Fabrication of open-top microchannel plate using deep X-ray exposure mask made with silicon on insulator substrate

CERN Document Server

Fujimura, T; Etoh, S I; Hattori, R; Kuroki, Y; Chang, S S

2003-01-01

We propose a high-aspect-ratio open-top microchannel plate structure. This type of microchannel plate has many advantages in electrophoresis. The plate was fabricated by deep X-ray lithography using synchrotron radiation (SR) light and the chemical wet etching process. A deep X-ray exposure mask was fabricated with a silicon on insulator (SOI) substrate. The patterned Si microstructure was micromachined into a thin Si membrane and a thick Au X-ray absorber was embedded in it by electroplating. A plastic material, polymethylmethacrylate (PMMA) was used for the plate substrate. For reduction of the exposure time and high-aspect-ratio fast wet development, the fabrication condition was optimized with respect to not the exposure dose but to the PMMA mean molecular weight (M.W.) changing after deep X-ray exposure as measured by gel permeation chromatography (GPC). Decrement of the PMMA M.W. and increment of the wet developer temperature accelerated the etching rate. Under optimized fabrication conditions, a microc...

Optimization of triangular microchannel heat sinks using constructible theory

International Nuclear Information System (INIS)

Mardani, Moloud; Salimpour, Mohammad Reza

2016-01-01

The present paper examines the optimization of triangular microchannel heat sinks. The impact of volume fraction of solid material and pressure drop on the maximum temperature of the microchannel heat sinks are investigated and their optimum operating conditions are compared. From the results, it is seen that increasing the side angle of the triangular microchannel, improves its performance. Furthermore, there is an appropriate agreement between the analytical and numerical results. Finally, the effect of degrees of freedom on the performance of microchannels is investigated. To accomplish this end, the triangular microchannels with the side angle of 60 degree have been chosen as it has the best performance compared to other microchannels. It is observed that the minimized maximum temperatures of optimized microchannel heat sinks with three degrees of freedom are 10% lower than the ones with two degrees of freedom

Laser-Induced Motion of a Nanofluid in a Micro-Channel

OpenAIRE

Tran X. Phuoc; Mehrdad Massoudi; Ping Wang

2016-01-01

Since a photon carries both energy and momentum, when it interacts with a particle, photon-particle energy and momentum transfer occur, resulting in mechanical forces acting on the particle. In this paper we report our theoretical study on the use of a laser beam to manipulate and control the flow of nanofluids in a micro-channel. We calculate the velocity induced by a laser beam for TiO2, Fe2O3, Al2O3 MgO, and SiO2 nanoparticles with water as the base fluid. The particle diameter is 50 nm an...

Micro-channel plates and vacuum detectors

Energy Technology Data Exchange (ETDEWEB)

Gys, T., E-mail: Thierry.Gys@cern.ch

2015-07-01

A micro-channel plate is an array of miniature electron multipliers that are each acting as a continuous dynode chain. The compact channel structure results in high spatial and time resolutions and robustness to magnetic fields. Micro-channel plates have been originally developed for night vision applications and integrated as an amplification element in image intensifiers. These devices show single-photon sensitivity with very low noise and have been used as such for scintillating fiber tracker readout in high-energy physics experiments. Given their very short transit time spread, micro-channel plate photomultiplier tubes are also being used in time-of-flight and particle identification detectors. The present paper will cover the history of the micro-channel plate development, basic features, and some of their applications. Emphasis will be put on various new manufacturing processes that have been developed over the last few years, and that result in a significant improvement in terms of efficiency, noise, and lifetime performance.

Integration of microplasma and microfluidic technologies for localised microchannel surface modification

Science.gov (United States)

Szili, Endre J.; Al-Bataineh, Sameer A.; Priest, Craig; Gruner, Philipp J.; Ruschitzka, Paul; Bradley, James W.; Ralston, John; Steele, David A.; Short, Robert D.

2011-12-01

In this paper we describe the spatial surface chemical modification of bonded microchannels through the integration of microplasmas into a microfluidic chip (MMC). The composite MMC comprises an array of precisely aligned electrodes surrounding the gas/fluid microchannel. Pairs of electrodes are used to locally ignite microplasmas inside the microchannel. Microplasmas, comprising geometrically confined microscopic electrically-driven gas discharges, are used to spatially functionalise the walls of the microchannels with proteins and enzymes down to scale lengths of 300 μm inside 50 μm-wide microchannels. Microchannels in poly(dimethylsiloxane) (PDMS) or glass were used in this study. Protein specifically adsorbed on to the regions inside the PDMS microchannel that were directly exposed to the microplasma. Glass microchannels required pre-functionalisation to enable the spatial patterning of protein. Firstly, the microchannel wall was functionalised with a protein adhesion layer, 3-aminopropyl-triethoxysilane (APTES), and secondly, a protein blocking agent (bovine serum albumin, BSA) was adsorbed onto APTES. The functionalised microchannel wall was then treated with an array of spatially localised microplasmas that reduced the blocking capability of the BSA in the region that had been exposed to the plasma. This enabled the functionalisation of the microchannel with an array of spatially separated protein. As an alternative we demonstrated the feasibility of depositing functional thin films inside the MMC by spatially plasma depositing acrylic acid and 1,7-octadiene within the microchannel. This new MMC technology enables the surface chemistry of microchannels to be engineered with precision, which is expected to broaden the scope of lab-on-a-chip type applications.

Boiling in microchannels: a review of experiment and theory

International Nuclear Information System (INIS)

Thome, John R.

2004-01-01

A summary of recent research on boiling in microchannels is presented. The review addresses the topics of macroscale versus microscale heat transfer, two-phase flow regimes, flow boiling heat transfer results for microchannels, heat transfer mechanisms in microchannels and flow boiling models for microchannels. In microchannels, the most dominant flow regime appears to be the elongated bubble mode that can persist up to vapor qualities as high as 60-70% in microchannels, followed by annular flow. Flow boiling heat transfer coefficients have been shown experimentally to be dependent on heat flux and saturation pressure while only slightly dependent on mass velocity and vapor quality. Hence, these studies have concluded that nucleate boiling controls evaporation in microchannels. Instead, a recent analytical study has shown that transient evaporation of the thin liquid films surrounding elongated bubbles is the dominant heat transfer mechanism as opposed to nucleate boiling and is able to predict these trends in the experimental data. Newer experimental studies have further shown that there is in fact a significant effect of mass velocity and vapor quality on heat transfer when covering a broader range of conditions, including a sharp peak at low vapor qualities at high heat fluxes. Furthermore, it is concluded that macroscale models are not realistic for predicting flowing boiling coefficients in microchannels as the controlling mechanism is not nucleate boiling nor turbulent convection but is transient thin film evaporation (also, microchannel flows are typically laminar and not turbulent as assumed by macroscopic models). A more advanced three-zone flow boiling model for evaporation of elongated bubbles in microchannels is currently under development that so far qualitatively describes all these trends. Numerous fundamental aspects of two-phase flow and evaporation remain to be better understood and some of these aspects are also discussed

Process for separating nitrogen from methane using microchannel process technology

Science.gov (United States)

Tonkovich, Anna Lee [Marysville, OH; Qiu, Dongming [Dublin, OH; Dritz, Terence Andrew [Worthington, OH; Neagle, Paul [Westerville, OH; Litt, Robert Dwayne [Westerville, OH; Arora, Ravi [Dublin, OH; Lamont, Michael Jay [Hilliard, OH; Pagnotto, Kristina M [Cincinnati, OH

2007-07-31

The disclosed invention relates to a process for separating methane or nitrogen from a fluid mixture comprising methane and nitrogen, the process comprising: (A) flowing the fluid mixture into a microchannel separator, the microchannel separator comprising a plurality of process microchannels containing a sorption medium, the fluid mixture being maintained in the microchannel separator until at least part of the methane or nitrogen is sorbed by the sorption medium, and removing non-sorbed parts of the fluid mixture from the microchannel separator; and (B) desorbing the methane or nitrogen from the sorption medium and removing the desorbed methane or nitrogen from the microchannel separator. The process is suitable for upgrading methane from coal mines, landfills, and other sub-quality sources.

Condensation in Microchannels

National Research Council Canada - National Science Library

Ameel, Timothy

1999-01-01

.... Evaporators and condensers for meso-scale energy systems will most likely be constructed of microchannels due to the microfabrication constraints that limit most structures to two-dimensional planar geometries...

Laser beam micro-milling of micro-channels in aerospace alloys

CERN Document Server

Ahmed, Naveed; Al-Ahmari, Abdulrahman

2017-01-01

This volume is greatly helpful to micro-machining and laser engineers as it offers obliging guidelines about the micro-channel fabrications through Nd:YAG laser beam micro-milling. The book also demonstrates how the laser beam micro-milling behaves when operating under wet conditions (under water), and explores what are the pros and cons of this hybrid technique. From the predictive mathematical models, the readers can easily estimate the resulting micro-channel size against the desired laser parametric combinations. The book considers micro-channels in three highly important research materials commonly used in aerospace industry: titanium alloy Ti-6Al-4V, nickel alloy Inconel 718 and aluminum alloy AA 2024. Therefore, the book is highly practicable in the fields of micro-channel heat exchangers, micro-channel aerospace turbine blades, micro-channel heat pipes, micro-coolers and micro-channel pulsating heat plates. These are frequently used in various industries such as aerospace, automotive, biomedical and m...

Heat transfer and fluid flow in minichannels and microchannels

CERN Document Server

Kandlikar, Satish; Li, Dongqing; Colin, Stephane; King, Michael R

2014-01-01

Heat exchangers with minichannel and microchannel flow passages are becoming increasingly popular due to their ability to remove large heat fluxes under single-phase and two-phase applications. Heat Transfer and Fluid Flow in Minichannels and Microchannels methodically covers gas, liquid, and electrokinetic flows, as well as flow boiling and condensation, in minichannel and microchannel applications. Examining biomedical applications as well, the book is an ideal reference for anyone involved in the design processes of microchannel flow passages in a heat exchanger. Each chapter is accompan

Microchannel boiling mechanisms leading to burnout

International Nuclear Information System (INIS)

Landram, C.S.; Riddle, R.A.

1994-01-01

The authors are analyzing the thermal performance of microchannel heat sinks to extend their applied heat loads beyond coolant single-phase limits. This is the first investigation of boiling in the narrow (50-μm) microchannels having typically high-aspect-ratio (of order 10/1) flow cross-sections. The prescription of local, wall-coolant, interfacial, two-phase correlations first required development of a validated, approximate, thermal-model accounting for conjugate heat transfer. The strongest mechanism for heat transfer in two-phase microchannel flow was found to be saturated boiling in a channel region near the heated base. When this region dried out, burnout occurred, both in the computations and in the experiment

Microchannel neural interface manufacture by stacking silicone and metal foil laminae

Science.gov (United States)

Lancashire, Henry T.; Vanhoestenberghe, Anne; Pendegrass, Catherine J.; Ajam, Yazan Al; Magee, Elliot; Donaldson, Nick; Blunn, Gordon W.

2016-06-01

Objective. Microchannel neural interfaces (MNIs) overcome problems with recording from peripheral nerves by amplifying signals independent of node of Ranvier position. Selective recording and stimulation using an MNI requires good insulation between microchannels and a high electrode density. We propose that stacking microchannel laminae will improve selectivity over single layer MNI designs due to the increase in electrode number and an improvement in microchannel sealing. Approach. This paper describes a manufacturing method for creating MNIs which overcomes limitations on electrode connectivity and microchannel sealing. Laser cut silicone—metal foil laminae were stacked using plasma bonding to create an array of microchannels containing tripolar electrodes. Electrodes were DC etched and electrode impedance and cyclic voltammetry were tested. Main results. MNIs with 100 μm and 200 μm diameter microchannels were manufactured. High electrode density MNIs are achievable with electrodes present in every microchannel. Electrode impedances of 27.2 ± 19.8 kΩ at 1 kHz were achieved. Following two months of implantation in Lewis rat sciatic nerve, micro-fascicles were observed regenerating through the MNI microchannels. Significance. Selective MNIs with the peripheral nervous system may allow upper limb amputees to control prostheses intuitively.

