moïra; Frolov, Sergey; Petek, Hrvoje

    2016-12-01

    We present time-resolved microscopy of motion and shape transformation of liquid indium (In) sessile droplets on InAs(001) surface. For temperatures up to 800 K, the droplets spontaneously move across the crystal undergoing stick-slip motion that is strongly affected by atomic steps and coalescence events. Above a critical temperature of around 800 K, the droplets stop moving and further increase in temperature causes them to change shape progressively from spherical to rectangular. The process of shape transformation is coherent, reversible and associated with temperature dependent wetting of the surface as well as crystalline anisotropy dependent arsenic solvation and evaporation rates. The etched rectangular substrate depressions formed under the droplets, giving them a rectangular shape, reveal unusual rheology with deeper regions at the corners. Our high spatial resolution measurements link the macroscopic behavior of the metallic droplets with the microscopic topography features and can be used for the metallic liquid droplet nano-manipulation.

  20. Encoding Microreactors with Droplet Chains in Microfluidics.

    Science.gov (United States)

    Song, Wenya; Lin, Gungun; Ge, Jin; Fassbender, Jürgen; Makarov, Denys

    2017-12-13

    Droplet-based high throughput biomolecular screening and combinatorial synthesis entail a viable indexing strategy to be developed for the identification of each microreactor. Here, we propose a novel indexing scheme based on the generation of droplet sequences on demand to form unique encoding droplet chains in fluidic networks. These codes are represented by multiunit and multilevel droplets packages, with each code unit possessing several distinct signal levels, potentially allowing large encoding capacity. For proof of concept, we use magnetic nanoparticles as the encoding material and a giant magnetoresistance (GMR) sensor-based active sorting system supplemented with an optical detector to generate and decode the sequence of one exemplar sample droplet reactor and a 4-unit quaternary magnetic code. The indexing capacity offered by 4-unit multilevel codes with this indexing strategy is estimated to exceed 104, which holds great promise for large-scale droplet-based screening and synthesis.

  1. Impact of flame-wall interaction on premixed flame dynamics and transfer function characteristics

    KAUST Repository

    Kedia, K.S.

    2011-01-01

    In this paper, we numerically investigate the response of a perforated-plate stabilized laminar methane-air premixed flame to imposed inlet velocity perturbations. A flame model using detailed chemical kinetics mechanism is applied and heat exchange between the burner plate and the gas mixture is incorporated. Linear transfer functions, for low mean inlet velocity oscillations, are analyzed for different equivalence ratio, mean inlet velocity, plate thermal conductivity and distance between adjacent holes. The oscillations of the heat exchange rate at the top of the burner surface plays a critical role in driving the growth of the perturbations over a wide range of conditions, including resonance. The flame response to the perturbations at its base takes the form of consumption speed oscillations in this region. Flame stand-off distance increases/decreases when the flame-wall interaction strengthens/weakens, impacting the overall dynamics of the heat release. The convective lag between the perturbations and the flame base response govern the phase of heat release rate oscillations. There is an additional convective lag between the perturbations at the flame base and the flame tip which has a weaker impact on the heat release rate oscillations. At higher frequencies, the flame-wall interaction is weaker and the heat release oscillations are driven by the flame area oscillations. The response of the flame to higher amplitude oscillations are used to gain further insight into the mechanisms. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.

  2. Droplet Deformation Prediction with the Droplet Deormation and Break Up Model (DDB)

    Science.gov (United States)

    Vargas, Mario

    2012-01-01

    The Droplet Deformation and Breakup Model was used to predict deformation of droplets approaching the leading edge stagnation line of an airfoil. The quasi-steady model was solved for each position along the droplet path. A program was developed to solve the non-linear, second order, ordinary differential equation that governs the model. A fourth order Runge-Kutta method was used to solve the equation. Experimental slip velocities from droplet breakup studies were used as input to the model which required slip velocity along the particle path. The center of mass displacement predictions were compared to the experimental measurements from the droplet breakup studies for droplets with radii in the range of 200 to 700 mm approaching the airfoil at 50 and 90 m/sec. The model predictions were good for the displacement of the center of mass for small and medium sized droplets. For larger droplets the model predictions did not agree with the experimental results.

  3. Droplet Deformation Prediction With the Droplet Deformation and Breakup Model (DDB)

    Science.gov (United States)

    Vargas, Mario

    2012-01-01

    The Droplet Deformation and Breakup Model was used to predict deformation of droplets approaching the leading edge stagnation line of an airfoil. The quasi-steady model was solved for each position along the droplet path. A program was developed to solve the non-linear, second order, ordinary differential equation that governs the model. A fourth order Runge-Kutta method was used to solve the equation. Experimental slip velocities from droplet breakup studies were used as input to the model which required slip velocity along the particle path. The center of mass displacement predictions were compared to the experimental measurements from the droplet breakup studies for droplets with radii in the range of 200 to 700 mm approaching the airfoil at 50 and 90 m/sec. The model predictions were good for the displacement of the center of mass for small and medium sized droplets. For larger droplets the model predictions did not agree with the experimental results.

  4. Simulations of flame generated particles

    KAUST Repository

    Patterson, Robert

    2016-01-05

    The nonlinear structure of the equations describing the evolution of a population of coagulating particles in a flame make the use of stochastic particle methods attractive for numerical purposes. I will present an analysis of the stochastic fluctuations inherent in these numerical methods leading to an efficient sampling technique for steady-state problems. I will also give some examples where stochastic particle methods have been used to explore the effect of uncertain parameters in soot formation models. In conclusion I will try to indicate some of the issues in optimising these methods for the study of uncertain model parameters.

  5. Simultaneous identification of multi-combustion-intermediates of alkanol-air flames by femtosecond filament excitation for combustion sensing

    Science.gov (United States)

    Li, Helong; Chu, Wei; Xu, Huailiang; Cheng, Ya; Chin, See-Leang; Yamanouchi, Kaoru; Sun, Hong-Bo

    2016-01-01

    Laser filamentation produced by the propagation of intense laser pulses in flames is opening up new possibility in application to combustion diagnostics that can provide useful information on understanding combustion processes, enhancing combustion efficiency and reducing pollutant products. Here we present simultaneous identification of multiple combustion intermediates by femtosecond filament excitation for five alkanol-air flames fueled by methanol, ethanol, n-propanol, n-butanol, and n-pentanol. We experimentally demonstrate that the intensities of filament-induced photoemission signals from the combustion intermediates C, C2, CH, CN increase with the increasing number of carbons in the fuel molecules, and the signal ratios between the intermediates (CH/C, CH/C2, CN/C, CH/C2, CN/CH) are different for different alkanol combustion flames. Our observation provides a way for sensing multiple combustion components by femtosecond filament excitation in various combustion conditions that strongly depend on the fuel species. PMID:27250021

  6. Droplet Vaporization in a Supercritical Microgravity Environment

    Science.gov (United States)

    Curtis, E. W.; Farrell, P. V.

    1987-01-01

    A model is presented which describes single liquid droplet vaporization at nearly critical liquid pressures and temperatures. A modified Redlich-Kwong equation of state is used to evaluate the fugacities and liquid and vapor mole fractions at the interface under the assumption of interface equilibrium. Results obtained for different droplet sizes and conditions indicate significant differences in behavior in comparison with low-pressure quasi-steady droplet vaporization.

  7. Coalescence Processes of Droplets and Liquid Marbles

    OpenAIRE

    Jing Jin; Chin Hong Ooi; Dzung Viet Dao; Nam-Trung Nguyen

    2017-01-01

    The coalescence process of droplets and, more recently, of liquid marbles, has become one of the most essential manipulation schemes in digital microfluidics. This process is indispensable for realising microfluidic functions such as mixing and reactions at microscale. This paper reviews previous studies on droplet coalescence, paying particular attention to the coalescence of liquid marbles. Four coalescence systems have been reviewed, namely, the coalescence of two droplets freely suspended...

  8. Biodegradation of brominated and organophosphorus flame retardants

    NARCIS (Netherlands)

    Waaijers, S.L.; Parsons, J.R.

    2016-01-01

    Brominated flame retardants account for about 21% of the total production of flame retardants and many of these have been identified as persistent, bioaccumulative and toxic. Nevertheless, debromination of these chemicals under anaerobic conditions is well established, although this can increase

  9. Flame retardant cotton based highloft nonwovens

    Science.gov (United States)

    Flame retardancy has been a serious bottleneck to develop cotton blended very high specific volume bulky High loft fabrics. Alternately, newer approach to produce flame retardant cotton blended High loft fabrics must be employed that retain soft feel characteristics desirable of furnishings. Hence, ...

  10. Flame retardant cotton barrier nonwovens for mattresses

    Science.gov (United States)

    According to regulation CPSC 16 CFR 1633, every new residential mattress sold in the United States since July 2007 must resist ignition by open flame. An environmentally benign “green”, inexpensive way to meet this regulation is to use a low-cost flame retardant (FR) barrier fabric. In this study, a...

  11. Chemical processes in the HNF flame

    NARCIS (Netherlands)

    Ermolin, N.E.; Zarko, V.E.; Keizers, H.L.J.

    2006-01-01

    Results of modeling the HNF flame structure are presented. From an analysis of literature data on the thermal decomposition and combustion of HNF, it is concluded that the dissociative vaporization of HNF proceeds via the route HNFliq → (N2H4)g + (HC(NO 2)3)g. The flame structure is modeled using a

  12. A Theory of Shape-Shifting Droplets

    Science.gov (United States)

    Haas, Pierre; Goldstein, Raymond; Smoukov, Stoyan; Denkov, Nikolai

    2016-11-01

    Recent observations of cooled oil emulsion droplets uncovered a remarkable array of shape transformations: the initially spherical droplets flatten into polygonal shapes, first hexagons, then triangles or quadrilaterals that ultimately grow thin protrusions from their corners. These transformations are driven by a partial phase transition of the bulk liquid phase. In this talk, we explore theoretically the simplest geometric competition between this phase transition and surface tension in planar polygons. We recover the experimental sequence of shapes and predict shape statistics in qualitative agreement with experiments. Extending the model to capture some of the three-dimensional structure of the droplets, we analyse the topological transition of droplet puncture observed in experiments.

  13. John H. Dillon Medal Talk: Polymer Droplets

    Science.gov (United States)

    Dalnoki-Veress, Kari

    2008-03-01

    The simplicity of a liquid droplet, say a dew drop on spider silk, is both esthetically beautiful and scientifically intriguing. The interplay of surface energies, thermal motion, and confinement of the liquid, especially on small length scales can reveal interesting physics. Droplets are an ideal confining geometry because the length scales can be easily controlled and it is possible to arrange the system such that each droplet acts as an independent experiment. The talk will focus on some recent examples where we have used the droplet geometry to learn about material properties. It will become apparent in the presentation that the deviations from the ``expected'' behaviour in confined systems are far from subtle!

  14. Droplets passing through a soap film

    Science.gov (United States)

    Zou, Jun; Wang, Wei; Ji, Chen; Pan, Min

    2017-06-01

    Here, we report an experimental study of droplets colliding with a soap film. The behavior of the droplet is found to be dependent on the impact velocity. The threshold for a droplet to pass through the soap film is influenced by the droplet diameter. The contact time decreases with increasing impact velocity. Emphasis is placed on whether the outer shell remains intact. When the dimensionless contact time approaches 1, collapse of the shell begins. However, the shell does not collapse with further increasing impact velocity.

  15. Quenching processes in flame-vortex interactions

    Science.gov (United States)

    Zingale, M.; Niemeyer, J. C.; Timmes, F. X.; Dursi, L. J.; Calder, A. C.; Fryxell, B.; Lamb, D. Q.; MacNeice, P.; Olson, K.; Ricker, P. M.; Rosner, R.; Truran, J. W.; Tufo, H. M.

    2001-10-01

    We show direct numerical simulations of flame-vortex interactions in order to understand quenching of thermonuclear flames. The key question is-can a thermonuclear flame be quenched? If not, the deflagration-detonation transition mechanisms that demand a finely tuned preconditioned region in the interior of a white dwarf are unlikely to work. In these simulations, we pass a steady-state laminar flame through a vortex pair. The vortex pair represents the most severe strain the flame front will encounter inside the white dwarf. We perform a parameter study, varying the speed and size of the vortex pair, in order to understand the quenching process. No quenching is observed in any of the calculations performed to date. .

  16. Controlling droplet spreading with topography

    Science.gov (United States)

    Kant, P.; Hazel, A. L.; Dowling, M.; Thompson, A. B.; Juel, A.

    2017-09-01

    We present an experimental system that can be used to study the dynamics of a picoliter droplet (in-flight radius of 12.2 μ m ) as it spreads over substrates with topographic variations. We concentrate on the spreading of a droplet within a recessed stadium-shaped pixel, with applications to the manufacture of polymer organic light-emitting-diode displays, and find that the sloping sidewall of the pixel can either locally enhance or hinder spreading depending on whether the topography gradient ahead of the contact line is positive or negative, respectively. Locally enhanced spreading occurs via the formation of thin pointed rivulets along the sidewalls of the pixel through a mechanism similar to capillary rise in sharp corners. We demonstrate that a simplified model involving quasistatic surface-tension effects within the framework of a thin-film approximation combined with an experimentally measured dynamic spreading law, relating the speed of the contact line to the contact angle, provides excellent predictions of the evolving liquid morphologies. A key feature of the liquid-substrate interaction studied here is the presence of significant contact angle hysteresis, which enables the persistence of noncircular fluid morphologies. We also show that the spreading law for an advancing contact line can be adequately approximated by a Cox-Voinov law for the majority of the evolution. The model does not include viscous effects in the bulk of the droplet and hence the time scales for the propagation of the thin pointed rivulets are not captured. Nonetheless, this simple model can be used very effectively to predict the areas covered by the liquid and may serve as a useful design tool for systems that require precise control of liquid on substrates.

  17. Multipoint ignition by flame dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Rychter, T.J.

    1989-03-01

    In conventional piston engines exothermic chemical reactions occur in flames that are tightly localized in space. This is a cause of many problems encountered in engine combustion, such as knock and cycle-to-cycle variability. An alternative to the classical combustion process based on the propagation of the flame can be the initiation of exothermic reactions by a set of ignition centers causing multipoint initiation of combustion. This can be achieved by spreading the chemically active hot gases through the combustion chamber. In practice this has been done by combustion-product recirculation or by the use of jets. Numerous investigations have been reported on the combustion system in which a jet of chemically active hot gases is dynamically introduced into the main combustion chamber causing multipoint ignition of a premixed charge. The jet has been generated either by burning a rich mixture in a large prechamber, in a small torch cell, or by the discharge of a relatively large amount of electrical energy in a small cavity to produce a jet of plasma. A way to reduce significantly the energy to generate the plasma jet has been proposed and has proved to be especially advantageous fur burning mixtures near their flammability limits.

  18. Ethanol concentration in breastmilk after the consumption of non-alcoholic beer.

    Science.gov (United States)

    Schneider, Claudia; Thierauf, Annette; Kempf, Jürgen; Auwärter, Volker

    2013-06-01

    During lactation, the consumption of ethanol is discussed controversially. After women drink alcoholic beverages, ethanol can be found in breastmilk with a time lag. To abstain from ethanol, but not from the taste of alcoholic beverages, in particular, non-alcoholic beer has become popular in recent years. According to regulations in the United States and most European countries, these "alcohol-free" beverages may still contain ethanol up to 1.2% by volume. To determine how much of this ethanol may reach the breastfed child, a drinking experiment with non-alcoholic beer was performed. Fifteen healthy breastfeeding women participated in the study. After at least 5 days of abstinence from ethanol and the donation of a void breastmilk sample, they were asked to drink 1.5 L of non-alcoholic beer within 1 hour. Breastmilk samples were collected using electronic breast pumps immediately after the end of drinking as well as 1 and 3 hours later. The milk was analyzed for ethanol by headspace-gas chromatography-flame ionization detection using a fully validated method. In two women, trace amounts of ethanol (up to 0.0021 g/L) were found in the samples gained immediately after the drinking period. In the other samples ethanol could not be detected (limit of detection=0.0006 g/L). The mother's consumption of non-alcoholic beer is likely innocuous for the breastfed infant.

  19. Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure

    KAUST Repository

    Al-Noman, Saeed M.

    2016-06-01

    Autoignition characteristics of pre-vaporized iso-octane, primary reference fuels, gasolines, and dimethyl ether (DME) have been investigated experimentally in a coflow with elevated temperature of air. With the coflow air at relatively low initial temperatures below autoignition temperature Tauto, an external ignition source was required to stabilize the flame. Non-autoignited lifted flames had tribrachial edge structures and their liftoff heights correlated well with the jet velocity scaled by the stoichiometric laminar burning velocity, indicating the importance of the edge propagation speed on flame stabilization balanced with local flow velocity. At high initial temperatures over Tauto, the autoignited flames were stabilized without requiring an external ignition source. The autoignited lifted flames exhibited either tribrachial edge structures or Mild combustion behaviors depending on the level of fuel dilution. For the iso-octane and n-heptane fuels, two distinct transition behaviors were observed in the autoignition regime from a nozzle-attached flame to a lifted tribrachial-edge flame and then a sudden transition to lifted Mild combustion as the jet velocity increased at a certain fuel dilution level. The liftoff data of the autoignited flames with tribrachial edges were analyzed based on calculated ignition delay times for the pre-vaporized fuels. Analysis of the experimental data suggested that ignition delay time may be much less sensitive to initial temperature under atmospheric pressure conditions as compared with predictions. For the gasoline fuels for advanced combustion engines (FACEs), and primary reference fuels (PRFs), autoignited liftoff data were correlated with Research Octane Number and Cetane Number. For the DME fuel, planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and CH* chemiluminescence were visualized qualitatively. In the autoignition regime for both tribrachial structure and mild combustion, formaldehyde were found

  20. ENERGY CHARACTERISTICS OF ETHANOL CHARACTERISTICS ...

    African Journals Online (AJOL)

    eobe

    ENERGY CHARACTERISTICS OF ETHANOL. CHARACTERISTICS OF ETHANOL. CHARACTERISTICS OF ETHANOL-DIESEL MIX FOR AUTOMOTIVE. DIESEL MIX FOR AUTOMOTIVE. USE. W. A. Akpan1, A. Offiong2 and E. G. Ikrang3, *. 1111, , , , 2222 DEPARTMENT OF MECHANICAL ENGINEERING, UNIVERSITY ...

  1. 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

  2. The Effects of Flame Structure on Extinction of CH4-O2-N2 Diffusion Flames

    Science.gov (United States)

    Du, J.; Axelbaum, R. L.; Gokoglu, S. (Technical Monitor)

    1996-01-01

    The effects of flame structure on the extinction limits of CH4-O2-N2 counterflow diffusion flames were investigated experimentally and numerically by varying the stoichiometric mixture fraction Z(sub st), Z(sub st) was varied by varying free-stream concentrations, while the adiabatic flame temperature T(sub ad) was held fixed by maintaining a fixed amount of nitrogen at the flame. Z(sub st) was varied between 0.055 (methane-air flame) and 0.78 (diluted- methane-oxygen flame). The experimental results yielded an extinction strain rate K(sub ext) of 375/s for the methane-air flame, increasing monotonically to 1042/s for the diluted-methane-oxygen flame. Numerical results with a 58-step Cl mechanism yielded 494/s and 1488/s, respectively. The increase in K(sub ext) with Z(sub st) for a fixed T(sub ad) is explained by the shift in the O2 profile toward the region of maximum temperature and the subsequent increase in rates for chain-branching reactions. The flame temperature at extinction reached a minimum at Z(sub st) = 0.65, where it was 200 C lower than that of the methane-air flame. This significant increase in resistance to extinction is seen to correspond to the condition in which the OH and O production zones are centered on the location of maximum temperature.

  3. Flame Structure and Chemiluminescence Emissions of Inverse Diffusion Flames under Sinusoidally Driven Plasma Discharges

    Directory of Open Access Journals (Sweden)

    Maria Grazia De Giorgi

    2017-03-01

    Full Text Available Reduction of nitric oxides (NOx in aircraft engines and in gas turbines by lean combustion is of great interest in the design of novel combustion systems. However, the stabilization of the flame under lean conditions is a main issue. In this context, the present work investigates the effects of sinusoidal dielectric barrier discharge (DBD on a lean inverse diffusive methane/air flame in a Bunsen-type burner under different actuation conditions. The flame appearance was investigated with fixed methane loading (mass flux, but with varying inner airflow rate. High-speed flame imaging was done by using an intensified (charge-coupled device CCD camera equipped with different optical filters in order to selectively record signals from the chemiluminescent species OH*, CH*, or CO2* to evaluate the flame behavior in presence of plasma actuation. The electrical power consumption was less than 33 W. It was evident that the plasma flame enhancement was significantly influenced by the plasma discharges, particularly at high inner airflow rates. The flame structure changes drastically when the dissipated plasma power increases. The flame area decreases due to the enhancement of mixing and chemical reactions that lead to a more anchored flame on the quartz exit with a reduction of the flame length.

  4. Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations

    Science.gov (United States)

    Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung K.

    2013-09-01

    In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a ReT,f0.5 scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given ReT,f, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by ReT,M0.5 irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.

  5. Influence of palmitoyl pentapeptide and Ceramide III B on the droplet size of nanoemulsion

    Science.gov (United States)

    Sondari, Dewi; Haryono, Agus; Harmami, Sri Budi; Randy, Ahmad

    2010-05-01

    The influence of the Palmitoyl Pentapeptide (PPp) and Ceramide IIIB (Cm III B) as active ingredients on the droplet size of nano-emulsion was studied using different kinds of oil (avocado oil, sweet almond oil, jojoba oil, mineral oil and squalene). The formation of nano-emulsions were prepared in water mixed non ionic surfactant/oils system using the spontaneous emulsification mechanism. The aqueous solution, which consist of water and Tween® 20 as a hydrophilic surfactant was mixed homogenously. The organic solution, which consist of oil and Span® 80 as a lipophilic surfactant was mixed homogenously in ethanol. Ethanol was used as a water miscible solvent, which can help the formation of nano-emulsion. The oil phase (containing the blend of surfactant Span® 80, ethanol, oil and active ingredient) and the aqueous phase (containing water and Tween® 20) were separately prepared at room temperatures. The oil phase was slowly added into aqueous phase under continuous mechanical agitation (18000 rpm). All samples were subsequently homogenized with Ultra-Turrax for 30 minutes. The characterizations of nano-emulsion were carried out using photo-microscope and particle size analyzer. Addition of active ingredients on the formation of nano-emulsion gave smallest droplet size compared without active ingredients addition on the formation of nano-emulsion. Squalene oil with Palmitoyl Pentapeptide (PPm) and Ceramide IIIB (Cm IIIB) gave smallest droplet size (184.0 nm) compared without Palmitoyl Pentapeptide and Ceramide IIIB (214.9 nm), however the droplets size of the emulsion prepared by the other oils still in the range of nano-emulsion (below 500 nm). The stability of nano-emulsion was observed using two methods. In one method, the stability of nano-emulsion was observed for three months at temperature of 5°C and 50°C, while in the other method, the stability nano-emulsion was observed by centrifuged at 12000 rpm for 30 minutes. Nanoemulsion with active ingredient

  6. Droplet Microfluidics for Virus Discovery

    Science.gov (United States)

    Rotem, Assaf; Cockrell, Shelley; Guo, Mira; Pipas, James; Weitz, David

    2012-02-01

    The ability to detect, isolate, and characterize an infectious agent is important for diagnosing and curing infectious diseases. Detecting new viral diseases is a challenge because the number of virus particles is often low and/or localized to a small subset of cells. Even if a new virus is detected, it is difficult to isolate it from clinical or environmental samples where multiple viruses are present each with very different properties. Isolation is crucial for whole genome sequencing because reconstructing a genome from fragments of many different genomes is practically impossible. We present a Droplet Microfluidics platform that can detect, isolate and sequence single viral genomes from complex samples containing mixtures of many viruses. We use metagenomic information about the sample of mixed viruses to select a short genomic sequence whose genome we are interested in characterizing. We then encapsulate single virions from the same sample in picoliter volume droplets and screen for successful PCR amplification of the sequence of interest. The selected drops are pooled and their contents sequenced to reconstruct the genome of interest. This method provides a general tool for detecting, isolating and sequencing genetic elements in clinical and environmental samples.

  7. On-demand Droplet Manipulation via Triboelectrification

    Science.gov (United States)

    Wang, Wei; Vahabi, Hamed; Cackovic, Matthew; Jiang, Rui; Kota, Arun

    2017-11-01

    Controlled manipulation of liquid droplets has attracted tremendous interest across different scientific fields over the past two decades. To date, a variety of external stimuli-mediated methods such as magnetic field, electric field, and light have been developed for manipulating droplets on surfaces. However, these methods usually have drawbacks such as complex fabrication of manipulation platform, low droplet motility, expensive actuation system and lack of precise control. In this work, we demonstrate the controlled manipulation of liquid droplet with both high (e.g., water) and low (e.g., n-hexadecane) dielectric strengths on a smooth, slippery surface via triboelectric effect. Our highly simple, facile and portable methodology enables on-demand, precise manipulation of droplets using solely the electrostatic attraction or repulsion force, which is exerted on the droplet by a simple charged actuator (e.g., Teflon film). We envision that our triboelectric effect enabled droplet manipulation methodology will open a new avenue for droplet based lab-on-a-chip systems, energy harvesting devices and biomedical applications.

  8. Spheroid droplets evaporation of water solutions

    OpenAIRE

    Misyura S. Y.; Morozov V.S.

    2017-01-01

    Droplet film boiling on a horizontal heating surface was studied experimentally. The heat transfer coefficient of droplet water solution in the spheroidal state decreases with a rise of wall overheating and spheroid diameter. Evaporation of small spheroid (diameter d 20 mm). At the evaporation of large spheroids a spheroid shape changes in time that significantly affect coefficients of generalizing curves that use dimensionless numbers.

  9. Analysis of coalescence behavior for compressed droplets

    Science.gov (United States)

    Choi, Sung Woong; Lee, Dong Eon; Lee, Woo Il; Kim, Han Sang

    2017-03-01

    Coalescence of droplets is a significant phenomenon, and it has been adapted to many applications such as raindrop formation, emulsion polymerization, ink-jet printing, coating, and multiphase flows. In this study, the morphological characteristics of two compressed adjacent droplets between two parallel plates were investigated to study the phenomenon of coalescence of droplets. By controlling the distance of the dispensed droplets, various results for coalescence of droplets were evaluated, especially, from the view of the minor axis, major axis, and meniscus liquid bridge of the coalesced droplet. Experimental results show that the length of the meniscus liquid bridge rapidly increases and then the rate of increase slows with time. The increase rate of the major and minor axes is largely influenced by the meniscus liquid bridge, which is mainly due to the curvature between the droplets. The numerical modeling of the coalescence of the two compressed droplets between two parallel plates was presented and simulation was conducted to realize the coalescence behavior. Comparison with numerical simulation showed that there was a good agreement with the experimental results.

  10. Coalescence Processes of Droplets and Liquid Marbles

    Directory of Open Access Journals (Sweden)

    Jing Jin

    2017-11-01

    Full Text Available The coalescence process of droplets and, more recently, of liquid marbles, has become one of the most essential manipulation schemes in digital microfluidics. This process is indispensable for realising microfluidic functions such as mixing and reactions at microscale. This paper reviews previous studies on droplet coalescence, paying particular attention to the coalescence of liquid marbles. Four coalescence systems have been reviewed, namely, the coalescence of two droplets freely suspended in a fluid; the coalescence of two sessile droplets on a solid substrate; the coalescence of a falling droplet and a sessile droplet on a solid substrate; and liquid marble coalescence. The review is presented according to the dynamic behaviors, physical mechanisms and experimental parameters of the coalescence process. It also provides a systematic overview of how the coalescence process of droplets and liquid marbles could be induced and manipulated using external energy. In addition, the practical applications of liquid marble coalescence as a novel microreactor are highlighted. Finally, future perspectives on the investigation of the coalescence process of liquid marbles are proposed. This review aims to facilitate better understanding of the coalescence of droplets and of liquid marbles as well as to shed new insight on future studies.

  11. Thermonuclear Quenching in Flame-Vortex Interactions

    Science.gov (United States)

    Zingale, M.; Niemeyer, J. C.; Timmes, F. X.; Dursi, L. J.; Calder, A. C.; Fryxell, B.; Olson, K.; Ricker, P.; Rosner, R.; Truran, J. W.; Tufo, H.; MacNeice, P.

    2000-12-01

    A Type Ia supernova begins as a flame, deep in the interior of a white dwarf. At some point, the burning may undergo a deflagration-detonation transition (DDT). Some mechanisms for this transition require a preconditioned region in the star. As the flame propagates down the temperature gradient, the speed increases, and the transition to a detonation may occur (see Khokhlov et al. 1997; Niemeyer & Woosley 1997). For this to happen, the region must be free of any temperature fluctuations -- any burning must be quenched. We show direct numerical simulations of flame-vortex interactions in order to understand quenching of thermonuclear flames. The key question is -- can a thermonuclear flame be quenched? If not, the DDT mechanisms that demand the finely tuned preconditioned region are unlikely to work. In these simulations, we pass a steady-state laminar flame through a vortex pair. The vortex pair represents the most severe strain the flame front will encounter inside the white dwarf. We perform a parameter study, varying the speed and size of the vortex pair, in order to understand the quenching process. These simulations were carried out with the FLASH Code. This work is supported by the Department of Energy under Grant No. B341495 to the Center for Astrophysical Thermonuclear Flashes at the University of Chicago. These calculations were performed on the Nirvana Cluster at Los Alamos National Laboratory

  12. Flame Color as a Lean Blowout Predictor

    Directory of Open Access Journals (Sweden)

    Rajendra R. Chaudhari

    2013-03-01

    Full Text Available The study characterizes the behavior of a premixed swirl stabilized dump plane combustor flame near its lean blow-out (LBO limit in terms of CH* chemiluminiscence intensity and observable flame color variations for a wide range of equivalence ratio, flow rates and degree of premixing (characterized by premixing length, Lfuel. LPG and pure methane are used as fuel. We propose a novel LBO prediction strategy based solely on the flame color. It is observed that as the flame approaches LBO, its color changes from reddish to blue. This observation is found to be valid for different levels of fuel-air premixing achieved by changing the available mixing length of the air and the fuel upstream of the dump plane although the flame dynamics were significantly different. Based on this observation, the ratio of the intensities of red and blue components of the flame as captured by a color CCD camera was used as a metric for detecting the proximity of the flame to LBO. Tests were carried out for a wide range of air flow rates and using LPG and CH4 as fuel. For all the operating conditions and both fuels tested, this ratio was found to monotonically decrease as LBO was approached. Moreover, the value of this ratio was within a small range close to LBO for all the cases investigated. This makes the ratio suitable as a metric for LBO detection at all levels of premixing.

  13. Iron Oxide Doped Alumina-Zirconia Nanoparticle Synthesis by Liquid Flame Spray from Metal Organic Precursors

    Directory of Open Access Journals (Sweden)

    Juha-Pekka Nikkanen

    2008-01-01

    Full Text Available The liquid flame spray (LFS method was used to make iron oxide doped alumina-zirconia nanoparticles. Nanoparticles were generated using a turbulent, high-temperature (Tmax⁡∼3000 K H2-O2 flame. The precursors were aluminium-isopropoxide, zirconium-n-propoxide, and ferrocene in xylene solution. The solution was atomized into micron-sized droplets by high velocity H2 flow and introduced into the flame where nanoparticles were formed. The particle morphology, size, phase, and chemical composition were determined by TEM, XRD, XPS, and N2-adsorption measurements. The collected particulate material consists of micron-sized aggregates with nanosized primary particles. In both doped and undoped samples, tetragonal phase of zirconia was detected in room temperature while alumina was found to be noncrystalline. In the doped powder, Fe was oxidized to Fe2O3. The primary particle size of collected sample was approximately from 6 nm to 40 nm. Doping was observed to increase the specific surface area of the powder from 39 m2/g to 47 m2/g.

  14. 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.

  15. 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.

  16. Acoustophoresis in Variously Shaped Liquid Droplets

    CERN Document Server

    Yu, Gan; Xu, Jie; 10.1039/c1sm05871a

    2012-01-01

    The ability to precisely trap, transport and manipulate micrometer-sized objects, including biological cells, DNA-coated microspheres and microorganisms, is very important in life science studies and biomedical applications. In this study, acoustic radiation force in an ultrasonic standing wave field is used for micro-objects manipulation, a technique termed as acoustophoresis. Free surfaces of liquid droplets are used as sound reflectors to confine sound waves inside the droplets. Two techniques were developed for precise control of droplet shapes: edge pinning and hydrophilic/hydrophobic interface pinning. For all tested droplet shapes, including circular, annular and rectangular, our experiments show that polymer micro particles can be manipulated by ultrasound and form into a variety of patterns, for example, concentric rings and radial lines in an annular droplet. The complexity of the pattern increases with increasing frequency, and the observations are in line with simulation results. The acoustic mani...

  17. Injection of micron size droplets into vacuum

    Science.gov (United States)

    Liu, Caroline; Poulose, John; Ogawa, Daisuke; Goeckner, Matthew; Overzet, Lawrence

    2013-09-01

    Previous experiments using direct liquid injection into plasma for film deposition produced films that had unwanted voids. We believe that the uneven deposition of polymer film is due to injected liquids not completely evaporating into the plasma and landing on the surface of the substrate instead. To address this issue, we chose to improve upon the previous film deposition chamber setup by modifying the injector to decrease the injected liquid droplet sizes. The literature presents multiple theories on liquid breakup into air and resultant droplet sizes but to the best of our knowledge, there is not much research on droplet breakup dynamics or resultant droplet sizes when liquid is injected into low pressure (poster, we will describe previous work done, experimental setup along with experimental data on droplet sizes produced by orifices of various sizes when liquid is injected into low pressure. This work was supported in part by the Department of Energy under grant No. DE-SC0001355.