Study of condensation of refrigerants in a micro-channel for development of future compact micro-channel condensers

Science.gov (United States)

Chowdhury, Sourav

2009-12-01

Mini- and micro-channel technology has gained considerable ground in the recent years in industry and is favored due to its several advantages stemming from its high surface to volume ratio and high values of proof pressure it can withstand. Micro-channel technology has paved the way to development of highly compact heat exchangers with low cost and mass penalties. In the present work, the issues related to the sizing of compact micro-channel condensers have been explored. The considered designs encompass both the conventional and MEMS fabrication techniques. In case of MEMS-fabricated micro-channel condenser, wet etching of the micro-channel structures, followed by bonding of two such wafers with silicon nitride layers at the interface was attempted. It was concluded that the silicon nitride bonding requires great care in terms of high degree of surface flatness and absence of roughness and also high degree of surface purity and thus cannot be recommended for mass fabrication. Following this investigation, a carefully prepared experimental setup and test micro-channel with hydraulic diameter 700 mum and aspect ratio 7:1 was fabricated and overall heat transfer and pressure drop aspects of two condensing refrigerants, R134a and R245fa were studied at a variety of test conditions. To the best of author's knowledge, so far no data has been reported in the literature on condensation in such high aspect ratio micro-channels. Most of the published experimental works on condensation of refrigerants are concerning conventional hydraulic diameter channels (> 3mm) and only recently some experimental data has been reported in the sub-millimeter scale channels for which the surface tension and viscosity effects play a dominant role and the effect of gravity is diminished. It is found that both experimental data and empirically-derived correlations tend to under-predict the present data by an average of 25%. The reason for this deviation could be because a high aspect ratio

Study of different cross-shaped microchannels affecting thermal-bubble-actuated microparticle manipulation

Science.gov (United States)

Li, Weichen; Tsou, Chingfu

2015-10-01

This paper presents a thermal-bubble-actuated microfluidic chip with cross-shaped microchannels for evaluating the effect of different microchannel designs on microparticle manipulation. Four cross-shaped microchannel designs, with orthogonal, misaligned, skewed, and antiskewed types, were proposed in this study. The thermal bubble micropump, which is based on a resistive bulk microheater, was used to drive fluid transportation, and it can be realized using a simple microfabrication process with a silicon-on-isolator wafer. Using commercial COMSOL software, the flow profiles of microfluidics in various cross-shaped microchannels were simulated qualitatively under different pumping pressures. Microbeads, with a diameter of 20 μm, manipulated in four cross-shaped microchannels, were also implemented in this experiment. The results showed that a skewed microchannel design has a higher sorting rate compared with orthogonal, misaligned, and antiskewed microchannels because its flow velocity in the main microchannel is significantly reduced by pumping pressure. Typically, the successful sorting rate for this type of skewed microchannel can reach 30% at a pumping frequency of 100 Hz.

Formation of microchannels from low-temperature plasma-deposited silicon oxynitride

Science.gov (United States)

Matzke, Carolyn M.; Ashby, Carol I. H.; Bridges, Monica M.; Manginell, Ronald P.

2000-01-01

A process for forming one or more fluid microchannels on a substrate is disclosed that is compatible with the formation of integrated circuitry on the substrate. The microchannels can be formed below an upper surface of the substrate, above the upper surface, or both. The microchannels are formed by depositing a covering layer of silicon oxynitride over a mold formed of a sacrificial material such as photoresist which can later be removed. The silicon oxynitride is deposited at a low temperature (.ltoreq.100.degree. C.) and preferably near room temperature using a high-density plasma (e.g. an electron-cyclotron resonance plasma or an inductively-coupled plasma). In some embodiments of the present invention, the microchannels can be completely lined with silicon oxynitride to present a uniform material composition to a fluid therein. The present invention has applications for forming microchannels for use in chromatography and electrophoresis. Additionally, the microchannels can be used for electrokinetic pumping, or for localized or global substrate cooling.

Effect of microchannel structure on the reaction performance of methanol steam reforming

International Nuclear Information System (INIS)

Pan, Minqiang; Wu, Qiuyu; Jiang, Lianbo; Zeng, Dehuai

2015-01-01

Highlights: • Effect of microchannel cross-section and distribution on MSR are investigated. • Microchannel distribution shows much more influence on reaction performance. • SLDR and ELR with rectangular cross-section present better reaction performance. • DLSR and EUU with tooth cross-section have better reaction performance. • Equal-distribution of microchannels present the best reaction performance. - Abstract: Methanol steam reforming inside microchannel reactors is regarded as one of effective methods for supplying hydrogen for fuel cells. Microchannel structure plays an important role on the reaction performance of methanol steam reforming. Parallel and uniform-distributed microchannels with rectangular cross-section are generally adopted. In this work, two kinds of microchannel cross-sections and four kinds of microchannel distributions are selected to investigate the effect of microchannel structure on the reaction performance of methanol steam reforming. The result indicates that microchannel distribution shows much more influences on the reaction performance of methanol steam reforming than the microchannel cross-section. Sparse-distribution in the Left direction and Dense-distribution in the Right direction (SLDR) as well as Equal-distribution in the Left–Right direction (ELR) with rectangular cross-section present relatively good reaction performances, whereas Dense-distribution in the Left direction and Sparse-distribution in the Right direction (DLSR) as well as Equal-distribution in the Upside–Underside direction (EUU) with tooth cross-section have relatively good performances. ELR presents the best reaction performances of methanol steam reforming among all the investigated microchannel structures, whether rectangular or tooth cross-section

Development of time-of-flight RBS system using multi microchannel plates

International Nuclear Information System (INIS)

Nguyen, N.V.; Abo, S.; Lohner, T.; Sawaragi, H.; Wakaya, F.; Takai, M.

2007-01-01

A new time-of-flight Rutherford backscattering spectroscopy (TOF-RBS) system with two circular microchannel plates (MCPs) installed at a distance of 140 mm from a sample holder and a scattering angle of 125 o and a 100 kV focused ion beam column having a liquid metal ion source (LMIS) of AuSiBe alloy has been assembled to obtain high counting rate and enhanced mass resolution. The possible influence of the two MCPs by logical summation of the output signals on the time resolution was investigated by measuring dedicated thin deposited metallic samples. And, the time resolution was found in the range of 1.5-2 ns

Microfabrication of Microchannels for Fuel Cell Plates

Directory of Open Access Journals (Sweden)

Ho Su Jang

2009-12-01

Full Text Available Portable electronic devices such as notebook computers, PDAs, cellular phones, etc., are being widely used, and they increasingly need cheap, efficient, and lightweight power sources. Fuel cells have been proposed as possible power sources to address issues that involve energy production and the environment. In particular, a small type of fuel-cell system is known to be suitable for portable electronic devices. The development of micro fuel cell systems can be achieved by the application of microchannel technology. In this study, the conventional method of chemical etching and the mechanical machining method of micro end milling were used for the microfabrication of microchannel for fuel cell separators. The two methods were compared in terms of their performance in the fabrication with regards to dimensional errors, flatness, straightness, and surface roughness. Following microchannel fabrication, the powder blasting technique is introduced to improve the coating performance of the catalyst on the surface of the microchannel. Experimental results show that end milling can remarkably increase the fabrication performance and that surface treatment by powder blasting can improve the performance of catalyst coating.

Aluminum Nitride Micro-Channels Grown via Metal Organic Vapor Phase Epitaxy for MEMs Applications

Energy Technology Data Exchange (ETDEWEB)

Rodak, L.E.; Kuchibhatla, S.; Famouri, P.; Ting, L.; Korakakis, D.

2008-01-01

Aluminum nitride (AlN) is a promising material for a number of applications due to its temperature and chemical stability. Furthermore, AlN maintains its piezoelectric properties at higher temperatures than more commonly used materials, such as Lead Zirconate Titanate (PZT) [1, 2], making AlN attractive for high temperature micro and nanoelectromechanical (MEMs and NEMs) applications including, but not limited to, high temperature sensors and actuators, micro-channels for fuel cell applications, and micromechanical resonators. This work presents a novel AlN micro-channel fabrication technique using Metal Organic Vapor Phase Epitaxy (MOVPE). AlN easily nucleates on dielectric surfaces due to the large sticking coefficient and short diffusion length of the aluminum species resulting in a high quality polycrystalline growth on typical mask materials, such as silicon dioxide and silicon nitride [3,4]. The fabrication process introduced involves partially masking a substrate with a silicon dioxide striped pattern and then growing AlN via MOVPE simultaneously on the dielectric mask and exposed substrate. A buffered oxide etch is then used to remove the underlying silicon dioxide and leave a free standing AlN micro-channel. The width of the channel has been varied from 5 ìm to 110 ìm and the height of the air gap from 130 nm to 800 nm indicating the stability of the structure. Furthermore, this versatile process has been performed on (111) silicon, c-plane sapphire, and gallium nitride epilayers on sapphire substrates. Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM), and Raman measurements have been taken on channels grown on each substrate and indicate that the substrate is influencing the growth of the AlN micro-channels on the SiO2 sacrificial layer.

Asymmetrical Supercapacitor Composed of Thin Co(OH)2 Nanoflakes on Three-Dimensional Ni/Si Microchannel Plates with Superior Electrochemical Performance

International Nuclear Information System (INIS)

Li, Mai; Xu, Shaohui; Cherry, Christopher; Zhu, Yiping; Huang, Rong; Qi, Ruijuan; Yang, Pingxiong; Wang, Lianwei; Chu, Paul K.

2014-01-01

Graphical abstract: The paper studied the formation mechanism and growth process of nanostructured Co(OH) 2 . The first step of Co(OH) 2 growth involves nucleation of nanorods and tiny nanowires and the second is interconnection growth based on those nanostructures. By using the Co(OH) 2 /Ni/Si-MCPs electrode as the positive electrode and CNTs/nickel foam (CNTs/NF) as the negative electrode, the device assembled with CR2025 batteries exhibits high energy density (38.39 Wh kg −1 ), high power density (5400 W kg −1 at 9.67 Wh kg −1 ), and stable power characteristic (2000 times with 80.63% retention). After charging each supercapacitor for 10 s, the device can power a 5 mm diameter light-emitting diode (LED) with different colors efficiently, for example, a blue LED for 20 min. - Abstract: Nanoscale cobalt hydroxide (Co(OH) 2 ) particles are fabricated by electrodeposition on three-dimensional nickel/silicon microchannel plates (Ni/Si-MCPs) as the active electrode materials on the surface and sidewall of the Ni/Si-MCPs for miniature supercapacitors. The relationship among the electrodeposition time, morphology, formation mechanism of Co(OH) 2 nanostructure, and capacitor performance is studied. Using an optimal electrodeposition time of 6 min, the Co(OH) 2 supercapacitor has a capacitance of 697.56 F g −1 (5.72 F cm −2 ) at 2 mA cm −2 and the retention ratio is 91.20% after 2500 cycles. The large areal capacitance and excellent rate capability can be attributed to the unique 3D ordered porous architecture which facilitates electron and ion transport, enlarges the liquid-solid interfacial area, and enhances the utilization efficiency of the active materials. Meanwhile, the weight and size of the device are reduced. By using the Co(OH) 2 /Ni/Si-MCPs electrode as the positive electrode and CNTs/nickel foam (CNTs/NF) as the negative electrode, the device assembled with CR2025 batteries exhibits high energy density (38.39 Wh kg −1 ), high power density (5400

Static response of deformable microchannels: a comparative modelling study

Science.gov (United States)

Shidhore, Tanmay C.; Christov, Ivan C.

2018-02-01

We present a comparative modelling study of fluid-structure interactions in microchannels. Through a mathematical analysis based on plate theory and the lubrication approximation for low-Reynolds-number flow, we derive models for the flow rate-pressure drop relation for long shallow microchannels with both thin and thick deformable top walls. These relations are tested against full three-dimensional two-way-coupled fluid-structure interaction simulations. Three types of microchannels, representing different elasticity regimes and having been experimentally characterized previously, are chosen as benchmarks for our theory and simulations. Good agreement is found in most cases for the predicted, simulated and measured flow rate-pressure drop relationships. The numerical simulations performed allow us to also carefully examine the deformation profile of the top wall of the microchannel in any cross section, showing good agreement with the theory. Specifically, the prediction that span-wise displacement in a long shallow microchannel decouples from the flow-wise deformation is confirmed, and the predicted scaling of the maximum displacement with the hydrodynamic pressure and the various material and geometric parameters is validated.

Microchannel plate assembly parameters with micron gaps

International Nuclear Information System (INIS)

Demchenkova, A.A.

1987-01-01

Performance of chevron microchannel plate assembly with 5 and 15 μm gaps between them has been investigated. The assembly is placed into a vacuum chamber under pressure -6 Torr and irradiated by neutral He and Ar atom beams with 1.5 and 3 keV energies as well as by ultraviolet photons with 147 nm wave length. Dependence of the gain and amplitude resolution on power voltage in plates are measured. The results obtained have shown that microchannel plates permit to obtain the gain up to 3x10 7 and amplitude resolution up to 30% when detecting both atomic particles and ultraviolet photons. The assembly can be effectively used in those cases when it is necessary to use microchannel plates with curved channels

Microchannel plate photodetectors

International Nuclear Information System (INIS)

Majka, R.