  18. The dilution effect on the extinction of wall diffusion flame

    Directory of Open Access Journals (Sweden)

    Ghiti Nadjib

    2014-12-01

    Full Text Available The dynamic process of the interaction between a turbulent jet diffusion methane flame and a lateral wall was experimentally studied. The evolution of the flame temperature field with the Nitrogen dilution of the methane jet flame was examined. The interaction between the diffusion flame and the lateral wall was investigated for different distance between the wall and the central axes of the jet flame. The dilution is found to play the central role in the flame extinction process. The flame response as the lateral wall approaches from infinity and the increasing of the dilution rate make the flame extinction more rapid than the flame without dilution, when the nitrogen dilution rate increase the flame temperature decrease.

  19. The Lipid-Droplet Proteome Reveals that Droplets Are a Protein-Storage Depot

    Energy Technology Data Exchange (ETDEWEB)

    Cermelli, Silvia; Guo, Yi; Gross, Steven P.; Welte, Michael

    2006-09-19

    Lipid droplets are ubiquitous organelles that are among the basic building blocks of eukaryotic cells. Despite central roles for cholesterol homeostasis and lipid metabolism, their function and protein composition are poorly understood. Results: We purified lipid droplets from Drosophila embryos and analyzed the associated proteins by capillary LC-MS-MS. Important functional groups include enzymes involved in lipid metabolism, signaling molecules, and proteins related to membrane trafficking. Unexpectedly, histones H2A, H2Av, and H2B were present. Using biochemistry, genetics, real-time imaging, and cell biology, we confirm that roughly 50% of certain embryonic histones are physically attached to lipid droplets, a localization conserved in other fly species. Histone association with droplets starts during oogenesis and is prominent in early embryos, but it is undetectable in later stages or in cultured cells. Histones on droplets are not irreversibly trapped; quantitation of droplet histone levels and transplantation experiments suggest that histones are transferred from droplets to nuclei as development proceeds. When this maternal store of histones is unavailable because lipid droplets are mislocalized, zygotic histone production starts prematurely. Conclusions: Because we uncover a striking proteomic similarity of Drosophila droplets to mammalian lipid droplets, Drosophila likely provides a good model for understanding droplet function in general. Our analysis also reveals a new function for these organelles; the massive nature of histone association with droplets and its developmental time-course suggest that droplets sequester maternally provided proteins until they are needed. We propose that lipid droplets can serve as transient storage depots for proteins that lack appropriate binding partners in the cell. Such sequestration may provide a general cellular strategy for handling excess proteins.

  20. Microfluidic generation of aqueous two-phase-system (ATPS) droplets by oil-droplet choppers.

    Science.gov (United States)

    Zhou, Chunmei; Zhu, Pingan; Tian, Ye; Tang, Xin; Shi, Rui; Wang, Liqiu

    2017-09-26

    Existing approaches for droplet generation with an ultra-low interfacial tension using aqueous two-phase systems, ATPS, are either constricted by a narrow range of flow conditions using passive methods or subjected to complex chip fabrication with the integration of external components using active actuation. To address these issues, we present a simple approach to produce uniform ATPS droplets facilitated by oil-droplet choppers in microfluidics. Our solution counts on the synchronized formation of high-interfacial-tension oil-in-water and low-interfacial-tension water-in-water droplets, where the ATPS interface is distorted by oil droplets and decays into water-in-water droplets. In the synchronization regime, the size and generation frequency of ATPS droplets can be controlled independently by tuning the flow rates of the dispersed aqueous and oil phases, respectively. Our method demonstrates high uniformity of droplets (coefficient of variation between 0.75% and 2.45%), a wide range of available droplet size (droplet radius from 5 μm to 180 μm), and a maximum generation frequency of about 2.1 kHz that is nearly two orders of magnitude faster than that in existing methods. We develop theoretical models to precisely predict the minimum and maximum frequencies of droplet generation and the droplet size. The produced ATPS droplets and oil choppers are separated in the channel using density difference. Our method would boost emulsion-based biological applications such as cell encapsulation, biomolecule delivery, bioreactors, and biomaterials synthesis with ATPS droplets.

  1. Flame Speed and Self-Similar Propagation of Expanding Turbulent Premixed Flames

    Science.gov (United States)

    Chaudhuri, Swetaprovo; Wu, Fujia; Zhu, Delin; Law, Chung K.

    2012-01-01

    In this Letter we present turbulent flame speeds and their scaling from experimental measurements on constant-pressure, unity Lewis number expanding turbulent flames, propagating in nearly homogeneous isotropic turbulence in a dual-chamber, fan-stirred vessel. It is found that the normalized turbulent flame speed as a function of the average radius scales as a turbulent Reynolds number to the one-half power, where the average radius is the length scale and the thermal diffusivity is the transport property, thus showing self-similar propagation. Utilizing this dependence it is found that the turbulent flame speeds from the present expanding flames and those from the Bunsen geometry in the literature can be unified by a turbulent Reynolds number based on flame length scales using recent theoretical results obtained by spectral closure of the transformed G equation.

  2. Aromatics oxidation and soot formation in flames

    Energy Technology Data Exchange (ETDEWEB)

    Howard, J.B.; Pope, C.J.; Shandross, R.A.; Yadav, T. [Massachusetts Institute of Technology, Cambridge (United States)

    1993-12-01

    This project is concerned with the kinetics and mechanisms of aromatics oxidation and soot and fullerenes formation in flames. The scope includes detailed measurements of profiles of stable and radical species concentrations in low-pressure one-dimensional premixed flames. Intermediate species identifications and mole fractions, fluxes, and net reaction rates calculated from the measured profiles are used to test postulated reaction mechanisms. Particular objectives are to identify and to determine or confirm rate constants for the main benzene oxidation reactions in flames, and to characterize fullerenes and their formation mechanisms and kinetics.

  3. Synthesis of Nano-Particles in Flames

    DEFF Research Database (Denmark)

    Johannessen, Tue

    flame burner and a premixed burner with a precursor jet. The experimental setups and results are shown and discussed in detail. Alumina powder with specific surface area between 45 m2/g and 190 m2/g was obtained.Temperature and flow fields of the flame processes are analysed by numerical simulations...... (Computational Fluid Dynamics) where the fundamental equation for flow, heat- and mass transfer are solved numerically in computational domains similar to the real systems.A model describing the particle dynamics in the flame is coupled with the flow-field information in order to compute effluent particle...

  4. Flaming alcoholic drinks: flirting with danger.

    Science.gov (United States)

    Tan, Alethea; Frew, Quentin; Yousif, Ali; Ueckermann, Nicola; Dziewulksi, Peter

    2014-01-01

    Alcohol-related burn injuries carry significant mortality and morbidity rates. Flaming alcoholic beverages served in trendy bars and clubs are becoming increasingly popular. The dangers associated with an ignited alcoholic drink are often underestimated by party goers whose risk assessment ability is already impaired by heavy alcohol consumption. The authors present two cases demonstrating the varied severity of burn injuries associated with flaming alcoholic drinks, and their clinical management. Consumption of flaming alcoholic drinks poses potential risks for burn injuries. Further support is required to enable national and local agencies to implement effective interventions in drinking environments.

  5. Systems and methods for controlling flame instability

    KAUST Repository

    Cha, Min Suk

    2016-07-21

    A system (62) for controlling flame instability comprising: a nozzle (66) coupled to a fuel supply line (70), an insulation housing (74) coupled to the nozzle, a combustor (78) coupled to the nozzle via the insulation housing, where the combustor is grounded (80), a pressure sensor (82) coupled to the combustor and configured to detect pressure in the combustor, and an instability controlling assembly coupled to the pressure sensor and to an alternating current power supply (86), where, the instability controlling assembly can control flame instability of a flame in the system based on pressure detected by the pressure sensor.

  6. Flame tolerant secondary fuel nozzle

    Science.gov (United States)

    Khan, Abdul Rafey; Ziminsky, Willy Steve; Wu, Chunyang; Zuo, Baifang; Stevenson, Christian Xavier

    2015-02-24

    A combustor for a gas turbine engine includes a plurality of primary nozzles configured to diffuse or premix fuel into an air flow through the combustor; and a secondary nozzle configured to premix fuel with the air flow. Each premixing nozzle includes a center body, at least one vane, a burner tube provided around the center body, at least two cooling passages, a fuel cooling passage to cool surfaces of the center body and the at least one vane, and an air cooling passage to cool a wall of the burner tube. The cooling passages prevent the walls of the center body, the vane(s), and the burner tube from overheating during flame holding events.

  7. Direct numerical simulations of non-premixed ethylene-air flames: Local flame extinction criterion

    KAUST Repository

    Lecoustre, Vivien R.

    2014-11-01

    Direct Numerical Simulations (DNS) of ethylene/air diffusion flame extinctions in decaying two-dimensional turbulence were performed. A Damköhler-number-based flame extinction criterion as provided by classical large activation energy asymptotic (AEA) theory is assessed for its validity in predicting flame extinction and compared to one based on Chemical Explosive Mode Analysis (CEMA) of the detailed chemistry. The DNS code solves compressible flow conservation equations using high order finite difference and explicit time integration schemes. The ethylene/air chemistry is simulated with a reduced mechanism that is generated based on the directed relation graph (DRG) based methods along with stiffness removal. The numerical configuration is an ethylene fuel strip embedded in ambient air and exposed to a prescribed decaying turbulent flow field. The emphasis of this study is on the several flame extinction events observed in contrived parametric simulations. A modified viscosity and changing pressure (MVCP) scheme was adopted in order to artificially manipulate the probability of flame extinction. Using MVCP, pressure was changed from the baseline case of 1 atm to 0.1 and 10 atm. In the high pressure MVCP case, the simulated flame is extinction-free, whereas in the low pressure MVCP case, the simulated flame features frequent extinction events and is close to global extinction. Results show that, despite its relative simplicity and provided that the global flame activation temperature is correctly calibrated, the AEA-based flame extinction criterion can accurately predict the simulated flame extinction events. It is also found that the AEA-based criterion provides predictions of flame extinction that are consistent with those provided by a CEMA-based criterion. This study supports the validity of a simple Damköhler-number-based criterion to predict flame extinction in engineering-level CFD models. © 2014 The Combustion Institute.

  8. Model Flames in the Boussinesq Limit: The Effects of Feedback

    OpenAIRE

    Vladimirova, N.; Rosner, R.

    2002-01-01

    We have studied the fully nonlinear behavior of pre-mixed flames in a gravitationally stratified medium, subject to the Boussinesq approximation. Key results include the establishment of criterion for when such flames propagate as simple planar flames; elucidation of scaling laws for the effective flame speed; and a study of the stability properties of these flames. The simplicity of some of our scalings results suggests that analytical work may further advance our understandings of buoyant f...

  9. Structure of diffusion flames from a vertical burner

    Science.gov (United States)

    Mark A. Finney; Dan Jimenez; Jack D. Cohen; Isaac C. Grenfell; Cyle Wold

    2010-01-01

    Non-steady and turbulent flames are commonly observed to produce flame contacts with adjacent fuels during fire spread in a wide range of fuel bed depths. A stationary gas-fired burner (flame wall) was developed to begin study of flame edge variability along an analagous vertical fuel source. This flame wall is surrogate for a combustion interface at the edge of a deep...

  10. Triple flame structure and dynamics at the stabilization point of a lifted jet diffusion flame

    Energy Technology Data Exchange (ETDEWEB)

    Najm, H.N.; Milne, R.B. [Sandia National Labs., Livermore, CA (United States); Devine, K.D.; Kempka, S.N. [Sandia National Labs., Albuquerque, NM (United States)

    1998-03-01

    A coupled Lagrangian-Eulerian low-Mach-number numerical scheme is developed, using the vortex method for the momentum equations, and a finite difference approach with adaptive mesh refinement for the scalar conservation equations. The scheme is used to study the structure and dynamics of a forced lifted buoyant planar jet flame. Outer buoyant structures, driven by baroclinic vorticity generation, are observed. The flame base is found to stabilize in a region where flow velocities are sufficiently small to allow its existence. A triple flame is observed at the flame base, a result of premixing of fuel and oxidizer upstream of the ignition point. The structure and dynamics of the triple flame, and its modulation by jet vortex structures, are studied. The spatial extent of the triple flame is small, such that it fits wholly within the rounded flame base temperature field. The dilatation rate field outlines the edge of the hot fluid at the flame base. Neither the temperature field nor the dilatation rate field seem appropriate for experimental measurement of the triple flame in this flow.

  11. Atmospheric tar balls: aged primary droplets from biomass burning?

    Science.gov (United States)

    Tóth, A.; Hoffer, A.; Nyirő-Kósa, I.; Pósfai, M.; Gelencsér, A.

    2014-07-01

    Atmospheric tar balls are particles of special morphology and composition that are fairly abundant in the plumes of biomass smoke. These particles form a specific subset of brown carbon (BrC) which has been shown to play a significant role in atmospheric shortwave absorption and, by extension, climate forcing. Here we suggest that tar balls are produced by the direct emission of liquid tar droplets followed by heat transformation upon biomass burning. For the first time in atmospheric chemistry we generated tar-ball particles from liquid tar obtained previously by dry distillation of wood in an all-glass apparatus in the laboratory with the total exclusion of flame processes. The particles were perfectly spherical with a mean optical diameter of 300 nm, refractory, externally mixed, and homogeneous in the contrast of the transmission electron microscopy (TEM) images. They lacked any graphene-like microstructure and exhibited a mean carbon-to-oxygen ratio of 10. All of the observed characteristics of laboratory-generated particles were very similar to those reported for atmospheric tar-ball particles in the literature, strongly supporting our hypothesis regarding the formation mechanism of atmospheric tar-ball particles.

  12. Liquid droplet heat exchanger studies

    Science.gov (United States)

    Bruckner, A. P.; Hedges, D. E.; Yungster, S.

    1987-01-01

    Recent analytical and experimental investigations of the liquid droplet heat exchanger (LDHX) concept for space power applications are described. The performance of the LDHX is compared to that of a conventional heat exchanger for heat rejection applications in a Brayton cycle, using the mass-specific heat exchanger effectiveness as a figure of merit. It is shown that the LDHX has an order of magnitude advantage over the conventional heat exchanger. Furthermore, significant improvement in cycle efficiency and power to mass ratio is possible. Two-phase flow experiments in a laboratory scale LDHX, using air and water as the two media, show very good agreement with the quasi-one-dimensional model used in the parametric studies.

  13. Droplet microfluidics for synthetic biology.

    Science.gov (United States)

    Gach, Philip C; Iwai, Kosuke; Kim, Peter W; Hillson, Nathan J; Singh, Anup K

    2017-10-11

    Synthetic biology is an interdisciplinary field that aims to engineer biological systems for useful purposes. Organism engineering often requires the optimization of individual genes and/or entire biological pathways (consisting of multiple genes). Advances in DNA sequencing and synthesis have recently begun to enable the possibility of evaluating thousands of gene variants and hundreds of thousands of gene combinations. However, such large-scale optimization experiments remain cost-prohibitive to researchers following traditional molecular biology practices, which are frequently labor-intensive and suffer from poor reproducibility. Liquid handling robotics may reduce labor and improve reproducibility, but are themselves expensive and thus inaccessible to most researchers. Microfluidic platforms offer a lower entry price point alternative to robotics, and maintain high throughput and reproducibility while further reducing operating costs through diminished reagent volume requirements. Droplet microfluidics have shown exceptional promise for synthetic biology experiments, including DNA assembly, transformation/transfection, culturing, cell sorting, phenotypic assays, artificial cells and genetic circuits.

  14. Effect of silver addition on the formation and deposition of titania nanoparticles produced by liquid flame spray

    Energy Technology Data Exchange (ETDEWEB)

    Keskinen, H., E-mail: helmi.keskinen@tut.fi; Maekelae, J. M.; Aromaa, M.; Ristimaeki, J. [Tampere University of Technology, Institute of Physics (Finland); Kanerva, T.; Levaenen, E.; Maentylae, T. [Tampere University of Technology, Institute of Materials Science (Finland); Keskinen, J. [Tampere University of Technology, Institute of Physics (Finland)

    2007-08-15

    In this study, liquid flame spray (LFS) was used to produce titania, silver and silver-titania deposits of nanoparticles. Titanium(IV)ethoxide (TEOT) and silver nitrate in ethanol solutions were used as precursors and sprayed into turbulent hydrogen-oxygen flame. Production rates of 1.5-40 mg/min of titania were used with silver additions of 1, 2, 4, and 8 wt% compared to titania. Nanoparticle deposits were collected by thermophoretic sampling at six different axial distances from the flame torch head: 3, 5, 10, 12, 15, and 20 cm, of which the all but the last one occurred inside the flame. The deposit samples were analysed by TEM and SAED analysis. The powder samples of the particles were also collected by electric precipitator to XPS and specific surface area analysis. Particle size and effective density after the flame in the aerosol were analysed with SMPS and ELPI. The results from the previous studies i.e. controlling the particle size by setting the production rates of the particles were seen to apply also for this binary system. Characterisation of the deposits showed that when the substrate is inserted into the flame, in the beginning of the flame the deposit is formed by gas phase deposition whereas further down the flame the particles are first formed in the gas phase and then deposited. The location of the transition from gas phase deposition to gas phase nucleation prior to deposition depends on chemical/physical properties (e.g. thermodynamics and gas phase interactions) of the precursor, precursor concentration in the flame and also flame temperature profile. Therefore, the deposit collection distance from the burner also affected the collected particle size and degree of agglomeration. The two component deposits were produced in two different ways: one-step method mixing both precursors in the same solute, and two-step method spraying each precursor separately. The particle morphology differs between these two cases. In one-step method the primary

  15. Effect of silver addition on the formation and deposition of titania nanoparticles produced by liquid flame spray

    Science.gov (United States)

    Keskinen, H.; Mäkelä, J. M.; Aromaa, M.; Ristimäki, J.; Kanerva, T.; Levänen, E.; Mäntylä, T.; Keskinen, J.

    2007-08-01

    In this study, liquid flame spray (LFS) was used to produce titania, silver and silver-titania deposits of nanoparticles. Titanium(IV)ethoxide (TEOT) and silver nitrate in ethanol solutions were used as precursors and sprayed into turbulent hydrogen-oxygen flame. Production rates of 1.5-40 mg/min of titania were used with silver additions of 1, 2, 4, and 8 wt% compared to titania. Nanoparticle deposits were collected by thermophoretic sampling at six different axial distances from the flame torch head: 3, 5, 10, 12, 15, and 20 cm, of which the all but the last one occurred inside the flame. The deposit samples were analysed by TEM and SAED analysis. The powder samples of the particles were also collected by electric precipitator to XPS and specific surface area analysis. Particle size and effective density after the flame in the aerosol were analysed with SMPS and ELPI. The results from the previous studies i.e. controlling the particle size by setting the production rates of the particles were seen to apply also for this binary system. Characterisation of the deposits showed that when the substrate is inserted into the flame, in the beginning of the flame the deposit is formed by gas phase deposition whereas further down the flame the particles are first formed in the gas phase and then deposited. The location of the transition from gas phase deposition to gas phase nucleation prior to deposition depends on chemical/physical properties (e.g. thermodynamics and gas phase interactions) of the precursor, precursor concentration in the flame and also flame temperature profile. Therefore, the deposit collection distance from the burner also affected the collected particle size and degree of agglomeration. The two component deposits were produced in two different ways: one-step method mixing both precursors in the same solute, and two-step method spraying each precursor separately. The particle morphology differs between these two cases. In one-step method the primary

  16. Brominated Flame Retardants and Perfluorinated Chemicals

    Science.gov (United States)

    Brominated flame retardants (BFRs) and perfluorinated chemicals (PFCs) belong to a large class of chemicals known as organohalogens. It is believed that both BFRs and PFCs saved lives by reducing flammability of materials commonly used and bactericidal (biocidal) properties. Thes...

  17. Nanocellular foam with solid flame retardant

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Liang; Kelly-Rowley, Anne M.; Bunker, Shana P.; Costeux, Stephane

    2017-11-21

    Prepare nanofoam by (a) providing an aqueous solution of a flame retardant dissolved in an aqueous solvent, wherein the flame retardant is a solid at 23.degree. C. and 101 kiloPascals pressure when in neat form; (b) providing a fluid polymer composition selected from a solution of polymer dissolved in a water-miscible solvent or a latex of polymer particles in a continuous aqueous phase; (c) mixing the aqueous solution of flame retardant with the fluid polymer composition to form a mixture; (d) removing water and, if present, solvent from the mixture to produce a polymeric composition having less than 74 weight-percent flame retardant based on total polymeric composition weight; (e) compound the polymeric composition with a matrix polymer to form a matrix polymer composition; and (f) foam the matrix polymer composition into nanofoam having a porosity of at least 60 percent.

  18. Effects of Droplet Spacing on Evaporation of a Cluster of 13 Fuel Droplets

    Science.gov (United States)

    Segawa, Daisuke; Nakaya, Shinji; Kadota, Toshikazu; Agata, Go; Hara, Dai; Sugihara, Hiroyuki

    The evaporation behavior of the central droplet in droplet clusters was observed in microgravity without combustion, and the effects of the droplet spacing were examined. The solidified-fuel fiber-suspension technique was utilized for preparing the monodispersed suspended-droplet cluster (MSDC) model. Most of the experiments were conducted with the HCP (hexagonal closest packing) structure cluster models of thirteen n-eicosane droplets at the atmospheric pressure, and some were conducted with the BCC (body-centered cubic) structure cluster models of nine 1-octadecanol droplets at an elevated pressure. The droplet images suggested that critical thermodynamic state was not attained at the ambient pressure above the critical pressure of the fuel, and the results at the elevated pressure were not largely different from those at the atmospheric pressure. The whole evaporation process was unsteady and the unsteadiness was enhanced with decreasing the droplet spacing. The initial heat-up time increased monotonically with decreasing the droplet spacing. The evaporation rate defined after the initial heat-up time was almost constant or showed an increasing trend with decreasing the droplet spacing.

  19. Doping of Green Fluorescent Protein into Superfluid Helium Droplets: Size and Velocity of Doped Droplets.

    Science.gov (United States)

    Alghamdi, Maha; Zhang, Jie; Oswalt, Andrew; Porter, Joseph J; Mehl, Ryan A; Kong, Wei

    2017-09-14

    We report doping of green fluorescent protein from an electrospray ionization (ESI) source into superfluid helium droplets. From analyses of the time profiles of the doped droplets, we identify two distinct groups of droplets. The faster group has a smaller average size, on the order of 10(6) helium atoms/droplet, and the slower group is much larger, by at least an order of magnitude. The relative populations of these two groups depend on the temperature of the droplet source: from 11 to 5 K, the signal intensity of the slower droplet group gradually increases, from near the detection limit to comparable to that of the faster group. We postulate that the smaller droplets are formed via condensation of gaseous helium upon expansion from the pulsed valve, while the larger droplets develop from fragmentation of ejected liquid helium. Our results on the size and velocity of the condensation peak at higher source temperatures (>7 K) agree with previous reports, but those at lower temperatures (<7 K) seem to be off. We attribute this discrepancy to the masking effect of the exceedingly large droplets from the fragmentation peak in previous measurements of droplet sizes. Within the temperature range of our investigation, although the expansion condition changes from subcritical to supercritical, there is no abrupt change in either the velocity distribution or the size distribution of the condensation peak, and the most salient effect is in the increasing intensity of the fragmentation peak. The absolute doping efficiency, as expressed by the ratio of ion-doped droplets over the total number of ions from the ESI source, is on the order of 10(-4), while only hundreds of doped ions have been detected. Further improvements in the ESI source are key to extending the technology for future experiments. On the other hand, the separation of the two groups of droplets in velocity is beneficial for size selection of only the smaller droplets for future experiments of electron

  20. Competitiveness of Brazilian Sugarcane Ethanol Compared to US Corn Ethanol

    OpenAIRE

    Crago, Christine Lasco; Khanna, Madhu; Barton, Jason; Giuliani, Eduardo; Amaral, Weber

    2010-01-01

    Corn ethanol produced in the US and sugarcane ethanol produced in Brazil are the world’s leading sources of biofuel. Current US biofuel policies create both incentives and constraints for the import of ethanol from Brazil, and together with the competitiveness and greenhouse gas intensity of sugarcane ethanol compared to corn ethanol will determine the extent of these imports. This study analyzes the supply-side determinants of this competitiveness and compares the greenhouse gas intensity of...

  1. 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.

  2. Self-arraying of charged levitating droplets.

    Science.gov (United States)

    Kauffmann, Paul; Nussbaumer, Jérémie; Masse, Alain; Jeandey, Christian; Grateau, Henri; Pham, Pascale; Reyne, Gilbert; Haguet, Vincent

    2011-06-01

    Diamagnetic levitation of water droplets in air is a promising phenomenon to achieve contactless manipulation of chemical or biochemical samples. This noncontact handling technique prevents contaminations of samples as well as provides measurements of interaction forces between levitating reactors. Under a nonuniform magnetic field, diamagnetic bodies such as water droplets experience a repulsive force which may lead to diamagnetic levitation of a single or few micro-objects. The levitation of several repulsively charged picoliter droplets was successfully performed in a ~1 mm(2) adjustable flat magnetic well provided by a centimeter-sized cylindrical permanent magnet structure. Each droplet position results from the balance between the centripetal diamagnetic force and the repulsive Coulombian forces. Levitating water droplets self-organize into satellite patterns or thin clouds, according to their charge and size. Small triangular lattices of identical droplets reproduce magneto-Wigner crystals. Repulsive forces and inner charges can be measured in the piconewton and the femtocoulomb ranges, respectively. Evolution of interaction forces is accurately followed up over time during droplet evaporation.

  3. Lipid droplet functions beyond energy storage.

    Science.gov (United States)

    Welte, Michael A; Gould, Alex P

    2017-10-01

    Lipid droplets are cytoplasmic organelles that store neutral lipids and are critically important for energy metabolism. Their function in energy storage is firmly established and increasingly well characterized. However, emerging evidence indicates that lipid droplets also play important and diverse roles in the cellular handling of lipids and proteins that may not be directly related to energy homeostasis. Lipid handling roles of droplets include the storage of hydrophobic vitamin and signaling precursors, and the management of endoplasmic reticulum and oxidative stress. Roles of lipid droplets in protein handling encompass functions in the maturation, storage, and turnover of cellular and viral polypeptides. Other potential roles of lipid droplets may be connected with their intracellular motility and, in some cases, their nuclear localization. This diversity highlights that lipid droplets are very adaptable organelles, performing different functions in different biological contexts. 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.

  4. Electrowetting Actuation of Polydisperse Nanofluid Droplets

    Directory of Open Access Journals (Sweden)

    Crismar Patacsil

    2017-01-01

    Full Text Available We present results of electrowetting experiments employing droplets formed from aqueous suspensions of Au nanoparticles. A planar electrowetting system, consisting of a Pt wire electrode and a bottom Cu electrode with an insulating silicone layer, is used to observe changes in droplet contact angle when an external electric field is applied. The equilibrium contact angle at 0 V decreases with increasing nanoparticle concentration, dropping from 100.4° for pure deionized water to 94.7° for a 0.5 μM nanofluid. Increasing the nanoparticle content also lowers the required voltage for effective actuation. With actuation at 15 V, contact angle decreases by 9% and 35% for droplets formed from pure water and a 0.5 μM nanoparticle suspension, respectively. Contact angle saturation is observed with nanofluid droplets, with the threshold voltage decreasing as nanoparticle concentration rises. Maximum droplet actuation before contact angle saturation is achieved at only 10 V for a concentration of 0.5 μM. A proposed mechanism for the enhanced electrowetting response of a nanofluid droplet involves a reduction in surface tension of the droplet as nanoparticles accumulate at the liquid-vapor interface.

  5. Transport velocity of droplets on ratchet conveyors.

    Science.gov (United States)

    Holmes, Hal R; Böhringer, Karl F

    2017-09-14

    Anisotropic ratchet conveyors (ARC) are a type of digital microfluidic system. Unlike electrowetting based systems, ARCs transport droplets through a passive, micro-patterned surface and applied orthogonal vibrations. The mechanics of droplet transport on ARC devices has yet to be as well characterized and understood as on electrowetting systems. In this work, we investigate how the design of the ARC substrate affects the droplet response to vibrations and perform the first characterization of transport velocity on ARC devices. We discovered that the design of the ARC device has a significant effect on both the transport efficiency and velocity of actuated droplets, and that the amplitude of the applied vibration can modulate the velocity of transported droplets. Finally, we show that the movement of droplet edges is not continuous but rather the sum of quantized steps between features of the ARC device. These results provide new insights into the behavior of droplets vibrated on asymmetric surface patterns and will serve as the foundation for the design and development of future lab-on-a-chip systems. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Characterization of flame radiosity in shrubland fires

    Science.gov (United States)

    Miguel G. Cruz; Bret W. Butler; Domingos X. Viegas; Pedro Palheiro

    2011-01-01

    The present study is aimed at quantifying the flame radiosity vertical profile and gas temperature in moderate to high intensity spreading fires in shrubland fuels. We report on the results from 11 experimental fires conducted over a range of fire rate of spread and frontal fire intensity varying respectively between 0.04-0.35ms-1 and 468-14,973kWm-1. Flame radiosity,...

  7. Physical and Chemical Processing in Flames

    Science.gov (United States)

    2013-08-12

    SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON a. REPORT...have experimentally acquired such chemistry-affected data as the ignition criteria and laminar flame speeds of fuel-air mixtures, which are...Chaos, A. Kazakov, Z. Zhao, F. L. Dryer , Int. J. Chem. Kinetics 39, 399–414 (2007) M. Lawes, M. P. Ormsby, C. G.W. Sheppard, R. Woolley, Combust. Flame

  8. NO concentration imaging in turbulent nonpremixed flames

    Energy Technology Data Exchange (ETDEWEB)

    Schefer, R.W. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    The importance of NO as a pollutant species is well known. An understanding of the formation characteristics of NO in turbulent hydrocarbon flames is important to both the desired reduction of pollutant emissions and the validation of proposed models for turbulent reacting flows. Of particular interest is the relationship between NO formation and the local flame zone, in which the fuel is oxidized and primary heat release occurs. Planar imaging of NO provides the multipoint statistics needed to relate NO formation to the both the flame zone and the local turbulence characteristics. Planar imaging of NO has been demonstrated in turbulent flames where NO was seeded into the flow at high concentrations (2000 ppm) to determine the gas temperature distribution. The NO concentrations in these experiments were significantly higher than those expected in typical hydrocarbon-air flames, which require a much lower detectability limit for NO measurements. An imaging technique based on laser-induced fluorescence with sufficient sensitivity to study the NO formation mechanism in the stabilization region of turbulent lifted-jet methane flames.

  9. Sensing flame structure by process tomography.

    Science.gov (United States)

    Liu, Jing; Liu, Shi; Zhou, Wanting; Qi, Xin; Lei, Jing; Mu, Huaiping

    2016-06-28

    Non-intrusive visualization of the structure of flames can offer us many advantages in studying the reaction mechanisms of combustion and observing special distributions of the parameters required for the development of equipment such as jet engines and gas turbines. Process tomography is a relatively new technique for such a task, but is useful owing to its fast speed and capability of detecting signals related to ionizations caused by chemical reactions and thermal effects. Electric capacitance tomography (ECT) is one of the process tomographic techniques. ECT usually comprises a sensor array of electrodes that detect permittivity variations in the measuring zone, a data-logging device and a computer that controls data acquisition and carries out image reconstruction. There have been studies on ECT imaging of flames; however, ECT has not been exploited sufficiently to reveal the inner structure of the flames. In this study, a sensor with planar electrodes is created, and the associated three-dimensional sensitivity map is generated by the finite-element method to detect flame structure. A series of experiments are carried out covering a range of feed rates of fuel and air. Data are collected by the ECT sensor and hardware. The results of the ECT reconstruction show good agreement with actual features, and the structure of the flame is found. This opens up a new route for the study of flames. This article is part of the themed issue 'Supersensing through industrial process tomography'. © 2016 The Author(s).

  10. Conical quarl swirl stabilized non-premixed flames: flame and flow field interaction

    KAUST Repository

    Elbaz, Ayman M.

    2017-09-19

    The flame-flow field interaction is studied in non-premixed methane swirl flames stabilized in quartz quarl via simultaneous measurements of the flow field using a stereo PIV and OH-PLIF at 5 KHz repetition rate. Under the same swirl intensity, two flames with different fuel jet velocity were investigated. The time-averaged flow field shows a unique flow pattern at the quarl exit, where two recirculation vortices are formed; a strong recirculation zone formed far from the quarl exit and a larger recirculation zone extending inside the quarl. However, the instantaneous images show that, the flow pattern near the quarl exit plays a vital role in the spatial location and structure of the reaction zone. In the low fuel jet velocity flame, a pair of vortical structures, located precisely at the corners of the quarl exit, cause the flame to roll up into the central region of low speed flow, where the flame sheet then tracks the axial velocity fluctuations. The vorticity field reveals a vortical structure surrounding the reaction zones, which reside on a layer of low compressive strain adjacent to that vortical structure. In the high fuel jet velocity flame, initially a laminar flame sheet resides at the inner shear layer of the main jet, along the interface between incoming fresh gas and high temperature recirculating gas. Further downstream, vortex breakdown alters the flame sheet path toward the central flame region. The lower reaction zones show good correlation to the regions of maximum vorticity and track the regions of low compressive strain associated with the inner shear layer of the jet flow. In both flames the reactions zones conform the passage of the large structure while remaining inside the low speed regions or at the inner shear layer.