1977-01-01

A review is given the status of development work on photodetectors using microchannel plates (MCP) as the electron gain element. Projections are made and opinions are presented on what might be available in the next few years. Several uses for these devices at ISABELLE are mentioned

Effect of nano-scale morphology on micro-channel wall surface and electrical characterization in lead silicate glass micro-channel plate

Science.gov (United States)

Cai, Hua; Li, Fangjun; Xu, Yanglei; Bo, Tiezhu; Zhou, Dongzhan; Lian, Jiao; Li, Qing; Cao, Zhenbo; Xu, Tao; Wang, Caili; Liu, Hui; Li, Guoen; Jia, Jinsheng

2017-10-01

Micro-channel plate (MCP) is a two dimensional arrays of microscopic channel charge particle multiplier. Silicate composition and hydrogen reduction are keys to determine surface morphology of micro-channel wall in MCP. In this paper, lead silicate glass micro-channel plates in two different cesium contents (0at%, 0.5at%) and two different hydrogen reduction temperatures (400°C,450°C) were present. The nano-scale morphology, elements content and chemical states of microporous wall surface treated under different alkaline compositions and reduction conditions was investigated by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS), respectively. Meanwhile, the electrical characterizations of MCP, including the bulk resistance, electron gain and the density of dark current, were measured in a Vacuum Photoelectron Imaging Test Facility (VPIT).The results indicated that the granular phase occurred on the surface of microporous wall and diffuses in bulk glass is an aggregate of Pb atom derived from the reduction of Pb2+. In micro-channel plate, the electron gain and bulk resistance were mainly correlated to particle size and distribution, the density of dark current (DDC) went up with the increasing root-mean-square roughness (RMS) on the microporous wall surface. Adding cesiums improved the size of Pb atomic aggregation, lowered the relative concentration of [Pb] reduced from Pb2+ and decreased the total roughness of micro-channel wall surface, leading a higher bulk resistance, a lower electron gain and a less dark current. Increasing hydrogen reduction temperature also improved the size of Pb atomic aggregation, but enhanced the relative concentration of [Pb] and enlarged the total roughness of micro-channel wall surface, leading a higher bulk resistance, a lower electron gain and a larger dark current. The reasons for the difference of electrical characteristics were discussed.

CW-laser induced microchannels in dye-polymethacrylic acid films

OpenAIRE

M.A. Camacho-López

2007-01-01

In this work we report on the formation of microchannels on dye-polymethacrylic acid films using a cw-laser. A focalized beam of a He-Ne laser (632.8 nm emission line) was used to form microchannels on the films. It was found that there exists a laser power density threshold for a pit formation that depends on the dye concentration. The dimensions of the laser-induced channels are dependent on the laser power density. Microchannel formation in the transparent polymethacrylic acid films was no...

Scanning Microscopes Using X Rays and Microchannels

Science.gov (United States)

Wang, Yu

2003-01-01

Scanning microscopes that would be based on microchannel filters and advanced electronic image sensors and that utilize x-ray illumination have been proposed. Because the finest resolution attainable in a microscope is determined by the wavelength of the illumination, the xray illumination in the proposed microscopes would make it possible, in principle, to achieve resolutions of the order of nanometers about a thousand times as fine as the resolution of a visible-light microscope. Heretofore, it has been necessary to use scanning electron microscopes to obtain such fine resolution. In comparison with scanning electron microscopes, the proposed microscopes would likely be smaller, less massive, and less expensive. Moreover, unlike in scanning electron microscopes, it would not be necessary to place specimens under vacuum. The proposed microscopes are closely related to the ones described in several prior NASA Tech Briefs articles; namely, Miniature Microscope Without Lenses (NPO-20218), NASA Tech Briefs, Vol. 22, No. 8 (August 1998), page 43; and Reflective Variants of Miniature Microscope Without Lenses (NPO-20610), NASA Tech Briefs, Vol. 26, No. 9 (September 2002) page 6a. In all of these microscopes, the basic principle of design and operation is the same: The focusing optics of a conventional visible-light microscope are replaced by a combination of a microchannel filter and a charge-coupled-device (CCD) image detector. A microchannel plate containing parallel, microscopic-cross-section holes much longer than they are wide is placed between a specimen and an image sensor, which is typically the CCD. The microchannel plate must be made of a material that absorbs the illuminating radiation reflected or scattered from the specimen. The microchannels must be positioned and dimensioned so that each one is registered with a pixel on the image sensor. Because most of the radiation incident on the microchannel walls becomes absorbed, the radiation that reaches the

Experimental investigation of heat transfer performance for a novel microchannel heat sink

International Nuclear Information System (INIS)

Wang, Y; Ding, G-F

2008-01-01

We demonstrated a novel microchannel heat sink with a high local heat transfer efficiency contributed by a complicated microchannel system, which comprises parallel longitudinal microchannels etched in a silicon substrate and transverse microchannels electroplated on a copper heat spreader. The thermal boundary layer develops in transverse microchannels. Meanwhile, the heat transfer area is increased compared with the conventional microchannel heat sink only having parallel longitudinal microchannels. Both benefits yield high local heat transfer efficiency and enhance the overall heat transfer, which is attractive for the cooling of high heat flux electronic devices. Infrared tests show the temperature distribution in the test objects. The effects of flow rate and heat flux levels on heat transfer characteristics are presented. A uniform temperature distribution is obtained through the heating area. The reference temperatures decrease with the increasing flow rate from 0.64 ml min −1 to 6.79 ml min −1 for a constant heat flux of 10.4 W cm −2 . A heat flux of 18.9 W cm −2 is attained at a flow rate of 6.79 ml min −1 for assuring the maximum temperature of the microchannel heat sink less than the maximum working temperature of electronic devices

Study on Boiling Heat Transfer Phenomenon in Micro-channels

Energy Technology Data Exchange (ETDEWEB)

Jeong, Namgyun [Inha Technical College, Incheon (Korea, Republic of)

2017-09-15

Recently, efficient heat dissipation has become necessary because of the miniaturization of devices, and research on boiling on micro-channels has attracted attention. However, in the case of micro-channels, the friction coefficient and heat transfer characteristics are different from those in macro-channels. This leads to large errors in the micro scale results, when compared to correlations derived from the macro scale. In addition, due to the complexity of the mechanism, the boiling phenomenon in micro-channels cannot be approached only by experimental and theoretical methods. Therefore, numerical methods should be utilized as well, to supplement these methods. However, most numerical studies have been conducted on macro-channels. In this study, we applied the lattice Boltzmann method, proposed as an alternative numerical tool to simulate the boiling phenomenon in the micro-channel, and predicted the bubble growth process in the channel.

A review on the analysis and experiment of fluid flow and mixing in micro-channels

International Nuclear Information System (INIS)

Kang, Sang Mo; Suh, Yong Kweon; Jayaraj, Simon

2007-01-01

The studies with respect to micro-channels and micro-mixers are expanding in many dimensions. Most significant area of micro-mixer study is the flow analysis in various micro-channel configurations. The flow phenomena in microchannel devices are quite different from that of the macro-scale devices. An attempt is made here to review the important recent literature available in the area of micro-channel flow analysis and mixing. The topics covered include the physics of flow in micro-channels and integrated simulation of the micro-channel flow. Also, the flow control models and electro-kinetically driven micro-channel flows are dealt in detail. A survey of important numerical methods, which are currently popular for micro-channel flow analysis, is carried out. Different options for mixing in microchannels are provided, in sufficient detail

Enabling Microliquid Chromatography by Microbead Packing of Microchannels

Science.gov (United States)

Balvin, Manuel; Zheng, Yun

2014-01-01

The microbead packing is the critical element required in the success of on-chip microfabrication of critical microfluidic components for in-situ analysis and detection of chiral amino acids. In order for microliquid chromatography to occur, there must be a stationary phase medium within the microchannel that interacts with the analytes present within flowing fluid. The stationary phase media are the microbeads packed by the process discussed in this work. The purpose of the microliquid chromatography is to provide a lightweight, low-volume, and low-power element to separate amino acids and their chiral partners efficiently to understand better the origin of life. In order to densely pack microbeads into the microchannels, a liquid slurry of microbeads was created. Microbeads were extracted from a commercially available high-performance liquid chromatography column. The silica beads extracted were 5 microns in diameter, and had surface coating of phenyl-hexyl. These microbeads were mixed with a 200- proof ethanol solution to create a microbead slurry with the right viscosity for packing. A microfilter is placed at the outlet via of the microchannel and the slurry is injected, then withdrawn across a filter using modified syringes. After each injection, the channel is flushed with ethanol to enhance packing. This cycle is repeated numerous times to allow for a tightly packed channel of microbeads. Typical microbead packing occurs in the macroscale into tubes or channels by using highly pressurized systems. Moreover, these channels are typically long and straight without any turns or curves. On the other hand, this method of microbead packing is completed within a microchannel 75 micrometers in diameter. Moreover, the microbead packing is completed into a serpentine type microchannel, such that it maximizes microchannel length within a microchip. Doing so enhances the interactions of the analytes with the microbeads to separate efficiently amino acids and amino acid

Production of monodispersed Oil-in Water Emulsion Using Crossflow-Type Silicon Microchannel Plate

Energy Technology Data Exchange (ETDEWEB)

Kawakatsu, Takahiro.; Komori, Hideaki.; Yonemoto, Toshikuni. [Tohoku University, Miyagi (Japan). Chemical Engineering Department; Nakajima, Mitsutoshi.; Kikuchi, Yuji. [National Food Research Institute, Ibaraki (Japan)

1999-04-01

A novel method for continuous productin of monodispersed oil-in-water (O/W) emulsion is developed using acrossflow-type silicaon microchannel plate. On the single crystal silicon plate, a liquid flow path for continuous phase was made, and at each side of th wall of the path an array of regular-sized slits was precisely fabricated. A flat glass plate was tightly attached on the microchannel plate to cover the top of the slits to form the array of microchannels. Regular-sized oil (triolein) droplets were generated by squeezing the oil through the microchannels into the continuous-phase water (0.3 wt% sodium lauryl sulfate solutin) flowing in the liquid path. Oil droplet size is significantly dependent on the microchannel structure, which is identified with the microchannel width, height, and the length of the terrace (a flat area at the microchannel outlet). Three types of microchannel plates having different microchannel structures generate monodispersed emulsions of different average droplet sizes, 16,20, and 48 {mu}m at the watr flow rate of 1.4x10{sup -2}mL{center_dot}min{sup -1}. For the microchannel plate which generates large droplets of 48 {mu}m, increasing the flow rate causes decreasing droplet size. However, for the microchannel plate which generates small droplets of 16 or 20 {mu}m, the size is not affected by the flow rate within the range from 1.4x10{sup -2}to 2.4 mL{center_dot}min{sup -1}. In every case, the droplet size distribution is narrow, and the geometric standard deviation is 1.03 or less. (author)

Transient response of nonideal ion-selective microchannel-nanochannel devices

Science.gov (United States)

Leibowitz, Neta; Schiffbauer, Jarrod; Park, Sinwook; Yossifon, Gilad

2018-04-01

We report evidence of variation in ion selectivity of a fabricated microchannel-nanochannel device resulting in the appearance of a distinct local maximum in the overlimiting chronopotentiometric response. In this system consisting of shallow microchannels joined by a nanochannel, viscous shear at the microchannel walls suppresses the electro-osmotic instability and prevents any associated contribution to the nonmonotonic response. Thus, this response is primarily electrodiffusive. Numerical simulations indicate that concentration polarization develops not only within the microchannel but also within the nanochannel itself, with a local voltage maximum in the chronopotentiometric response correlated with interfacial depletion and having the classic i-2 Sands time dependence. Furthermore, the occurrence of the local maxima is correlated with the change in selectivity due to internal concentration polarization. Understanding the transient nonideal permselective response is essential for obtaining fundamental insight and for optimizing efficient operation of practical fabricated nanofluidic and membrane devices.

Periodic flow patterns of the magnetic fluid in microchannel

International Nuclear Information System (INIS)

Chang, C.-W.; Cheng, Y.-T.; Tsai, C.-Y.; Chien, J.-H.; Wang, P.-Y.; Chen, P.-H.

2007-01-01

In this study, of interests are the periodic flow patterns of the oil-based magnetic fluid in microchannels. A microfluidic chip is made of poly-dimethylsiloxane (PDMS) and contains cross-shape microchannels. The microchannels are 1000 μm in width and 200 μm in depth. A syringe pump was used to drive the fluids. Periodic flow patterns were seen and the slugs of magnetic fluid and DI water were generated. The operating factors discussed in the present work are the flow rates and the magnetic field. The frequency of generation of the slugs increases with increase in the flow rates. Besides, by settling the permanent magnet around the microchannel, the periods of the slug generation are changed. Different positions of the magnet lead to different periods for generating the slugs. By adjusting operating conditions, to control the frequency and the volume of the slugs is practical

Surface roughness influences on the behaviour of flow inside microchannels

Science.gov (United States)

Farias, M. H.; Castro, C. S.; Garcia, D. A.; Henrique, J. S.

2018-03-01

This work discusses influence of the surface roughness on the behavior of liquids flowing inside microchannels. By measuring the flow profile using the micro-PIV technique, the flow of water inside two rectangular microchannels of different wall roughness and in a circular smooth microchannel was studied. Comparisons were made among the experimental results, showing that a metrological approach concerning surface characteristics of microdevices is required to ensure reliability of the measurements for flow analyses in microfluidic processes.

Study of a high gain microchannel plate photomultiplier having low statistical gain fluctuations

International Nuclear Information System (INIS)

Audier, M.

1980-12-01

A new photomultiplier configuration which synthesizes the performances of several models is proposed. The principles of microchannel plate photomultipliers are reviewed. The physical phenomena which limit the electron multiplication process in a microchannel and the detection efficiency of the microchannel plates are investigated. The operation of a herring-bone pattern device and of a system of two microchannel plate photomultipliers are described and characterized [fr

Numerical Simulation and Analysis of Gas-Liquid Flow in a T-Junction Microchannel

Directory of Open Access Journals (Sweden)

Hongtruong Pham

2012-01-01

Full Text Available Gas-liquid flow in microchannels is widely used in biomedicine, nanotech, sewage treatment, and so forth. Particularly, owing to the high qualities of the microbubbles and spheres produced in microchannels, it has a great potential to be used in ultrasound imaging and controlled drug release areas; therefore, gas-liquid flow in microchannels has been the focus in recent years. In this paper, numerical simulation of gas-liquid flows in a T-junction microchannel was carried out with computational fluid dynamics (CFD software FLUENT and the Volume-of-Fluid (VOF model. The distribution of velocity, pressure, and phase of fluid in the microchannel was obtained, the pressure distribution along the channel walls was analyzed in order to give a better understanding on the formation of microbubbles in the T-junction microchannel.

Critical heat flux in flow boiling in microchannels

CERN Document Server

Saha, Sujoy Kumar

2015-01-01

This Brief concerns the important problem of critical heat flux in flow boiling in microchannels. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to “Heat Transfer and Pressure Drop in Flow Boiling in Microchannels,” by the same author team, this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling.

Axisymmetric polydimethysiloxane microchannels for in vitro hemodynamic studies

International Nuclear Information System (INIS)

Lima, Rui; Oliveira, Monica S N; Ishikawa, Takuji; Kaji, Hirokazu; Nishizawa, Matsuhiko; Tanaka, Shuji; Yamaguchi, Takami

2009-01-01

The current microdevices used for biomedical research are often manufactured using microelectromechanical systems (MEMS) technology. Although it is possible to fabricate precise and reproducible rectangular microchannels using soft lithography techniques, this kind of geometry may not reflect the actual physiology of the microcirculation. Here, we present a simple method to fabricate circular polydimethysiloxane (PDMS) microchannels aiming to mimic an in vivo microvascular environment and suitable for state-of-the-art microscale flow visualization techniques, such as confocal μPIV/PTV. By using a confocal μPTV system individual red blood cells (RBCs) were successfully tracked trough a 75 μm circular PDMS microchannel. The results show that RBC lateral dispersion increases with the volume fraction of RBCs in the solution, i.e. with the hematocrit.

Systems and methods of manufacturing microchannel arrays

Energy Technology Data Exchange (ETDEWEB)

Paul, Brian K.; Brannon, Samuel T.

2018-03-20

The present application relates to apparatus and methods of reducing the cost of microchannel array production and operation. In a representative embodiment, a microchannel array can comprise a first lamina having one or more flanges and a plurality of elongated bosses. The one or more flanges can extend along a perimeter of the first lamina, the plurality of elongated bosses can at least partially define a plurality of first flow paths, and the first lamina can define at least one opening. The microchannel array can also comprise a second lamina having a plurality of second flow paths, and can define at least one opening. The second lamina can be disposed above the first lamina such that the second lamina encloses the first flow paths of the first lamina and the at least one opening of the first lamina is coaxial with the at least one opening of the second lamina.

NASA's Platform for Cross-Disciplinary Microchannel Research

Science.gov (United States)

Son, Sang Young; Spearing, Scott; Allen, Jeffrey; Monaco, Lisa A.

2003-01-01

A team from the Structural Biology group located at the NASA Marshall Space Flight Center in Huntsville, Alabama is developing a platform suitable for cross-disciplinary microchannel research. The original objective of this engineering development effort was to deliver a multi-user flight-certified facility for iterative investigations of protein crystal growth; that is, Iterative Biological Crystallization (IBC). However, the unique capabilities of this facility are not limited to the low-gravity structural biology research community. Microchannel-based research in a number of other areas may be greatly accelerated through use of this facility. In particular, the potential for gas-liquid flow investigations and cellular biological research utilizing the exceptional pressure control and simplified coupling to macroscale diagnostics inherent in the IBC facility will be discussed. In conclusion, the opportunities for research-specific modifications to the microchannel configuration, control, and diagnostics will be discussed.

Non-Newtonian fluid structure interaction in flexible biomimetic microchannels

Science.gov (United States)

Kiran, M.; Dasgupta, Sunando; Chakraborty, Suman

2017-11-01

To investigate the complex fluid structure interactions in a physiologically relevant microchannel with deformable wall and non-Newtonian fluid that flows within it, we fabricated cylindrical microchannels of various softness out of PDMS. Experiments to measure the transient pressure drop across the channel were carried out with high sampling frequencies to capture the intricate flow physics. In particular, we showed that the waveforms varies greatly for each of the non-Newtonian and Newtonian cases for both non-deformable and deformable microchannels in terms of the peak amplitude, r.m.s amplitude and the crest factor. In addition, we carried out frequency sweep experiments to evaluate the frequency response of the system. We believe that these results will aid in the design of polymer based microfluidic phantoms for arterial FSI studies, and in particular for studying blood analog fluids in cylindrical microchannels as well as developing frequency specific Lab-on-chip systems for medical diagnostics.

Microchannel electron multiplier

International Nuclear Information System (INIS)

Beranek, I.; Janousek, L.; Vitovsky, O.

1981-01-01

A microchannel electron multiplier is described for detecting low levels of alpha, beta, soft X-ray and UV radiations. It consists of a glass tube or a system of tubes of various shapes made of common technological glass. The inner tube surface is provided with an active coat with photoemitter and secondary emitter properties. (B.S.)

Integrated microchannel cooling in a three dimensional integrated circuit: A thermal management

Directory of Open Access Journals (Sweden)

Wang Kang-Jia

2016-01-01

Full Text Available Microchannel cooling is a promising technology for solving the three-dimensional integrated circuit thermal problems. However, the relationship between the microchannel cooling parameters and thermal behavior of the three dimensional integrated circuit is complex and difficult to understand. In this paper, we perform a detailed evaluation of the influence of the microchannel structure and the parameters of the cooling liquid on steady-state temperature profiles. The results presented in this paper are expected to aid in the development of thermal design guidelines for three dimensional integrated circuit with microchannel cooling.

Thermal performance of nanofluid flow in microchannels

Energy Technology Data Exchange (ETDEWEB)

Li Jie [Department of Mechanical and Aerospace Engineering, University of North Carolina, Campus Box 7910, Broungton Hall 4160, Raleigh, NC 27695-7910 (United States); Kleinstreuer, Clement [Department of Mechanical and Aerospace Engineering, University of North Carolina, Campus Box 7910, Broungton Hall 4160, Raleigh, NC 27695-7910 (United States)], E-mail: ck@eos.ncsu.edu

2008-08-15

Two effective thermal conductivity models for nanofluids were compared in detail, where the new KKL (Koo-Kleinstreuer-Li) model, based on Brownian motion induced micro-mixing, achieved good agreements with the currently available experimental data sets. Employing the commercial Navier-Stokes solver CFX-10 (Ansys Inc., Canonsburg, PA) and user-supplied pre- and post-processing software, the thermal performance of nanofluid flow in a trapezoidal microchannel was analyzed using pure water as well as a nanofluid, i.e., CuO-water, with volume fractions of 1% and 4% CuO-particles with d{sub p} = 28.6 nm. The results show that nanofluids do measurably enhance the thermal performance of microchannel mixture flow with a small increase in pumping power. Specifically, the thermal performance increases with volume fraction; but, the extra pressure drop, or pumping power, will somewhat decrease the beneficial effects. Microchannel heat sinks with nanofluids are expected to be good candidates for the next generation of cooling devices.

Dynamic Modelling of the DEP Controlled Boiling in a Microchannel

Science.gov (United States)

Lackowski, Marcin; Kwidzinski, Roman

2018-04-01

The paper presents theoretical analysis of flow dynamics in a heated microchannel in which flow rate may be controlled by dielectrophoretic (DEP) forces. Proposed model equations were derived in terms of lumped parameters characterising the system comprising of DEP controller and the microchannel. In result, an equation for liquid height of rise in the controller was obtained from momentum balances in the two elements of the considered system. In the model, the boiling process in the heated section of microchannel is taken into account through a pressure drop, which is a function of flow rate and uniform heat flux. Presented calculation results show that the DEP forces influence mainly the flow rate in the microchannel. In this way, by proper modulation of voltage applied to the DEP controller, it is possible to lower the frequency of Ledinegg instabilities.

Slip flow through a converging microchannel: experiments and 3D simulations

International Nuclear Information System (INIS)

Varade, Vijay; Agrawal, Amit; Pradeep, A M

2015-01-01

An experimental and 3D numerical study of gaseous slip flow through a converging microchannel is presented in this paper. The measurements reported are with nitrogen gas flowing through the microchannel with convergence angles (4°, 8° and 12°), hydraulic diameters (118, 147 and 177 µm) and lengths (10, 20 and 30 mm). The measurements cover the entire slip flow regime and a part of the continuum and transition regimes (the Knudsen number is between 0.0004 and 0.14); the flow is laminar (the Reynolds number is between 0.5 and 1015). The static pressure drop is measured for various mass flow rates. The overall pressure drop increases with a decrease in the convergence angle and has a relatively large contribution of the viscous component. The numerical solutions of the Navier–Stokes equations with Maxwell’s slip boundary condition explore two different flow behaviors: uniform centerline velocity with linear pressure variation in the initial and the middle part of the microchannel and flow acceleration with nonlinear pressure variation in the last part of the microchannel. The centerline velocity and the wall shear stress increase with a decrease in the convergence angle. The concept of a characteristic length scale for a converging microchannel is also explored. The location of the characteristic length is a function of the Knudsen number and approaches the microchannel outlet with rarefaction. These results on gaseous slip flow through converging microchannels are observed to be considerably different than continuum flow. (paper)

Acoustophoretic Synchronization of Mammalian Cells in Microchannels

DEFF Research Database (Denmark)

Thévoz, P.; Adams, J.D.; Shea, H.

2010-01-01

We report the first use of ultrasonic standing waves to achieve cell cycle phase synchronization in mammalian cells in a high-throughput and reagent-free manner. The acoustophoretic cell synchronization (ACS) device utilizes volume-dependent acoustic radiation force within a microchannel to selec......We report the first use of ultrasonic standing waves to achieve cell cycle phase synchronization in mammalian cells in a high-throughput and reagent-free manner. The acoustophoretic cell synchronization (ACS) device utilizes volume-dependent acoustic radiation force within a microchannel...

Influence of sinusoidal flow on the thermal and hydraulic performance of microchannel heat sink

International Nuclear Information System (INIS)

Om, N I; Gunnasegaran, P; Rajasegaran, S

2013-01-01

In this paper, the effect of sinusoidal flow on the thermal and hydraulic performance of microchannel heat sink (MCHS) is numerically investigated. This investigation covers Reynolds number in the range of 100 ≤ Re ≤ 1000 and pure water is used as a working fluid. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using finite volume method (FVM). The water flow field and heat transfer performance inside the sinusoidal microchannels is simulated and the results are compared with the straight microchannels. The effect of using sinusoidal microchannels on temperature distribution, Nusselt number, friction factor and thermal resistance is presented in this paper. It is found that with same rectangular cross-section, sinusoidal microchannels have a better heat transfer performance compared to the straight microchannels.