  11. 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.

  12. Nonisothermal desorption of droplets of complex compositions

    Directory of Open Access Journals (Sweden)

    Nakoryakov Vladimir E.

    2012-01-01

    Full Text Available This paper presents the process of nonstationary evaporation of aqueous solutions of LiBr-H2O, CaCl2-H2O, NaCl-H2O droplets on a horizontal heating surface. The following typical stages of heat and mass transfer depending on wall temperature have been considered: evaporation below boiling temperature and nucleate boiling. The significant decrease in desorption intensity with a rise of initial mass concentration of salt has been observed. Formation of a surface crystallization front at evaporation of a droplet has been detected. We have developed the experimental method for direct measurements of the mass of evaporating droplet.

  13. 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.

    2017-08-01

    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.

  14. 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.

  15. Preparation of Flame Retardant Modified with Titanate for Asphalt Binder

    Directory of Open Access Journals (Sweden)

    Bo Li

    2014-01-01

    Full Text Available Improving the compatibility between flame retardant and asphalt is a difficult task due to the complex nature of the materials. This study explores a low dosage compound flame retardant and seeks to improve the compatibility between flame retardants and asphalt. An orthogonal experiment was designed taking magnesium hydroxide, ammonium polyphosphate, and melamine as factors. The oil absorption and activation index were tested to determine the effect of titanate on the flame retardant additive. The pavement performance test was conducted to evaluate the effect of the flame retardant additive. Oxygen index test was conducted to confirm the effect of flame retardant on flame ability of asphalt binder. The results of this study showed that the new composite flame retardant is more effective in improving the compatibility between flame retardant and asphalt and reducing the limiting oxygen index of asphalt binder tested in this study.

  16. Size dependent droplet actuation in digital microfluidic systems

    Science.gov (United States)

    Bhattacharjee, Biddut; Najjaran, Homayoun

    2009-05-01

    Digital microfluidic systems (DMFS) manipulate liquid droplets with volumes in submicroliter range in two dimensional arrays of cells. Among possible droplet actuation mechanisms, Electrowetting-on-dielectric (EWOD) actuation has been found to be most feasible and advantageous because of low power consumption, ease of signal generation and basic device fabrication. In EWOD based DMFS, droplets are actuated by applying an electric field and thus increasing the wettability on one side of the droplet. In this paper, we show that the EWOD actuation of a droplet can be modeled as a closed loop system having unity feedback of position. Electrode, dielectric and droplet are modeled as a capacitor with variable area as the droplet, considered as a conductor, moves over the dielectric layer. The EWOD force depends on the rate of change of droplet area over the actuated electrode, which in turn depends on the direction of motion and the position of the droplet between the actuated and previous electrode. Thus, EWOD actuation intrinsically utilizes the droplet position to generate sufficient force to accelerate the droplet. When the droplet approaches the final position, the magnitude of force reduces automatically so the droplet decelerates. In case the droplet has sufficient momentum to exceed the final position, the EWOD force, according to the model, will act on the opposite side of the droplet in order to bring it back to the desired position. The dynamic response has been characterized using the proposed model for different droplet sizes, actuation voltages, dielectric thicknesses and electrode sizes.

  17. Autoignition and flame stabilisation processes in turbulent non-premixed hot coflow flames

    NARCIS (Netherlands)

    Oldenhof, E.

    2012-01-01

    This dissertation examines stabilisation processes in turbulent non-premixed jet flames, created by injecting gaseous fuel into a co-flowing stream of hot, low-oxygen combustion products. Being able to predict whether and how a flame achieves stable and reliable combustion is a matter of great

  18. Competitiveness of Brazilian sugarcane ethanol compared to US corn ethanol

    Energy Technology Data Exchange (ETDEWEB)

    Crago, Christine L. [Energy Biosciences Institute, 1115 IGB Bldg., 1206 W Gregory Drive, Urbana, IL (United States); Khanna, Madhu [Department of Agricultural and Consumer Economics, 301A Mumford Hall, 1301 W Gregory Drive, Urbana, IL (United States); Barton, Jason [Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC (Canada); Giuliani, Eduardo [Venture Partners do Brasil, Rua Iguatemi 354 82, Sao Paulo, SP (Brazil); Amaral, Weber [Av. Padua Dias 11 - CP 9, Forest Sciences Departament - ESALQ, University of Sao Paulo, 13148-900, Piracicaba, SP (Brazil)

    2010-11-15

    Corn ethanol produced in the US and sugarcane ethanol produced in Brazil are the world's leading sources of biofuel. Current US biofuel policies create both incentives and constraints for the import of ethanol from Brazil and together with the cost competitiveness and greenhouse gas intensity of sugarcane ethanol compared to corn ethanol will determine the extent of these imports. This study analyzes the supply-side determinants of cost competitiveness and compares the greenhouse gas intensity of corn ethanol and sugarcane ethanol delivered to US ports. We find that while the cost of sugarcane ethanol production in Brazil is lower than that of corn ethanol in the US, the inclusion of transportation costs for the former and co-product credits for the latter changes their relative competitiveness. We also find that the relative cost of ethanol in the US and Brazil is highly sensitive to the prevailing exchange rate and prices of feedstocks. At an exchange rate of US1=R2.15 the cost of corn ethanol is 15% lower than the delivered cost of sugarcane ethanol at a US port. Sugarcane ethanol has lower GHG emissions than corn ethanol but a price of over $113 per ton of CO{sub 2} is needed to affect competitiveness. (author)

  19. A, a Brominated Flame Retardant

    Directory of Open Access Journals (Sweden)

    Tomomi Takeshita

    2013-01-01

    Full Text Available Tetrabromobisphenol A (TBBPA, a brominated flame retardant, has been found to exacerbate pneumonia in respiratory syncytial virus- (RSV- infected mice. We examined the effect of Brazilian propolis (AF-08 on the exacerbation of RSV infection by TBBPA exposure in mice. Mice were fed a powdered diet mixed with 1% TBBPA alone, 0.02% AF-08 alone, or 1% TBBPA and 0.02% AF-08 for four weeks and then intranasally infected with RSV. TBBPA exposure increased the pulmonary virus titer and level of IFN-γ, a representative marker of pneumonia due to RSV infection, in the lungs of infected mice without toxicity. AF-08 was significantly effective in reducing the virus titers and IFN-γ level increased by TBBPA exposure. Also, AF-08 significantly reduced proinflammatory cytokine (TNF-α and IL-6 levels in the lungs of RSV-infected mice with TBBPA exposure, but Th2 cytokine (IL-4 and IL-10 levels were not evidently increased. Neither TBBPA exposure nor AF-08 treatment affected the anti-RSV antibody production in RSV-infected mice. In flow cytometry analysis, AF-08 seemed to be effective in reducing the ratio of pulmonary CD8a+ cells in RSV-infected mice with TBBPA exposure. TBBPA and AF-08 did not exhibit anti-RSV activity in vitro. Thus, AF-08 probably ameliorated pneumonia exacerbated by TBBPA exposure in RSV-infected mice by limiting excess cellular immune responses.

  20. Turbulence-flame interactions in DNS of a laboratory high Karlovitz premixed turbulent jet flame

    Science.gov (United States)

    Wang, Haiou; Hawkes, Evatt R.; Chen, Jacqueline H.

    2016-09-01

    In the present work, direct numerical simulation (DNS) of a laboratory premixed turbulent jet flame was performed to study turbulence-flame interactions. The turbulent flame features moderate Reynolds number and high Karlovitz number (Ka). The orientations of the flame normal vector n, the vorticity vector ω and the principal strain rate eigenvectors ei are examined. The in-plane and out-of-plane angles are introduced to quantify the vector orientations, which also measure the flame geometry and the vortical structures. A general observation is that the distributions of these angles are more isotropic downstream as the flame and the flow become more developed. The out-of-plane angle of the flame normal vector, β, is a key parameter in developing the correction of 2D measurements to estimate the corresponding 3D quantities. The DNS results show that the correction factor is unity at the inlet and approaches its theoretical value of an isotropic distribution downstream. The alignment characteristics of n, ω and ei, which reflect the interactions of turbulence and flame, are also studied. Similar to a passive scalar gradient in non-reacting flows, the flame normal has a tendency to align with the most compressive strain rate, e3, in the flame, indicating that turbulence contributes to the production of scalar gradient. The vorticity dynamics are examined via the vortex stretching term, which was found to be the predominant source of vorticity generation balanced by dissipation, in the enstrophy transport equation. It is found that although the vorticity preferentially aligns with the intermediate strain rate, e2, the contribution of the most extensive strain rate, e1, to vortex stretching is comparable with that of the intermediate strain rate, e2. This is because the eigenvalue of the most extensive strain rate, λ1, is always large and positive. It is confirmed that the vorticity vector is preferentially positioned along the flame tangential plane, contributing

  1. Assessment of transpulmonary absorption of ethanol from alcohol-based hand rub.

    Science.gov (United States)

    Hautemanière, Alexis; Ahmed-Lecheheb, Djihane; Cunat, Lisiane; Hartemann, Philippe

    2013-03-01

    Alcohol-based hand rubs (ABHRs) have been associated with a reduction of nosocomial infections. Despite the worldwide introduction of these products in health care settings, the aim of this study was to assess the transpulmonary absorption of ethanol contains in ABHRs used by health care workers (HCWs) in real conditions of work shift. Twenty-six HCWs of Nancy University Hospital were included. Research consisted in monitoring participants during 4 hours of work shift to assess their exposure to ethanol. The measurement of ethanol vapors in exhaled breath was performed using a class B ethylometer (Alco-Sensor FST). Ethanol concentration in inhaled breath was measured using Gilian pump LFS-113. Concentration of ethanol, acetaldehyde, and acetate in blood and urine samples were determined using gas chromatography with flame ionization detector. Participants were 12% male and 88% female. The mean age was 40 ± 8 years. None of the employees included in the study presented any traces of ethanol or its metabolites in the blood or urine. Ethanol (0.08 ± 0.07 mg/L) was detected in the breath of 10 HCWs at 1 to 2 minutes postexposure. The mean concentration of ethanol in the inhaled air was 46.2 mg/m. Absorption of ethanol vapor from ABHRs among HCWs during their care activities was not detected. Quantification of ethanol fumes inhaled during 4 hours of work shift was below the regulatory limitations of exposure to ethanol. Copyright © 2013 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Mosby, Inc. All rights reserved.

  2. Energy storage by means of exciton droplets

    Energy Technology Data Exchange (ETDEWEB)

    Zuev, V.A.; Litovchenko, V.G.

    1980-01-01

    Certain characteristics of electron-hole droplets and ball lightning are investigated and compared with a view to evaluating energy storage and transfer processes. Models for plasma processes in the atmosphere and in semiconductors are briefly examined.

  3. Droplet Microfluidics for Chip-Based Diagnostics

    Science.gov (United States)

    Kaler, Karan V. I. S.; Prakash, Ravi

    2014-01-01

    Droplet microfluidics (DMF) is a fluidic handling technology that enables precision control over dispensing and subsequent manipulation of droplets in the volume range of microliters to picoliters, on a micro-fabricated device. There are several different droplet actuation methods, all of which can generate external stimuli, to either actively or passively control the shape and positioning of fluidic droplets over patterned substrates. In this review article, we focus on the operation and utility of electro-actuation-based DMF devices, which utilize one or more micro-/nano-patterned substrates to facilitate electric field-based handling of chemical and/or biological samples. The underlying theory of DMF actuations, device fabrication methods and integration of optical and opto-electronic detectors is discussed in this review. Example applications of such electro-actuation-based DMF devices have also been included, illustrating the various actuation methods and their utility in conducting chip-based laboratory and clinical diagnostic assays. PMID:25490590

  4. Biofilm Formation in Microscopic Double Emulsion Droplets

    Science.gov (United States)

    Chang, Connie; Weitz, David

    2012-02-01

    In natural, medical, and industrial settings, there exist surface-associated communities of bacteria known as biofilms. These highly structured films are composed of bacterial cells embedded within self-produced extracellular matrix, usually composed of exopolysaccharides, proteins, and nucleic acids; this matrix serves to protect the bacterial community from antibiotics and environmental stressors. Here, we form biofilms encapsulated within monodisperse, microscopically-sized double emulsion droplets using microfluidics. The bacteria self-organize at the inner liquid-liquid droplet interfaces, multiply, and differentiate into extracellular matrix-producing cells, forming manifold three-dimensional shell-within-a-shell structures of biofilms, templated upon the inner core of spherical liquid droplets. By using microfluidics to encapsulate bacterial cells, we have the ability to view individual cells multiplying in microscopically-sized droplets, which allows for high-throughput analysis in studying the genetic program leading to biofilm development, or cell signaling that induces differentiation.

  5. Chemical composition of polluted mist droplets

    Science.gov (United States)

    Igawa, Manabu; Kamijo, Kosuke; Nanzai, Ben; Matsumoto, Kiyoshi

    2017-12-01

    Mist events occur frequently worldwide, but the chemical characteristics of the mist droplets has never been investigated because of very low liquid water contents of them. We estimated the concentrations of the mist water, the average concentration of the mist droplets, via the determination of water-soluble components of the coarse aerosol and the observation of the imprints of the droplets on a MgO-coated glass slide. The pH of the mist water was estimated from the equilibrium calculation with the data of the Gran plot of the solution of the dissolved coarse particles, the inorganic ion concentrations of aerosol larger than 10 μm, and the estimated volume of mist water. The mist water was measured as about 1 eq/L total concentration for typical inorganic ions and about pH 4.5 in Yokohama. Such highly concentrated mist droplets may have intense environmental effects.

  6. Droplet Microfluidics for Artificial Lipid Bilayers

    Science.gov (United States)

    Punnamaraju, Srikoundinya; Steckl, Andrew

    2012-02-01

    Droplet interface bilayer is a versatile approach that allows formation of artificial lipid bilayer membrane at the interface of two lipid monolayer coated aqueous droplets in a lipid filled oil medium. Versatility exists in the form of voltage control of DIB area, ability of forming networks of DIBs, volume control of droplets and lipid-oil, and ease of reformation. Significant effect of voltage on the area and capacitance of DIB as well as DIB networks are characterized using simultaneous optical and electrical recordings. Mechanisms behind voltage-induced effects on DIBs are investigated. Photo induced effect on the DIB membrane porosity is obtained by incorporating UVC-sensitive photo-polymerizable lipids in DIB. Photo-induced effects can be extended for in-vitro studies of triggered release of encapsulated contents across membranes. A droplet based low voltage digital microfluidic platform is developed to automate DIB formation, which could potentially be used for forming arrays of lipid bilayer membranes.

  7. Computational Simulation of Droplet Collision Dynamics

    National Research Council Canada - National Science Library

    Law, Chung

    2000-01-01

    ..., and the energy partition among the various modes was identified. By using the molecular dynamics method, bouncing and coalescence were successfully simulated for the first time without the artificial manipulation of the inter-droplet gaseous film...

  8. Temperature-induced droplet coalescence in microchannels.

    Science.gov (United States)

    Xu, Bin; Nguyen, Nam-Trung; Wong, Teck Neng

    2012-03-01

    This paper reports a technique for temperature-induced merging of droplets in a microchannel. The multiphase system consists of water droplet and oil as the dispersed phase and the carrying continuous phase. A resistive heater provides heating in a rectangular merging chamber. The temperature of the chamber is controlled by the voltage applied to the heater. The merging process of two neighboring droplets was investigated with different applied voltage, flow rate ratio between water and oil and total flowrate. Merging is found to be effective at high flow rate ratio, high temperature, and low total flowrate. The presented technique could be used for merging and mixing in droplet-based lab-on-a-chip platforms.

  9. Sprouting Droplets Driven by Physical Effects Alone.

    Science.gov (United States)

    Rumble, Katherine A; Stoev, Iliya D; French, David J; Abou-Hassan, Ali; Clegg, Paul S

    2017-05-02

    Combining a partially miscible three-liquid system with interfacially trapped silica colloids, we show that small droplets can exhibit dramatic growth phenomena driven by physical effects alone. The mass dense droplets sprout tubes which grow vertically upward in a gravitational field and respond to the presence of other droplets in their path. Two of the liquids in our system are water and toluene. By varying the third liquid, we are able to relate the growth behavior to the details of the underlying three-fluid phase diagram and the changes to the interfacial tension. Additionally, we introduce a pendant drop in the path of our growing drop. We use this to confirm that growth is driven by the partitioning of solvents, that exchange of solvents between droplets is chemically selective, and that the exchange behavior can itself generate further growth phenomena.

  10. 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.

  11. Droplet Microfluidics for Chip-Based Diagnostics

    Directory of Open Access Journals (Sweden)

    Karan V. I. S. Kaler

    2014-12-01

    Full Text Available Droplet microfluidics (DMF is a fluidic handling technology that enables precision control over dispensing and subsequent manipulation of droplets in the volume range of microliters to picoliters, on a micro-fabricated device. There are several different droplet actuation methods, all of which can generate external stimuli, to either actively or passively control the shape and positioning of fluidic droplets over patterned substrates. In this review article, we focus on the operation and utility of electro-actuation-based DMF devices, which utilize one or more micro-/nano-patterned substrates to facilitate electric field-based handling of chemical and/or biological samples. The underlying theory of DMF actuations, device fabrication methods and integration of optical and opto-electronic detectors is discussed in this review. Example applications of such electro-actuation-based DMF devices have also been included, illustrating the various actuation methods and their utility in conducting chip-based laboratory and clinical diagnostic assays.

  12. Flame Quenching Dynamics of High Velocity Flames in Rectangular Cross-section Channels

    KAUST Repository

    Mahuthannan, Ariff Magdoom

    2017-01-05

    Understanding flame quenching for different conditions is necessary to develop safety devices like flame arrestors. In practical applications, the speed of a deflagration in the lab-fixed reference frame will be a strong function of the geometry through which the deflagration propagates. This study reports on the effect of the flame speed, at the entrance of a quenching section, on the quenching distance. A 2D rectangular channel joining two main spherical vessels is considered for studying this effect. Two different velocity regimes are investigated and referred to as configurations A, and B. For configuration A, the velocity of the flame is 20 m/s, while it is about 100 m/s for configuration B. Methane-air stoichiometric mixtures at 1 bar and 298 K are used. Simultaneous dynamic pressure measurements along with schlieren imaging are used to analyze the quenching of the flame. Risk assessment of re-ignition is also reported and analyzed.

  13. Effect of oil droplet size on activation energy for coalescence of oil droplets in an O/W emulsion.

    Science.gov (United States)

    Miyagawa, Yayoi; Katsuki, Kazutaka; Matsuno, Ryuichi; Adachi, Shuji

    2015-01-01

    The activation energy of a reasonable order of magnitude was estimated for the coalescence of oil droplets in an O/W emulsion by formulating the balance of forces acting on a droplet that crosses over the potential barrier to coalesce with another droplet by the DLVO theory and Stokes' law. An emulsion with smaller oil droplets was shown to be more stable.

  14. Superheated droplet detector response to fabrication variations

    Energy Technology Data Exchange (ETDEWEB)

    Felizardo, M., E-mail: felizardo@itn.p [Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavem (Portugal); Centro de Fisica Nuclear, Universidade de Lisboa, 1649-003 Lisbon (Portugal); Instituto de Telecomunicacoes, IST, Av. Rovisco Pais 1, 1049-001 Lisbon (Portugal); Morlat, T.; Girard, T.A. [Centro de Fisica Nuclear, Universidade de Lisboa, 1649-003 Lisbon (Portugal); Martins, R.C. [Instituto de Telecomunicacoes, IST, Av. Rovisco Pais 1, 1049-001 Lisbon (Portugal); Ramos, A.R.; Marques, J.G. [Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavem (Portugal); Centro de Fisica Nuclear, Universidade de Lisboa, 1649-003 Lisbon (Portugal)

    2010-03-01

    Constructions of superheated droplet detectors (SDDs) are easily (and sometimes unavoidably) altered in the fabrication process by small variations in the ingredient concentrations and fractionating of the superheated liquid. The devices have moreover been stored at temperatures below 0 deg. C prior to usage in order to de-sensitize their response during transport. We report studies of the response differences of high concentration SDDs with respect to variations common to their fabrication, to include ageing, concentration, gel stiffness, and droplet size.

  15. The atomization and the flame structure in the combustion of residual fuel oils; La atomizacion y estructura de flama en la combustion de combustibles residuales

    Energy Technology Data Exchange (ETDEWEB)

    Bolado Estandia, Ramon [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

    1985-12-31

    In this article a research on the combustion of heavy residual fuel oils is presented. The type of flames studied were obtained by means of the burning of sprays produced by an atomizer designed and calibrated specially for the research purpose. The flame characteristics that were analyzed are its length, its luminosity, the temperature, the distribution of the droplets size and mainly the burning regime of the droplets in the flame. The experimental techniques that were used for these studies were shadow micro-photography, suction pyrometry and of total radiation, laser diffraction, 35 mm photography, and impact push. The analysis of the experimental results, together with the results of the application of a mathematical model, permitted to establish two parameters, that quantitatively related determine the burning regime of the droplets in a flame of sprays of residual heavy fuel oil. [Espanol] En este articulo se presenta una investigacion sobre la combustion de combustibles residuales pesados. El tipo de flamas estudiadas se obtuvieron mediante el quemado de sprays producidos por un atomizador disenado y calibrado especialmente para el proposito de la investigacion. Las caracteristicas de flama que se analizaron son la longitud, la luminosidad, la temperatura, la distribucion de tamano de gotas y, principalmente, el regimen de quemado de gotas en la flama. Las tecnicas experimentales que se usaron para estos estudios fueron microfotografia de sombras, pirometria de succion y de radiacion total, difraccion laser, fotografia de 35 mm y empuje de impacto. El analisis de resultados experimentales, junto con los resultados de la aplicacion de un modelo matematico, permitio establecer dos parametros, que relacionados cuantitativamente, determinan el regimen de quemado de gotas en una flama de sprays de combustible residual pesado.

  16. Dipolar droplets in bosonic erbium quantum fluids

    Science.gov (United States)

    Chomaz, Lauriane; Baier, Simon; Petter, Daniel; Faraoni, Giulia; Becher, Jan-Hendrik; van Bijnen, Rick; Mark, Manfred J.; Ferlaino, Francesca

    2017-04-01

    Due to their large magnetic moment and exotic electronic configuration, atoms of the lanthanide family, such as dysprosium (Dy) and erbium (Er), are an ideal platform for exploring the competition between inter-particle interactions of different origins and behaviors. Recently, a novel phase of dilute droplet has been observed in an ultracold gas of bosonic Dy when changing the ratio of the contact and dipole-dipole interactions and setting the mean-field interactions to slightly attractive. This has been attributed to the distinct, non-vanishing, beyond-mean-field effects in dipolar gases when the mean interaction cancels. Here we report on the investigation of droplet physics in fluids of bosonic Er. By precise control of the scattering length a, we quantitatively probe the Bose-Einstein condensate (BEC)-to-droplet phase diagram and the rich underlying dynamics. In a prolate geometry, we observe a crossover from a BEC to a single macro-droplet, prove the stabilizing role of quantum fluctuations and characterize the special dynamical properties of the droplet. In an oblate geometry, we observe the formation of assemblies of tinier droplets arranged in a chain and explore the special state dynamics following a quench of a, marked by successive merging and reformation events. L.C. is supported within the Marie Curie Individual Fellowship DIPPHASE No. 706809 of the European Commission.

  17. Droplet flows through periodic loop networks

    Science.gov (United States)

    Jeanneret, Raphael; Schindler, Michael; Bartolo, Denis

    2010-11-01

    Numerous microfluidic experiments have revealed non-trivial traffic dynamics when droplets flow through a channel including a single loop. A complex encoding of the time intervals between the droplets is achieved by the binary choices they make as they enter the loop. Very surprisingly, another set of experiments has demonstrated that the addition of a second loop does not increase the complexity of the droplet pattern. Conversely, the second loop decodes the temporal signal encrypted by the first loop [1]. In this talk we show that no first principle argument based on symmetry or conservation laws can account for this unexpected decoding process. Then, to better understand how a loop maps time intervals between droplets, we consider a simplified model which has proven to describe accurately microfluidic droplet flows. Combining numerical simulations and analytical calculations for the dynamic of three droplets travelling through N loops: (i) We show that three different traffic regimes exist, yet none of them yields exact decoding. (ii) We uncover that for a wide class of loop geometry, the coding process is analogous to a Hamiltonian mapping: regular orbits are destabilized in island chains and separatrix. (iii) Eventually, we propose a simple explanation to solve the apparent paradox with the coding/decoding dynamics observed in experiments. [1] M.J. Fuerstman, P. Garstecki, and G.M. Whitesides, Science, 315:828, 2007.

  18. Droplet impact on vibrating superhydrophobic surfaces

    Science.gov (United States)

    Weisensee, Patricia B.; Ma, Jingcheng; Shin, Young Hwan; Tian, Junjiao; Chang, Yujin; King, William P.; Miljkovic, Nenad

    2017-10-01

    Many unanswered questions remain pertaining to droplet dynamics during impact on vibrating surfaces. Using optical high-speed imaging, we investigate the impact dynamics of macroscopic water droplets (≈2.5 mm ) on rigid and elastic superhydrophobic surfaces vibrating at 60-320 Hz and amplitudes of 0.2-2.7 mm. Specifically, we study the influence of the frequency, amplitude, rigidity, and substrate phase at the moment of impact on the contact time of impacting droplets. We show that a critical impact phase exists at which the contact time transitions from a minimum to a maximum greater than the theoretical contact time on a rigid, nonvibrating superhydrophobic surface. For impact at phases higher than the critical phase, contact times decrease until reaching a minimum of half the theoretical contact time just before the critical phase. The frequency of oscillation determines the phase-dependent variability of droplet contact times at different impact phases: higher frequencies (> 120 Hz) show less contact time variability and have overall shorter contact times compared to lower frequencies (60-120 Hz). The amplitude of vibration has little direct effect on the contact time. Through semiempirical modeling and comparison to experiments, we show that phase-averaged contact times can increase or decrease relative to a nonvibrating substrate for low (100 Hz ) vibration frequencies, respectively. This study not only provides new insights into droplet impact physics on vibrating surfaces, but also develops guidelines for the rational design of surfaces to achieve controllable droplet wetting in applications utilizing vibration.

  19. Cars temperature measurements in sooting, laminar diffusion flames

    Science.gov (United States)

    Boedeker, L. R.; Dobbs, G. M.

    1984-07-01

    Temperature distributions have been measured in axisymmetric ethylene-air diffusion flames using high spatial resolution coherent anti-Stokes Raman spectroscopy. As ethylene flow increased and the flame approached a smoke-point condition, the temperatures attained in the upper part of the flame were reduced by about 300K below the maximum radial temperatures low in the flame. Addition of diluent N2 to ethylene caused a reduction in temperature low in the flame but increased temperature higher in the flame. Maximum temperatures attained in all ethylene flames were between 0.84 and 0.89 of respective adiabatic flame temperatures (AFT). The upper temperature of the near-smoke-point flame was only 0.76 of AFT. Results are compared with the generalized flame front model of Mitchell. MIE scattering measurements are also discussed. Brief studies with propane and a nonsooting, CO flame are reported; maximum axial and radial temperatures were between 0.84 and 0.87 of AFT. Results indicate the importance of thermal loss from soot radiation, radial transport processes and fuel pyrolysis. Nonluminous radiation and finite reaction rates are other possible factors. The upper luminous part of the highly sooting ethylene flame is likely above the primary flame front and is a soot burnout zone.

  20. Launch Pad Flame Trench Refractory Materials

    Science.gov (United States)

    Calle, Luz M.; Hintze, Paul E.; Parlier, Christopher R.; Bucherl, Cori; Sampson, Jeffrey W.; Curran, Jerome P.; Kolody, Mark; Perusich, Steve; Whitten, Mary

    2010-01-01

    The launch complexes at NASA's John F. Kennedy Space Center (KSC) are critical support facilities for the successful launch of space-based vehicles. These facilities include a flame trench that bisects the pad at ground level. This trench includes a flame deflector system that consists of an inverted, V-shaped steel structure covered with a high temperature concrete material five inches thick that extends across the center of the flame trench. One side of the "V11 receives and deflects the flames from the orbiter main engines; the opposite side deflects the flames from the solid rocket boosters. There are also two movable deflectors at the top of the trench to provide additional protection to shuttle hardware from the solid rocket booster flames. These facilities are over 40 years old and are experiencing constant deterioration from launch heat/blast effects and environmental exposure. The refractory material currently used in launch pad flame deflectors has become susceptible to failure, resulting in large sections of the material breaking away from the steel base structure and creating high-speed projectiles during launch. These projectiles jeopardize the safety of the launch complex, crew, and vehicle. Post launch inspections have revealed that the number and frequency of repairs, as well as the area and size of the damage, is increasing with the number of launches. The Space Shuttle Program has accepted the extensive ground processing costs for post launch repair of damaged areas and investigations of future launch related failures for the remainder of the program. There currently are no long term solutions available for Constellation Program ground operations to address the poor performance and subsequent failures of the refractory materials. Over the last three years, significant liberation of refractory material in the flame trench and fire bricks along the adjacent trench walls following Space Shuttle launches have resulted in extensive investigations of

  1. On Soot Inception in Nonpremixed Flames and the Effects of Flame Structure

    Science.gov (United States)

    Chao, B. H.; Liu, S.; Axelbaum, R. L.; Gokoglu, Suleyman (Technical Monitor)

    1998-01-01

    A simplified three-step model of soot inception has been employed with high activation energy asymptotics to study soot inception in nonpremixed counterflow systems with emphasis on understanding the effects of hydrodynamics and transport. The resulting scheme yields three zones: (1) a fuel oxidation zone wherein the fuel and oxidizer react to form product as well as a radical R, (e.g., H), (2) a soot/precursor formation zone where the radical R reacts with fuel to form "soot/precursor" S, and (3) a soot/precursor consumption zone where S reacts with the oxidizer to form product. The kinetic scheme, although greatly simplified, allows the coupling between soot inception and flame structure to be assessed. The results yield flame temperature, flame location, and a soot/precursor index S(sub I) as functions of Damkohler number for S formation. The soot/precursor index indicates the amount of S at the boundary of the formation region. The flame temperature indirectly indicates the total amount of S integrated over the formation region because as S is formed less heat release is available. The results show that unlike oxidation reactions, an extinction turning-point behavior does not exist for soot. Instead, the total amount of S slowly decreases with decreasing Damkohler number (increasing strain rate), which is consistent with counterflow flame experiments. When the Lewis number of the radical is decreased from unity, the total S reduces due to reduced residence time for the radical in the soot formation region. Similarly, when the Lewis number of the soot/precursor is increased from unity the amount of S increases for all Damkohler numbers. In addition to studying fuel-air (low stoichiometric mixture fraction) flames, the air-side nitrogen was substituted into the fuel, yielding diluted fuel-oxygen (high stoichiometric mixture fraction) flames with the same flame temperature as the fuel - air flames. The relative flame locations were different however, and

  2. Chaotic radiation/turbulence interactions in flames

    Energy Technology Data Exchange (ETDEWEB)

    Menguec, M.P.; McDonough, J.M.

    1998-11-01

    In this paper, the authors present a review of their recent efforts to model chaotic radiation-turbulence interactions in flames. The main focus is to characterize soot volume fraction fluctuations in turbulent diffusion flames, as they strongly contribute to these interaction. The approach is based on the hypothesis that the fluctuations of properties in turbulent flames are deterministic in nature, rather than random. The authors first discuss the theoretical details and then they briefly outline the experiments conducted to measure the scattered light signals from fluctuating soot particles along the axis of an ethylene-air diffusion flame. They compare the power spectra and time series obtained from experiments against the ad-hoc and rigorous models derived using a series of logistic maps. These logistic maps can be used in simulation of the fluctuations in these type of flames, without extensive computational effort or sacrifice of physical detail. Availability of accurate models of these kinds allows investigation of radiation-turbulence interactions at a more fundamental level than it was previously possible.

  3. Characteristics of diffusion flames with accelerated motion

    Directory of Open Access Journals (Sweden)

    Lou Bo

    2016-01-01

    Full Text Available The aim of this work is to present an experiment to study the characteristics of a laminar diffusion flame under acceleration. A Bunsen burner (nozzle diameter 8 mm, using liquefied petroleum gas as its fuel, was ignited under acceleration. The temperature field and the diffusion flame angle of inclination were visualised with the assistance of the visual display technology incorporated in MATLAB™. Results show that the 2-d temperature field under different accelerations matched the variation in average temperatures: they both experience three variations at different time and velocity stages. The greater acceleration has a faster change in average temperature with time, due to the accumulation of combustion heat: the smaller acceleration has a higher average temperature at the same speed. No matter what acceleration was used, in time, the flame angle of inclination increased, but the growth rate decreased until an angle of 90°: this could be explained by analysis of the force distribution within the flame. It is also found that, initially, the growth rate of angle with velocity under the greater acceleration was always smaller than that at lower accelerations; it was also different in flames with uniform velocity fire conditions.

  4. Visualization of ionic wind in laminar jet flames

    KAUST Repository

    Park, Daegeun

    2017-07-03

    Electric field, when it is applied to hydrocarbon flames, generates ionic wind due to the electric body force on charge carrying species. Ionic wind has been shown to influence soot emission, propagation speed, and stability of flames; however, a detailed behavior of ionic wind and its effects on flames is still not clear. Here, we investigated the dynamic behaviors of flames and ionic wind in the presence of direct current (DC) and alternating current (AC) electric fields in nonpremixed and premixed jet flames with a jet nozzle placed between two parallel electrodes. We observed a skewed flame toward a lower potential electrode with DC and lower frequency AC (e.g., 10Hz) and a steady flame with higher frequencies AC (1000Hz), while we found that the ionic wind blew toward both the anode and cathode regardless of flame type (nonpremixed or premixed) or the source of the electric field (DC and AC).