Characterization of microchannel anechoic corners formed by surface acoustic waves

Science.gov (United States)

Destgeer, Ghulam; Alam, Ashar; Ahmed, Husnain; Park, Jinsoo; Jung, Jin Ho; Park, Kwangseok; Sung, Hyung Jin

2018-02-01

Surface acoustic waves (SAWs) generated in a piezoelectric substrate couple with a liquid according to Snell's law such that a compressional acoustic wave propagates obliquely at a Rayleigh angle ( θ t) inside the microchannel to form a region devoid of a direct acoustic field, which is termed a microchannel anechoic corner (MAC). In the present study, we used microchannels with various heights and widths to characterize the width of the MAC region formed by a single travelling SAW. The attenuation of high-frequency SAWs produced a strong acoustic streaming flow that moved the particles in and out of the MAC region, whereas reflections of the acoustic waves within the microchannel resulted in standing acoustic waves that trapped particles at acoustic pressure nodes located within or outside of the MAC region. A range of actuation frequencies and particle diameters were used to investigate the effects of the acoustic streaming flow and the direct acoustic radiation forces by the travelling as well as standing waves on the particle motion with respect to the MAC region. The width of the MAC ( w c), measured experimentally by tracing the particles, increased with the height of the microchannel ( h m) according to a simple trigonometric equation w c = h m × tan ( θ t ).

Electrokinetic microchannel battery by means of electrokinetic and microfluidic phenomena

Science.gov (United States)

Yang, Jun; Lu, Fuzhi; Kostiuk, Larry W.; Kwok, Daniel Y.

2003-11-01

Pressure-driven flow in a microchannel induces a streaming current due to the presence of an electrical double layer in the interface between the electrolyte solution and channel wall. As the streaming current is of the order of a nano-amphere and is additive, we propose here a method to develop an electrokinetic battery consisting of an array of microchannels that converts the hydrostatic pressure of a liquid into electrical work. We have given oscillating analytical solutions by means of an electrical circuit analysis to model the multi-microchannel battery. Using superposition of the appropriate Fourier series, the derived analytical solutions are useful to predict the current when there is more general time-dependent flow through a microchannel array. To illustrate the idea, we have studied steady-state pressure-driven flow in micropore porous glass filter and compared the results with those predicted from our model. From a 30 cm hydrostatic pressure drop, an external current of 1-2 µA was obtained by means of water passing through the micropore porous glass filter. A larger current can be obtained by simply using a solution with higher salt concentration. This results in a new and potentially useful method of energy conversion by means of an array of microchannels.

Detection of Aeromonas hydrophila Using Fiber Optic Microchannel Sensor

Directory of Open Access Journals (Sweden)

Samla Gauri

2017-01-01

Full Text Available This research focuses on the detection of Aeromonas hydrophila using fiber optic microchannel biosensor. Microchannel was fabricated by photolithography method. The fiber optic was chosen as signal transmitting medium and light absorption characteristic of different microorganisms was investigated for possible detection. Experimental results showed that Aeromonas hydrophila can be detected at the region of UV-Vis spectra between 352 nm and 354 nm which was comparable to measurement provided by UV spectrophotometer and also theoretical calculation by Beer-Lambert Absorption Law. The entire detection can be done in less than 10 minutes using a total volume of 3 μL only. This result promises good potential of this fiber optic microchannel sensor as a reliable, portable, and disposable sensor.

Two-phase flow instabilities in a silicon microchannels heat sink

International Nuclear Information System (INIS)

Bogojevic, D.; Sefiane, K.; Walton, A.J.; Lin, H.; Cummins, G.

2009-01-01

Two-phase flow instabilities are highly undesirable in microchannels-based heat sinks as they can lead to temperature oscillations with high amplitudes, premature critical heat flux and mechanical vibrations. This work is an experimental study of boiling instabilities in a microchannel silicon heat sink with 40 parallel rectangular microchannels, having a length of 15 mm and a hydraulic diameter of 194 μm. A series of experiments have been carried out to investigate pressure and temperature oscillations during the flow boiling instabilities under uniform heating, using water as a cooling liquid. Thin nickel film thermometers, integrated on the back side of a heat sink with microchannels, were used in order to obtain a better insight related to temperature fluctuations caused by two-phase flow instabilities. Flow regime maps are presented for two inlet water temperatures, showing stable and unstable flow regimes. It was observed that boiling leads to asymmetrical flow distribution within microchannels that result in high temperature non-uniformity and the simultaneously existence of different flow regimes along the transverse direction. Two types of two-phase flow instabilities with appreciable pressure and temperature fluctuations were observed, that depended on the heat to mass flux ratio and inlet water temperature. These were high amplitude/low frequency and low amplitude/high frequency instabilities. High speed camera imaging, performed simultaneously with pressure and temperature measurements, showed that inlet/outlet pressure and the temperature fluctuations existed due to alternation between liquid/two-phase/vapour flows. It was also determined that the inlet water subcooling condition affects the magnitudes of the temperature oscillations in two-phase flow instabilities and flow distribution within the microchannels.

Stabilization of two-phase octanol/water flows inside poly(dimethylsiloxane) microchannels using polymer coatings

NARCIS (Netherlands)

van der Linden, H. J.; Jellema, L. C.; Holwerda, M.; Verpoorte, E.

In this paper we present our first results on the realization of stable water/octanol, two-phase flows inside poly(dimethylsiloxane) (PDMS) microchannels. Native PDMS microchannels were coated with high molecular weight polymers to change the surface properties of the microchannels and thus

Enhanced MicroChannel Heat Transfer in Macro-Geometry using Conventional Fabrication Approach

Science.gov (United States)

Ooi, KT; Goh, AL

2016-09-01

This paper presents studies on passive, single-phase, enhanced microchannel heat transfer in conventionally sized geometry. The intention is to allow economical, simple and readily available conventional fabrication techniques to be used for fabricating macro-scale heat exchangers with microchannel heat transfer capability. A concentric annular gap between a 20 mm diameter channel and an 19.4 mm diameter insert forms a microchannel where heat transfer occurs. Results show that the heat transfer coefficient of more than 50 kW/m·K can be obtained for Re≈4,000, at hydraulic diameter of 0.6 mm. The pressure drop values of the system are kept below 3.3 bars. The present study re-confirms the feasibility of fabricating macro-heat exchangers with microchannel heat transfer capability.

Developing a method of fabricating microchannels using plant root structure

Science.gov (United States)

Nakashima, Shota; Tokumaru, Kazuki; Tsumori, Fujio

2018-06-01

Complicated three-dimensional (3D) microchannels are expected to be applied to a lab-on-a-chip, especially an organ-on-a-chip. There are fine microchannel networks such as blood vessels in a living organ. However, it is difficult to recreate the complicated 3D microchannels of real living structures. Plant roots have a similar structure to blood vessels. They spread radially and three-dimensionally, and become thinner as they branch. In this research, we propose a method of fabricating microchannels using a live plant root as a template to mimic a blood vessel structure. We grew a plant in ceramic slurry instead of soil. The slurry consists of ceramic powder, binder and water, so it plays a similar role to soil consisting of fine particles in water. After growing the plant, the roots inside the slurry were burned and a sintered ceramic body with channel structures was obtained by heating. We used two types of slurry with different composition ratios, and compared the internal channel structures before and after sintering.

High Flux Microchannel Receiver Development with Adap-tive Flow Control

Energy Technology Data Exchange (ETDEWEB)

Drost, Kevin [Oregon State Univ., Corvallis, OR (United States)

2015-08-15

This project is focused on the demonstration of a microchannel-based solar receiver (MSR). The MSR concept consists of using a modular arrangement of arrayed microchannels to heat a working fluid in a concentrating solar receiver, allowing a much higher solar flux on the receiver and consequently a significant reduction in thermal losses, size, and cost.

Thermal mixing of two miscible fluids in a T-shaped microchannel.

Science.gov (United States)

Xu, Bin; Wong, Teck Neng; Nguyen, Nam-Trung; Che, Zhizhao; Chai, John Chee Kiong

2010-10-01

In this paper, thermal mixing characteristics of two miscible fluids in a T-shaped microchannel are investigated theoretically, experimentally, and numerically. Thermal mixing processes in a T-shaped microchannel are divided into two zones, consisting of a T-junction and a mixing channel. An analytical two-dimensional model was first built to describe the heat transfer processes in the mixing channel. In the experiments, de-ionized water was employed as the working fluid. Laser induced fluorescence method was used to measure the fluid temperature field in the microchannel. Different combinations of flow rate ratios were studied to investigate the thermal mixing characteristics in the microchannel. At the T-junction, thermal diffusion is found to be dominant in this area due to the striation in the temperature contours. In the mixing channel, heat transfer processes are found to be controlled by thermal diffusion and convection. Measured temperature profiles at the T-junction and mixing channel are compared with analytical model and numerical simulation, respectively.

Experimental and theoretical analysis of defocused CO2 laser microchanneling on PMMA for enhanced surface finish

Science.gov (United States)

Prakash, Shashi; Kumar, Subrata

2017-02-01

The poor surface finish of CO2 laser-micromachined microchannel walls is a major limitation of its utilization despite several key advantages, like low fabrication cost and low time consumption. Defocused CO2 laser beam machining is an effective solution for fabricating smooth microchannel walls on polymer and glass substrates. In this research work, the CO2 laser microchanneling process on PMMA has been analyzed at different beam defocus positions. Defocused processing has been investigated both theoretically and experimentally, and the depth of focus and beam diameter have been determined experimentally. The effect of beam defocusing on the microchannel width, depth, surface roughness, heat affected zone and microchannel profile were examined. A previously developed analytical model for microchannel depth prediction has been improved by incorporating the threshold energy density factor. A semi-analytical model for predicting the microchannel width at different defocus positions has been developed. A semi-empirical model has also been developed for predicting microchannel widths at different defocusing conditions for lower depth values. The developed models were compared and verified by performing actual experiments. Multi-objective optimization was performed to select the best optimum set of input parameters for achieving the desired surface roughness.

A two-step sealing-and-reinforcement SU8 bonding paradigm for the fabrication of shallow microchannels

Science.gov (United States)

Mehboudi, Aryan; Yeom, Junghoon

2018-03-01

Adhesive bonding is a key technique to create microfluidic devices when two separate substrates are used to form microchannels. Among many adhesives explored in microchannel fabrication, SU8 has been widely used as an adhesive layer for sealing the microchannel sidewalls. The majority of the available SU8-based bonding methods, however, suffer from the difficulties associated with sealing of two important types of the microchannel architecture: (1) shallow microchannels with small patterns on a large area, and (2) microchannels with ultra-low aspect ratios (e.g. 6 mm in width and 2~μ m in height). In this paper, a new bonding paradigm based upon the low-temperature and low-pressure SU8 bonding, consisting of two steps of sealing using a thin-SU8-coated PET film and bonding reinforcement using a SU8-coated glass slide, is proposed to resolve the aforementioned difficulties. Since it does not need complicated instruments such as a wafer bonding machine and a lamination device, the developed bonding paradigm is convenient and economical. We successfully demonstrate the compatibility of the proposed bonding paradigm with the two microchannel fabrication approaches based on the glass wet etching and the SU8 photo-lithography, where small microchannels with the innermost surfaces fully made of SU8 are obtained. A theoretical model is employed to better investigate the flow characteristics and the structural behavior of the microchannel including the PET film deformation, strain and von Mises stress distributions, bonding strength, etc. Moreover, we demonstrate the fabrication of the multi-height deep-shallow microchannel sidewalls and their sealing using the SU8-coated PET film. Finally, as a proof-of-concept device, a microfluidic filter consisting of the double-height deep-shallow microchannel is fabricated for separation of 3 µm and 10 µm particles.

Micromachined Si channel width and tortuosity on human osteoblast cell attachment and proliferation

International Nuclear Information System (INIS)

Leber, Christopher; Choi, Hongsoo; Bose, Susmita; Bandyopadhyay, Amit

2010-01-01

In this study, influence of coating chemistry, channel width and tortuosity of various two-dimensional micro-channels were explored on micromachined Si using osteoblast precursor cells line 1 (OPC1). The rationale for our study is to delineate the influence of different porosity parameters on bone cell attachment and proliferation in vitro. Channel widths of 100, 200, 300, 400, and 600 μm; channel bends of 0, 1, and 2 right angles; and gold and silicon dioxide coatings on single-crystal Si were studied. Experiments were conducted with channel tops under glass covered and uncovered conditions keeping the channel depth at 220 μm. Independent samples were evaluated using SEM imaging and MTT assay to measure bone cell morphology and quantity. Images were taken of micro-channels and exterior chambers at 50x, 500x, 1000x, and 5000x magnifications. Channel and chamber cell densities were scored as follows: bare (score = 0), scattered (1), limited (2), abundant (3), and overflowing (4). Samples were then scored and statistically analyzed for major differences. In general, OPC1 cells proliferated at least 5% or better based on cell numbers under uncovered conditions than glass covered. Channel widths of 100 μm largely prohibited cell proliferation and diffusion by narrow path inhibition with the lowest average score of 1.17. Among channel bends of 0, 1, and 2 right angles, an increase in micro-channel tortuosity from 0-2 bends amplified OPC1 cell growth upwards of ∼ 6.6%. A one-way ANOVA showed significant differences in cell quantity for alternating channel tortuosity at a significance level of p < 0.05. No preference was found for gold or silicon dioxide coatings on Si for bone cell proliferation.