  5. Beam steering effects in turbulent high pressure flames

    Energy Technology Data Exchange (ETDEWEB)

    Hemmerling, B.; Kaeppeli, B. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-06-01

    The propagation of a laser beam through a flame is influenced by variations of the optical density. Especially in turbulent high pressure flames this may seriously limit the use of laser diagnostic methods. (author) 1 fig., 2 refs.

  6. Coalescence-induced droplet jumping on superhydrophobic surfaces: Effects of droplet mismatch

    Science.gov (United States)

    Wasserfall, Joram; Figueiredo, Patric; Kneer, Reinhold; Rohlfs, Wilko; Pischke, Philipp

    2017-12-01

    On low-adhesion surfaces, coalescing droplets can spontaneously jump off, known as coalescence-induced droplet jumping. It is observed on a variety of synthetic and natural superhydrophobic surfaces, and gives rise to a range of applications, such as self-cleaning condensers, anti-icing coatings, and thermal diodes. Through three-dimensional simulations, this paper demonstrates the fluid dynamics of droplet jumping upon binary unequal-sized-droplet coalescence. Parametric studies show the influence of droplet mismatch, viscosity, and contact angle on jumping velocities, where liftoff regimes are defined on the basis of Ohnesorge number and droplet size ratio. Because of the strong asymmetric flow behavior, the well-known small conversion efficiency for equal-sized-droplet jumping, where around 6 % of the released surface energy is convertible into translational kinetic energy, is further reduced for unequal-sized-droplet jumping. The findings offer insights into their fluid dynamics and give a starting point for further modeling of dropwise condensation on superhydrophobic surfaces.

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

    CSIR Research Space (South Africa)

    Musehane, Ndivhuwo M

    2016-10-01

    Full Text Available In this work, droplet-droplet interaction is modelled using a multiphase flow computational fluid dynamics approach coupled with a reduced order surface thin-film model. An existing multiphase flow model based on a multiple marker volume of fluid...

  8. Effects of the Burner Diameter on the Flame Structure and Extinction Limit of Counterflow Non-Premixed Flames

    Directory of Open Access Journals (Sweden)

    Chang Bo Oh

    2010-09-01

    Full Text Available Experiments and numerical simulations were conducted to investigate the effects of the burner diameter on the flame structure and extinction limit of counterflow non-premixed methane flames in normal gravity and microgravity. Experiments were performed for counterflow flames with a large inner diameter (d of 50 mm in normal gravity to compare the extinction limits with those obtained by previous studies where a small burner (d < 25 mm was used. Two-dimensional (2D simulations were performed to clarify the flame structure and extinction limits of counterflow non-premixed flame with a three-step global reaction mechanism. One-dimensional (1D simulations were also performed with the same three-step global reaction mechanism to provide reference data for the 2D simulation and experiment. For microgravity, the effect of the burner diameter on the flame location at the centerline was negligible at both high (ag = 50 s−1 and low (ag = 10 s−1 strain rates. However, a small burner flame (d = 15 mm in microgravity showed large differences in the maximum flame temperature and the flame size in radial direction compared to a large burner flame (d = 50 mm at low strain rate. In addition, for normal gravity, a small burner flame (d = 23.4 mm showed differences in the flame thickness, flame location, local strain rate, and maximum heat release rate compared to a large burner flame (d = 50 mm at low strain rate. Counterflow non-premixed flames with low and high strain rates that were established in a large burner were approximated by 1D simulation for normal gravity and microgravity. However, a counterflow non-premixed flame with a low strain rate in a small burner could not be approximated by 1D simulation for normal gravity due to buoyancy effects. The 2D simulations of the extinction limits correlated well with experiments for small and large burner flames. For microgravity, the extinction limit of a small burner flame (d = 15 mm was much lower than that

  9. Scavenging dissolved oxygen via acoustic droplet vaporization.

    Science.gov (United States)

    Radhakrishnan, Kirthi; Holland, Christy K; Haworth, Kevin J

    2016-07-01

    Acoustic droplet vaporization (ADV) of perfluorocarbon emulsions has been explored for diagnostic and therapeutic applications. Previous studies have demonstrated that vaporization of a liquid droplet results in a gas microbubble with a diameter 5-6 times larger than the initial droplet diameter. The expansion factor can increase to a factor of 10 in gassy fluids as a result of air diffusing from the surrounding fluid into the microbubble. This study investigates the potential of this process to serve as an ultrasound-mediated gas scavenging technology. Perfluoropentane droplets diluted in phosphate-buffered saline (PBS) were insonified by a 2 MHz transducer at peak rarefactional pressures lower than and greater than the ADV pressure amplitude threshold in an in vitro flow phantom. The change in dissolved oxygen (DO) of the PBS before and after ADV was measured. A numerical model of gas scavenging, based on conservation of mass and equal partial pressures of gases at equilibrium, was developed. At insonation pressures exceeding the ADV threshold, the DO of air-saturated PBS decreased with increasing insonation pressures, dropping as low as 25% of air saturation within 20s. The decrease in DO of the PBS during ADV was dependent on the volumetric size distribution of the droplets and the fraction of droplets transitioned during ultrasound exposure. Numerically predicted changes in DO from the model agreed with the experimentally measured DO, indicating that concentration gradients can explain this phenomenon. Using computationally modified droplet size distributions that would be suitable for in vivo applications, the DO of the PBS was found to decrease with increasing concentrations. This study demonstrates that ADV can significantly decrease the DO in an aqueous fluid, which may have direct therapeutic applications and should be considered for ADV-based diagnostic or therapeutic applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. Droplet Microfluidics for the Production of Microparticles and Nanoparticles

    Directory of Open Access Journals (Sweden)

    Jianmei Wang

    2017-01-01

    Full Text Available Droplet microfluidics technology is recently a highly interesting platform in material fabrication. Droplets can precisely monitor and control entire material fabrication processes and are superior to conventional bulk techniques. Droplet production is controlled by regulating the channel geometry and flow rates of each fluid. The micro-scale size of droplets results in rapid heat and mass-transfer rates. When used as templates, droplets can be used to develop reproducible and scalable microparticles with tailored sizes, shapes and morphologies, which are difficult to obtain using traditional bulk methods. This technology can revolutionize material processing and application platforms. Generally, microparticle preparation methods involve three steps: (1 the formation of micro-droplets using a microfluidics generator; (2 shaping the droplets in micro-channels; and (3 solidifying the droplets to form microparticles. This review discusses the production of microparticles produced by droplet microfluidics according to their morphological categories, which generally determine their physicochemical properties and applications.

  11. The Transition to Turbulence of Rayleigh-Taylor Unstable Flames

    Science.gov (United States)

    Hicks, Elizabeth P.; Rosner, R.

    2011-01-01

    Part of the uncertainty surrounding the explosion mechanism of Type 1A supernovae is the extent to which the turbulence created by the flame front can speed the flame up. A premixed flame moving against a sufficiently strong gravitational field becomes deformed and creates vorticity. If gravity is strong enough, this vorticity is shed and deposited behind the flame front. We have completed some two-dimensional direct numerical simulations of this shedding process for various values of the gravitational force. If gravity is weak enough, the flame front remains flat and no vorticity is created. If gravity is slightly stronger, the flame front becomes cusped and creates vorticity; long vortices attach to the flame front and extend behind it. For even larger values of gravity, the far end of these vortices becomes unstable and sheds more vortices. For simulations with increased gravity, the position of the shedding instability moves closer to the flame front. Next, the vortex shedding disturbs the flame front, causing the flame to pulsate. These pulsations lose their left/right symmetry and the period of oscillation doubles. For even higher values of gravity, an additional frequency is introduced into the system as the Rayleigh-Taylor instability begins to dominate over burning. Eventually, the pulsations of the flame become quite complex and the interaction between the flame front and the vortices can't be simply described. We have measured the subsequent wrinkling of the flame front by computing its fractal dimension and the energy spectra behind the flame front. Measurements of the fractal dimension suggest that it saturates, implying that any additional speed up of the flame must be due to large-scale stretching or disruption of the flame front. Our simulations were performed at NERSC which is supported by the Department of Energy.

  12. Effectiveness of Flame Retardants in TufFoam.

    Energy Technology Data Exchange (ETDEWEB)

    Abelow, Alexis Elizabeth [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Nissen, April [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Massey, Lee Taylor [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Whinnery, LeRoy L. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2017-12-01

    An investigation of polyurethane foam filled with known flame retardant fillers including hydroxides, melamine, phosphate-containing compounds, and melamine phosphates was carried out to produce a low-cost material with high flame retardant efficiency. The impact of flame retardant fillers on the physical properties such a s composite foam density, glass transition temperature, storage modulus, and thermal expansion of composite foams was investigated with the goal of synthesizing a robust rigid foam with excellent flame retardant properties.

  13. On stability of premixed flames in stagnation - Point flow

    Science.gov (United States)

    Sivashinsky, G. I.; Law, C. K.; Joulin, G.

    1982-01-01

    A quantitative description of flame stabilization in stagnation-point flow is proposed. Asymptotic and stability analyses are made for a flame model where the density of the gas is assumed to be constant and the reaction zone is assumed to be narrow and concentrated over the flame front. It is shown that, if blowing is sufficiently strong, the corrugations disappear and a plane flame results. The phenomena cannot be fully described by means of classical linear stability analysis.

  14. Acoustically Forced Coaxial Hydrogen / Liquid Oxygen Jet Flames

    Science.gov (United States)

    2016-05-15

    in a dramatic reduction in the fibrous na- ture of the surface, as expected, due to evaporation pro - Figure 3. An instant in time of PAN and PN...attached flame to inner lip of the GH2 exit. No local flame extinction was observed regardless of the acoustic forcing amplitude. It has been...experi- mentally observed when the strain rates associated with acoustic forcing is high enough [22], local extinction of the flame and the flame holding

  15. Front roughening of flames in discrete media

    Science.gov (United States)

    Lam, Fredric; Mi, XiaoCheng; Higgins, Andrew J.

    2017-07-01

    The morphology of flame fronts propagating in reactive systems composed of randomly positioned, pointlike sources is studied. The solution of the temperature field and the initiation of new sources is implemented using the superposition of the Green's function for the diffusion equation, eliminating the need to use finite-difference approximations. The heat released from triggered sources diffuses outward from each source, activating new sources and enabling a mechanism of flame propagation. Systems of 40 000 sources in a 200 ×200 two-dimensional domain were tracked using computer simulations, and statistical ensembles of 120 realizations of each system were averaged to determine the statistical properties of the flame fronts. The reactive system of sources is parameterized by two nondimensional values: the heat release time (normalized by interparticle diffusion time) and the ignition temperature (normalized by adiabatic flame temperature). These two parameters were systematically varied for different simulations to investigate their influence on front propagation. For sufficiently fast heat release and low ignition temperature, the front roughness [defined as the root mean square deviation of the ignition temperature contour from the average flame position] grew following a power-law dependence that was in excellent agreement with the Kardar-Parisi-Zhang (KPZ) universality class (β =1 /3 ). As the reaction time was increased, lower values of the roughening exponent were observed, and at a sufficiently great value of reaction time, reversion to a steady, constant-width thermal flame was observed that matched the solution from classical combustion theory. Deviation away from KPZ scaling was also observed as the ignition temperature was increased. The features of this system that permit it to exhibit both KPZ and non-KPZ scaling are discussed.

  16. Numerical modelling of ion transport in flames

    KAUST Repository

    Han, Jie

    2015-10-20

    This paper presents a modelling framework to compute the diffusivity and mobility of ions in flames. The (n, 6, 4) interaction potential is adopted to model collisions between neutral and charged species. All required parameters in the potential are related to the polarizability of the species pair via semi-empirical formulas, which are derived using the most recently published data or best estimates. The resulting framework permits computation of the transport coefficients of any ion found in a hydrocarbon flame. The accuracy of the proposed method is evaluated by comparing its predictions with experimental data on the mobility of selected ions in single-component neutral gases. Based on this analysis, the value of a model constant available in the literature is modified in order to improve the model\\'s predictions. The newly determined ion transport coefficients are used as part of a previously developed numerical approach to compute the distribution of charged species in a freely propagating premixed lean CH4/O2 flame. Since a significant scatter of polarizability data exists in the literature, the effects of changes in polarizability on ion transport properties and the spatial distribution of ions in flames are explored. Our analysis shows that changes in polarizability propagate with decreasing effect from binary transport coefficients to species number densities. We conclude that the chosen polarizability value has a limited effect on the ion distribution in freely propagating flames. We expect that the modelling framework proposed here will benefit future efforts in modelling the effect of external voltages on flames. Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/13647830.2015.1090018. © 2015 Taylor & Francis.

  17. Small GTPase Rab40c associates with lipid droplets and modulates the biogenesis of lipid droplets.

    Directory of Open Access Journals (Sweden)

    Ran Tan

    Full Text Available The subcellular location and cell biological function of small GTPase Rab40c in mammalian cells have not been investigated in detail. In this study, we demonstrated that the exogenously expressed GFP-Rab40c associates with lipid droplets marked by neutral lipid specific dye Oil red or Nile red, but not with the Golgi or endosomal markers. Further examination demonstrated that Rab40c is also associated with ERGIC-53 containing structures, especially under the serum starvation condition. Rab40c is increasingly recruited to the surface of lipid droplets during lipid droplets formation and maturation in HepG2 cells. Rab40c knockdown moderately decreases the size of lipid droplets, suggesting that Rab40c is involved in the biogenesis of lipid droplets. Stimulation for adipocyte differentiation increases the expression of Rab40c in 3T3-L1 cells. Rab40c interacts with TIP47, and is appositionally associated with TIP47-labeled lipid droplets. In addition, over-expression of Rab40c causes the clustering of lipid droplets independent of its GTPase activity, but completely dependent of the intact SOCS box domain of Rab40c. In addition, Rab40c displayed self-interaction as well as interaction with TIP47 and the SOCS box is essential for its ability to induce clustering of lipid droplets. Our results suggest that Rab40c is a novel Rab protein associated with lipid droplets, and is likely involved in modulating the biogenesis of lipid droplets.

  18. Ethanol : separating fact from fiction

    Science.gov (United States)

    1999-08-01

    This fact sheet presents documented information that dispels some of the myths that people have developed about ethanol. Once the facts are revealed, it becomes clear that using and producing ethanol for transportation is good for the country's econo...

  19. Pdf prediction of supersonic hydrogen flames

    Science.gov (United States)

    Eifler, P.; Kollmann, W.

    1993-01-01

    A hybrid method for the prediction of supersonic turbulent flows with combustion is developed consisting of a second order closure for the velocity field and a multi-scalar pdf method for the local thermodynamic state. It is shown that for non-premixed flames and chemical equilibrium mixture fraction, the logarithm of the (dimensionless) density, internal energy per unit mass and the divergence of the velocity have several advantages over other sets of scalars. The closure model is applied to a supersonic non-premixed flame burning hydrogen with air supplied by a supersonic coflow and the results are compared with a limited set of experimental data.

  20. Computatonal and experimental study of laminar flames

    Energy Technology Data Exchange (ETDEWEB)

    Smooke, M.D.; Long, M.B. [Yale Univ., New Haven, CT (United States)

    1993-12-01

    This research has centered on an investigation of the effects of complex chemistry and detailed transport on the structure and extinction of hydrocarbon flames in counterflow, cylindrical and coflowing axisymmetric configurations. The authors have pursued both computational and experimental aspects of the research in parallel. The computational work has focused on the application of accurate and efficient numerical methods for the solution of the one and two-dimensional nonlinear boundary value problems describing the various reacting systems. Detailed experimental measurements were performed on axisymmetric coflow flames using two-dimensional imaging techniques. In particular, spontaneous Raman scattering and laser induced fluorescence were used to measure the temperature, major and minor species profiles.

  1. Brominated flame retardants: occurrence, dietary intake and risk assessment

    NARCIS (Netherlands)

    Winter-Sorkina R de; Bakker MI; Wolterink G; Zeijlmaker MJ; SIR

    2006-01-01

    Brominated flame retardants have entered the human food chain. For the time being the occurrence of these chemicals in Dutch food does not pose a human health risk. However, this might easily change at increasing contents of flame retardants in Dutch food. The monitoring of brominated flame

  2. Phosphorus flame retardants: Properties, production, environmental occurrence, toxicity and analysis

    NARCIS (Netherlands)

    van der Veen, I.; de Boer, J.

    2012-01-01

    Since the ban on some brominated flame retardants (BFRs), phosphorus flame retardants (PFRs), which were responsible for 20% of the flame retardant (FR) consumption in 2006 in Europe, are often proposed as alternatives for BFRs. PFRs can be divided in three main groups, inorganic, organic and

  3. 30 CFR 75.600-1 - Approved cables; flame resistance.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Approved cables; flame resistance. 75.600-1 Section 75.600-1 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE... cables; flame resistance. Cables shall be accepted or approved by MSHA as flame resistant. ...

  4. Single Mobile Micro Droplet-Particle Pairs Spatially Captured by Macro Host Droplets on a Superhydrophobic Surface

    Directory of Open Access Journals (Sweden)

    Gregory S. Watson

    2015-01-01

    Full Text Available In this preliminary study, we demonstrate how small single water droplets can be spatially captured on the surface of individual micron sized hydrophobic coated particles (C18 which adhere to the surface of a nonmobile larger host water droplet resting on a superhydrophobic surface. The formation of the larger droplet, particle adhesion to that droplet, and smaller droplet formation on the particle all take place spontaneously from condensation conditions. These micro droplet-particle pairs are confined to the surface (liquid-air interface of the larger host droplet; however, they are free to engage with external forces to promote mobility. This response may find applications for particle pair transport on liquid surfaces. We also demonstrate that droplets can be captured or removed from the larger droplet surface via a self-propulsion mechanism.

  5. 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.

  6. An evaporation model of colloidal suspension droplets

    Science.gov (United States)

    Sartori, Silvana; Li\\ Nán, Amable; Lasheras, Juan C.

    2009-11-01

    Colloidal suspensions of polymers in water or other solvents are widely used in the pharmaceutical industry to coat tablets with different agents. These allow controlling the rate at which the drug is delivered, taste or physical appearance. The coating is performed by simultaneously spraying and drying the tablets with the colloidal suspension at moderately high temperatures. The spreading of the coating on the pills surface depends on the droplet Webber and Reynolds numbers, angle of impact, but more importantly on the rheological properties of the drop. We present a model for the evaporation of a colloidal suspension droplet in a hot air environment with temperatures substantially lower than the boiling temperature of the carrier fluid. As the liquid vaporizes from the surface, a compacting front advances into the droplet faster than the liquid surface regresses, forming a shell of a porous medium where the particles reach their maximum packing density. While the surface regresses, the evaporation rate is determined by both the rate at which heat is transported to the droplet surface and the rate at which liquid vapor is diffused away from it. This regime continues until the compacting front reaches the center of the droplet, at which point the evaporation rate is drastically reduced.

  7. Bead mediated separation of microparticles in droplets.

    Directory of Open Access Journals (Sweden)

    Sida Wang

    Full Text Available Exchange of components such as particles and cells in droplets is important and highly desired in droplet microfluidic assays, and many current technologies use electrical or magnetic fields to accomplish this process. Bead-based microfluidic techniques offer an alternative approach that uses the bead's solid surface to immobilize targets like particles or biological material. In this paper, we demonstrate a bead-based technique for exchanging droplet content by separating fluorescent microparticles in a microfluidic device. The device uses posts to filter surface-functionalized beads from a droplet and re-capture the filtered beads in a new droplet. With post spacing of 7 μm, beads above 10 μm had 100% capture efficiency. We demonstrate the efficacy of this system using targeted particles that bind onto the functionalized beads and are, therefore, transferred from one solution to another in the device. Binding capacity tests performed in the bulk phase showed an average binding capacity of 5 particles to each bead. The microfluidic device successfully separated the targeted particles from the non-targeted particles with up to 98% purity and 100% yield.

  8. Droplet coalescence on water repellant surfaces.

    Science.gov (United States)

    Nam, Youngsuk; Seo, Donghyun; Lee, Choongyeop; Shin, Seungwon

    2015-01-07

    We report our hydrodynamic and energy analyses of droplet coalescence on water repellent surfaces including hydrophobic, superhydrophobic and oil-infused superhydrophobic surfaces. The receding contact angle has significant effects on the contact line dynamics since the contact line dissipation was more significant during the receding mode than advancing. The contact line dynamics is modeled by the damped harmonic oscillation equation, which shows that the damping ratio and angular frequency of merged droplets decrease as the receding contact angle increases. The fast contact line relaxation and the resulting decrease in base area during coalescence were crucial to enhance the mobility of coalescing sessile droplets by releasing more surface energy with reducing dissipation loss. The superhydrophobic surface converts ∼42% of the released surface energy to the kinetic energy via coalescence before the merged droplet jumps away from the surface, while oil-infused superhydrophobic and hydrophobic surfaces convert ∼30% and ∼22%, respectively, for the corresponding time. This work clarifies the mechanisms of the contact line relaxation and energy conversion during the droplet coalescence on water repellent surfaces, and helps develop water repellent condensers.

  9. Modeling the coalescence of sessile droplets

    Science.gov (United States)

    Sellier, M.; Trelluyer, E.

    2009-01-01

    This paper proposes a simple scenario to describe the coalescence of sessile droplets. This scenario predicts a power-law growth of the bridge between the droplets. The exponent of this power law depends on the driving mechanism for the spreading of each droplet. To validate this simple idea, the coalescence is simulated numerically and a basic experiment is performed. The fluid dynamics problem is formulated in the lubrication approximation framework and the governing equations are solved in the commercial finite element software COMSOL. Although a direct comparison of the numerical results with experiment is difficult because of the sensitivity of the coalescence to the initial and operating conditions, the key features of the event are qualitatively captured by the simulation and the characteristic time scale of the dynamics recovered. The experiment consists of inducing coalescence by pumping a droplet through a substrate which grows and ultimately coalesces with another droplet resting on the substrate. The coalescence was recorded using high-speed imaging and also confirmed the power-law growth of the neck. PMID:19693347

  10. Arrested coalescence of viscoelastic droplets: polydisperse doublets.

    Science.gov (United States)

    Dahiya, Prerna; Caggioni, Marco; Spicer, Patrick T

    2016-07-28

    Arrested droplet coalescence produces stable anisotropic shapes and is a key mechanism for microstructure development in foods, petroleum and pharmaceutical formulations. Past work has examined the dynamic elastic arrest of coalescing monodisperse droplet doublets and developed a simple model of doublet strain as a function of physical variables. Although the work describes experimental data well, it is limited to describing same-size droplets. A new model incorporating a generalized description of doublet shape is developed to describe polydisperse doublet formation in more realistic emulsion systems. Polydisperse doublets are shown to arrest at lower strains than monodisperse doublets as a result of the smaller contribution of surface area in a given pair. Larger droplet size ratios have lower relative degrees of strain because coalescence is arrested at an earlier stage than in more monodisperse cases. Experimental observations of polydisperse doublet formation indicate that the model under-predicts arrest strains at low solid levels and small droplet sizes. The discrepancy is hypothesized to be the result of nonlinear elastic deformation at high strains.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. © 2016 The Author(s).

  11. Simulating droplet motion on virtual leaf surfaces.

    Science.gov (United States)

    Mayo, Lisa C; McCue, Scott W; Moroney, Timothy J; Forster, W Alison; Kempthorne, Daryl M; Belward, John A; Turner, Ian W

    2015-05-01

    A curvilinear thin film model is used to simulate the motion of droplets on a virtual leaf surface, with a view to better understand the retention of agricultural sprays on plants. The governing model, adapted from Roy et al. (2002 J. Fluid Mech. 454, 235-261 (doi:10.1017/S0022112001007133)) with the addition of a disjoining pressure term, describes the gravity- and curvature-driven flow of a small droplet on a complex substrate: a cotton leaf reconstructed from digitized scan data. Coalescence is the key mechanism behind spray coating of foliage, and our simulations demonstrate that various experimentally observed coalescence behaviours can be reproduced qualitatively. By varying the contact angle over the domain, we also demonstrate that the presence of a chemical defect can act as an obstacle to the droplet's path, causing break-up. In simulations on the virtual leaf, it is found that the movement of a typical spray size droplet is driven almost exclusively by substrate curvature gradients. It is not until droplet mass is sufficiently increased via coalescence that gravity becomes the dominating force.

  12. Jumping Mechanism of Self-Propelled Droplet

    Science.gov (United States)

    Lian, Yongsheng; Chen, Yan

    2017-11-01

    The self-propelled behavior of coalesced droplets can be utilized to enhance heat transfer performance of dropwise condensation. It has been recognized that the droplet self-propelling is the combined result of the conversion of surface energy to kinetic energy and the unsymmetrical boundary conditions imposed on the droplets. However, the roles of boundary conditions, which largely determine the conversion ratio of surface energy to the effective jumping kinetic energy, are not well understood. In this paper we use a numerical approach to investigate the boundary condition effect on the self-propelling behavior. A Navier-Stokes equation solver for multiphase flows is used to describe the flow field. The moment of fluid interface reconstruction technique is applied to resolute the interfaces. A direction splitting method is applied to advect the interface. And an approximate projection method is used to decouple the calculation of velocity and pressure. Comparisons are made with experimental results and show the simulation can accurately capture self-propelling behavior. Our simulation show the vertical flow velocity inside the coalesced droplet can increase the normalized jumping velocity but the contact area between droplets and substrate can decrease jumping velocity. High viscous dissipation is observed at the beginning of the coalescence which reduces jumping velocity.

  13. Mathematical Modeling of an Oscillating Droplet

    Science.gov (United States)

    Berry, S.; Hyers, R. W.; Racz, L. M.; Abedian, B.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    Oscillating droplets are of interest in a number of disciplines. A practical application is the oscillating drop method, which is a technique for measuring surface tension and viscosity of liquid metals. It is especially suited to undercooled and highly reactive metals, because it is performed by electromagnetic levitation. The natural oscillation frequency of the droplets is related to the surface tension of the material, and the decay of oscillations is related to its viscosity. The fluid flow inside the droplet must be laminar in order for this technique to yield good results. Because no experimental method has yet been developed to visualize flow in electromagnetically-levitated oscillating metal droplets, mathematical modeling is required to determine whether or not turbulence occurs. Three mathematical models of the flow: (1) assuming laminar conditions, (2) using the k-epsilon turbulence model, and (3) using the RNG turbulence model, respectively, are compared and contrasted to determine the physical characteristics of the flow. It is concluded that the RNG model is the best suited for describing this problem. The goal of the presented work was to characterize internal flow in an oscillating droplet of liquid metal, and to verify the accuracy of the characterization by comparing calculated surface tension and viscosity.

  14. MODEL OF LASER INTERACTION WITH LIQUID DROPLET

    Directory of Open Access Journals (Sweden)

    K. N. Volkov,

    2016-09-01

    Full Text Available Subject of Research. A mathematical model of optical breakdown in the dielectric liquid droplets when exposed to pulsed laser radiation was developed. The process is considered in several stages: heating, evaporation of the particle, forming a steam halo, ionization of the steam halo. Numerical study was carried out on the basis of the mathematical model to determine the threshold characteristics of the laser pulse. Main Results.Distributions of pressure, density and temperature of the particle steam halo were obtained by means of a calculation. The temperature field around the liquid droplet was determined. It has been found that at high energies in the gas bubble, the conditions are provided for thermal gas ionization and start of the electron avalanche, leading to plasma formation. Due to the volumetric heat generation, the droplet is overheated and is in a metastable state. The plasma cloud is almost opaque to radiation that causes an abrupt increase of temperature. As a result, an explosion occurs inside the droplet with the formation of a shock wave that is propagating outward. Practical Relevance.The results can be used to assess the performance of high-power laser scanning (LIDAR under the presence of liquid droplets in the atmosphere and other suspensions. Lasers can be used in fire and explosion aerospace systems. Obtained findings can be applied also in the systems of laser ignition and detonation initiation.

  15. Bioeffects due to acoustic droplet vaporization

    Science.gov (United States)

    Bull, Joseph

    2015-11-01

    Encapsulated micro- and nano-droplets can be vaporized via ultrasound, a process termed acoustic droplet vaporization. Our interest 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 microdroplets. Additionally, the microdroplets 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. Early timescale vaporization events, including phase change, are directly visualized using ultra-high speed imaging, and the influence of acoustic parameters on droplet/bubble dynamics is discussed. Acoustic and fluid mechanics parameters affecting the severity of endothelial cell bioeffects are explored. These findings suggest parameter spaces for which bioeffects may be reduced or enhanced, depending on the objective of the therapy. This work was supported by NIH grant R01EB006476.

  16. New mechanisms of macroion-induced disintegration of charged droplets

    Science.gov (United States)

    Consta, Styliani; Oh, Myong In; Malevanets, Anatoly

    2016-10-01

    Molecular modeling has revealed that the presence of charged macromolecules (macroions) in liquid droplets dramatically changes the pathways of droplet fission. These mechanisms are not captured by the traditional theories such as ion-evaporation and charge-residue models. We review the general mechanisms by which macroions emerge from droplets and the factors that determine the droplet fission. These mechanisms include counter-intuitive ;star; droplet formations and extrusion of linear macroions from droplets. These findings may play a direct role in determining macromolecule charge states in electrospray mass spectrometry experiments.

  17. 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 were...... conveyed to the posterior surface and released to the aqueous solution. Thus the persistent movement becomes possible in this chemical system, because the processing of chemical energy to mechanical movement proceeds by consuming exogenous fuel, not consuming the oil droplet itself. The mechanism...... of the unidirectional motion is hypothesized in terms of an asymmetric interfacial tension around the surface of the oil droplet....

  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. Fabrication of disk droplets and evaluation of their lasing action.

    Science.gov (United States)

    Saito, Mitsunori; Hashimoto, Takuya; Taniguchi, Jumpei

    2017-10-15

    Disk resonators are difficult to create with droplets, since they self-form spheres due to the surface tension. In this study, disk (cylindrical) droplets were created by enclosing a dye (rhodamine 6G) solution in silicone rubber. Lasing actions of these droplets were examined by pulsed green laser excitation. In a large droplet (2 mm diameter), the whispering gallery mode emission was difficult to attain, since it competed with the radial or axial modes that made a round trip in the droplet. A disk droplet of 150 μm diameter exhibited a comb-like spectrum of the whispering gallery mode resonant emission.

  20. Dynamics of surface tension driven mixing of an alcohol droplet with water

    Science.gov (United States)

    Dandekar, Raj; Pant, Anurag; Puthenveettil, Baburaj

    2016-11-01

    We study the flow induced by the surface tension driven spreading of an ethanol droplet of radius rd on the surface of a 5mm water layer, visualizing the flow using aluminium flakes on the surface of the water layer with backlighting and high speed imaging. The concentration of tracer aluminium particles was found to have no effect on the scaling law for spreading.The drop,when brought in contact with the water surface causes a local depression in surface tension ,resulting in a thin circular region to expand radially outwards.We observe that the dimensionless radius of the expanding front (r* =r/rd) scales with the dimensionless time (t* = μ rd/ Δγ) , as r* t*1/4,where μ is the viscosity of water and Δγ is the surface tension difference between water and the ethanol droplet.A scaling analysis taking the viscous and the marangoni forces into account explains the observed scaling law.Our observations differ from that in the case of continuous alcohol supply where the observed scaling law is r* t*1/2. The expanding front radius reaches a maximum value and then decreases with time.

  1. The genetic relationships between ethanol preference, acute ethanol sensitivity, and ethanol tolerance in Drosophila melanogaster

    National Research Council Canada - National Science Library

    Devineni, Anita V; McClure, Kimberly; Guarnieri, Douglas; Corl, Ammon; Wolf, Frederick; Eddison, Mark; Heberlein, Ulrike

    2011-01-01

    .... However, many conflicting results have been observed. To complement these studies, we utilized a different organism and approach to analyze the relationship between ethanol consumption and other ethanol responses...

  2. Coloring Rate of Phenolphthalein by Reaction with Alkaline Solution Observed by Liquid-Droplet Collision.

    Science.gov (United States)

    Takano, Yuuka; Kikkawa, Shigenori; Suzuki, Tomoko; Kohno, Jun-ya

    2015-06-11

    Many important chemical reactions are induced by mixing two solutions. This paper presents a new way to measure rates of rapid chemical reactions induced by mixing two reactant solutions using a liquid-droplet collision. The coloring reaction of phenolphthalein (H2PP) by a reaction with NaOH is investigated kinetically. Liquid droplets of H2PP/ethanol and NaOH/H2O solutions are made to collide, which induces a reaction that transforms H2PP into a deprotonated form (PP(2-)). The concentration of PP(2-) is evaluated from the RGB values of pixels in the colored droplet images, and is measured as a function of the elapsed time from the collision. The obtained rate constant is (2.2 ± 0.7) × 10(3) M(-1) s(-1), which is the rate constant for the rate-determining step of the coloring reaction of H2PP. This method was shown to be applicable to determine rate constants of rapid chemical reactions between two solutions.

  3. Spectral characteristics of the radiation of artificial opal crystals in the presence of the photonic flame effect

    Science.gov (United States)

    Gorelik, V. S.; Kudryavtseva, A. D.; Tareeva, M. V.; Tcherniega, N. V.

    2007-01-01

    The results of investigation of the spectral characteristics of radiation in the presence of the photonic flame effect recently discovered experimentally are presented. Radiation from a ruby laser operating in the Q-factor modulation regime with a generation wavelength of 694.3 nm is focused near the oriented surface of a globular photon crystal (artificial opal with a globule size of 230 nm) placed on a copper cold guide whose temperature is close to the liquid-nitrogen boiling point (77 K). The spectrum of long-term afterglow (with a duration of about several seconds when the duration of a pump pulse is equal to 20 ns) appearing in the photonic flame effect is detected using a fiber optic minispectrometer and consists of several comparatively narrow lines whose intensity strongly varies with the pumping power. A similar glow is observed in opal samples filled with acetone or ethanol.

  4. Sorghum to Ethanol Research

    Energy Technology Data Exchange (ETDEWEB)

    Dahlberg, Jeffrey A. [Univ. of California, Parlier, CA (United States). Kearney Research and Extension Center; Wolfrum, Edward J. [National Renewable Energy Lab. (NREL), Golden, CO (United States). Process and Analytical Engineering Group

    2010-09-28

    The development of a robust source of renewable transportation fuel will require a large amount of biomass feedstocks. It is generally accepted that in addition to agricultural and forestry residues, we will need crops grown specifically for subsequent conversion into fuels. There has been a lot of research on several of these so-called "dedicated bioenergy crops" including switchgrass, miscanthus, sugarcane, and poplar. It is likely that all of these crops will end up playing a role as feedstocks, depending on local environmental and market conditions. Many different types of sorghum have been grown to produce syrup, grain, and animal feed for many years. It has several features that may make it as compelling as other crops mentioned above as a renewable, sustainable biomass feedstock; however, very little work has been done to investigate sorghum as a dedicated bioenergy crop. The goal of this project was to investigate the feasibility of using sorghum biomass to produce ethanol. The work performed included a detailed examination of the agronomics and composition of a large number of sorghum varieties, laboratory experiments to convert sorghum to ethanol, and economic and life-cycle analyses of the sorghum-to-ethanol process. This work showed that sorghum has a very wide range of composition, which depended on the specific sorghum cultivar as well as the growing conditions. The results of laboratory- and pilot-scale experiments indicated that a typical high-biomass sorghum variety performed very similarly to corn stover during the multi-step process required to convert biomass feedstocks to ethanol; yields of ethanol for sorghum were very similar to the corn stover used as a control in these experiments. Based on multi-year agronomic data and theoretical ethanol production, sorghum can achieve more than 1,300 gallons of ethanol per acre given the correct genetics and environment. In summary, sorghum may be a compelling dedicated bioenergy crop that could help

  5. Effect of confinement on droplet coalescence in shear flow.

    Science.gov (United States)

    Chen, Dongju; Cardinaels, Ruth; Moldenaers, Paula

    2009-11-17

    The effect of confinement on the coalescence of Newtonian (polydimethylsiloxane) droplets in a Newtonian (polyisobutylene) matrix is investigated experimentally. A counter rotating parallel plate device, equipped with a microscopy setup, is used to visualize two interacting droplets during shear flow. The ratio of droplet-to-matrix viscosity is kept constant at 1.1. Droplet collisions are studied for a range of droplet sizes, both in bulk conditions and for gap spacings that are comparable to the droplet size. As a result, we present the first quantitative experimental data set for the coalescence of two equal-sized droplets in a pure shear flow with varying degrees of confinement. Compared to bulk conditions, for droplets smaller than roughly 0.2 times the gap spacing, a slight degree of confinement only decreases the orientation angle at which the droplets coalesce whereas the critical conditions for coalescence remain unaltered. For more confined conditions, the critical capillary number up to which coalescence can occur, increases. Therefore, confinement clearly promotes coalescence. In addition, the droplet trajectories, the time-dependent orientation angle of the droplet pair, and the droplet deformation prior to the coalescence event are systematically studied, and a comparison between the confined and the unconfined situation is provided. It is shown that the presence of two parallel walls can induce changes in the flow field around the droplet pair, which cause an increase of the interaction time between the droplets. Moreover, for sufficiently confined droplets, the additional force originating from the presence of the walls becomes comparable to the hydrodynamic force on the droplet pair, thus influencing the drainage of the matrix film between the droplet surfaces.

  6. Physics of puffing and microexplosion of emulsion fuel droplets

    Science.gov (United States)

    Shinjo, J.; Xia, J.; Ganippa, L. C.; Megaritis, A.

    2014-10-01

    The physics of water-in-oil emulsion droplet microexplosion/puffing has been investigated using high-fidelity interface-capturing simulation. Varying the dispersed-phase (water) sub-droplet size/location and the initiation location of explosive boiling (bubble formation), the droplet breakup processes have been well revealed. The bubble growth leads to local and partial breakup of the parent oil droplet, i.e., puffing. The water sub-droplet size and location determine the after-puffing dynamics. The boiling surface of the water sub-droplet is unstable and evolves further. Finally, the sub-droplet is wrapped by boiled water vapor and detaches itself from the parent oil droplet. When the water sub-droplet is small, the detachment is quick, and the oil droplet breakup is limited. When it is large and initially located toward the parent droplet center, the droplet breakup is more extensive. For microexplosion triggered by the simultaneous growth of multiple separate bubbles, each explosion is local and independent initially, but their mutual interactions occur at a later stage. The degree of breakup can be larger due to interactions among multiple explosions. These findings suggest that controlling microexplosion/puffing is possible in a fuel spray, if the emulsion-fuel blend and the ambient flow conditions such as heating are properly designed. The current study also gives us an insight into modeling the puffing and microexplosion of emulsion droplets and sprays.

  7. Arrested coalescence of viscoelastic droplets: triplet shape and restructuring

    Science.gov (United States)

    Dahiya, Prerna; DeBenedictis, Andrew; Atherton, Timothy J.; Caggioni, Marco; Prescott, Stuart W.; Hartel, Richard W.; Spicer, Patrick T.

    The stability of shapes formed by three viscoelastic droplets during their arrested coalescence has been investigated using micromanipulation experiments. Addition of a third droplet to arrested droplet doublets is shown to be controlled by the balance between interfacial pressures driving coalescence and internal elasticity that resists total consolidation. The free fluid available within the droplets controls the transmission of stress during droplet combination and allows connections to occur via formation of a neck between the droplets. The anisotropy of three-droplet systems adds complexity to the symmetric case of two-droplet aggregates because of the multiplicity of orientations possible for the third droplet. When elasticity dominates, the initial orientation of the third droplet is preserved in the triplet's final shape. When elasticity is dominated by the interfacial driving force, the final shape can deviate strongly from the initial positioning of droplets. Movement of the third droplet to a more compact packing occurs, driven by liquid meniscus expansion that minimizes the surface energy of the triplet. A range of compositions and orientations are examined and the resulting domains of restructuring and stability are mapped based on the final triplet structure. A geometric and a physical model are used to explain the mechanism driving meniscus-induced restructuring and are related to the impact of these phenomena on multiple droplet emulsions.

  8. Combustion of emulsified fuel droplets under microgravity

    Science.gov (United States)

    Okajima, S.; Kanno, H.; Kumagai, S.

    Single-droplet experiments have been conducted under a zero-gravity condition in a freely falling chamber as a fundamental step of study on the spray combustion of hydrocarbon-water emulsified fuels. Such a behavior as the secondary micro-atomization was observed by taking schlieren photographs with a 35-mm movie camera installed on the falling assembly. Under zero gravity the emulsion droplet initiates steam discharge and puffing—that is, a mild atomization—at a time from ignition, but it does not lead to such a micro-explosion or disruption as is experienced under normal gravity. The apparent burning rate constant under zero gravity is about 30% smaller than that under normal gravity. These facts suggest that the internal convection in emulsion droplets plays an important role in causing the micro-explosion.

  9. Edge effects on water droplet condensation.

    Science.gov (United States)

    Medici, Marie-Gabrielle; Mongruel, Anne; Royon, Laurent; Beysens, Daniel

    2014-12-01

    In this study we investigate the effect of geometrical or thermal discontinuities on the growth of water droplets condensing on a cooled substrate. Edges, corners, and cooled and noncooled boundaries can have a strong effect on the vapor concentration profile and mass diffusion around the drops. In comparison to growth in a pattern where droplets have to compete to catch vapor, which results in a linear water concentration profile directed perpendicularly to the substrate, droplets near discontinuities can get more vapor (outer edges, corners), resulting in faster growth or less vapor (inner edges), giving lower growth. When the cooling heat flux limits growth instead of mass diffusion (substrate with low thermal conductivity, strong heat exchange with air), edge effects can be canceled. In certain cases, growth enhancement can reach nearly 500% on edges or corners.

  10. 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

  11. A study of oil droplet coalescence.

    Science.gov (United States)

    Boyson, T K; Pashley, R M

    2007-12-01

    Oil droplets dispersed in water can be readily studied when they are coated with surfactants, which lower their interfacial tension and enhance their stability. Pure oil droplets are more difficult to study because of their high interfacial tension, which facilitates coalescence and the adsorption of contaminants. In this study, we have characterised the surface charging properties of a water insoluble oil, bromododecane, which has a density close to water. The small density difference allows us to study relatively large drops of this oil and to analyse its coalescence behaviour. The results obtained with this simple, surfactant-free, system suggest that an additional attractive force, such as the long range hydrophobic interaction, might be required to explain oil droplet coalescence behaviour.

  12. Droplet Manipulations in Two Phase Flow Microfluidics

    Directory of Open Access Journals (Sweden)

    Arjen M. Pit

    2015-11-01

    Full Text Available Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of the emergence of new techniques, whose potential has not been fully realized. This review summarizes the currently existing techniques for manipulating droplets in two-phase flow microfluidics. Specifically, very recent developments like the use of acoustic waves, magnetic fields, surface energy wells, and electrostatic traps and rails are discussed. The physical principles are explained, and (potential advantages and drawbacks of different methods in the sense of versatility, flexibility, tunability and durability are discussed, where possible, per technique and per droplet operation: generation, transport, sorting, coalescence and splitting.

  13. Gel-like double-emulsion droplets

    Science.gov (United States)

    Guzowski, Jan; Korczyk, Piotr; Garstecki, Piotr; Stone, Howard

    2015-11-01

    We experimentally study the problem of packing of micro-droplets inside a droplet of another immiscible liquid phase. We use microfluidics to encapsulate multiple monodisperse aqueous segments inside a drop of oil. For small numbers N (Nencapsulating phase are comparable, the energy barriers are high enough to trap elongated structures or even linear chains, independently of N. However, when the surface tension of the encapsulating phase is much larger than that of the droplets, non-spherical morphologies are stable only at sufficiently high N. In such a case multiple internal interfaces can hold stresses and prevent relaxation of the global deformations which leads to a plastic, gel-like behavior. Our findings can serve as guidelines for synthesis of functional particles as well as for designing biomimetic materials, e.g. for tissue engineering. J.G. acknowledges financial support from Polish Ministry of Science provided within the framework Mobility Plus.

  14. Radiative Structures of Lycopodium-Air Flames in Low Gravity

    Science.gov (United States)

    Berlad, A. L.; Tangirala, V.; Ross, H.; Facca, L.

    1989-01-01

    Initially uniform clouds of fuel particulates in air sustain processes which may lead to particle cloud nonuniformities. In low gravity, flame-induced Kundt's Tube phenomena are observed to form regular patterns of nonuniform particle concentrations. Irregular patterns of particle concentrations also are observed to result from selected nonuniform mixing processes. Low gravity flame propagation for each of these classes of particle cloud flames has been found to depend importantly on the flame-generated infrared radiative fields. The spatial structures of these radiative fields are described. Application is made for the observed clases of lycopodium-air flames.

  15. Ionic Mechanisms of Carbon Formation in Flames.

    Science.gov (United States)

    1983-01-01

    is that of Street and Thonas 1 1. These au- the burner temperature and burner and chimney thors used an apparatus in which a flow of heated dimensions...slitlctuies would overlap; It is classital mythology [hat prcmixed and dif. the molecules with greatest deviation from the fusion flames have different

  16. Radical recombinations in acetylene-air flames

    NARCIS (Netherlands)

    Zeegers, P.J.Th.; Alkemade, C.T.J.

    In this paper an analysis is given of the behaviour of excess radical concentrations, H, OH and O as a function of height above the reaction zone in premixed acetylene-air flames at 2–200° to 2400°K and 1 atmosphere pressure. The intensity was measured of the Li resonance line which is related to

  17. Numerical study of one swirling flame

    DEFF Research Database (Denmark)

    Yang, Yang; Kær, Søren Knudsen; Yin, Chungen

    This paper presents numerical study of one of Sydney swirl flames. Good agreements gained between numerical results and the experimental data. Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) methods show different flow patterns in isothermal and reacting case. The influence...

  18. Electro-tactic ionic liquid droplets

    OpenAIRE

    Francis, Wayne; Wagner, Klaudia; Beirne, Stephen; Officer, David; Wallace, Gordon; Florea, Larisa; Diamond, Dermot

    2015-01-01

    Here we report for the first time electro-guided, self-propelled droplets, which are composed solely of an ionic liquid (IL), namely trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These self-propelled droplets travel along an aqueous-air boundary and are guided to specific destinations within the fluidic network through the use of electro-chemically generated Cl- gradients. The direction of movement can be controlled by switching the impressed voltage (9V, ON or OFF) and polarity...

  19. Droplets bouncing on a standing wave field

    Science.gov (United States)

    Pucci, Giuseppe; Tambasco, Lucas; Harris, Daniel; Bush, John

    2017-11-01

    A liquid bath subject to a vertical vibration becomes unstable to standing surface waves at a critical vibrational acceleration known as the Faraday threshold. We examine the behavior of a millimetric droplet bouncing on the surface of a quasi-one-dimensional fluid channel above the Faraday threshold. We identify a sequence of bifurcations that occurs as the vibrational acceleration is increased progressively, ultimately leading to the erratic, diffusive motion of the droplet along the length of the channel. A simple theoretical model is presented. This work was supported by the US National Science Foundation through Grants CMMI-1333242 and DMS-1614043.

  20. Recent Advances in Applications of Droplet Microfluidics

    Directory of Open Access Journals (Sweden)

    Wei-Lung Chou

    2015-09-01

    Full Text Available Droplet-based microfluidics is a colloidal and interfacial system that has rapidly progressed in the past decade because of the advantages of low fabrication costs, small sample volumes, reduced analysis durations, high-throughput analysis with exceptional sensitivity, enhanced operational flexibility, and facile automation. This technology has emerged as a new tool for many recently used applications in molecular detection, imaging, drug delivery, diagnostics, cell biology and other fields. Herein, we review recent applications of droplet microfluidics proposed since 2013.

  1. Superpropulsion of Droplets and Soft Elastic Solids

    Science.gov (United States)

    Raufaste, Christophe; Chagas, Gabriela Ramos; Darmanin, Thierry; Claudet, Cyrille; Guittard, Frédéric; Celestini, Franck

    2017-09-01

    We investigate the behavior of droplets and soft elastic objects propelled with a catapult. Experiments show that the ejection velocity depends on both the projectile deformation and the catapult acceleration dynamics. With a subtle matching given by a peculiar value of the projectile/catapult frequency ratio, a 250% kinetic energy gain is obtained as compared to the propulsion of a rigid projectile with the same engine. This superpropulsion has strong potentialities: actuation of droplets, sorting of objects according to their elastic properties, and energy saving for propulsion engines.

  2. Flame speeds and curvature of premixed, spherically expanding flames advecting in a turbulent channel flow

    Science.gov (United States)

    Fries, Dan; Ochs, Bradley; Ranjan, Devesh; Menon, Suresh

    2016-11-01

    A new facility has been developed at the Georgia Institute of Technology to study sub- and supersonic combustion, which is based on classical flame bomb studies but incorporates a mean flow, allowing for a wider variety of turbulent conditions and the inclusion of effects like compressibility, while supporting shear-free spherical flames. Homogeneous, isotropic turbulence is generated via an active vane grid. Methane-air flame kernels advecting with the mean flow are generated using Laser Induced Breakdown ignition. The facility is accessing the thin reaction zone regime with uRMS' /SL0 = 6 . 9 - 22 , L11 /δF = 44 - 68 and Reλ = 190 - 550 . The flame kernels are probed with OH-Planar Laser Induced Fluorescence (PLIF). To validate the facility, results at Ū = 30 m/s are compared to existing data using a scaling derived from a spectral closure of the G-equation. This indicates the reacting flow remains Galilean invariant under the given conditions. The differences between global and local turbulent consumption speeds derived from OH-PLIF results are discussed with a focus on modeling efforts. The curvature of flame wrinkles is evaluated to examine the impact of different turbulent scales on flame development. This work was supported by the Air Force Office of Scientific Research under basic research Grant FA9550-15-1-0512 (Project monitor: Dr. Chiping Li).

  3. Flame exposure time on Langmuir probe degradation, ion density, and thermionic emission for flame temperature.

    Science.gov (United States)

    Doyle, S J; Salvador, P R; Xu, K G

    2017-11-01

    The paper examines the effect of exposure time of Langmuir probes in an atmospheric premixed methane-air flame. The effects of probe size and material composition on current measurements were investigated, with molybdenum and tungsten probe tips ranging in diameter from 0.0508 to 0.1651 mm. Repeated prolonged exposures to the flame, with five runs of 60 s, resulted in gradual probe degradations (-6% to -62% area loss) which affected the measurements. Due to long flame exposures, two ion saturation currents were observed, resulting in significantly different ion densities ranging from 1.16 × 1016 to 2.71 × 1019 m-3. The difference between the saturation currents is caused by thermionic emissions from the probe tip. As thermionic emission is temperature dependent, the flame temperature could thus be estimated from the change in current. The flame temperatures calculated from the difference in saturation currents (1734-1887 K) were compared to those from a conventional thermocouple (1580-1908 K). Temperature measurements obtained from tungsten probes placed in rich flames yielded the highest percent error (9.66%-18.70%) due to smaller emission current densities at lower temperatures. The molybdenum probe yielded an accurate temperature value with only 1.29% error. Molybdenum also demonstrated very low probe degradation in comparison to the tungsten probe tips (area reductions of 6% vs. 58%, respectively). The results also show that very little exposure time (probe tip.

  4. Analysis of Flame Extinguishment and Height in Low Frequency Acoustically Excited Methane Jet Diffusion Flame

    Science.gov (United States)

    Zong, Ruowen; Kang, Ruxue; Liu, Chen; Zhang, Zhiyang; Zhi, Youran

    2018-01-01

    The exploration of microgravity conditions in space is increasing and existing fire extinguishing technology is often inadequate for fire safety in this special environment. As a result, improving the efficiency of portable extinguishers is of growing importance. In this work, a visual study of the effects on methane jet diffusion flames by low frequency sound waves is conducted to assess the extinguishing ability of sound waves. With a small-scale sound wave extinguishing bench, the extinguishing ability of certain frequencies of sound waves are identified, and the response of the flame height is observed and analyzed. Results show that the flame structure changes with disturbance due to low frequency sound waves of 60-100 Hz, and quenches at effective frequencies in the range of 60-90 Hz. In this range, 60 Hz is considered to be the quick extinguishing frequency, while 70-90 Hz is the stable extinguishing frequency range. For a fixed frequency, the flame height decreases with sound pressure level (SPL). The flame height exhibits the greatest sensitivity to the 60 Hz acoustic waves, and the least to the 100 Hz acoustic waves. The flame height decreases almost identically with disturbance by 70-90 Hz acoustic waves.

  5. Analysis of Fuel Vaporization, Fuel-Air Mixing, and Combustion in Integrated Mixer-Flame Holders

    Science.gov (United States)

    Deur, J. M.; Cline, M. C.

    2004-01-01

    Requirements to limit pollutant emissions from the gas turbine engines for the future High-Speed Civil Transport (HSCT) have led to consideration of various low-emission combustor concepts. One such concept is the Integrated Mixer-Flame Holder (IMFH). This report describes a series of IMFH analyses performed with KIVA-II, a multi-dimensional CFD code for problems involving sprays, turbulence, and combustion. To meet the needs of this study, KIVA-II's boundary condition and chemistry treatments are modified. The study itself examines the relationships between fuel vaporization, fuel-air mixing, and combustion. Parameters being considered include: mixer tube diameter, mixer tube length, mixer tube geometry (converging-diverging versus straight walls), air inlet velocity, air inlet swirl angle, secondary air injection (dilution holes), fuel injection velocity, fuel injection angle, number of fuel injection ports, fuel spray cone angle, and fuel droplet size. Cases are run with and without combustion to examine the variations in fuel-air mixing and potential for flashback due to the above parameters. The degree of fuel-air mixing is judged by comparing average, minimum, and maximum fuel/air ratios at the exit of the mixer tube, while flame stability is monitored by following the location of the flame front as the solution progresses from ignition to steady state. Results indicate that fuel-air mixing can be enhanced by a variety of means, the best being a combination of air inlet swirl and a converging-diverging mixer tube geometry. With the IMFH configuration utilized in the present study, flashback becomes more common as the mixer tube diameter is increased and is instigated by disturbances associated with the dilution hole flow.

  6. 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

  7. Effects of Swirl on Strongly-Pulsed Turbulent Diffusion Flames

    Science.gov (United States)

    Liao, Y.-H.; Hermanson, J. C.

    2009-11-01

    The dynamics of large-scale structures in strongly-pulsed, swirling, turbulent jet diffusion flames were examined experimentally. The combustor used a combination of axial and tangentially-injected air to produce a range of swirl numbers. Gaseous ethylene fuel was injected through a 2 mm diameter nozzle on the combustor centerline with a jet-on Reynolds number of 5000. The flames were fully-modulated, with the fuel flow completely shut off between pulses. High-speed imaging of the flame luminosity was employed to examine the flame dimensions and the celerity of the large-scale flame structures. The flames were found to be approximately 15-20% shorter when swirl was imposed, depending on the injection time. The more compact flames in swirl appear to be due to the presence of recirculation inside the flames. For longer injection times, the celerity of the flame structures generally decreases as the swirl intensity increases. This is evidently due to the reversed velocity in the recirculation zone. For shorter injection times, the flame celerity has an increasing trend with increased swirl intensity due to flames being closer to the fuel nozzle at burnout.

  8. Kerosene wick lamp flame deformation in gradient magnetic fields

    Science.gov (United States)

    Saeedi, A.; Moghiman, M.

    2014-03-01

    The behavior of a kerosene wick lamp flame in the presence of non-uniform DC magnetic fields has been investigated and the results of this experimental study are presented. It has long been recognized that magnetic fields can influence the behavior of diffusion flames as a result of the paramagnetic and diamagnetic properties of the constituent gases. Using an electromagnet consisting of two coils and cores to generate a horizontal magnetic field, a non-uniform upward increasing and decreasing magnetic field was applied to a kerosene wick lamp flame. The experimental results show that the influence of DC gradient magnetic field on diffusion flame structure deformation depends on the flame position in the increasing or decreasing magnetic field, the flame situation relative to the maximum of the absolute value of the gradient and the quantity of the gradient magnetic field. It was also observed that both flame front area and flame height decrease in the positive and negative gradient field below the maximum of the absolute value of the gradient. Also, increasing the absolute of the gradient of the square magnetic induction in the positive and negative gradient field above the maximum of the absolute value of the gradient cause to elongate the flame and increase in the flame front area and then the flame height and front area decrease.

  9. Laser-saturated fluorescence measurements in laminar sooting diffusion flames

    Science.gov (United States)

    Wey, Changlie

    1993-01-01

    The hydroxyl radical is known to be one of the most important intermediate species in the combustion processes. The hydroxyl radical has also been considered a dominant oxidizer of soot particles in flames. In this investigation the hydroxyl concentration profiles in sooting diffusion flames were measured by the laser-saturated fluorescence (LSF) method. The temperature distributions in the flames were measured by the two-line LSF technique and by thermocouple. In the sooting region the OH fluorescence was too weak to make accurate temperature measurements. The hydroxyl fluorescence profiles for all four flames presented herein show that the OH fluorescence intensities peaked near the flame front. The OH fluorescence intensity dropped sharply toward the dark region of the flame and continued declining to the sooting region. The OH fluorescence profiles also indicate that the OH fluorescence decreased with increasing height in the flames for all flames investigated. Varying the oxidizer composition resulted in a corresponding variation in the maximum OH concentration and the flame temperature. Furthermore, it appears that the maximum OH concentration for each flame increased with increasing flame temperature.

  10. Combinatorial microfluidic droplet engineering for biomimetic material synthesis

    Science.gov (United States)

    Bawazer, Lukmaan A.; McNally, Ciara S.; Empson, Christopher J.; Marchant, William J.; Comyn, Tim P.; Niu, Xize; Cho, Soongwon; McPherson, Michael J.; Binks, Bernard P.; deMello, Andrew; Meldrum, Fiona C.

    2016-01-01

    Although droplet-based systems are used in a wide range of technologies, opportunities for systematically customizing their interface chemistries remain relatively unexplored. This article describes a new microfluidic strategy for rapidly tailoring emulsion droplet compositions and properties. The approach uses a simple platform for screening arrays of droplet-based microfluidic devices and couples this with combinatorial selection of the droplet compositions. Through the application of genetic algorithms over multiple screening rounds, droplets with target properties can be rapidly generated. The potential of this method is demonstrated by creating droplets with enhanced stability, where this is achieved by selecting carrier fluid chemistries that promote titanium dioxide formation at the droplet interfaces. The interface is a mixture of amorphous and crystalline phases, and the resulting composite droplets are biocompatible, supporting in vitro protein expression in their interiors. This general strategy will find widespread application in advancing emulsion properties for use in chemistry, biology, materials, and medicine. PMID:27730209

  11. The Evaporation of Liquid Droplets in Highly Turbulent Gas Streams

    National Research Council Canada - National Science Library

    Gould, Richard

    1998-01-01

    Single acetone and heptane droplets were suspended from a hypodermic needle in turbulent airflow, and the Nusselt number was obtained from direct measurements of the droplet diameter and evaporation rate...

  12. One-to-one encapsulation based on alternating droplet generation.

    Science.gov (United States)

    Hirama, Hirotada; Torii, Toru

    2015-10-21

    This paper reports the preparation of encapsulated particles as models of cells using an alternating droplet generation encapsulation method in which the number of particles in a droplet is controlled by a microchannel to achieve one-to-one encapsulation. Using a microchannel in which wettability is treated locally, the fluorescent particles used as models of cells were successfully encapsulated in uniform water-in-oil-in-water (W/O/W) emulsion droplets. Furthermore, 20% of the particle-containing droplets contained one particle. Additionally, when a surfactant with the appropriate properties was used, the fluorescent particles within each inner aqueous droplet were enclosed in the merged droplet by spontaneous droplet coalescence. This one-to-one encapsulation method based on alternating droplet generation could be used for a variety of applications, such as high-throughput single-cell assays, gene transfection into cells or one-to-one cell fusion.

  13. Non-equilibrium solidification of undercooled droplets during ...

    Indian Academy of Sciences (India)

    equilibrium solidification of ... A mathematical model, based on classical theory of heterogeneous nucleation and volume separation of nucleants among droplets size distribution, is described to predict undercooling of droplets. Newtonian heat flow ...

  14. Habitats for Shaped Droplets in the Origin of Life

    Science.gov (United States)

    Gordon, R.; Hanczyc, M. M.; Smoukov, S. K.

    2017-11-01

    Cooled oil droplets are flat and polygonal, like some Archaea and Bacteria. Shaped droplet protocells would constrain habitats for the origin of life to those where oil/water emulsions can form, remain, concentrate, and undergo temperature cycling.

  15. 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.

  16. Leading-Edge Velocities and Lifted Methane Jet Flame Stability

    Directory of Open Access Journals (Sweden)

    W. Wang

    2010-01-01

    Full Text Available Current interest exists in understanding reaction-zone dynamics and mechanisms with respect to how they counterpropagate against incoming reactants. Images of flame position and flow-field morphology are presented from flame chemiluminescence and particle image velocimetry (PIV measurements. In the present study, PIV experiments were carried out to measure the methane jet lifted-flame flow-field velocities in the vicinity of the flame leading edge. Specifically, velocity fields within the high-temperature zone were examined in detail, which complements previous studies, whose prime focus is the flow-field upstream of the high-temperature boundary. PIV data is used not only to determine the velocities, but, along with chemiluminescence images, to also indicate the approximate location of the reaction zone (further supported by/through the leading-edge flame velocity distributions. The velocity results indirectly support the concept that the flame is anchored primarily through the mechanism of partially premixed flame propagation.

  17. Drying of liquid food droplets : enzyme inactivation and multicomponent diffusion

    OpenAIRE

    Meerdink, G.

    1993-01-01

    In this thesis the drying of liquid food droplets is studied from three different points of view: drying kinetics, enzyme inactivation and multicomponent diffusion. Mathematical models are developed and validated experimentally.

    Drying experiments are performed with suspended droplets and with free falling droplets under spray-drying conditions. The experiments with the free falling droplets are performed in a specially designed drying tower using a resonance nozzle. The reso...

  18. Modelling of coughed droplets in a hospital ward

    DEFF Research Database (Denmark)

    Sadrizadeh, Sasan; Nielsen, Peter Vilhelm

    2016-01-01

    Coughing and its importance for spreading respiratory infectious diseases has been confirmed in many previous studies. The dispersion process of respiratory droplets released by the coughing of a patient in a hospital ward was studied using computational fluid dynamics simulation. Two relatively...... that the transport characteristic of droplets due to coughing is highly influenced by their size. Although the effects of gravity or inertia on small droplets (transport, droplets of > 40 μm are significantly affected by gravity and soon fall...

  19. Experimental and Numerical Investigation of Ethanol/Diethyl Ether Mixtures in a CI Engine

    KAUST Repository

    Sivasankaralingam, Vedharaj

    2016-10-17

    The auto-ignition characteristics of diethyl ether (DEE)/ethanol mixtures are investigated in compression ignition (CI) engines both numerically and experimentally. While DEE has a higher derived cetane number (DCN) of 139, ethanol exhibits poor ignition characteristics with a DCN of 8. DEE was used as an ignition promoter for the operation of ethanol in a CI engine. Mixtures of DEE and ethanol (DE), i.e., DE75 (75% DEE + 25% ethanol), DE50 (50% DEE + 50% ethanol) and DE25 (25% DEE + 75% ethanol), were tested in a CI engine. While DE75 and DE50 auto-ignited at an inlet air pressure of 1.5 bar, DE25 failed to auto-ignite even at boosted pressure of 2 bar. The peak in-cylinder pressure for diesel and DE75 were comparable, while DE50 showed reduced peak in-cylinder pressure with delayed start of combustion (SOC). Numerical simulations were conducted to study the engine combustion characteristics of DE mixture. A comprehensive detailed chemical kinetic model was created to represent the combustion of DE mixtures. The detailed mechanism was then reduced using standard direct relation graph (DRG-X) method and coupled with 3D CFD code, CONVERGE, to simulate the experimental data. The simulation results showed that the effects of physical properties on DE50 combustion are negligible. Simulations of DE50 mixture revealed that the combustion is nearly homogenous, while diesel (n-heptane used as a surrogate) and DE75 showed similar combustion behavior with flame liftoff and diffusion controlled combustion. Diesel exhibited auto-ignition at an equivalence ratio of 2, while DE75 and DE50 showed auto-ignition in the equivalence ratio range of 1-1.5 and 0-1, respectively. The experiments and numerical simulations demonstrate how the high reactivity of DEE supports the auto-ignition of ethanol, while ethanol acts as a radical scavenger.

  20. Determination of Ethanol in Kombucha Products: Single-Laboratory Validation, First Action 2016.12.

    Science.gov (United States)

    Ebersole, Blake; Liu, Ying; Schmidt, Rich; Eckert, Matt; Brown, Paula N

    2017-05-01

    Kombucha is a fermented nonalcoholic beverage that has drawn government attention due to the possible presence of excess ethanol (≥0.5% alcohol by volume; ABV). A validated method that provides better precision and accuracy for measuring ethanol levels in kombucha is urgently needed by the kombucha industry. The current study validated a method for determining ethanol content in commercial kombucha products. The ethanol content in kombucha was measured using headspace GC with flame ionization detection. An ethanol standard curve ranging from 0.05 to 5.09% ABV was used, with correlation coefficients greater than 99.9%. The method detection limit was 0.003% ABV and the LOQ was 0.01% ABV. The RSDr ranged from 1.62 to 2.21% and the Horwitz ratio ranged from 0.4 to 0.6. The average accuracy of the method was 98.2%. This method was validated following the guidelines for single-laboratory validation by AOAC INTERNATIONAL and meets the requirements set by AOAC SMPR 2016.001, "Standard Method Performance Requirements for Determination of Ethanol in Kombucha."

  1. Repressive effects of oat extracts on intracellular lipid-droplet formation in adipocytes and a three-dimensional subcutaneous adipose tissue model.