Study of the electric field inside microchannel plate multipliers

International Nuclear Information System (INIS)

Gatti, E.; Oba, K.; Rehak, P.

1982-01-01

Electric field inside high gain microchannel plate multipliers was studied. The calculations were based directly on the solution of the Maxwell equations applied to the microchannel plate (MCP) rather than on the conventional lumped RC model. The results are important to explain the performance of MCP's, (1) under a pulsed bias tension and, (2) at high rate conditions. The results were tested experimentally and a new method of MCP operation free from the positive ion feedback was demonstrated

Compact Ceramic Microchannel Heat Exchangers

Energy Technology Data Exchange (ETDEWEB)

Lewinsohn, Charles [Ceramatec, Inc., Salt Lake City, UT (United States)

2016-10-31

The objective of the proposed work was to demonstrate the feasibility of a step change in power plant efficiency at a commercially viable cost, by obtaining performance data for prototype, compact, ceramic microchannel heat exchangers. By performing the tasks described in the initial proposal, all of the milestones were met. The work performed will advance the technology from Technology Readiness Level 3 (TRL 3) to Technology Readiness Level 4 (TRL 4) and validate the potential of using these heat exchangers for enabling high efficiency solid oxide fuel cell (SOFC) or high-temperature turbine-based power plants. The attached report will describe how this objective was met. In collaboration with The Colorado School of Mines (CSM), specifications were developed for a high temperature heat exchanger for three commercial microturbines. Microturbines were selected because they are a more mature commercial technology than SOFC, they are a low-volume and high-value target for market entry of high-temperature heat exchangers, and they are essentially scaled-down versions of turbines used in utility-scale power plants. Using these specifications, microchannel dimensions were selected to meet the performance requirements. Ceramic plates were fabricated with microchannels of these dimensions. The plates were tested at room temperature and elevated temperature. Plates were joined together to make modular, heat exchanger stacks that were tested at a variety of temperatures and flow rates. Although gas flow rates equivalent to those in microturbines could not be achieved in the laboratory environment, the results showed expected efficiencies, robust operation under significant temperature gradients at high temperature, and the ability to cycle the stacks. Details of the methods and results are presented in this final report.

Microchannel fabrication on cyclic olefin polymer substrates via 1064 nm Nd:YAG laser ablation

Energy Technology Data Exchange (ETDEWEB)

McCann, Ronán [Advanced Processing Technology Research Centre, Dublin City University, Glasnevin, Dublin 9 (Ireland); School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin 9 (Ireland); Irish Separation Science Cluster, National Centre for Sensor Research, Dublin City University, Dublin 9 (Ireland); National Centre for Plasma Science and Technology, Dublin City University, Dublin 9 (Ireland); Bagga, Komal; Groarke, Robert [Advanced Processing Technology Research Centre, Dublin City University, Glasnevin, Dublin 9 (Ireland); School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin 9 (Ireland); Irish Separation Science Cluster, National Centre for Sensor Research, Dublin City University, Dublin 9 (Ireland); Stalcup, Apryll [Irish Separation Science Cluster, National Centre for Sensor Research, Dublin City University, Dublin 9 (Ireland); School of Chemical Sciences, Dublin City University, Dublin 9 (Ireland); Vázquez, Mercedes, E-mail: mercedes.vazquez@dcu.ie [Advanced Processing Technology Research Centre, Dublin City University, Glasnevin, Dublin 9 (Ireland); Irish Separation Science Cluster, National Centre for Sensor Research, Dublin City University, Dublin 9 (Ireland); School of Chemical Sciences, Dublin City University, Dublin 9 (Ireland); Brabazon, Dermot [Advanced Processing Technology Research Centre, Dublin City University, Glasnevin, Dublin 9 (Ireland); School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin 9 (Ireland); Irish Separation Science Cluster, National Centre for Sensor Research, Dublin City University, Dublin 9 (Ireland); National Centre for Plasma Science and Technology, Dublin City University, Dublin 9 (Ireland)

2016-11-30

Highlights: • Rapid single-step microchannel fabrication on optically transparent cyclic olefin polymer using IR Nd:YAG laser. • Ability to tailor channel depth between 12–47 μm demonstrated for single laser pass. • Use of multiple laser passes showed capability for finer depth control. • Potential applications in lab-on-chip and microfluidic devices. - Abstract: This paper presents a method for fabrication of microchannels on cyclic olefin polymer films that have application in the field of microfluidics and chemical sensing. Continuous microchannels were fabricated on 188-μm-thick cyclic olefin polymer substrates using a picosecond pulsed 1064 nm Nd:YAG laser. The effect of laser fluence on the microchannel morphology and dimensions was analysed via scanning electron microscopy and optical profilometry. Single laser passes were found to produce v-shaped microchannels with depths ranging from 12 μm to 47 μm and widths from 44 μm to 154 μm. The ablation rate during processing was lower than predicted theoretically. Multiple laser passes were applied to examine the ability for finer control over microchannel morphology with channel depths ranging from 22 μm to 77 μm and channel widths from 59 μm to 155 μm. For up to five repeat passes, acceptable reproducibility was found in the produced microchannel morphology. Infrared spectroscopy revealed oxidation and dehydrogenation of the polymer surface following laser ablation. These results were compared to other work conducted on cyclic olefin polymers.

Microchannel fabrication on cyclic olefin polymer substrates via 1064 nm Nd:YAG laser ablation

International Nuclear Information System (INIS)

McCann, Ronán; Bagga, Komal; Groarke, Robert; Stalcup, Apryll; Vázquez, Mercedes; Brabazon, Dermot

2016-01-01

Highlights: • Rapid single-step microchannel fabrication on optically transparent cyclic olefin polymer using IR Nd:YAG laser. • Ability to tailor channel depth between 12–47 μm demonstrated for single laser pass. • Use of multiple laser passes showed capability for finer depth control. • Potential applications in lab-on-chip and microfluidic devices. - Abstract: This paper presents a method for fabrication of microchannels on cyclic olefin polymer films that have application in the field of microfluidics and chemical sensing. Continuous microchannels were fabricated on 188-μm-thick cyclic olefin polymer substrates using a picosecond pulsed 1064 nm Nd:YAG laser. The effect of laser fluence on the microchannel morphology and dimensions was analysed via scanning electron microscopy and optical profilometry. Single laser passes were found to produce v-shaped microchannels with depths ranging from 12 μm to 47 μm and widths from 44 μm to 154 μm. The ablation rate during processing was lower than predicted theoretically. Multiple laser passes were applied to examine the ability for finer control over microchannel morphology with channel depths ranging from 22 μm to 77 μm and channel widths from 59 μm to 155 μm. For up to five repeat passes, acceptable reproducibility was found in the produced microchannel morphology. Infrared spectroscopy revealed oxidation and dehydrogenation of the polymer surface following laser ablation. These results were compared to other work conducted on cyclic olefin polymers.

Theoretical Study of Molecular Transport Through a Permeabilized Cell Membrane in a Microchannel.

Science.gov (United States)

Mahboubi, Masoumeh; Movahed, Saeid; Hosseini Abardeh, Reza; Hoshyargar, Vahid

2017-06-01

A two-dimensional model is developed to study the molecular transport into an immersed cell in a microchannel and to investigate the effects of finite boundary (a cell is suspended in a microchannel), amplitude of electric pulse, and geometrical parameter (microchannel height and size of electrodes) on cell uptake. Embedded electrodes on the walls of the microchannel generate the required electric pulse to permeabilize the cell membrane, pass the ions through the membrane, and transport them into the cell. The shape of electric pulses is square with the time span of 6 ms; their intensities are in the range of 2.2, 2.4, 2.6, 3 V. Numerical simulations have been performed to comprehensively investigate the molecular uptake into the cell. The obtained results of the current study demonstrate that calcium ions enter the cell from the anodic side (the side near positive electrode); after a while, the cell faces depletion of the calcium ions on a positive electrode-facing side within the microchannel; the duration of depletion depends on the amplitude of electric pulse and geometry that lasts from microseconds to milliseconds. By keeping geometrical parameters and time span constant, increment of a pulse intensity enhances molecular uptake and rate of propagation inside the cell. If a ratio of electrode size to cell diameter is larger than 1, the transported amount of Ca 2+ into the cell, as well as the rate of propagation, will be significantly increased. By increasing the height of the microchannel, the rate of uptake is decreased. In an infinite domain, the peak concentration becomes constant after reaching the maximum value; this value depends on the intra-extracellular conductivity and diffusion coefficient of interior and exterior domains of the cell. In comparison, the maximum concentration is changed by geometrical parameters in the microchannel. After reaching the maximum value, the peak concentration reduces due to the depletion of Ca 2+ ions within the

Laser-Induced Motion of a Nanofluid in a Micro-Channel

Directory of Open Access Journals (Sweden)

Tran X. Phuoc

2016-10-01

Full Text Available Since a photon carries both energy and momentum, when it interacts with a particle, photon-particle energy and momentum transfer occur, resulting in mechanical forces acting on the particle. In this paper we report our theoretical study on the use of a laser beam to manipulate and control the flow of nanofluids in a micro-channel. We calculate the velocity induced by a laser beam for TiO2, Fe2O3, Al2O3 MgO, and SiO2 nanoparticles with water as the base fluid. The particle diameter is 50 nm and the laser beam is a 4 W continuous beam of 6 mm diameter and 532 nm wavelength. The results indicate that, as the particle moves, a significant volume of the surrounding water (up to about 8 particle diameters away from the particle surface is disturbed and dragged along with the moving particle. The results also show the effect of the particle refractive index on the particle velocity and the induced volume flow rate. The velocity and the volume flowrate induced by the TiO2 nanoparticle (refractive index n = 2.82 are about 0.552 mm/s and 9.86 fL, respectively, while those induced by SiO2 (n = 1.46 are only about 7.569 μm/s and 0.135, respectively.

Investigation of Size Effects to the Mixing Performance on the X-shaped Micro-Channels

Directory of Open Access Journals (Sweden)

S Tu

2016-09-01

Full Text Available Due to the developing of micro-electro-mechanical-system, MEMS, the fabrication of the microminiaturization devices becomes obviously important. The advances in the basic understanding of fluid physics have opened an era of application of fluid dynamics systems using microchannels. The purpose of this study is to research the flow transport phenomenon by employing different kinds of micro-channel sizing in X-shaped micro-channels. As the working fluid, water is injected to microchannel at different mass flow rate. Over a wide range of flow condition, 1.06 < Re < 514, in X-shaped micro-channels, the mixture performances of numerical simulation, flow visualization, and temperature distribution remain the same. At the same mass flow rate as the Reynolds number below 112.53, the biggest channel size had the slowest flow velocity and got the best mixing performance; as the Reynolds number above 112.53, the smaller the channel sizing, the lower the pressure drops and the faster velocity becomes. The transition form early from laminar flow, the unsteady flow is an advantage for mixing in the limited mixing area, therefore 0.7 mm got the best mixing performance. It is clear that the size of the channel plays an important role in the X-shaped micro-channels.

Micro-channel convective boiling heat transfer with flow instabilities

International Nuclear Information System (INIS)

Consolini, L.; Thome, J.R.

2009-01-01

Flow boiling heat transfer in micro-channels has attracted much interest in the past decade, and is currently a strong candidate for high performance compact heat sinks, such as those required in electronics systems, automobile air conditioning units, micro-reactors, fuel cells, etc. Currently the literature presents numerous experimental studies on two-phase heat transfer in micro-channels, providing an extensive database that covers many different fluids and operating conditions. Among the noteworthy elements that have been reported in previous studies, is the sensitivity of micro-channel evaporators to oscillatory two-phase instabilities. These periodic fluctuations in flow and pressure drop either result from the presence of upstream compressibility, or are simply due to the interaction among parallel channels in multi-port systems. An oscillating flow presents singular characteristics that are expected to produce an effect on the local heat transfer mechanisms, and thus on the estimation of the two-phase heat transfer coefficients. The present investigation illustrates results for flow boiling of refrigerants R-134a, R-236fa, and R-245fa in a 510 μm circular micro-channel, exposed to various degrees of oscillatory compressible volume instabilities. The data describe the main features of the fluctuations in the temperatures of the heated wall and fluid, and draw attention to the differences in the measured unstable time-averaged heat transfer coefficients with respect to those for stable flow boiling. (author)

Micro-channel convective boiling heat transfer with flow instabilities

Energy Technology Data Exchange (ETDEWEB)

Consolini, L.; Thome, J.R. [Ecole Polytechnique Federale de Lausanne (Switzerland). Lab. de Transfert de Chaleur et de Masse], e-mail: lorenzo.consolini@epfl.ch, e-mail: john.thome@epfl.ch

2009-07-01

Flow boiling heat transfer in micro-channels has attracted much interest in the past decade, and is currently a strong candidate for high performance compact heat sinks, such as those required in electronics systems, automobile air conditioning units, micro-reactors, fuel cells, etc. Currently the literature presents numerous experimental studies on two-phase heat transfer in micro-channels, providing an extensive database that covers many different fluids and operating conditions. Among the noteworthy elements that have been reported in previous studies, is the sensitivity of micro-channel evaporators to oscillatory two-phase instabilities. These periodic fluctuations in flow and pressure drop either result from the presence of upstream compressibility, or are simply due to the interaction among parallel channels in multi-port systems. An oscillating flow presents singular characteristics that are expected to produce an effect on the local heat transfer mechanisms, and thus on the estimation of the two-phase heat transfer coefficients. The present investigation illustrates results for flow boiling of refrigerants R-134a, R-236fa, and R-245fa in a 510 {mu}m circular micro-channel, exposed to various degrees of oscillatory compressible volume instabilities. The data describe the main features of the fluctuations in the temperatures of the heated wall and fluid, and draw attention to the differences in the measured unstable time-averaged heat transfer coefficients with respect to those for stable flow boiling. (author)

3D printed microchannel networks to direct vascularisation during endochondral bone repair.