    Science.gov (United States)

    Kato, Shinya; Kato, Yuko; Shibata, Hiroki; Saitoh, Yasukazu; Miwa, Nobuhiko

    2015-04-01

    We assessed the repression of lipid-droplet formation in mouse mesenchymal stromal preadipocytes OP9 by specified oat extracts (Hatomugi, Coix lacryma-jobi var. ma-yuen) named "SPH" which were proteolytically and glucosyl-transferredly prepared from finely-milled oat whole-grain. Stimulation of OP9 preadipocytes with insulin-containing serum-replacement promoted differentiation to adipocytes, concurrently with an increase in the intracellular lipid droplets by 51.5%, which were repressed by SPH-bulk or SPH-water-extract at 840ppm, to 33.5% or 46.9%, respectively, but not by SPH-ethanol-extract at the same dose, showing the hydrophilic property of the anti-adipogenetic ingredients. The intracellular lipid droplets were scanty for intact preadipocytes, small-sized but abundant for the SPH-unadministered adipocytes, and large-sized but few for SPH-bulk-administered adipocytes being coexistent with many lipid-droplet-lacking viable cells, suggesting "the all-or-none rule" for lipid-droplet generation in cell-to-cell. Hydrogen-peroxide-induced cell death in human epidermal keratinocytes HaCaT was prevented by SPH-bulk at 100 or 150ppm by 5.6-8.1%, being consistent with higher viabilities of SPH-bulk-administered OP9 cells, together with repressions of both cell shrinkage and cell detachment from the culture substratum. In three-dimensional subcutaneous adipose tissue models reconstructed with HaCaT-keratinocytes and OP9-preadipocytes, lipid droplets were accumulated in dermal OP9-cell-parts, and repressed to 43.5% by SPH-bulk at 840ppm concurrently with marked diminishment of huge aggregates of lipid droplets. Thus SPH-bulk suppresses adipogenesis-associated lipid-droplet accumulation during differentiation of OP9 preadipocytes together with lowered cytotoxicity to either HaCaT keratinocytes or the preadipocytes. Copyright © 2015 Elsevier B.V. All rights reserved.

  2. Non-equilibrium solidification of undercooled droplets during ...

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Thermal history of droplets associated with gas atomization of melt has been investigated. A mathematical model, based on classical theory of heterogeneous nucleation and volume separation of nucleants among droplets size distribution, is described to predict undercooling of droplets. Newtonian heat flow.

  3. Understanding the Lipid Droplet Proteome and Protein Targeting.

    Science.gov (United States)

    Goodman, Joel M

    2018-01-08

    Reporting in this issue of Developmental Cell, Bersuker et al. (2018) adapt APEX technology to lipid droplets for a more accurate view of the droplet proteome and Prévost et al. (2018) provide important insights into the basis of droplet protein targeting that altogether extend the understanding of this organelle. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Chemically induced coalescence in droplet-based microfluidics.

    Science.gov (United States)

    Akartuna, Ilke; Aubrecht, Donald M; Kodger, Thomas E; Weitz, David A

    2015-02-21

    We present a new microfluidic method to coalesce pairs of surfactant-stabilized water-in-fluorocarbon oil droplets. We achieve this through the local addition of a poor solvent for the surfactant, perfluorobutanol, which induces cohesion between droplet interfaces causing them to merge. The efficiency of this technique is comparable to existing techniques providing an alternative method to coalesce pairs of droplets.

  5. Segregation in dissolving binary-component sessile droplets

    NARCIS (Netherlands)

    Dietrich, E.; Rump, M.; Lyu, Pengyu; Kooij, Ernst S.; Zandvliet, Henricus J.W.; Lohse, Detlef

    2017-01-01

    The dissolution of a single droplet, containing a mixture of oils, in water is experimentally studied. The oils in the droplet varied in terms of their solubility in water and their hydrophobicity. We demonstrate that the polarity of the droplet constituents strongly influences the dissolution

  6. 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

  7. Stick-Jump Mode in Surface Droplet Dissolution

    NARCIS (Netherlands)

    Dietrich, E.; Kooij, Ernst S.; Zhang, Xuehua; Zandvliet, Henricus J.W.; Lohse, Detlef

    2015-01-01

    The analogy between evaporating surface droplets in air to dissolving long-chain alcohol droplets in water is worked out. We show that next to the three known modi for surface droplet evaporation or dissolution (constant contact angle mode, constant contact radius mode, and stickslide mode), a

  8. Lattice Boltzmann simulations of droplet formation during microchannel emulsification

    NARCIS (Netherlands)

    Zwan, van der E.A.; Sman, van der R.G.M.; Schroën, C.G.P.H.; Boom, R.M.

    2009-01-01

    In this study, we compared microchannel droplet formation in a microfluidics device with a two phase lattice Boltzmann simulation. The droplet formation was found to be qualitatively described, with a slightly smaller droplet in the simulation. This was due to the finite thickness of the interface

  9. The mechanism of droplet formation in microfluidic EDGE systems

    NARCIS (Netherlands)

    Dijke, van K.C.; Ruiter, de R.; Schroën, C.G.P.H.; Boom, R.M.

    2010-01-01

    Edge-based droplet generation (EDGE) emulsification, which produces multiple, monodispersed droplets simultaneously at one droplet forming unit (introduced recently by our group), is studied in more detail with high-speed imaging, computational fluid dynamics and geometric modeling as research

  10. Behaviors of tribrachial edge flames and their interactions in a triple-port burner

    KAUST Repository

    Yamamoto, Kazuhiro

    2015-05-01

    In a triple-port burner, various non-premixed flames have been observed previously. Especially for the case with two lifted flames, such configuration could be suitable in studying interaction between two tribrachial flames. In the present study, the flame characteristics have been investigated numerically by adopting a reduced kinetic mechanism in the triple-port burner. Four different types of flame configurations, including two attached flames, inner lifted/outer attached flames, inner attached/outer lifted flames, and twin lifted flames, were successfully simulated depending on the flow conditions. The representative edge propagation speed of a single lifted flame or an upstream lifted flame in the case of twin lifted flames increased as the liftoff height became higher. In the twin lifted flames, the inner lifted flame was affected appreciably when the other flame was located further upstream such that the lifted flame located further downstream encountered the axial velocity acceleration induced by the gas expansion from the lifted flame located upstream, while thermal effects were not observed since the temperature of the incoming flow toward the lifted flame was not affected. A unique flip-flop behavior between the inner and outer flames, observed experimentally previously, was successfully captured in the simulation such that the inner lifted flame became attached to the nozzle as the liftoff height of the outer lifted flame grew higher with an increase in the outer air velocity.

  11. Sound propagation in saturated gas-vapor-droplet suspensions with droplet evaporation and nonlinear relaxation.

    Science.gov (United States)

    Kandula, Max

    2012-06-01

    The Sound attenuation and dispersion in saturated gas-vapor-droplet mixture in the presence of evaporation has been investigated theoretically. The theory is based on an extension of the work of Davidson [J. Atmos. Sci. 32(11), 2201-2205 (1975)] to accommodate the effects of nonlinear particle relaxation processes of mass, momentum and energy transfer on sound attenuation and dispersion. The results indicate the existence of a spectral broadening effect in the attenuation coefficient (scaled with respect to the peak value) with a decrease in droplet mass concentration. It is further shown that for large values of the droplet concentration the scaled attenuation coefficient is characterized by a universal spectrum independent of droplet mass concentration.

  12. 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

  13. Adjuvants for single droplet application of glyphosate

    DEFF Research Database (Denmark)

    Mathiassen, Solvejg K.; Kudsk, Per; Lund, Ivar

    2016-01-01

    Retention and biological activity of droplets of glyphosate deposited onto plant leaves using a Drop on Demand inkjet printer application system, was examined on pot-grown Brassica napus, Solanum nigrum, Chenopodium album, Silene noctiflora and Echinocloa crus-galli plants. Retention was measured...... but the biological activity of glyphosate was not improved....

  14. Lipid Structure in Triolein Lipid Droplets

    DEFF Research Database (Denmark)

    Chaban, Vitaly V; Khandelia, Himanshu

    2014-01-01

    Lipid droplets (LDs) are primary repositories of esterified fatty acids and sterols in animal cells. These organelles originate on the lumenal or cytoplasmic side of endoplasmic reticulum (ER) membrane and are released to the cytosol. In contrast to other intracellular organelles, LDs are compose...

  15. Droplet Manipulations in Two Phase Flow Microfluidics

    NARCIS (Netherlands)

    Pit, Arjen; Duits, Michael H.G.; Mugele, Friedrich Gunther

    2015-01-01

    Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of the emergence of

  16. Droplet vaporization in a supercritical microgravity environment

    Science.gov (United States)

    Curtis, E. W.; Farrell, P. V.

    A model has been developed for non-convective vaporization of liquid fuel droplets in an environment above the liquid critical pressure and near or above the liquid critical temperature. The model employs conservation of mass, energy and chemical species, along with transport properties which vary with temperature and species concentration. The liquid interface is assumed to be in thermodynamic equilibrium. The interface problem is solved using the Gibbs-Duhem relationship, and evaluating mixture fugacities using a modified Redlich-Kwong equation of state for the mixture. Due to the limited range of this equation, a curve-fit equation of state suitable for conditions far from the liquid critical point was applied. Results are presented for an n-octane liquid drop in nitrogen gas. For two gas conditions, several droplet sizes are modeled. Results include droplet size histories, surface temperature histories, and liquid and gas phase temperature profiles. The liquid vaporization rate is increased significantly for supercritical conditions compared to subcritical conditions. Using the specified equation of state for the ambient conditions tested, the droplet is completely vaporized before the liquid surface is heated to the liquid critical temperature.

  17. 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.

  18. Droplet microfluidics in (bio) chemical analysis

    Czech Academy of Sciences Publication Activity Database

    Basova, E. Y.; Foret, František

    2015-01-01

    Roč. 140, č. 1 (2015), s. 22-38 ISSN 0003-2654 R&D Projects: GA ČR(CZ) GBP206/12/G014 Institutional support: RVO:68081715 Keywords : droplet chemistry * bioanalysis * microfluidics * protein Subject RIV: CB - Analytical Chemistry, Separation Impact factor: 4.033, year: 2015

  19. Adjuvants for single droplet application of glyphosate

    DEFF Research Database (Denmark)

    Mathiassen, Solvejg Kopp; Kudsk, Per; Lund, Ivar

    2016-01-01

    Retention and biological activity of droplets of glyphosate deposited onto plant leaves using a Drop on Demand inkjet printer application system, was examined on pot-grown Brassica napus, Solanum nigrum, Chenopodium album, Silene noctiflora and Echinocloa crus-galli plants. Retention was measured...

  20. Precise quantitative addition of multiple reagents into droplets in sequence using glass fiber-induced droplet coalescence.

    Science.gov (United States)

    Li, Chunyu; Xu, Jian; Ma, Bo

    2015-02-07

    Precise quantitative addition of multiple reagents into droplets in sequence is still a bottleneck in droplet-based analysis. To address this issue, we presented a simple and robust glass fiber-induced droplet coalescence method. The hydrophilic glass fiber embedded in the microchannels can induce the deformation of droplets and trigger the coalescence. Serial addition of reagents with controlled volumes was performed by this method without the requirement for an external power source.

  1. Steam reforming of ethanol

    DEFF Research Database (Denmark)

    Trane-Restrup, Rasmus; Dahl, Søren; Jensen, Anker Degn

    2013-01-01

    Steam reforming (SR) of oxygenated species like bio-oil or ethanol can be used to produce hydrogen or synthesis gas from renewable resources. However, deactivation due to carbon deposition is a major challenge for these processes. In this study, different strategies to minimize carbon deposition...... on Ni-based catalysts during SR of ethanol were investigated in a flow reactor. Four different supports for Ni were tested and Ce0.6Zr0.4O2 showed the highest activity, but also suffered from severe carbon deposition at 600 °C or below. Operation at 600 °C or above were needed for full conversion...... of ethanol over the most active catalysts at the applied conditions. At these temperatures the offgas composition was close to the thermodynamical equilibrium. Operation at high temperatures, 700 °C and 750 °C, gave the lowest carbon deposition corresponding to 30–60 ppm of the carbon in the feed ending...

  2. Xylose fermentation to ethanol

    Energy Technology Data Exchange (ETDEWEB)

    McMillan, J.D.

    1993-01-01

    The past several years have seen tremendous progress in the understanding of xylose metabolism and in the identification, characterization, and development of strains with improved xylose fermentation characteristics. A survey of the numerous microorganisms capable of directly fermenting xylose to ethanol indicates that wild-type yeast and recombinant bacteria offer the best overall performance in terms of high yield, final ethanol concentration, and volumetric productivity. The best performing bacteria, yeast, and fungi can achieve yields greater than 0.4 g/g and final ethanol concentrations approaching 5%. Productivities remain low for most yeast and particularly for fungi, but volumetric productivities exceeding 1.0 g/L-h have been reported for xylose-fermenting bacteria. In terms of wild-type microorganisms, strains of the yeast Pichia stipitis show the most promise in the short term for direct high-yield fermentation of xylose without byproduct formation. Of the recombinant xylose-fermenting microorganisms developed, recombinant E. coli ATTC 11303 (pLOI297) exhibits the most favorable performance characteristics reported to date.

  3. 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.

  4. An interface tracking model for droplet electrocoalescence.

    Energy Technology Data Exchange (ETDEWEB)

    Erickson, Lindsay Crowl

    2013-09-01

    This report describes an Early Career Laboratory Directed Research and Development (LDRD) project to develop an interface tracking model for droplet electrocoalescence. Many fluid-based technologies rely on electrical fields to control the motion of droplets, e.g. microfluidic devices for high-speed droplet sorting, solution separation for chemical detectors, and purification of biodiesel fuel. Precise control over droplets is crucial to these applications. However, electric fields can induce complex and unpredictable fluid dynamics. Recent experiments (Ristenpart et al. 2009) have demonstrated that oppositely charged droplets bounce rather than coalesce in the presence of strong electric fields. A transient aqueous bridge forms between approaching drops prior to pinch-off. This observation applies to many types of fluids, but neither theory nor experiments have been able to offer a satisfactory explanation. Analytic hydrodynamic approximations for interfaces become invalid near coalescence, and therefore detailed numerical simulations are necessary. This is a computationally challenging problem that involves tracking a moving interface and solving complex multi-physics and multi-scale dynamics, which are beyond the capabilities of most state-of-the-art simulations. An interface-tracking model for electro-coalescence can provide a new perspective to a variety of applications in which interfacial physics are coupled with electrodynamics, including electro-osmosis, fabrication of microelectronics, fuel atomization, oil dehydration, nuclear waste reprocessing and solution separation for chemical detectors. We present a conformal decomposition finite element (CDFEM) interface-tracking method for the electrohydrodynamics of two-phase flow to demonstrate electro-coalescence. CDFEM is a sharp interface method that decomposes elements along fluid-fluid boundaries and uses a level set function to represent the interface.

  5. Imaging Studies of the Effects of Ethanol/Gasoline Blends on Spark-Assisted HCCI

    Science.gov (United States)

    Fatouraie, Mohammad; Wooldridge, Margaret

    2012-10-01

    Spark assist (SA) has been demonstrated to extend the operating limits of homogeneous charge compression ignition (HCCI) modes of engine operation. This experimental investigation focuses on the effects caused by the SA HCCI operation on ignition and combustion properties of 100% indolene and 70% indolene/30% ethanol blends. The spark assist effects are compared to base line HCCI for each blend by varying spark timing at different fuel/air equivalence ratio (φ= 0.4--0.6). High speed imaging is used to understand the effects of flame propagation on heat release rates. Ethanol generally improves engine performance with higher indicated mean effective pressure (IMEP) and higher stability compared to 100% indolene. SA advances phasing within a range of 5 CAD at lower engine speeds (700 rpm) and 11 CAD at higher engine speeds (1200 rpm). SA does not affect heat release rates until immediately (within 5 CAD) prior to autoignition. Unlike previous studies, flames were not observed for all SA conditions. During SA operation, more fuel mass was burned by flame propagation with gasoline compared to E30.

  6. Detailed Multidimensional Simulations of the Structure and Dynamics of Flames

    Science.gov (United States)

    Patnaik, G.; Kailasanath, K.

    1999-01-01

    Numerical simulations in which the various physical and chemical processes can be independently controlled can significantly advance our understanding of the structure, stability, dynamics and extinction of flames. Therefore, our approach has been to use detailed time-dependent, multidimensional, multispecies numerical models to perform carefully designed computational experiments of flames on Earth and in microgravity environments. Some of these computational experiments are complementary to physical experiments performed under the Microgravity Program while others provide a fundamental understanding that cannot be obtained from physical experiments alone. In this report, we provide a brief summary of our recent research highlighting the contributions since the previous microgravity combustion workshop. There are a number of mechanisms that can cause flame instabilities and result in the formation of dynamic multidimensional structures. In the past, we have used numerical simulations to show that it is the thermo-diffusive instability rather than an instability due to preferential diffusion that is the dominant mechanism for the formation of cellular flames in lean hydrogen-air mixtures. Other studies have explored the role of gravity on flame dynamics and extinguishment, multi-step kinetics and radiative losses on flame instabilities in rich hydrogen-air flames, and heat losses on burner-stabilized flames in microgravity. The recent emphasis of our work has been on exploring flame-vortex interactions and further investigating the structure and dynamics of lean hydrogen-air flames in microgravity. These topics are briefly discussed after a brief discussion of our computational approach for solving these problems.

  7. Early structure of LPG partially premixed conically stabilized flames

    KAUST Repository

    Elbaz, Ayman M.

    2013-01-01

    This paper presents experimental investigation of LPG partially premixed turbulent flames stabilized within a conical nozzle burner under constant degree of partial premixing. The stability limits and mean flame structure are presented based on the mean gas temperature and the concentration of CO, O 2, NO, and HC at the flame early region of reaction. The investigation covered the influence of the nozzle cone angle, the jet exit velocity and the jet equivalence ratio. The stability results show that the flames with cone are more stable than those without cone. For conical stabilized flames, the stability results exhibit three different sensitivity regions between the jet velocity and equivalence ratio. The inflame measurements prove that the flame stability could be attributed to the triple flame structure at the flame leading edge. The data show that the triple flame structure is influenced by cone angle, the jet velocity and the equivalence ratio. The flame is believed to be controlled by the recirculation flow inside the cone. Increasing the cone angle induced higher air entrainment to the reaction zone as depicted by a higher O 2 concentration within the flame leading edge. Increasing the jet velocity to a certain limit enhances the intensity of combustion at the flame leading edge, while excessive increase in jet velocity reduces this intensity. At a fixed jet velocity the higher the equivalence ratio, the higher the amount of fuel diffused and engulfed to the reaction zone, the more delay of the combustion completion and the higher the emission concentrations of the flame. © 2012 Elsevier Inc.

  8. Flame spread over inclined electrical wires with AC electric fields

    KAUST Repository

    Lim, Seung J.

    2017-07-21

    Flame spread over polyethylene-insulated electrical wires was studied experimentally with applied alternating current (AC) by varying the inclination angle (θ), applied voltage (VAC), and frequency (fAC). For the baseline case with no electric field applied, the flame spread rate and the flame width of downwardly spreading flames (DSFs) decreased from the horizontal case for −20° ≤ θ < 0° and maintained near constant values for −90° ≤ θ < −20°, while the flame spread rate increased appreciably as the inclination angle of upwardly spreading flames (USFs) increased. When an AC electric field was applied, the behavior of flame spread rate in DSFs (USFs) could be classified into two (three) sub-regimes characterized by various functional dependences on VAC, fAC, and θ. In nearly all cases of DSFs, a globular molten polyethylene formed ahead of the spreading flame edge, occasionally dripping onto the ground. In these cases, an effective flame spread rate was defined to represent the burning rate by measuring the mass loss due to dripping. This effective spread rate was independent of AC frequency, while it decreased linearly with voltage and was independent of the inclination angle. In DSFs, when excessively high voltage and frequency were applied, the dripping led to flame extinction during propagation and the extinction frequency correlated well with applied voltage. In USFs, when high voltage and frequency were applied, multiple globular molten PEs formed at several locations, leading to ejections of multiple small flame segments from the main flame, thereby reducing the flame spread rate, which could be attributed to the electrospray phenomenon.

  9. Effect of Wind Velocity on Flame Spread in Microgravity

    Science.gov (United States)

    Prasad, Kuldeep; Olson, Sandra L.; Nakamura, Yuji; Fujita, Osamu; Nishizawa, Katsuhiro; Ito, Kenichi; Kashiwagi, Takashi; Simons, Stephen N. (Technical Monitor)

    2002-01-01

    A three-dimensional, time-dependent model is developed describing ignition and subsequent transition to flame spread over a thermally thin cellulosic sheet heated by external radiation in a microgravity environment. A low Mach number approximation to the Navier Stokes equations with global reaction rate equations describing combustion in the gas phase and the condensed phase is numerically solved. The effects of a slow external wind (1-20 cm/s) on flame transition are studied in an atmosphere of 35% oxygen concentration. The ignition is initiated at the center part of the sample by generating a line-shape flame along the width of the sample. The calculated results are compared with data obtained in the 10s drop tower. Numerical results exhibit flame quenching at a wind speed of 1.0 cm/s, two localized flames propagating upstream along the sample edges at 1.5 cm/s, a single line-shape flame front at 5.0 cm/s, three flames structure observed at 10.0 cm/s (consisting of a single line-shape flame propagating upstream and two localized flames propagating downstream along sample edges) and followed by two line-shape flames (one propagating upstream and another propagating downstream) at 20.0 cm/s. These observations qualitatively compare with experimental data. Three-dimensional visualization of the observed flame complex, fuel concentration contours, oxygen and reaction rate isosurfaces, convective and diffusive mass flux are used to obtain a detailed understanding of the controlling mechanism, Physical arguments based on lateral diffusive flux of oxygen, fuel depletion, oxygen shadow of the flame and heat release rate are constructed to explain the various observed flame shapes.

  10. Flame Retardation Modification of Paper-Based PVC Wallcoverings

    Directory of Open Access Journals (Sweden)

    Lin Hui

    2016-01-01

    Full Text Available The flame-retarded paper-based polyvinyl chloride (PVC wallcoverings were successfully prepared, using plant fiber paper as base material and adding inorganic flame retardants and flame-retarded plasticizer as additives. Flame retardancy, thermostability, smoke suppression and mechanical properties were tested regarding to the prepared wallcoverings. The results showed that 2ZnO·3B2O3·3.5H2O could improve flame retardancy and thermostability of paper-based PVC wallcoverings; plasticizer tricresyl phosphate increased flame retardancy of the prepared materials auxiliarily. Also, flame-retarded paper-based PVC wallcoverings with higher flame retardancy, smoke suppression and mechanical property was prepared using plant fiber paper with fix quantity of 90 g/m3 as base material, using 2ZnO·3B2O3·3.5H2O as inorganic flame retardant, and using tricresyl phosphate as plasticizer. For the flame-retarded paper-based PVC wallcoverings in this study, the limit oxygen index (LOI reaches 32.3, maximal smoke density is 16.91 %, and the horizontal and longitudinal wet tensile strength reaches 1.38 kN·m−1 and 1.51 kN·m−1 respectively. Meanwhile, its flame retardancy meets the requirements about flame retardancy for material Class B1 listed in Chinese National Standards GB 8624-2012, Classification for burning behavior of building materials and products. This research creates an effective path to prepare paper-based PVC wallcoverings with high flame retardancy.

  11. Photophoretic trampoline - Interaction of single airborne absorbing droplets with light

    CERN Document Server

    Esseling, Michael; Alpmann, Christina; Denz, Cornelia

    2012-01-01

    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.

  12. Experimental Study of Supercooled Large Droplet Impingement Effects

    Science.gov (United States)

    Papadakis, M.; Rachman, A.; Wong, S. C.; Hung, K. E.; Vu, G. T.

    2003-01-01

    Typically, ice accretion results from small supercooled droplets (droplets cooled below freezing), usually 5 to 50 microns in diameter, which can freeze upon impact with an aircraft surface. Recently, ice accretions resulting from supercooled large droplet (SLD) conditions have become a safety concern. Current ice accretion codes have been extensively tested for Title 14 Code of Federal Regulations Part 25, Appendix C icing conditions but have not been validated for SLD icing conditions. This report presents experimental methods for investigating large droplet impingement dynamics and for obtaining small and large water droplet impingement data.

  13. An oil droplet that spontaneously climbs up stairs

    OpenAIRE

    Sumino, Yutaka; Magome, Nobuyuki; Yoshikawa, Kenichi

    2006-01-01

    It has been reported that an oil droplet on a glass surface moves spontaneously in an oil-water system. This motion of an oil droplet can be understood as the spreading of a reactive droplet, which is induced by the interfacial tension gradient at the glass surface. In this paper, we focus on the spontaneous motion of an oil droplet climbing up stairs. We found that an oil droplet tends to move tip the stairs rather than to step down. We describe some of the mechanisms of this unique behavior.

  14. 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.

  15. Flame Retardant Polyamide Fibres: The Challenge of Minimising Flame Retardant Additive Contents with Added Nanoclays

    Directory of Open Access Journals (Sweden)

    Richard Horrocks

    2016-08-01

    Full Text Available This work shows that halogen-free, flame retarded polyamide 6 (PA6, fabrics may be produced in which component fibres still have acceptable tensile properties and low levels (preferably ≤10 wt % of additives by incorporating a nanoclay along with two types of flame retardant formulations. The latter include (i aluminium diethyl phosphinate (AlPi at 10 wt %, known to work principally in the vapour phase and (ii ammonium sulphamate (AS/dipentaerythritol (DP system present at 2.5 and 1 wt % respectively, believed to be condense phase active. The nanoclay chosen is an organically modified montmorillonite clay, Cloisite 25A. The effect of each additive system is analysed in terms of its ability to maximise both filament tensile properties relative to 100% PA6 and flame retardant behaviour of knitted fabrics in a vertical orientation. None of the AlPi-containing formulations achieved self-extinguishability, although the presence of nanoclay promoted lower burning and melt dripping rates. The AS/DP-containing formulations with total flame retardant levels of 5.5 wt % or less showed far superior properties and with nanoclay, showed fabric extinction times ≤ 39 s and reduced melt dripping. The tensile and flammability results, supported by thermogravimetric analysis, have been interpreted in terms of the mechanism of action of each flame retardant/nanoclay type.

  16. Influence of Pilot Flame Parameters on the Stability of Turbulent Jet Flames

    KAUST Repository

    Guiberti, Thibault F.

    2016-11-08

    This paper presents a comprehensive study of the effects of pilot parameters on flame stability in a turbulent jet flame. The Sydney inhomogeneous piloted burner is employed as the experimental platform with two main fuels, namely, compressed natural gas and liquefied petroleum gas. Various concentrations of five gases are used in the pilot stream, hydrogen, acetylene, oxygen, nitrogen, and argon, to enable a sufficient range in exploring the following parameters: pilot heat release, temperature, burnt gas velocity, equivalence ratio, and H/C ratio. The experimental results are mainly presented in the form of blow-off limits and supported by simple calculations, which simulate various conditions of the pilot–mixture interface. It is found that increasing the pilot adiabatic flame temperature benefits the flame stability and has an even greater influence than the heat release, which is also known to enhance the blow-off limits. Conversely, increasing the pilot burnt gas velocity reduces the blow-off velocity, except for the limiting case when the jet is fully non-premixed. The H/C ratio has negligible effects, while resorting to lean pilots significantly increases the stability of globally rich partially premixed and premixed jets. Such findings are consistent with trends obtained from laminar flame calculations for rich fuel/air mixtures issuing against hot combustion products to simulate the pilot stream.

  17. Numerical investigation of air mediated droplet bouncing on flat surfaces

    Science.gov (United States)

    Shetabivash, H.; Dolatabadi, A.

    2017-09-01

    A liquid droplet can bounce off a flat substrate independent of surface wettability if the impact occurs at low velocities, i.e., We of less than seven. In this case, the droplet spreads on a sub-micrometer air layer and rebounds subsequently without any direct contact with the surface. We have numerically investigated the process of air layer formation beneath the droplet. The numerical simulations are validated using experimental results available in the literature based on morphology of the droplet interface and thickness of the air layer. Numerical results revealed that the formation of a high pressure zone at the center of impact deforms the droplet to a kink shape at the moment of impact. The deformation leads to displacement of high pressure zone from center to kink edge of the droplet interface. Further investigation of pressure and velocity of air beneath the droplet divulged that high pressure region at the kink edge suppresses air flow at the inner region while accelerating flow at the outer region. In addition, it is demonstrated that fluid flow at the kink edge where droplet interface has the minimum distance from the substrate resembles Couette flow. It is demonstrated that the deformation of droplet along with displacement of high pressure region from the center to kink edge are responsible for stabilizing the air layer beneath the droplet and consequently spreading and receding of droplet over a thin air cushion.

  18. 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)].

  19. Numerical study of laminar nonpremixed methane flames in coflow jets: Autoignited lifted flames with tribrachial edges and MILD combustion at elevated temperatures

    KAUST Repository

    M. Al-Noman, Saeed

    2016-07-07

    Autoignition characteristics of laminar nonpremixed methane jet flames in high-temperature coflow air are studied numerically. Several flame configurations are investigated by varying the initial temperature and fuel mole fraction. At a relatively low initial temperature, a non-autoignited nozzle-attached flame is simulated at relatively low jet velocity. When the initial temperature is higher than that required for autoignition, two regimes are investigated: an autoignited lifted flame with tribrachial edge structure and an autoignited lifted flame with Mild combustion. The autoignited lifted flame with tribrachial edge exhibited three branches: lean and rich premixed flame wings and a trailing diffusion flame. Characteristics of kinetic structure for autoignited lifted flames are discussed based on the kinetic structures of homogeneous autoignition and flame propagation of stoichiometric mixture. Results showed that a transition from autoignition to flame propagation modes occurs for reasonably stoichiometric mixtures. The autoignited lifted flame with Mild combustion occurs when methane fuel is highly diluted with nitrogen. The kinetic structure analysis shows that the characteristics of Mild combustion can be treated as an autoignited lean premixed lifted flame. Transition behavior from Mild combustion to nozzle-attached flame was investigated by increasing the fuel mole fraction. As the maximum flame temperature increases with decreasing liftoff height, the kinetic structure showed a transition behavior from autoignition to flame propagation of a lean premixed flame. © 2016 The Combustion Institute

  20. Electrically Charged Droplets in Microgravity. Impact and Trajectories

    Science.gov (United States)

    Brandenbourger, Martin; Caps, Hervé; Vitry, Youen; Dorbolo, Stéphane

    2017-06-01

    In this work, the interaction between electrically charged droplets in microgravity is considered. During the 22 s of microgravity brought by a parabolic flight, water droplets with a radius r ∈ [0.41 - 0.97] mm were released one in front of the other. A high-speed camera allowed studying their interaction in the focal plane. The trajectories of the droplets are well adjusted by a punctual charge model. In some experiments, a physical contact between the charged droplets was observed. These collisions are studied via a phase diagram comparing the droplet Weber number, We, and the collision parameter, χ. By comparing these collisions to experiments involving neutral droplets, we deduce how the collision diagram is affected by electric charges. In particular, we show that the criterion for an impact between two droplets is no more χ < 1.

  1. Stick-jump mode in surface droplet dissolution

    CERN Document Server

    Dietrich, Erik; Zhang, Xuehua; Zandvliet, Harold J W; Lohse, Detlef

    2016-01-01

    The analogy between evaporating surface droplets in air to dissolving long-chain alcohol droplets in water is worked out. We show that next to the three known modi for surface droplet evaporation or dissolution (constant contact angle mode, constant contact radius mode, and stick-slide mode), a fourth mode exists for small droplets on supposedly smooth substrates, namely the stick-jump mode: intermittent contact line pinning causes the droplet to switch between sticking and jumping during the dissolution. We present experimental data and compare them to theory to predict the dissolution time in this stick-jump mode. We also explain why these jumps were easily observed for microscale droplets but not for larger droplets.

  2. Impact of Droplets on Inclined Flowing Liquid Films

    CERN Document Server

    Che, Zhizhao; Matar, Omar K

    2015-01-01

    The impact of droplets on an inclined falling liquid film is studied experimentally using high-speed imaging. The falling film is created on a flat substrate with controllable thicknesses and flow rates. Droplets with different sizes and speeds are used to study the impact process under various Ohnesorge and Weber numbers, and film Reynolds numbers. A number of phenomena associated with droplet impact are identified and analysed, such as bouncing, partial coalescence, total coalescence, and splashing. The effects of droplet size, speed, as well the film flow rate are studied culminating in the generation of an impact regime map. The analysis of the lubrication force acted on the droplet via the gas layer shows that a higher flow rate in the liquid film produces a larger lubrication force, slows down the drainage process, and increases the probability of droplet bouncing. Our results demonstrate that the flowing film has a profound effect on the droplet impact process and associated phenomena, which are marked...

  3. Effective doping of low energy ions into superfluid helium droplets

    Science.gov (United States)

    Zhang, Jie; Chen, Lei; Freund, William M.; Kong, Wei

    2015-01-01

    We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 104 ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 105/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies. PMID:26298127

  4. Small Levitating Ordered Droplet Clusters: Stability, Symmetry, and Voronoi Entropy.

    Science.gov (United States)

    Fedorets, Alexander A; Frenkel, Mark; Bormashenko, Edward; Nosonovsky, Michael

    2017-11-16

    A method to generate levitating monodisperse microdroplet clusters with an arbitrary number of identical droplets is presented. Clusters with 1-28 droplets levitate over a locally heated water layer in an ascending vapor-air jet. Due to the attraction to the center of the heated area combined with aerodynamic repulsion between the droplets, the clusters form structures that are quite diverse and different from densest packing of hard spheres. The clusters self-organize into stable and reproducible configurations dependent on the number of droplets while independent of the droplets' size. The central parts of larger clusters reproduce the shape of smaller clusters. The ability to synthesize stable clusters with a given number of droplets is important for tracing droplets, which is crucial for potential applications such as microreactors and for chemical analysis of small volumes of liquid.

  5. Thermal Insulation System for Large Flame Buckets

    Science.gov (United States)

    Callens, E. Eugene, Jr.; Gamblin, Tonya Pleshette

    1996-01-01

    The objective of this study is to investigate the use of thermal protection coatings, single tiles, and layered insulation systems to protect the walls of the flame buckets used in the testing of the Space Shuttle Main Engine, while reducing the cost and maintenance of the system. The physical behavior is modeled by a plane wall boundary value problem with a convective frontface condition and a backface condition designed to provide higher heat rates through the material.