Science.gov (United States)

Daly, Andrew C; Pitacco, Pierluca; Nulty, Jessica; Cunniffe, Gráinne M; Kelly, Daniel J

2018-04-01

Bone tissue engineering strategies that recapitulate the developmental process of endochondral ossification offer a promising route to bone repair. Clinical translation of such endochondral tissue engineering strategies will require overcoming a number of challenges, including the engineering of large and often anatomically complex cartilage grafts, as well as the persistence of core regions of avascular cartilage following their implantation into large bone defects. Here 3D printing technology is utilized to develop a versatile and scalable approach to guide vascularisation during endochondral bone repair. First, a sacrificial pluronic ink was used to 3D print interconnected microchannel networks in a mesenchymal stem cell (MSC) laden gelatin-methacryloyl (GelMA) hydrogel. These constructs (with and without microchannels) were next chondrogenically primed in vitro and then implanted into critically sized femoral bone defects in rats. The solid and microchanneled cartilage templates enhanced bone repair compared to untreated controls, with the solid cartilage templates (without microchannels) supporting the highest levels of total bone formation. However, the inclusion of 3D printed microchannels was found to promote osteoclast/immune cell invasion, hydrogel degradation, and vascularisation following implantation. In addition, the endochondral bone tissue engineering strategy was found to support comparable levels of bone healing to BMP-2 delivery, whilst promoting lower levels of heterotopic bone formation, with the microchanneled templates supporting the lowest levels of heterotopic bone formation. Taken together, these results demonstrate that 3D printed hypertrophic cartilage grafts represent a promising approach for the repair of complex bone fractures, particularly for larger defects where vascularisation will be a key challenge. Copyright © 2018 Elsevier Ltd. All rights reserved.

Monte Carlo simulations of microchannel plate detectors I: steady-state voltage bias results

Energy Technology Data Exchange (ETDEWEB)

Ming Wu, Craig Kruschwitz, Dane Morgan, Jiaming Morgan

2008-07-01

X-ray detectors based on straight-channel microchannel plates (MCPs) are a powerful diagnostic tool for two-dimensional, time-resolved imaging and timeresolved x-ray spectroscopy in the fields of laser-driven inertial confinement fusion and fast z-pinch experiments. Understanding the behavior of microchannel plates as used in such detectors is critical to understanding the data obtained. The subject of this paper is a Monte Carlo computer code we have developed to simulate the electron cascade in a microchannel plate under a static applied voltage. Also included in the simulation is elastic reflection of low-energy electrons from the channel wall, which is important at lower voltages. When model results were compared to measured microchannel plate sensitivities, good agreement was found. Spatial resolution simulations of MCP-based detectors were also presented and found to agree with experimental measurements.

Experimental investigation of two-phase gas-liquid flow in microchannel with T-junction

Science.gov (United States)

Bartkus, German; Kozulin, Igor; Kuznetsov, Vladimir

2017-10-01

Using high-speed video recording and the method of dual laser scanning the gas-liquid flow was investigated in rectangular microchannels with an aspect ratio of 2.35 and 1.26. Experiments were earned out for the vertical flow of ethanol-nitrogen mixture in a microchannel with a cross section of 553×235 µm and for the horizontal flow of water-nitrogen mixture in a microchannel with a cross section of 315×250 µm. The T-mixer was used at the channel's inlet for gas-liquid flow formation. It was observed that elongated bubble, transition, and annular flows are the main regimes for a microchannel with a hydraulic diameter substantially less than the capillary constant. Using laser scanning, the maps of flow regimes for ethanol-nitrogen and water-nitrogen mixtures were obtained and discussed.

Micro-PIV/LIF measurements on electrokinetically-driven flow in surface modified microchannels

International Nuclear Information System (INIS)

Ichiyanagi, Mitsuhisa; Sasaki, Seiichi; Sato, Yohei; Hishida, Koichi

2009-01-01

Effects of surface modification patterning on flow characteristics were investigated experimentally by measuring electroosmotic flow velocities, which were obtained by micron-resolution particle image velocimetry using a confocal microscope. The depth-wise velocity was evaluated by using the continuity equation and the velocity data. The microchannel was composed of a poly(dimethylsiloxane) chip and a borosilicate cover-glass plate. Surface modification patterns were fabricated by modifying octadecyltrichlorosilane (OTS) on the glass surface. OTS can decrease the electroosmotic flow velocity compared to the velocity in the glass microchannel. For the surface charge varying parallel to the electric field, the depth-wise velocity was generated at the boundary area between OTS and the glass surfaces. For the surface charge varying perpendicular to the electric field, the depth-wise velocity did not form because the surface charge did not vary in the stream-wise direction. The surface charge pattern with the oblique stripes yielded a three-dimensional flow in a microchannel. Furthermore, the oblique patterning was applied to a mixing flow field in a T-shaped microchannel, and mixing efficiencies were evaluated from heterogeneity degree of fluorescent dye intensity, which was obtained by laser-induced fluorescence. It was found that the angle of the oblique stripes is an important factor to promote the span-wise and depth-wise momentum transport and contributes to the mixing flow in a microchannel

3D simulation of Heat transfer in MEMS-based microchannel

International Nuclear Information System (INIS)

Choi, Chi Woong; Huh, Cheol; Kim, Dong Eok; Kim, Moo Hwan

2007-01-01

The microchannel heat sink is promising heat dissipation method for high heat flux source. Contrary to conventional circular channel, MEMS based microchannel had rectangular or trapezoidal cross-sectional shape. In our study, we conducted three dimensional conjugate heat transfer calculation for rectangular shape microchannel. First, we simulated that channel was completely drained with known heating power. As a result we obtained calibration line, which indicates heat loss was function of temperature. Second, we simulated single phase heat transfer with various mass flux, 100-400 kg/m 2 s. In conclusion, the single phase test verified that the present heat loss evaluation method is applicable to micro scale heat transfer devices. Heat fluxes from each side wall shows difference due to non-uniform heating. However those ratios were correlated with supplied total heat. Finally, we proposed effective area correction factor to evaluate appropriate heat flux

Microchannel Reactor System for Catalytic Hydrogenation

Energy Technology Data Exchange (ETDEWEB)

Adeniyi Lawal; Woo Lee; Ron Besser; Donald Kientzler; Luke Achenie

2010-12-22

We successfully demonstrated a novel process intensification concept enabled by the development of microchannel reactors, for energy efficient catalytic hydrogenation reactions at moderate temperature, and pressure, and low solvent levels. We designed, fabricated, evaluated, and optimized a laboratory-scale microchannel reactor system for hydrogenation of onitroanisole and a proprietary BMS molecule. In the second phase of the program, as a prelude to full-scale commercialization, we designed and developed a fully-automated skid-mounted multichannel microreactor pilot plant system for multiphase reactions. The system is capable of processing 1 – 10 kg/h of liquid substrate, and an industrially relevant immiscible liquid-liquid was successfully demonstrated on the system. Our microreactor-based pilot plant is one-of-akind. We anticipate that this process intensification concept, if successfully demonstrated, will provide a paradigm-changing basis for replacing existing energy inefficient, cost ineffective, environmentally detrimental slurry semi-batch reactor-based manufacturing practiced in the pharmaceutical and fine chemicals industries.

Electrochemical corrosion behaviour of Mg-Al alloys with thermal spray Al/SiCp composite coatings

International Nuclear Information System (INIS)

Pardo, A.; Feliu Jr, S.; Merino, M. C.; Mohedano, M.; Casajus, P.; Arrabal, R.

2010-01-01

The corrosion protection of Mg-Al alloys by flame thermal spraying of Al/SiCp composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiC particles (SiCp) varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of micro-channels, largely in the vicinity of the SiC particles, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5-30 vol.% SiCp compared with the un reinforced thermal spray aluminium coatings. (Author) 31 refs.

Electrochemical corrosion behaviour of Mg-Al alloys with thermal spray Al/SiCp composite coatings; Comportamiento a la corrosion electroquimica de aleaciones MgAl con recubrimientos de materiales compuestos Al/SiCp mediante proyeccion termica

Energy Technology Data Exchange (ETDEWEB)

Pardo, A.; Feliu Jr, S.; Merino, M. C.; Mohedano, M.; Casajus, P.; Arrabal, R.

2010-07-01

The corrosion protection of Mg-Al alloys by flame thermal spraying of Al/SiCp composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiC particles (SiCp) varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of micro-channels, largely in the vicinity of the SiC particles, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5-30 vol.% SiCp compared with the un reinforced thermal spray aluminium coatings. (Author) 31 refs.

Microchannel plates as detectors and amplifiers of x-ray images

International Nuclear Information System (INIS)

Wiedwald, J.D.

1992-08-01

Two decades of development driven largely by military night vision applications has led to the availability of a wide selection of microchannel plates for use by the scientific community. Microchannel plates (MCPs) are electron multipliers which retain a high degree of spatial resolution making it possible to amplify electron images by factors of 1,000 or more. Plates having 40 mm diameter and intrinsic spatial resolution of 8 μm are readily available. By coating the front surface of a microchannel plate with an x-ray sensitive photocathode material, x-ray images can be detected and amplified. While the detective quantum efficiency is relatively low, the low noise of the MCP (including the ability to construct images by single photon detection) and its high dynamic range make it suitable for some x-ray microscopy applications. The principles of MCP operation and typical performance are discussed. Examples of related applications and commercial capabilities are also presented

Effects of surface roughness and electrokinetic heterogeneity on electroosmotic flow in microchannel

Energy Technology Data Exchange (ETDEWEB)

Masilamani, Kannan; Ganguly, Suvankar; Feichtinger, Christian; Bartuschat, Dominik; Rüde, Ulrich, E-mail: suva_112@yahoo.co.in [Department of Computer Science 10 University of Erlangen-Nuremberg, Cauerstr.11 91058 Erlangen (Germany)

2015-06-15

In this paper, a hybrid lattice-Boltzmann and finite-difference (LB-FD) model is applied to simulate the effects of three-dimensional surface roughness and electrokinetic heterogeneity on electroosmotic flow (EOF) in a microchannel. The lattice-Boltzmann (LB) method has been employed to obtain the flow field and a finite-difference (FD) method is used to solve the Poisson-Boltzmann (PB) equation for the electrostatic potential distribution. Numerical simulation of flow through a square cross-section microchannel with designed roughness is conducted and the results are critically analysed. The effects of surface heterogeneity on the electroosmotic transport are investigated for different roughness height, width, roughness interval spacing, and roughness surface potential. Numerical simulations reveal that the presence of surface roughness changes the nature of electroosmotic transport through the microchannel. It is found that the electroosmotic velocity decreases with the increase in roughness height and the velocity profile becomes asymmetric. For the same height of the roughness elements, the EOF velocity rises with the increase in roughness width. For the heterogeneously charged rough channel, the velocity profile shows a distinct deviation from the conventional plug-like flow pattern. The simulation results also indicate locally induced flow vortices which can be utilized to enhance the flow and mixing within the microchannel. The present study has important implications towards electrokinetic flow control in the microchannel, and can provide an efficient way to design a microfluidic system of practical interest. (paper)

Microchannel Methanation Reactors Using Nanofabricated Catalysts, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — Makel Engineering, Inc. (MEI) and the Pennsylvania State University (Penn State) propose to develop and demonstrate a microchannel methanation reactor based on...