  6. Computational and experimental study of laminar flames

    Energy Technology Data Exchange (ETDEWEB)

    Smooke, Mitchell [Yale Univ., New Haven, CT (United States)

    2015-05-29

    During the past three years, our research has centered on an investigation of the effects of complex chemistry and detailed transport on the structure and extinction of hydrocarbon flames in coflowing axisymmetric configurations. We have pursued both computational and experimental aspects of the research in parallel on both steady-state and time-dependent systems. The computational work has focused on the application of accurate and efficient numerical methods for the solution of the steady-state and time-dependent boundary value problems describing the various reacting systems. Detailed experimental measurements were performed on axisymmetric coflow flames using two-dimensional imaging techniques. Previously, spontaneous Raman scattering, chemiluminescence, and laser-induced fluorescence were used to measure the temperature, major and minor species profiles. Particle image velocimetry (PIV) has been used to investigate velocity distributions and for calibration of time-varying flames. Laser-induced incandescence (LII) with an extinction calibration was used to determine soot volume fractions, while soot surface temperatures were measured with three-color optical pyrometry using a color digital camera. A blackbody calibration of the camera allows for determination of soot volume fraction as well, which can be compared with the LII measurements. More recently, we have concentrated on a detailed characterization of soot using a variety of techniques including time-resolved LII (TiRe-LII) for soot primary particles sizes, multi-angle light scattering (MALS) for soot radius of gyration, and spectrally-resolved line of sight attenuation (spec-LOSA). Combining the information from all of these soot measurements can be used to determine the soot optical properties, which are observed to vary significantly depending on spatial location and fuel dilution. Our goal has been to obtain a more fundamental understanding of the important fluid dynamic and chemical interactions in

  7. The advanced flame quality indicator system

    Energy Technology Data Exchange (ETDEWEB)

    Oman, R.; Rossi, M.J.; Calia, V.S.; Davis, F.L.; Rudin, A. [Insight Technologies, Inc., Bohemia, NY (United States)

    1997-09-01

    By combining oil tank monitoring, systems diagnostics and flame quality monitoring in an affordable system that communicates directly with dealers by telephone modem, Insight Technologies offers new revenue opportunities and the capability for a new order of customer relations to oil dealers. With co-sponsorship from New York State Energy Research and Development Authority, we have incorporated several valuable functions to a new product based on the original Flame Quality Indicator concept licensed from the US DOE`s Brookhaven National Laboratory. The new system is the Advanced Flame Quality Indicator, or AFQI. As before, the AFQI monitors and reports the intensity of the burner flame relative to a calibration established when the burner is set up at AFQI installation. Repairs or adjustments are summoned by late-night outgoing telephone calls when limits are exceeded in either direction, indicating an impending contamination or other malfunction. A independently, a pressure transducer for monitoring oil tank level and filter condition, safety lockout alarms and a temperature monitor; all reporting automatically at instructed intervals via an on-board modem to a central station PC computer (CSC). Firmware on each AFQI unit and Insight-supplied software on the CSC automatically interact to maintain a customer database for an oil dealer, an OEM, or a regional service contractor. In addition to ensuring continuously clean and efficient operation, the AFQI offers the oil industry a new set of immediate payoffs, among which are reduced outages and emergency service calls, shorter service calls from cleaner operation, larger oil delivery drops, the opportunity to stretch service intervals to as along as three years in some cases, new selling features to keep and attract customers, and greatly enhanced customer contact, quality and reliability.

  8. Analytical study in the mechanism of flame movement in horizontal tubes. II. Flame acceleration in smooth open tubes

    CERN Document Server

    Kazakov, Kirill A

    2013-01-01

    The problem of spontaneous acceleration of premixed flames propagating in open horizontal tubes with smooth walls is revisited. It is proved that in long tubes, this process can be considered quasi-steady, and an equation for the flame front position is derived using the on-shell description. Numerical solutions of this equation are found which show that as in the case of uniform flame movement, there are two essentially different regimes of flame propagation. In the type I regime, the flame speed and its acceleration are comparatively low, whereas the type II regime is characterized by significant flame acceleration that rapidly increases as the flame travels along the tube. A detailed comparison of the obtained results with the experimental data on flame acceleration in methane-air mixtures is given. In particular, it is confirmed that flames propagating in near-stoichiometric mixtures and mixtures near the limits of inflammability belong to the types II and I, respectively, whereas flames in transient mixt...

  9. Similarity and Scaling of Turbulent Flame Speeds for Expanding Premixed Flames of C4-C8 n -alkanes

    Science.gov (United States)

    Wu, Fujia; Saha, Abhishek; Chaudhuri, Swetaprovo; Yang, Sheng; Law, Chung K.

    2013-11-01

    We experimentally investigated the propagation speed of constant-pressure expanding flames in near isotropic turbulence using a dual-chamber, fan-stirred vessel. The motivation is to test whether the fuel similarity concept among C4-C8 n-alkanes on laminar flames also holds for turbulent flames. Previously it was found that the laminar flame speed and Markstein length are almost identical for C4-C8 n-alkanes. If this fuel similarity concept can also be shown for turbulent flames, it will suggest a canonical flame structure for large hydrocarbon fuels, i . e . , large fuels always decompose to small C0-C4 fuel fragments before being oxidized, and would significantly simplify the description of the flames. Preliminary results show that in the flamelet and thin-reaction zone, turbulent flame speeds of C4-C8 n-alkanes are indeed largely similar at various conditions, thereby suggesting the fuel similarity for turbulent flames. In addition, it is found that the normalized turbulent flame speed also approximately scales with the square root of an appropriately-defined Reynolds number recently found for C0-C4 fuels. This work was supported by the AFOSR under the technical monitoring of Dr. Chiping Li.

  10. Flames in fractal grid generated turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Goh, K H H; Hampp, F; Lindstedt, R P [Department of Mechanical Engineering, Imperial College, London SW7 2AZ (United Kingdom); Geipel, P, E-mail: p.lindstedt@imperial.ac.uk [Siemens Industrial Turbomachinery AB, SE-612 83 Finspong (Sweden)

    2013-12-15

    Twin premixed turbulent opposed jet flames were stabilized for lean mixtures of air with methane and propane in fractal grid generated turbulence. A density segregation method was applied alongside particle image velocimetry to obtain velocity and scalar statistics. It is shown that the current fractal grids increase the turbulence levels by around a factor of 2. Proper orthogonal decomposition (POD) was applied to show that the fractal grids produce slightly larger turbulent structures that decay at a slower rate as compared to conventional perforated plates. Conditional POD (CPOD) was also implemented using the density segregation technique and the results show that CPOD is essential to segregate the relative structures and turbulent kinetic energy distributions in each stream. The Kolmogorov length scales were also estimated providing values {approx}0.1 and {approx}0.5 mm in the reactants and products, respectively. Resolved profiles of flame surface density indicate that a thin flame assumption leading to bimodal statistics is not perfectly valid under the current conditions and it is expected that the data obtained will be of significant value to the development of computational methods that can provide information on the conditional structure of turbulence. It is concluded that the increase in the turbulent Reynolds number is without any negative impact on other parameters and that fractal grids provide a route towards removing the classical problem of a relatively low ratio of turbulent to bulk strain associated with the opposed jet configuration. (paper)

  11. Smoldering, Transition and Flaming in Microgravity

    Science.gov (United States)

    Fernandez-Pello, A. C.; Bar-Ilan, A.; Lo, T. L.; Walther, D. C.; Urban, D. L.

    2001-01-01

    A research project is underway to study smolder and the transition to flaming in microgravity. The Microgravity Smoldering Combustion (MSC) flight project is an ongoing research project to provide a better understanding of the controlling mechanisms of smoldering combustion. The Smoldering Transition and Flaming (STAF) project is a recently established research program that will utilize the Fluids and Combustion Facility (FCF) of the ISS to examine the transition from smolder to flaming in microgravity. In forced flow smolder experiments ambient pressure in the MSC chamber rises, thus motivating the need to understand the effects of pressure on smoldering combustion. Further, the STAF experiment has constraints on experimental scale and testing at elevated pressure may be a mechanism to reduce the sample size by enhancing the smolder reaction. In the work we are reporting here, a series of ground-based tests determine the effects of pressure on smoldering combustion. These tests are compared with data obtained from experiments conducted aboard the Space Shuttle in flights STS-69 and STS-77. Measurements of one-dimensional smolder propagation velocity are made by thermocouple probing and a non-intrusive Ultrasound Imaging System (UIS)]. Thermocouples are also used to obtain reaction temperatures and the UIS is used to determine permeabilities of the fuel in real-time.

  12. Lysozyme pattern formation in evaporating droplets

    Science.gov (United States)

    Gorr, Heather Meloy

    Liquid droplets containing suspended particles deposited on a solid, flat surface generally form ring-like structures due to the redistribution of solute during evaporation (the "coffee ring effect"). The forms of the deposited patterns depend on complex interactions between solute(s), solvent, and substrate in a rapidly changing, far from equilibrium system. Solute self-organization during evaporation of colloidal sessile droplets has attracted the attention of researchers over the past few decades due to a variety of technological applications. Recently, pattern formation during evaporation of various biofluids has been studied due to potential applications in medical screening and diagnosis. Due to the complexity of 'real' biological fluids and other multicomponent systems, a comprehensive understanding of pattern formation during droplet evaporation of these fluids is lacking. In this PhD dissertation, the morphology of the patterns remaining after evaporation of droplets of a simplified model biological fluid (aqueous lysozyme solutions + NaCl) are examined by atomic force microscopy (AFM) and optical microscopy. Lysozyme is a globular protein found in high concentration, for example, in human tears and saliva. The drop diameters, D, studied range from the micro- to the macro- scale (1 microm -- 2 mm). In this work, the effect of evaporation conditions, solution chemistry, and heat transfer within the droplet on pattern formation is examined. In micro-scale deposits of aqueous lysozyme solutions (1 microm < D < 50 microm), the protein motion and the resulting dried residue morphology are highly influenced by the decreased evaporation time of the drop. The effect of electrolytes on pattern formation is also investigated by adding varying concentrations NaCl to the lysozyme solutions. Finally, a novel pattern recognition program is described and implemented which classifies deposit images by their solution chemistries. The results presented in this Ph

  13. Flame Propagation Through Swirling Eddys, A Recursive Pattern

    CERN Document Server

    Ashurst, W T

    1993-01-01

    Abstract: Computed flame motion through and between swirling eddys exhibits a maximum advancement rate which is related to the time duration of flame motion between eddys. This eddy spatial structure effect upon the apparent turbulent flame speed appears to be similar to the square-root dependence observed in wrinkled flamelet data. The rate-limiting behavior at one eddy length-scale can be removed by inclusion of smaller eddys which reside between the larger eddys. This large-eddy, small-eddy concept yields a recursion relation and repeated functional iteration can be done to approximate a desired flame speed relation. As an example, an iteration to produce $S_T Currently, the iteration process is a post-diction of flame speed, but if a universality can be developed, then a predictive theory of turbulent flame propagation might be achieved.

  14. New developments in the theory of flame propagation

    Energy Technology Data Exchange (ETDEWEB)

    Sivashinsky, G.I. [City College of the City Univ. of New York, NY (United States)

    1996-12-31

    Two topics in combustion fluid mechanics are discussed. The first is a theory of the outward propagating spherical flame in the regime of well-developed hydrodynamic instability. In a qualitative agreement with experimental observations it is shown that the flame assumes a fractal-like wrinkled structure resulting in the overall burning rate acceleration. In contrast to hydrodynamically unstable flames, the expanding flame subject exclusively to the effect of diffusive instability does not indicate any disposition toward acceleration. The second topic concerns the dynamics of diffusively unstable flames subjected to radiative heat losses. At high enough heat losses the flame breaks up into separate self-propagating cap-like flamelets while a significant portion of the fuel remains unconsumed.

  15. Stability of a laminar flame front propagating within a tube

    Energy Technology Data Exchange (ETDEWEB)

    Salamandra, G.D.; Maiorov, N.I.

    1983-01-01

    The present study examines the deformation of a flame propagating in a semi-closed horizontal tube under the action of perturbations artificially created on the flame surface by brief action of a transverse electrical field on the combustion zone. The fuel mixture used was a dry methane-air mixture containing 10% CH4, which produced a flame front with relatively low convexity. Flame front propagation was recorded by high-speed photographic methods. Interpretation of the photographs reveals that the magnitude of the perturbations increases by an exponential law; fine scale perturbations on the flame surface are suppressed by coarse scale perturbations, while the stable curved form of the flame front in the tube is ensured by the stabilizing action of the tube walls.

  16. The influence of initial atomized droplet size on residual particle size from pressurized metered dose inhalers.

    Science.gov (United States)

    Sheth, Poonam; Stein, Stephen W; Myrdal, Paul B

    2013-10-15

    Pressurized metered dose inhalers (pMDIs) are widely used for the treatment of diseases of the lung, including asthma and chronic obstructive pulmonary disease. The mass median aerodynamic diameter of the residual particles (MMADR) delivered from a pMDI plays a key role in determining the amount and location of drug deposition in the lung and thereby the efficacy of the inhaler. The mass median diameter of the initial droplets (MMDI), upon atomization of a formulation, is a significant factor influencing the final particle size. The purpose of this study was to evaluate the extent that MMDI and initial droplet geometric standard deviation (GSD) influence the residual aerodynamic particle size distribution (APSDR) of solution and suspension formulations. From 48 solution pMDI configurations with varying ethanol concentrations, valve sizes and actuator orifice diameters, it was experimentally found that the effective MMDI ranged from 7.8 to 13.3 μm. Subsequently, computational methods were utilized to determine the influence of MMDI on MMADR, by modulating the MMDI for solution and suspension pMDIs. For solution HFA-134a formulations of 0.5% drug in 10% ethanol, varying the MMDI from 7.5 to 13.5 μm increased the MMADR from 1.4 to 2.5 μm. For a suspension formulation with a representative particle size distribution of micronized drug (MMAD=2.5 μm, GSD=1.8), the same increase in MMDI resulted in an increase in the MMADR from 2.7 to only 3.3 μm. Hence, the same increase in MMDI resulted in a 79% increase in MMADR for the solution formulation compared to only a 22% increase for the suspension formulation. Similar trends were obtained for a range of drug concentrations and input micronized drug sizes. Thus, APSDR is more sensitive to changes in MMDI for solution formulations than suspension formulations; however, there are situations in which hypothetically small micronized drug in suspension (e.g. 500 nm MMAD) could resemble trends observed for solution formulations

  17. Methane Formation by Flame-Generated Hydrogen Atoms in the Flame Ionization Detector

    DEFF Research Database (Denmark)

    Holm, Torkil; Madsen, Jørgen Øgaard

    1996-01-01

    The precombustion degradation of organic compounds in the flame ionization detector has been studied (1) by heating the additives in hydrogen in a quartz capillary and analyzing the reaction products by GC and (2) by following the degradation of the additives in a hydrogen flame, by means of a thin......, and conceivably all hydrocarbons are quantitatively converted into methane at temperatures below 600 C, that is, before the proper combustion has started. The splitting of the C-C bonds is preceded by hydrogenation of double and triple bonds and aromatic rings. The reactions, no doubt, are caused by hydrogen...... atoms, which are formed in the burning hydrogen and which diffuse into the inner core of the flame. The quantitative formation of methane appears to explain the "equal per carbon" rule for the detector response of hydrocarbons, since all carbons are "exchanged" for methane molecules....

  18. Effect of Intense Sound Waves on a Stationary Gas Flame

    Science.gov (United States)

    Hahnemann, H; Ehret, L

    1950-01-01

    Intense sound waves with a resonant frequency of 5000 cycles per second were imposed on a stationary propane-air flame issuing from a nozzle. In addition to a slight increase of the flame velocity, a fundamental change both in the shape of the burning zone and in the flow pattern could be observed. An attempt is made to explain the origin of the variations in the flame configuration on the basis of transition at the nozzle from jet flow to potential flow.

  19. A Counterflow Diffusion Flame Study Of Branched Octane Isomers

    Science.gov (United States)

    2012-09-26

    public release; distribution is unlimited. A counterflow diffusion flame study of branched octane isomers The views, opinions and/or findings contained...MC 0934 La Jolla, CA 92093 -0934 ABSTRACT A counterflow diffusion flame study of branched octane isomers Report Title Conventional petroleum, Fischer...counterflow diffusion flame study of branched octane isomers Approved for public release; distribution is unlimited. 61657.7-EG REPORT DOCUMENTATION PAGE

  20. Investigation of flame structure in plasma-assisted turbulent premixed methane-air flame

    Science.gov (United States)

    Hualei, ZHANG; Liming, HE; Jinlu, YU; Wentao, QI; Gaocheng, CHEN

    2018-02-01

    The mechanism of plasma-assisted combustion at increasing discharge voltage is investigated in detail at two distinctive system schemes (pretreatment of reactants and direct in situ discharge). OH-planar laser-induced fluorescence (PLIF) technique is used to diagnose the turbulent structure methane-air flame, and the experimental apparatus consists of dump burner, plasma-generating system, gas supply system and OH-PLIF system. Results have shown that the effect of pretreatment of reactants on flame can be categorized into three regimes: regime I for voltage lower than 6.6 kV; regime II for voltage between 6.6 and 11.1 kV; and regime III for voltage between 11.1 and 12.5 kV. In regime I, aerodynamic effect and slower oxidation of higher hydrocarbons generated around the inner electrode tip plays a dominate role, while in regime III, the temperature rising effect will probably superimpose on the chemical effect and amplify it. For wire-cylinder dielectric barrier discharge reactor with spatially uneven electric field, the amount of radicals and hydrocarbons are decreased monotonically in radial direction which affects the flame shape. With regard to in situ plasma discharge in flames, the discharge pattern changes from streamer type to glow type. Compared with the case of reactants pretreatment, the flame propagates further in the upstream direction. In the discharge region, the OH intensity is highest for in situ plasma assisted combustion, indicating that the plasma energy is coupled into flame reaction zone.

  1. NEUROPEPTIDE Y (NPY) SUPPRESSES ETHANOL DRINKING IN ETHANOL-ABSTINENT, BUT NOT NON-ETHANOL-ABSTINENT, WISTAR RATS

    OpenAIRE

    Gilpin, N.W.; Stewart, R.B.; Badia-Elder, N.E.

    2008-01-01

    In outbred rats, increases in brain neuropeptide Y (NPY) activity suppress ethanol consumption in a variety of access conditions, but only following a history of ethanol dependence. NPY reliably suppresses ethanol drinking in alcohol-preferring (P) rats and this effect is augmented following a period of ethanol abstinence. The purpose of this experiment was to examine the effects of NPY on 2-bottle choice ethanol drinking and feeding in Wistar rats that had undergone chronic ethanol vapor exp...

  2. FIELD TEST OF THE FLAME QUALITY INDICATOR

    Energy Technology Data Exchange (ETDEWEB)

    Rudin, Andrew M; Butcher, Thomas; Troost, Henry

    2003-02-04

    The flame quality indicator concept was developed at BNL specifically to monitor the brightness of the flame in a small oil burner and to provide a ''call for service'' notification when the brightness has changed from its setpoint, either high or low. In prior development work BNL has explored the response of this system to operational upsets such as excess air changes, fouled atomizer nozzles, poor fuel quality, etc. Insight Technologies, Inc. and Honeywell, Inc. have licensed this technology from the U.S. Department of Energy and have been cooperating to develop product offerings which meet industry needs with an optimal combination of function and price. Honeywell has recently completed the development of the Flame Quality Monitor (FQM or Honeywell QS7100F). This is a small module which connects via a serial cable to the burners primary operating control. Primary advantages of this approach are simplicity, cost, and ease of installation. Call-for-service conditions are output in the form of front panel indicator lights and contact closure which can trigger a range of external communication options. Under this project a field test was conducted of the FQM in cooperation with service organizations in Virginia, Pennsylvania, New Jersey, New York, and Connecticut. At total of 83 field sites were included. At each site the FQM was installed in parallel with another embodiment of this concept--the Insight AFQI. The AFQI incorporates a modem and provides the ability to provide detailed information on the trends in the flame quality over the course of the two year test period. The test site population was comprised of 79.5% boilers, 13.7% warm air furnaces, and 6.8% water heaters. Nearly all were of residential size--with firing rates ranging from 0.6 gallons of oil per hour to 1.25. During the course of the test program the monitoring equipment successfully identified problems including: plugged fuel lines, fouled nozzles, collapsed combustion

  3. Vaporization of droplets in premixing chambers

    Science.gov (United States)

    Yule, A. J.; Chigier, N. A.

    1980-01-01

    Detailed measurements were made of the structures of turbulent fuel sprays vaporizing in heated airstreams. The measurements show the size dependent vaporization and dispersion of the droplets and the important influence of the large eddies in the turbulence. The measurements form a data base for the development of models of fuel spray vaporization. Two laser techniques were specially developed for the investigation. A laser tomography technique converts line-of-sight light scattering measurements into time averaged 'point' measurements of droplet size distribution and volume concentration. A laser anemometer particle sizing technique was further developed to permit accurate measurements of individual particle sizes and velocities, with backscatter collection of light. The experiments are combined with heat transfer models to analyze the performance of miniature thermocouples in liquid sprays.

  4. Solute-mediated interactions between active droplets

    Science.gov (United States)

    Moerman, Pepijn G.; Moyses, Henrique W.; van der Wee, Ernest B.; Grier, David G.; van Blaaderen, Alfons; Kegel, Willem K.; Groenewold, Jan; Brujic, Jasna

    2017-09-01

    Concentration gradients play a critical role in embryogenesis, bacterial locomotion, as well as the motility of active particles. Particles develop concentration profiles around them by dissolution, adsorption, or the reactivity of surface species. These gradients change the surface energy of the particles, driving both their self-propulsion and governing their interactions. Here, we uncover a regime in which solute gradients mediate interactions between slowly dissolving droplets without causing autophoresis. This decoupling allows us to directly measure the steady-state, repulsive force, which scales with interparticle distance as F ˜1 /r2 . Our results show that the dissolution process is diffusion rather than reaction rate limited, and the theoretical model captures the dependence of the interactions on droplet size and solute concentration, using a single fit parameter, l =16 ±3 nm , which corresponds to the length scale of a swollen micelle. Our results shed light on the out-of-equilibrium behavior of particles with surface reactivity.

  5. Sessile droplet evaporation on superheated superhydrophobic surfaces

    CERN Document Server

    Hays, Robb C; Maynes, Daniel; Webb, Brent W

    2013-01-01

    This fluid dynamics video depicts the evaporation of sessile water droplets placed on heated superhydrophobic (SH) surfaces of varying cavity fraction, F_c, and surface temperature, T_s, above the saturation temperature, T_sat. Images were captured at 10,000 FPS and are played back at 30 FPS in this video. Teflon-coated silicon surfaces of F_c = 0, 0.5, 0.8, and 0.95 were used for these experiments. T_s ranging from 110{\\deg}C to 210{\\deg}C were studied. The video clips show how the boiling behavior of sessile droplets is altered with changes in surface microstructure. Quantitative results from heat transfer rate experiments conducted by the authors are briefly discussed near the end of the video.

  6. Field measurements of cloud droplet dynamics

    Science.gov (United States)

    Molacek, Jan; Bagheri, Gholamhossein; Bertens, Augustinus; Xu, Haitao; Bodenschatz, Eberhard

    2017-11-01

    We present an in-situ experiment investigating the dynamics of cloud droplets and its dependence on the turbulent flow properties. This dynamics plays a major role in the rate of growth of cloud particles by coalescence and the resulting precipitation rate. The experiment takes place at a mountain research station at an altitude of 2650m, and will make use of a movable platform that can travel with the mean wind velocity. Here we present preliminary results using a stationary setup. Simultaneous measurements of other variables such as droplet size distribution and humidity fluctuations are done in order to develop a more complete picture of the microphysical conditions within clouds. We thank the Bavarian State Ministry of the Environment and Consumer Protection for their generous financial support. We also acknowledge funding from European Union Horizon 2020 Programme via the COMPLETE project.

  7. Dancing droplets: Chemical space, substrates, and control

    Science.gov (United States)

    Cira, Nate; Benusiglio, Adrien; Prakash, Manu

    2015-11-01

    Previously we showed that droplets of propylene glycol and water display remarkable properties when placed on clean glass due to an interplay between surface tension and evaporation. (Cira, Benusiglio, Prakash: Nature, 2015). We showed that these mechanisms apply to a range of two-component mixtures of miscible liquids where one component has both higher surface tension and higher vapor pressure on a variety of high energy surfaces. We now show how this rule can be cheated using a simple trick. We go on to demonstrate applications for cleaning, and show how this system works on substrates prepared only with sunlight. We finish by demonstrating active control of droplets, allowing access to a host of new possibilities.

  8. Combustion characteristics of subsonic hydrogen jet diffusion flame

    Energy Technology Data Exchange (ETDEWEB)

    Torii, S. [Kumamoto Univ., Kumamoto City (Japan)

    2008-07-01

    This study investigated the split flame and re-ignition phenomenon of subsonic jet diffusion flames. The aim of the study was to characterize the underlying combustion characteristics of hydrogen micro-jet diffusion flames. The effects of nozzle diameter and rim thickness on flame re-ignition characteristics were examined. Hydrogen gas was used as a fuel during the experiments, and the flame was visualized suing the Schlieren technique in order to determine temperature and concentration measurements. The experimental apparatus consisted of a fuel nozzle, a fuel supply system, a stagnation pressure measuring device, a high-speed camera, and an image-processing system. The study showed that re-ignition phenomenon occurred in certain region of the nozzle, a small flamelet was located in the vicinity of the nozzle rim after the blowout of the main flame occurred. Further increases in mass flow rates then caused the flamelet to become extinguished. The study demonstrated that intermittence of the flame re-ignition depended on fuel mass flow rates. Rim thickness did not influence mass flow rates at the onset or at the end of the re-ignition phenomenon. It was concluded that rim thickness had a significant influence on the flamelet formed near the nozzle rim. Increases in height differences of the rim extended flame blowouts and alleviated flame lift-off behaviour. 10 refs., 9 figs.

  9. Measurement and Modeling of Particle Radiation in Coal Flames

    DEFF Research Database (Denmark)

    Bäckström, Daniel; Johansson, Robert; Andersson, Klas Jerker

    2014-01-01

    This work aims at developing a methodology that can provide information of in-flame particle radiation in industrial-scale flames. The method is based on a combination of experimental and modeling work. The experiments have been performed in the high-temperature zone of a 77 kWth swirling lignite...... properties. The in-flame particle radiation was measured with a Fourier transform infrared (FTIR) spectrometer connected to a water-cooled probe via fiber optics. In the cross-section of the flame investigated, the particles were found to be the dominating source of radiation. Apart from giving information...

  10. Electrical perturbation of cellular premixed propane/air flames

    Energy Technology Data Exchange (ETDEWEB)

    Maupin, C.L.; Harris, H.H. (Univ. of Missouri, St. Louis, MO (United States). Dept. of Chemistry)

    1994-06-01

    The phenomenon originally called polyhedral flame structure was first reported 100 years ago. Subsequent investigations showed that polyhedral structure was only one example of a more general phenomenon known now as cellular flame structure, and the range of combustion mixtures that produce them has been broadened to include lean mixtures of H[sub 2]/air, lean H[sub 2]/Br[sub 2], and rich mixtures of hydrocarbons from ethylene to octane with air. Of particular interest to the authors is the role of charged species in flames, and especially in flames that exhibit cellular structure. The electrical aspects of combustion has a long and distinguished history and this subject has been the subject of a classic monograph by Lawton and Weinberg. Electrical perturbation has been reported to affect the temperature of flames, to stabilize them at high flow rates and, in the absence of gravity, to change the speed of flame propagation, and to affect the amount of soot produced. The authors report here that premixed propane/air flames exhibiting cellular structure are quite susceptible to perturbation by electric fields. Since only charged species in the flame would be affected by the potential, and a small current would not modify transport properties of neutral species appreciably, this observation suggests that studies of this type may be useful in helping to further elucidate the role of charged species in flames.

  11. Measurements of turbulent premixed flame dynamics using cinema stereoscopic PIV

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, Adam M.; Driscoll, James F. [University of Michigan, Department of Aerospace Engineering, Ann Arbor, MI (United States); Ceccio, Steven L. [University of Michigan, Department of Mechanical Engineering, Ann Arbor, MI (United States)

    2008-06-15

    A new experimental method is described that provides high-speed movies of turbulent premixed flame wrinkling dynamics and the associated vorticity fields. This method employs cinema stereoscopic particle image velocimetry and has been applied to a turbulent slot Bunsen flame. Three-component velocity fields were measured with high temporal and spatial resolutions of 0.9 ms and 140{mu}m, respectively. The flame-front location was determined using a new multi-step method based on particle image gradients, which is described. Comparisons are made between flame fronts found with this method and simultaneous CH-PLIF images. These show that the flame contour determined corresponds well to the true location of maximum gas density gradient. Time histories of typical eddy-flame interactions are reported and several important phenomena identified. Outwardly rotating eddy pairs wrinkle the flame and are attenuated at they pass through the flamelet. Significant flame-generated vorticity is produced downstream of the wrinkled tip. Similar wrinkles are caused by larger groups of outwardly rotating eddies. Inwardly rotating pairs cause significant convex wrinkles that grow as the flame propagates. These wrinkles encounter other eddies that alter their behavior. The effects of the hydrodynamic and diffusive instabilities are observed and found to be significant contributors to the formation and propagation of wrinkles. (orig.)

  12. In Situ Monitoring of the Deposition of Flame-Made Chemoresistive Gas-Sensing Films.

    Science.gov (United States)

    Blattmann, Christoph O; Güntner, Andreas T; Pratsinis, Sotiris E

    2017-07-19

    Flame-deposited semiconducting nanomaterials on microelectronic circuitry exhibit exceptional performance as chemoresistive gas sensors. Current manufacturing technology, however, does not monitor in situ the formation of such nanostructured films, even though this can facilitate the controlled and economic synthesis of these sensors. Here, the resistance of such growing films is measured in situ during fabrication to monitor the creation of a semiconducting nanoparticle network for gas sensors. Upon formation of that network, the film resistance drops drastically to an asymptotic value that depends largely on the film structure or morphology rather than on its thickness and size of nanoparticle building blocks. Precursor solutions of various concentrations enable the flame deposition of Sb-doped SnO2 sensing films of different morphologies, each of which exhibit a characteristic in situ resistance pattern. Low precursor concentrations (1 mM) lead to thin (ca. 0.16 μm) films with slender columnar structures of increasing diameter (up to 25 nm) after prolonged deposition (up to 6 min) and show an oscillating in situ resistance during their fabrication. On the other extreme, high precursor concentrations (100 mM) lead to thick (up to 80 μm) dendritic and porous films consisting of nanoparticles with relatively small primary particle diameter (around 7 nm) that remain invariant of deposition duration, which is in agreement with the stable in situ resistance. Such dendritic films exhibit a sensor recovery time that is an order of magnitude longer than that of those made at lower concentrations. The above understanding enables the rapid and economic flame synthesis of thin gas sensors consisting of minimal semiconducting nanomaterial mass possessing a tuned baseline resistance and exhibiting excellent response to ethanol vapor.

  13. Spreading of charged micro-droplets

    Directory of Open Access Journals (Sweden)

    Joseph Iaia

    2013-09-01

    Full Text Available We consider the spreading of a charged microdroplet on a flat dielectric surface whose spreading is driven by surface tension and electrostatic repulsion. This leads to a third order nonlinear partial differential equation that gives the evolution of the height profile. Assuming the droplets are circular we are able to prove existence of solutions with infinite contact angle and in many cases we are able to prove nonexistence of solutions with finite contact angle.

  14. Computational Fluid Dynamics of rising droplets

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Matthew [Lake Superior State University; Francois, Marianne M. [Los Alamos National Laboratory

    2012-09-05

    The main goal of this study is to perform simulations of droplet dynamics using Truchas, a LANL-developed computational fluid dynamics (CFD) software, and compare them to a computational study of Hysing et al.[IJNMF, 2009, 60:1259]. Understanding droplet dynamics is of fundamental importance in liquid-liquid extraction, a process used in the nuclear fuel cycle to separate various components. Simulations of a single droplet rising by buoyancy are conducted in two-dimensions. Multiple parametric studies are carried out to ensure the problem set-up is optimized. An Interface Smoothing Length (ISL) study and mesh resolution study are performed to verify convergence of the calculations. ISL is a parameter for the interface curvature calculation. Further, wall effects are investigated and checked against existing correlations. The ISL study found that the optimal ISL value is 2.5{Delta}x, with {Delta}x being the mesh cell spacing. The mesh resolution study found that the optimal mesh resolution is d/h=40, for d=drop diameter and h={Delta}x. In order for wall effects on terminal velocity to be insignificant, a conservative wall width of 9d or a nonconservative wall width of 7d can be used. The percentage difference between Hysing et al.[IJNMF, 2009, 60:1259] and Truchas for the velocity profiles vary from 7.9% to 9.9%. The computed droplet velocity and interface profiles are found in agreement with the study. The CFD calculations are performed on multiple cores, using LANL's Institutional High Performance Computing.

  15. Oil droplets as light absorbents in seawater

    Science.gov (United States)

    Otremba, Zbigniew

    2007-07-01

    This paper presents spectra of light absorption coefficient of oil-in-water emulsion, derived using the Mie theory. In order to achieve that concentration of oil, degree of oil dispersion in seawater as well as spectra of light absorption coefficient and refractive index of chosen oils must be known. A significant role of the size distribution of oil droplets has been revealed: light absorption coefficient of emulsion increases with the rate of dispersion.

  16. Droplet Burning of JP-8/Silica Gels

    OpenAIRE

    Arnold, R.; Anderson, W. E.

    2010-01-01

    For future high performance rocket launchers, gelled propellants have the potential to replace conventional solid and liquid fuels by combining the individual advantages of both systems and neglecting the most disadvantages at the same time. Since gels show different atomization, spray and combustion behavior in comparison to liquid propellants, the investigation of single droplet vaporization and combustion is fundamental for the understanding of designing a gel operated injector system. Bas...

  17. Removal of brominated flame retardant from electrical and electronic waste plastic by solvothermal technique

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Cong-Cong [Research Center For Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085 (China); Zhang, Fu-Shen, E-mail: fszhang@rcees.ac.cn [Research Center For Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085 (China)

    2012-06-30

    Highlights: Black-Right-Pointing-Pointer A process for brominated flame retardants (BFRs) removal in plastic was established. Black-Right-Pointing-Pointer The plastic became bromine-free with the structure maintained after this treatment. Black-Right-Pointing-Pointer BFRs transferred into alcohol solvent were easily debrominated by metallic copper. - Abstract: Brominated flame retardants (BFRs) in electrical and electronic (E and E) waste plastic are toxic, bioaccumulative and recalcitrant. In the present study, tetrabromobisphenol A (TBBPA) contained in this type of plastic was tentatively subjected to solvothermal treatment so as to obtain bromine-free plastic. Methanol, ethanol and isopropanol were examined as solvents for solvothermal treatment and it was found that methanol was the optimal solvent for TBBPA removal. The optimum temperature, time and liquid to solid ratio for solvothermal treatment to remove TBBPA were 90 Degree-Sign C, 2 h and 15:1, respectively. After the treatment with various alcohol solvents, it was found that TBBPA was finally transferred into the solvents and bromine in the extract was debrominated catalyzed by metallic copper. Bisphenol A and cuprous bromide were the main products after debromination. The morphology and FTIR properties of the plastic were generally unchanged after the solvothermal treatment indicating that the structure of the plastic maintained after the process. This work provides a clean and applicable process for BFRs-containing plastic disposal.

  18. 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.

  19. Numerical and experimental studies of ethanol flames and autoignition theory for higher alkanes

    OpenAIRE

    Saxena, Priyank

    2007-01-01

    In order to enhance the fuel efficiency of an engine and to control pollutant formation, an improved understanding of the combustion chemistry of the fuels at a fundamental level is paramount. This knowledge can be gained by developing detailed reaction mechanisms of the fuels for various combustion processes and by studying combustion analytically employing reduced-chemistry descriptions. There is a need for small detailed reaction mechanisms for alkane and alcohol fuels with reduced uncerta...

  20. Adaptive Liquid Lens Actuated by Droplet Movement

    Directory of Open Access Journals (Sweden)

    Chao Liu

    2014-08-01

    Full Text Available In this paper we report an adaptive liquid lens actuated by droplet movement. Four rectangular PMMA (Polymethyl Methacrylate substrates are stacked to form the device structure. Two ITO (Indium Tin Oxide sheets stick on the bottom substrate. One PMMA sheet with a light hole is inserted in the middle of the device. A conductive droplet is placed on the substrate and touches the PMMA sheet to form a small closed reservoir. The reservoir is filled with another immiscible non-conductive liquid. The non-conductive liquid can form a smooth concave interface with the light hole. When the device is applied with voltage, the droplet stretches towards the reservoir. The volume of the reservoir reduces, changing the curvature of the interface. The device can thus achieve the function of an adaptive lens. Our experiments show that the focal length can be varied from −10 to −159 mm as the applied voltage changes from 0 to 65 V. The response time of the liquid lens is ~75 ms. The proposed device has potential applications in many fields such as information displays, imaging systems, and laser scanning systems.

  1. Liquid marble and water droplet interactions and stability.

    Science.gov (United States)

    Ueno, Kazuyuki; Bournival, Ghislain; Wanless, Erica J; Nakayama, Saori; Giakoumatos, Emma C; Nakamura, Yoshinobu; Fujii, Syuji

    2015-10-21

    The interactions between two individual water droplets were investigated in air using a combination of coalescence rig and high speed video camera. This combination allows the visualization of droplet coalescence dynamics with millisecond resolution which provides information on droplet stability. Bare water droplets coalesced rapidly upon contact, while droplet stability was achieved by coating the droplets with polystyrene particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] hairs (PDEA-PS particles) to form liquid marbles. The asymmetric interaction of a water droplet (pH 3 or 10) armoured with the PDEA-PS particles (liquid marble) with a bare droplet at pH 3 exhibited intermediate stability with coalescence observed following an induction time. The induction time was longer for the pH 10 liquid marble, where the PDEA-PS particles have a hydrophobic surface, than in the case of a pH 3 liquid marble, where the PDEA-PS particles have a hydrophilic surface. Furthermore, film formation of PDEA-PS particles on the liquid marble surface with toluene vapour confirmed capsule formation which prevented coalescence with the neighbouring water droplet instead wetting the capsule upon contact within 3 milliseconds. This study illuminates the stability of individual particle-stabilized droplets and has potential impact on processes and formulations which involve their interaction.

  2. Droplet ejection and sliding on a flapping film

    Science.gov (United States)

    Chen, Xi; Doughramaji, Nicole; Betz, Amy Rachel; Derby, Melanie M.

    2017-03-01

    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.

  3. 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.

  4. Droplet Demulsification Using Ultralow Voltage-Based Electrocoalescence.

    Science.gov (United States)

    Srivastava, A; Karthick, S; Jayaprakash, K S; Sen, A K

    2018-01-30

    Demulsification of droplets stabilized with surfactant is very challenging due to their low surface energy. We report ultralow voltage-based electrocoalescence phenomenon for the demulsification of aqueous droplets with an aqueous stream. In the absence of electric field, due to the disjoining pressure resulting from the tail-tail interaction between the surfactant molecules present on the aqueous droplets and interface, coalescence of aqueous droplets with the aqueous stream is prevented. However, above a critical electric field, the electrical stress overcomes the disjoining pressure, thus leading to the droplet coalescence. The influence of surfactant concentration, droplet diameter, and velocity on the electrocoalescence phenomena is studied. The macroscopic contact between the aqueous droplet with the aqueous stream enables droplet coalescence at much lower voltage (10 to 90 V), which is at least two orders of magnitude smaller than voltages used in prior works (1.0 to 3.0 kV). The electrocoalescence phenomena is used for the extraction of microparticles encapsulated in aqueous droplets into the aqueous stream and size-based selective demulsification. A new paradigm of droplet electrocoalescence and content extraction is presented that would find significant applications in chemistry and biology.

  5. Arrested coalescence of viscoelastic droplets with internal microstructure.

    Science.gov (United States)

    Pawar, Amar B; Caggioni, Marco; Hartel, Richard W; Spicer, Patrick T

    2012-01-01

    There are many new approaches to designing complex anisotropic colloids, often using droplets as templates. However, droplets themselves can be designed to form anisotropic shapes without any external templates. One approach is to arrest binary droplet coalescence at an intermediate stage before a spherical shape is formed. Further shape relaxation of such anisotropic, arrested structures is retarded by droplet elasticity, either interfacial or internal. In this article we study coalescence of structured droplets, containing a network of anisotropic colloids, whose internal elasticity provides a resistance to full shape relaxation and interfacial energy minimization during coalescence. Precise tuning of droplet elasticity arrests coalescence at different stages and leads to various anisotropic shapes, ranging from doublets to ellipsoids. A simple model balancing interfacial and elastic energy is used to explain experimentally observed coalescence arrest in viscoelastic droplets. During coalescence of structured droplets the interfacial energy is continuously reduced while the elastic energy is increased by compression of the internal structure and, when the two processes balance one another, coalescence is arrested. Experimentally we observe that if either interfacial energy or elasticity dominates, total coalescence or total stability of droplets results. The stabilization mechanism is directly analogous to that in a Pickering emulsion, though here the resistance to coalescence is provided via an internal volume-based, rather than surface, structure. This study provides guidelines for designing anisotropic droplets by arrested coalescence but also explains some observations of "partial" coalescence observed in commercial foods like ice cream and whipped cream.

  6. Charging and Release Mechanisms of Flexible Macromolecules in Droplets

    Science.gov (United States)

    Oh, Myong In; Consta, Styliani

    2017-08-01

    We study systematically the charging and release mechanisms of a flexible macromolecule, modeled by poly(ethylene glycol) (PEG), in a droplet by using molecular dynamics simulations. We compare how PEG is solvated and charged by sodium Na+ ions in a droplet of water (H2O), acetonitrile (MeCN), and their mixtures. Initially, we examine the location and the conformation of the macromolecule in a droplet bearing no net charge. It is revealed that the presence of charge carriers do not affect the location of PEG in aqueous and MeCN droplets compared with that in the neutral droplets, but the location of the macromolecule and the droplet size do affect the PEG conformation. PEG is charged on the surface of a sodiated aqueous droplet that is found close to the Rayleigh limit. Its charging is coupled to the extrusion mechanism, where PEG segments leave the droplet once they coordinate a Na+ ion or in a correlated motion with Na+ ions. In contrast, as PEG resides in the interior of a MeCN droplet, it is sodiated inside the droplet. The compact macro-ion transitions through partially unwound states to an extended conformation, a process occurring during the final stage of desolvation and in the presence of only a handful of MeCN molecules. For charged H2O/MeCN droplets, the sodiation of PEG is determined by the H2O component, reflecting its slower evaporation and preference over MeCN for solvating Na+ ions. We use the simulation data to construct an analytical model that suggests that the droplet surface electric field may play a role in the macro-ion-droplet interactions that lead to the extrusion of the macro-ion. This study provides the first evidence of the effect of the surface electric field by using atomistic simulations. [Figure not available: see fulltext.

  7. Reactions of ethanol on Ru

    NARCIS (Netherlands)

    Sturm, Jacobus Marinus; Liu, Feng; Lee, Christopher James; Bijkerk, Frederik

    2012-01-01

    The adsorption and reactions of ethanol on Ru(0001) were studied with temperatureprogrammed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS). Ethanol was found to adsorb intact onto Ru(0001) below 100 K. Heating to 250 K resulted in formation of ethoxy groups, which undergo

  8. Nonpremixed flame in a counterflow under electric fields

    KAUST Repository

    Park, Daegeun

    2016-05-08

    Electrically assisted combustion has been studied in order to control or improve flame characteristics, and emphasizing efficiency and emission regulation. Many phenomenological observations have been reported on the positive impact of electric fields on flame, however there is a lack of detailed physical mechanisms for interpreting these. To clarify the effects of electric fields on flame, I have investigated flame structure, soot formation, and flow field with ionic wind electrical current responses in nonpremixed counterflow flames. The effects of direct current (DC) electric field on flame movement and flow field was also demonstrated in premixed Bunsen flames. When a DC electric field was applied to a lower nozzle, the flames moved toward the cathode side due to Lorentz force action on the positive ions, soot particles simultaneously disappeared completely and laser diagnostics was used to identify the results from the soot particles. To understand the effects of an electric field on flames, flow visualization was performed by Mie scattering to check the ionic wind effect, which is considered to play an important role in electric field assisted combustion. Results showed a bidirectional ionic wind, with a double-stagnant flow configuration, which blew from the flame (ionic source) toward both the cathode and the anode. This implies that the electric field affects strain rate and the axial location of stoichiometry, important factors in maintaining nonpremixed counterflow flames; thus, soot formation of the counterflow flame can also be affected by the electric field. In a test of premixed Bunsen flames having parallel electrodes, flame movement toward the cathode and bidirectional ionic wind were observed. Using PIV measurement it was found that a created radial velocity caused by positive ions (i.e. toward a cathode), was much faster than the velocity toward the anode. Even in a study of alternating current (AC) electric fields, bidirectional ionic wind could

  9. In-Flame Characterization of a 30 MWth Bio-Dust Flame

    DEFF Research Database (Denmark)

    Johansen, Joakim Myung; Jensen, Peter Arendt; Clausen, Sønnik

    This work presents a comprehensive flame characterization campaign on an operating full-scale Danish power plant. Amagerværket Unit 1 (AMV1, 350 MWth, 12 identical burners on 3 burner levels) is 100 % fuelled with wood dust burned in suspension and stabilized by swirling flows in a triple concent...

  10. Oscillating gas flow induces reptation of granular droplets

    Science.gov (United States)

    Pastenes, Javier C.; Géminard, Jean-Christophe; Melo, Francisco

    2013-07-01

    We report on the reptation of vertically vibrated droplets of fine particles lying on a solid incline. On the one hand, time-resolved measurements show that the gas pressure in the gap between the droplet bottom and the solid surface can be accounted for by a Darcy law. The cumulative effect of the viscous drag is responsible for the droplet formation. On the other hand, we show that the gap pressure is responsible for an effective horizontal acceleration whose cumulative effect is the upward reptation of the droplets. Using various geometries of the solid substrate, we manipulate the droplets and study the effects of the substrate geometry and of the experimental parameters on the droplet shape and dynamics. The experimental results are discussed in the light of theoretical arguments. This study demonstrates that, by the choice of a suitable geometry of the surface and characteristics of the vibration, one can develop tools for precise powder handling and control.

  11. Making robust electrowetting processes: dielectric breakdown and satellite droplets

    Science.gov (United States)

    Randall, Greg; Blue, Brent

    2011-03-01

    For over ten years, charge-related wetting phenomena such as electrowetting or dielectrophoresis have been used to manipulate individual liquid droplets on grids of patterned electrodes. Many proof-of-principle droplet actuations have been shown, however some physics-based problems are complicating this technology's move to industry. These problems include: breakdown of a device's dielectric coating at field strengths lower than anticipated and generation of satellite droplets from the primary droplet's surface. We use atomic layer deposition (ALD) to fabricate high-quality dielectric layers required for robust droplet electrowetting and generate operating plots for several dielectric materials. Using scanning electron microscopy and X-ray spectroscopy, we study damage and ionic penetration into the device's dielectric layer. Using video and current measurements, we examine the physics of satellite droplet generation. We apply these findings to engineer a microfluidic process to mass produce inertial fusion energy targets.

  12. 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.

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

    DEFF Research Database (Denmark)

    Yin, Chungen

    2015-01-01

    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......-oil droplets are two key tasks. This paper presents an effort towards a generic model that is beneficial to both the tasks. A computer code for droplet heating and evaporation is developed in a generic 3D model framework. The droplets are discretized into a number of control volumes along the radial, polar...... and size are also updated accordingly. The model is validated by analytical solutions to simplified cases and also by experimental data on heating and evaporation of n-Heptane droplets available in literature. Finally, the routines to extend the validated model for the two tasks of the project...

  14. Compound Droplet Levitation for Lab-on-a-Chip

    Science.gov (United States)

    Black, James; Neitzel, G. Paul

    2016-11-01

    A fluid transport mechanism utilizing thermocapillarity has been previously shown to successfully levitate and translate both microliter- and nanoliter-volume droplets of silicone oil. The surface flow required to drive levitation and transport has not been achieved for aqueous droplets, and encapsulation of samples within a layer of silicone oil is necessary. A droplet-on-demand generator capable of producing nanoliter-volume compound droplets has been developed and previously reported. The work presented here discusses efforts to demonstrate the applicability of this microfluidic transport mechanism to lab-on-a-chip systems. We elaborate on translation speeds of single-phase, nanoliter-volume, silicone-oil droplets. Compound droplets of varying compositions of oil and water are then generated, captured, levitated, and merged to explore the composition limits thereof. Work supported by NSF and NASA.

  15. Stochastic growth of cloud droplets by collisions during settling

    Science.gov (United States)

    Madival, Deepak G.

    2017-12-01

    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.

  16. 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.

  17. Communication and computation by bacteria compartmentalized within microemulsion droplets.

    Science.gov (United States)

    Weitz, Maximilian; Mückl, Andrea; Kapsner, Korbinian; Berg, Ronja; Meyer, Andrea; Simmel, Friedrich C

    2014-01-08

    Amphiphilic inducer molecules such as N-acyl-L-homoserine lactones (AHLs) or isopropyl-β-D-thio-galactopyranoside (IPTG) can be utilized for the implementation of an artificial communication system between groups of E. coli bacteria encapsulated within water-in-oil microemulsion droplets. Using spatially extended arrays of microdroplets, we study the diffusion of both AHL and IPTG from inducer-filled reservoirs into bacteria-containing droplets, and also from droplets with AHL producing sender bacteria into neighboring droplets containing receiver cells. Computational modeling of gene expression dynamics within the droplets suggests a strongly reduced effective diffusion coefficient of the inducers, which markedly affects the spatial communication pattern in the neighborhood of the senders. Engineered bacteria that integrate AHL and IPTG signals with a synthetic AND gate gene circuit are shown to respond only in the presence of both types of sender droplets, which demonstrates the potential of the system for genetically programmed pattern formation and distributed computing.

  18. Collective waves in dense and confined microfluidic droplet arrays.

    Science.gov (United States)

    Schiller, Ulf D; Fleury, Jean-Baptiste; Seemann, Ralf; Gompper, Gerhard

    2015-08-07

    Excitation mechanisms for collective waves in confined dense one-dimensional 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. Excited longitudinal modes exhibit a short-lived cascade of pairs of laterally displacing droplets. Transversely excited modes obey the dispersion relation of microfluidic phonons and induce a coupling between longitudinal and transverse modes, whose origin is the hydrodynamic interaction of the droplets with the confining walls. Moreover, we investigate the long-time behaviour of the oscillations and discuss possible mechanisms for the onset of instabilities. Our findings demonstrate that the collective dynamics of microfluidic droplet ensembles can be studied particularly well in dense and confined systems. Experimentally, the ability to control microfluidic droplets may allow the modulation of the refractive index of optofluidic crystals, which is a promising approach for the production of dynamically programmable metamaterials.

  19. Bio-ethanol

    DEFF Research Database (Denmark)

    Wenzel, Henrik

    2007-01-01

    Throughout the world, nations are seeking ways to decrease CO2 emissions and to reduce their dependency on fossil fuels, especially oil and gas deriving from so-called politically unstable regions. The efforts comprise the energy sector (heat and electricity) as well as the transport sector....... An increasing use of biomass as energy carrier is in both sectors a prioritised way of achieving these aims, and for the transport sector, the conversion of biomass to ethanol is at present the technological pathway most strongly promoted by governments in countries all over the world. Recent research has...... available for energy purposes - be it from waste, agricultural residues or energy crops - show, however, that biomass is very limited compared to the potential use of it. Even in the most optimistic near term scenarios (30 years ahead), the total physically available biomass can at maximum substitute around...

  20. Electromagnetic emission of a strongly charged oscillating droplet

    Science.gov (United States)

    Grigor'ev, A. I.; Kolbneva, N. Yu.; Shiryaeva, S. O.

    2016-08-01

    Analytical expressions for electric field in the vicinity of an oscillating strongly charged droplet of nonviscous conducting liquid and intensity of electromagnetic radiation are derived in the linear approximation with respect to perturbation amplitude of the droplet surface. Order-of-magnitude estimations of the radiation intensity are presented. The intensity of electromagnetic radiation of a ball lightning that can be simulated using a charged droplet is not related to the surface oscillations.

  1. Engineering of Droplet Manipulation in Tertiary Junction Microfluidic Channels

    Science.gov (United States)

    2017-06-30

    AFRL-AFOSR-JP-TR-2017-0055 Engineering of Droplet Manipulation in Tertiary Junction Microfluidic Channels Shalini Gupta INDIAN INSTITUTE OF...2017 2. REPORT TYPE Final 3. DATES COVERED (From - To) 14 May 2015 to 13 Nov 2016 4. TITLE AND SUBTITLE Engineering of Droplet Manipulation in...dispersed phase was increased, the critical droplet size for transition also decreased. This multivariate approach can in future be used to engineer

  2. Simulations of droplet coalescence in simple shear flow.

    Science.gov (United States)

    Shardt, Orest; Derksen, J J; Mitra, Sushanta K

    2013-05-28

    Simulating droplet coalescence is challenging because small-scale (tens of nanometers) phenomena determine the behavior of much larger (micrometer- to millimeter-scale) droplets. In general, liquid droplets colliding in a liquid medium coalesce when the capillary number is less than a critical value. We present simulations of droplet collisions and coalescence in simple shear flow using the free-energy binary-liquid lattice Boltzmann method. In previous simulations of low-speed collisions, droplets coalesced at unrealistically high capillary numbers. Simulations of noncoalescing droplets have not been reported, and therefore, the critical capillary number for simulated collisions was unknown. By simulating droplets with radii up to 100 lattice nodes, we determine the critical capillary number for coalescence and quantify the effects of several numerical and geometric parameters. The simulations were performed with a well-resolved interface, a Reynolds number of one, and capillary numbers from 0.01 to 0.2. The ratio of the droplet radius and interface thickness has the greatest effect on the critical capillary number. As in experiments, the critical capillary number decreases with increasing droplet size. A second numerical parameter, the interface diffusivity (Péclet number) also influences the conditions for coalescence: coalescence occurs at higher capillary numbers with lower Péclet numbers (higher diffusivity). The effects of the vertical offset between the droplets and the confinement of the droplets were also studied. Physically reasonable results were obtained and provide insight into the conditions for coalescence. Simulations that match the conditions of experiments reported in the literature remain computationally impractical. However, the scale of the simulations is now sufficiently large that a comparison with experiments involving smaller droplets (≈10 μm) and lower viscosities (≈10(-6) m(2)/s, the viscosity of water) may be possible

  3. Critical parameters for the partial coalescence of a droplet

    OpenAIRE

    Gilet, T.; Mulleners, K.; Lecomte, J. P.; Vandewalle, N.; Dorbolo, S.

    2006-01-01

    The partial coalescence of a droplet onto a planar liquid/liquid interface is investigated experimentally by tuning the viscosities of both liquids. The problem mainly depends on four dimensionless parameters: the Bond number (gravity vs. surface tension), the Ohnesorge numbers (viscosity in both fluids vs. surface tension), and the density relative difference. The ratio between the daughter droplet size and the mother droplet size is investigated as a function of these dimensionless numbers....

  4. Toxicity of new generation flame retardants to Daphnia magna

    NARCIS (Netherlands)

    Waaijers, S.L.; Hartmann, J; Soeter, A.M.; Helmus, R.; Kools, S.A.E.; de Voogt, P.; Admiraal, W.; Parsons, J.R.; Kraak, M.H.S.

    2013-01-01

    There is a tendency to substitute frequently used, but relatively hazardous brominated flame retardants (BFRs) with halogen-free flame retardants (HFFRs). Consequently, information on the persistence, bioaccumulation and toxicity (PBT) of these HFFRs is urgently needed, but large data gaps and

  5. Iso-Surface Analysis of a Trubulent Diffusion Flame

    NARCIS (Netherlands)

    Geurts, Bernardus J.; Di Bucchianico, A.; Mattheij, R.M.M.; Peletier, M.A.

    2006-01-01

    We analyze the evolution of a diffusion flame in a turbulent mixing layer. The location of the flame-center is defined by the "stoichiometric" interface. Geometrical properties such as its surface-area, wrinkling and curvature are characterized using an accurate numerical level-set quadrature

  6. Diamond growth in premixed propylene-oxygen flames

    OpenAIRE

    Shin, Ho Seon; Goodwin, David G.

    1995-01-01

    Diamond film growth in low-pressure premixed propylene/oxygen flames is demonstrated. Well-faceted films are grown at a pressure of 180 Torr and a fuel/oxygen ratio of 0.47. Using propylene as the fuel may greatly improve the economics of flame synthesis of diamond, since propylene is an order of magnitude cheaper than acetylene.

  7. Environmental fate & effects of new generation flame retardants

    NARCIS (Netherlands)

    Waaijers, S.L.

    2014-01-01

    There is a pressing need for substituting several halogenated flame retardants, given the human and environmental health concerns of many of these compounds. Halogen Free Flame Retardants (HFFRs) have been suggested as alternatives and are already being marketed, although their potential impact on

  8. Histopathology of the organs of Broiler Chickens exposed to flames ...

    African Journals Online (AJOL)

    Histopathology of the organs of broiler chickens exposed to the flame and fumes of refined petroleum product kerosene at varying distances over a period of 16hrs daily for 56 days in a poultry house were evaluated. Kerosene burning was simulated in a designed burner. Kerosene flame in a designed burner was placed 4, ...

  9. Comparative Analysis of Flame Characteristics of Castor Oil and ...

    African Journals Online (AJOL)

    The flame characteristics of castor oil based foam and that of polyether foam impregnated with inorganic flame retardants (FR) were investigated. The polyether foams were impregnated with measured concentration of Antimony trioxide and Sodium bromide, Ammonium dihydrogen orthophosphate, Diammonium hydrogen ...

  10. Comparative Analysis of Flame Characteristics of Castor Oil and ...

    African Journals Online (AJOL)

    ABSTRACT: The flame characteristics of castor oil based foam and that of polyether foam impregnated with inorganic flame retardants (FR) were investigated. The polyether foams were impregnated with measured concentration of Antimony trioxide and Sodium bromide, Ammonium dihydrogen orthophosphate ...

  11. Flame retardant antibacterial cotton high-loft nonwoven fabrics

    Science.gov (United States)

    Flame retardant treated gray cotton fibers were blended with antibacterial treated gray cotton fibers and polyester/polyester sheath/core bicomponent fibers to form high-loft fabrics. The high flame retardancy (FR) and antibacterial property of these high lofts were evaluated by limiting oxygen inde...

  12. 30 CFR 75.600 - Trailing cables; flame resistance.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Trailing cables; flame resistance. 75.600 Section 75.600 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR COAL MINE... cables; flame resistance. Trailing cables used in coal mines shall meet the requirements established by...

  13. Camping Burner-Based Flame Emission Spectrometer for Classroom Demonstrations

    Science.gov (United States)

    Ne´el, Bastien; Crespo, Gasto´n A.; Perret, Didier; Cherubini, Thomas; Bakker, Eric

    2014-01-01

    A flame emission spectrometer was built in-house for the purpose of introducing this analytical technique to students at the high school level. The aqueous sample is sprayed through a homemade nebulizer into the air inlet of a consumer-grade propane camping burner. The resulting flame is analyzed by a commercial array spectrometer for the visible…

  14. Reconstructing the Cryptanalytic Attack behind the Flame Malware

    NARCIS (Netherlands)

    M.J. Fillinger (Max)

    2013-01-01

    textabstractFlame was an advanced malware, used for espionage, which infected computers running a Microsoft Windows operating system. Once a computer in a local network was infected, Flame could spread to the other computers in the network via Windows Update, disguised as a security patch from

  15. Influences of diesel pilot injection on ethanol autoignition - a numerical analysis

    Science.gov (United States)

    Burnete, N. V.; Burnete, N.; Jurchis, B.; Iclodean, C.

    2017-10-01

    The aim of this study is to highlight the influences of the diesel pilot quantity as well as the timing on the autoignition of ethanol and the pollutant emissions resulting from the combustion process. The combustion concept presented in this paper requires the injection of a small quantity of diesel fuel in order to create the required autoignition conditions for ethanol. The combustion of the diesel droplets injected in the combustion chamber lead to the creation of high temperature locations that favour the autoignition of ethanol. However, due to the high vaporization enthalpy and the better distribution inside the combustion chamber of ethanol, the peak temperature values are reduced. Due to the lower temperature values and the high burning velocity of ethanol (combined with the fact that there are multiple ignition sources) the conditions required for the formation of nitric oxides are not achieved anymore, thus leading to significantly lower NOx emissions. This way the benefits of the Diesel engine and of the constant volume combustion are combined to enable a more efficient and environmentally friendly combustion process.

  16. Adsorption and solvation of ethanol at the water liquid-vapor interface: a molecular dynamics study

    Science.gov (United States)

    Wilson, M. A.; Pohorille, A.

    1997-01-01

    The free energy profiles of methanol and ethanol at the water liquid-vapor interface at 310K were calculated using molecular dynamics computer simulations. Both alcohols exhibit a pronounced free energy minimum at the interface and, therefore, have positive adsorption at this interface. The surface excess was computed from the Gibbs adsorption isotherm and was found to be in good agreement with experimental results. Neither compound exhibits a free energy barrier between the bulk and the surface adsorbed state. Scattering calculations of ethanol molecules from a gas phase thermal distribution indicate that the mass accommodation coefficient is 0.98, and the molecules become thermalized within 10 ps of striking the interface. It was determined that the formation of the solvation structure around the ethanol molecule at the interface is not the rate-determining step in its uptake into water droplets. The motion of an ethanol molecule in a water lamella was followed for 30 ns. The time evolution of the probability distribution of finding an ethanol molecule that was initially located at the interface is very well described by the diffusion equation on the free energy surface.

  17. Long-resident droplets at the stratocumulus top

    Directory of Open Access Journals (Sweden)

    A. de Lozar

    2016-05-01

    Full Text Available Turbulence models predict low droplet-collision rates in stratocumulus clouds, which should imply a narrow droplet size distribution and little rain. Contrary to this expectation, rain is often observed in stratocumuli. In this paper, we explore the hypothesis that some droplets can grow well above the average because small-scale turbulence allows them to reside at cloud top for a time longer than the convective-eddy time t*. Long-resident droplets can grow larger because condensation due to longwave radiative cooling, and collisions have more time to enhance droplet growth. We investigate the trajectories of 1 billion Lagrangian droplets in direct numerical simulations of a cloudy mixed-layer configuration that is based on observations from the flight 11 from the VERDI campaign. High resolution is employed to represent a well-developed turbulent state at cloud top. Only one-way coupling is considered. We observe that 70 % of the droplets spend less than 0.6t* at cloud top before leaving the cloud, while 15 % of the droplets remain at least 0.9t* at cloud top. In addition, 0.2 % of the droplets spend more than 2.5t* at cloud top and decouple from the large-scale convective eddies that brought them to the top, with the result that they become memoryless. Modeling collisions like a Poisson process leads to the conclusion that most rain droplets originate from those memoryless droplets. Furthermore, most long-resident droplets accumulate at the downdraft regions of the flow, which could be related to the closed-cell stratocumulus pattern. Finally, we see that condensation due to longwave radiative cooling considerably broadens the cloud-top droplet size distribution: 6.5 % of the droplets double their mass due to radiation in their time at cloud top. This simulated droplet size distribution matches the flight measurements, confirming that condensation due to longwave radiation can be an important mechanism for broadening the droplet size

  18. Electric field mediated spraying of miniaturized droplets inside microchannel.

    Science.gov (United States)

    Timung, Seim; Chaudhuri, Joydip; Borthakur, Manash Pratim; Mandal, Tapas Kumar; Biswas, Gautam; Bandyopadhyay, Dipankar

    2017-06-01

    We report a facile and noninvasive way to disintegrate a microdroplet into a string of further miniaturized ones under the influence of an external electrohydrodynamic field inside a microchannel. The deformation and breakup of the droplet was engendered by the Maxwell's stress originating from the accumulation of induced and free charges at the oil-water interface. While at smaller field intensities, for example less than 1 MV/m, the droplet deformed into a plug, at relatively higher field intensities, e.g. ∼1.16 MV/m, a pair of droplets having opposite surface charge was formed. The charged droplets showed an interesting periodic bridging and breakup during their translation motion across the channel. For even higher field intensities, for example more than 1.2 MV/m, the entire droplet underwent dielectrophoresis toward one of the electrodes before experiencing a strong attractive force from the other electrode to deform into a shape of a Taylor cone. With progress in time, mimicking the electrospraying phenomenon, the cone tip periodically ejected a string of miniaturized water droplets to form a microemulsion inside the channel. The frequency and size of the droplet ejection could be tuned by varying the applied field intensity. A water droplet of ∼214 μm diameter could continuously eject droplets of size ∼10 μm or even smaller to form a microemulsion inside the channel. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Instabilities, motion and deformation of active fluid droplets

    Science.gov (United States)

    Whitfield, Carl A.; Hawkins, Rhoda J.

    2016-12-01

    We consider two minimal models of active fluid droplets that exhibit complex dynamics including steady motion, deformation, rotation and oscillating motion. First we consider a droplet with a concentration of active contractile matter adsorbed to its boundary. We analytically predict activity driven instabilities in the concentration profile, and compare them to the dynamics we find from simulations. Secondly, we consider a droplet of active polar fluid of constant concentration. In this system we predict, motion and deformation of the droplets in certain activity ranges due to instabilities in the polarisation field. Both these systems show spontaneous transitions to motility and deformation which resemble dynamics of the cell cytoskeleton in animal cells.

  20. Electro-coalescence of particle-coated droplets

    Science.gov (United States)

    Shum, Anderson Ho Cheung

    Droplets in air or in an immiscible liquid phase are used widely in applications ranging from personal hygiene products to drug delivery. The stability of the droplets are highly linked to their utility, and thus have been systematically studied. To enhance the stability of the droplets, particles are often added to the droplets. In this talk, I will discuss how the particle layer at droplet interfaces responds to electrical charging of the droplets. The electrical forces can distort the droplet shape, which is opposed by the layer of particles adsorbed. A balance of the electrical and interfacial effects provides a quantitative indicator of the droplet instability. The coalescence of droplets in both air and liquid induced by electrically charging, which we call ``electro-coalescence'', will be introduced, with its potential application in devising a digital millifluidic platform. We thank the Research Grants Council of Hong Kong (No. HKU 719813E, 17304514 and 17306315 and C6004-14G) from the and National Natural Science Foundation of China (No. 21476189/B060201 and 91434202).