Computational Fluid Dynamics Study of Channel Geometric Effect for Fischer-Tropsch Microchannel Reactor

International Nuclear Information System (INIS)

Na, Jonggeol; Jung, Ikhwan; Kshetrimayum, Krishnadash S.; Park, Seongho; Park, Chansaem; Han, Chonghun

2014-01-01

Driven by both environmental and economic reasons, the development of small to medium scale GTL(gas-to-liquid) process for offshore applications and for utilizing other stranded or associated gas has recently been studied increasingly. Microchannel GTL reactors have been preferred over the conventional GTL reactors for such applications, due to its compactness, and additional advantages of small heat and mass transfer distance desired for high heat transfer performance and reactor conversion. In this work, multi-microchannel reactor was simulated by using commercial CFD code, ANSYS FLUENT, to study the geometric effect of the microchannels on the heat transfer phenomena. A heat generation curve was first calculated by modeling a Fischer-Tropsch reaction in a single-microchannel reactor model using Matlab-ASPEN integration platform. The calculated heat generation curve was implemented to the CFD model. Four design variables based on the microchannel geometry namely coolant channel width, coolant channel height, coolant channel to process channel distance, and coolant channel to coolant channel distance, were selected for calculating three dependent variables namely, heat flux, maximum temperature of coolant channel, and maximum temperature of process channel. The simulation results were visualized to understand the effects of the design variables on the dependent variables. Heat flux and maximum temperature of cooling channel and process channel were found to be increasing when coolant channel width and height were decreased. Coolant channel to process channel distance was found to have no effect on the heat transfer phenomena. Finally, total heat flux was found to be increasing and maximum coolant channel temperature to be decreasing when coolant channel to coolant channel distance was decreased. Using the qualitative trend revealed from the present study, an appropriate process channel and coolant channel geometry along with the distance between the adjacent

Coordinate sensitive detectors based on microchannel plates

International Nuclear Information System (INIS)

Gruntman, M.A.

1984-01-01

Coordinate-sensitive detectors (CSD) on the basis of microchannel plates permit to determine in a digital form the coordinates of every recorded particle and they are used in different fields of physical experiment. The sensitive surface diameter of such detectors can reach 10 cm, and spatial resolution - 10 μm. In the review provided CSD with microchannel plates are classified according to the ways of coordinate determination, different types of the detectors, pecUliarities of their design and electron flowsheet are described. It is pointed out that there are reasons for introduction of CSD into practice of laboratory physical investigations in various fields, where the particle recorded is electron or is able to form a secondary electron. It is attributed to nuclear physics, physics of electron and atom collisions, optics, mass-spectrometry, electron microscopy, X-ray analysis, investigation of surfaces

Micro-Channel Embedded Pulsating Heat Pipes, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — As the need for thermal control technology becomes more demanding Micro-Channel Embedded Pulsating Heat Pipes (ME-PHPs) represents a sophisticated and enabling...

Distillation process using microchannel technology

Science.gov (United States)

Tonkovich, Anna Lee [Dublin, OH; Simmons, Wayne W [Dublin, OH; Silva, Laura J [Dublin, OH; Qiu, Dongming [Carbondale, IL; Perry, Steven T [Galloway, OH; Yuschak, Thomas [Dublin, OH; Hickey, Thomas P [Dublin, OH; Arora, Ravi [Dublin, OH; Smith, Amanda [Galloway, OH; Litt, Robert Dwayne [Westerville, OH; Neagle, Paul [Westerville, OH

2009-11-03

The disclosed invention relates to a distillation process for separating two or more components having different volatilities from a liquid mixture containing the components. The process employs microchannel technology for effecting the distillation and is particularly suitable for conducting difficult separations, such as the separation of ethane from ethylene, wherein the individual components are characterized by having volatilities that are very close to one another.

Numerical study on boiling heat transfer enhancement in a microchannel heat exchanger

International Nuclear Information System (INIS)

Jeon, Jin Ho; Suh, Young Ho; Son, Gi Hun

2008-01-01

Flow boiling in a microchannel heat exchanger has received attention as an effective heat removal mechanism for high power-density microelectronics. Despite extensive experimental studied, the bubble dynamics coupled with boiling heat transfer in a microchannel heat exchanger is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulations are performed to further clarify the dynamics of flow boiling in a microchannel heat exchanger. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle and to treat an immersed solid surface. Based on the numerical results, the effects of modified channel shape on the bubble growth and heat transfer are quantified

An experimental study on flow friction and heat transfer of water in sinusoidal wavy silicon microchannels

Science.gov (United States)

Huang, Houxue; Wu, Huiying; Zhang, Chi

2018-05-01

Sinusoidal wavy microchannels have been known as a more heat transfer efficient heat sink for the cooling of electronics than normal straight microchannels. However, the existing experimental study on wavy silicon microchannels with different phase differences are few. As a result of this, in this paper an experimental study has been conducted to investigate the single phase flow friction and heat transfer of de-ionized water in eight different sinusoidal wavy silicon microchannels (SWSMCs) and one straight silicon microchannel (SMC). The SWSMCs feature different phase differences (α  =  0 to π) and different relative wavy amplitudes (β  =  A/l  =  0.05 to 0.4), but the same average hydraulic diameters (D h  =  160 µm). It is found that both flow friction constant fRe and the Nusselt number depend on the phase difference and relative wavy amplitude. For sinusoidal wavy microchannels with a relative wavy amplitude (β  =  0.05), the Nusselt number increased noticeably with the phase difference for Re  >  250, but the effect was insignificant for Re  reducing the wavy wave length induced higher pressure drop and apparent friction constant fRe, while the Nusselt number increased with relative wavy amplitude for Re  >  300. The results indicate that the thermal resistances of sinusoidal wavy silicon microchannels were generally lower than that of straight silicon microchannels, and the thermal resistance decreased with the increase in relative wavy amplitude. The enhancement of thermal performance is attributed to the flow re-circulation occurring in the corrugation troughs and the secondary flows or Dean vortices introduced by curved channels. It is concluded that silicon sinusoidal wavy microchannels provide higher heat transfer rate albeit with a higher flow friction, making it a better choice for the cooling of high heat flux electronics.

Use of the μPIV technique for an indirect determination of the microchannel cross-section passage geometry

International Nuclear Information System (INIS)

Puccetti, G; Pulvirenti, B; Morini, G L

2014-01-01

In this work the possible use of the μPIV technique for the experimental determination of the microchannel cross-section geometry has been investigated by means of a blind test in which a series of experimental measurements obtained using glass microchannels having a declared rectangular cross-section with a depth of 100 μm and width of 300 μm and a square microchannel with a 300 μm side have been compared with the direct SEM visualisation of the real cross section of the microchannels. For the (oPIV measurements water is used as working fluid. The laminar fully developed 2D velocity profile has been reconstructed by moving the focal plane of the microscope objective from the bottom to the top of the microchannel. The results shown in this paper demonstrate that the real cross section geometry of the microchannel can be predicted by minimizing the difference between the theoretical and the experimental 2D velocity profiles. When the right passage geometry is determined, the average difference between the theoretical and the experimental velocity is within 4-6%.

Imaging microchannel plate detectors for XUV sky survey experiments

International Nuclear Information System (INIS)

Barstow, M.A.; Fraser, G.W.; Milward, S.R.

1986-01-01

Attention is given to the development of microchannel plate detectors for the Wide Field Camera (WFC) XUV (50-300 A) sky survey experiment on Rosat. A novel feature of the detector design is that the microchannel plates and their resistive anode readout are curved to the same radius as the WFC telescope focal surface. It is shown that curving the channel plates is not detrimental to gain uniformity. The paper describes the design of a curved resistive anode readout element and contrasts the present measurements of spatial resolution, global and local uniformity and temperature coefficient of resistance with the poor performance recently ascribed to resistive anodes in the literature. 18 references

The Effect of the Rolling Direction, Temperature, and Etching Time on the Photochemical Machining of Monel 400 Microchannels

Directory of Open Access Journals (Sweden)

Deepakkumar H. Patil

2016-01-01

Full Text Available The present paper describes the effect of the rolling direction on the quality of microchannels manufactured using photochemical machining (PCM of Monel 400. Experiments were carried out to fabricate microchannels along and across the rolling direction to investigate the effect of the grain orientation on microchannel etching. The input parameters considered were channel width and rolling direction, whereas the depth of etch was the response parameters. Different channels of widths of 60, 100, 150, 200, and 250 μm were etched. The effects of the etching time and temperature of the etchant solution on the undercut and depth of the microchannels were studied. For good quality microchannels, the effects of spinning time, spinning speed, exposure time, and photoresist film strength were also taken into consideration. Optimized values of the above were used for the experimentation. The results show that the depth of etch of the microchannel increases more along the rolling direction than across the rolling direction. The channel width and depth are significantly affected by the etching time and temperature. The proposed study reports an improvement in the quality of microchannels produced using PCM.

Thermal effect of a thermoelectric generator on parallel microchannel heat sink

DEFF Research Database (Denmark)

Kolaei, Alireza Rezania; Rosendahl, Lasse

2012-01-01

Thermoelectric generators (TEG) convert heat energy to electrical power by means of semiconductor charge carriers serving as working fluid. In this work, a TEG is applied to a parallel microchannel heat sink. The effect of the inlet plenum arrangement on the laminar flow distribution...... in the channels is considered at a wide range of the pressure drop along the heat sink. The particular focus of this study is geometrical effect of the TEG on the heat transfer characteristics in the micro-heat sink. The hydraulic diameter of the microchannels is 270 μm, and three heat fluxes are applied...... on the hot surface of the TEG. By considering the maximum temperature limitation for Bi_2 Te_3 material and using the microchannel heat sink for cooling down the TEG system, an optimum pumping power is achieved. The results are in a good agreement with the previous experimental and theoretical studies....

Flow friction and heat transfer of ethanol–water solutions through silicon microchannels

International Nuclear Information System (INIS)

Wu Huiying; Wu Xinyu; Wei Zhen

2009-01-01

An experimental investigation was performed on the flow friction and convective heat transfer characteristics of the ethanol–water solutions flowing through five sets of trapezoidal silicon microchannels having hydraulic diameters ranging from 141.7 µm to 268.6 µm. Four kinds of ethanol–water solutions with the ethanol volume concentrations ranging from 0 to 0.8 were tested under different flow and heating conditions. It was found that the cross-sectional geometric parameters had great effect on the flow friction and heat transfer, and the microchannels with a larger W b /W t (bottom width-to-top width ratio) and a smaller H/W t (depth-to-top width ratio) usually had a larger friction constant and a higher Nusselt number. Entrance effects were significant for the flow friction and heat transfer in silicon microchannels, and decreased with the increase of dimensionless hydrodynamic length L and dimensionless thermal length L + h . When L > 1.0, the hydrodynamic entrance effect on the flow friction was ignorable. For the developed laminar flow in silicon microchannels, the Navier–Stokes equation was applicable. It was also found that the volume concentrations had different effects on the flow friction and heat transfer. Within the experimental range, the effect of volume concentrations on the flow friction was ignorable, and the friction constants of the ethanol–water solutions having different concentrations were the same as those of the pure water. However, volume concentrations had great effect on the convection heat transfer in silicon microchannels. With the increase of the volume concentrations, the Nusselt number of the ethanol–water solutions increased obviously, which was attributed to the combination effect of the increase in the Prantdtl number as well as the volatilization effect of the ethanol. Based on the experimental data, the dimensionless correlations for the flow friction and heat transfer of the ethanol–water solutions in the silicon

Electro-osmotic flows inside triangular microchannels

International Nuclear Information System (INIS)

Vocale, P; Spiga, M; Geri, M; Morini, G L

2014-01-01

This work presents a numerical investigation of both pure electro-osmotic and combined electro-osmotic/pressure-driven flows inside triangular microchannels. A finite element analysis has been adopted to solve the governing equations for the electric potential and the velocity field, accounting for a finite thickness of the electric double layer. The influence of non-dimensional parameters such as the aspect ratio of the cross-section, the electrokinetic diameter and the ratio of the pressure force to the electric force on the flow behavior has been investigated. Numerical results point out that the velocity field is significantly influenced by the aspect ratio of the cross section and the electrokinetic diameter. More specifically, the aspect ratio plays an important role in determining the maximum volumetric flow rate, while the electrokinetic diameter is crucial to establishing the range of pressures that may be sustained by the electro-osmotic flow. Numerical results are also compared with two correlations available in the literature which enable to assess the volumetric flow rate and the pressure head for microchannels featuring a rectangular, a trapezoidal or an elliptical cross-section.

Numerical investigation of fluid flow and heat transfer under high heat flux using rectangular micro-channels

KAUST Repository

Mansoor, Mohammad M.

2012-02-01

A 3D-conjugate numerical investigation was conducted to predict heat transfer characteristics in a rectangular cross-sectional micro-channel employing simultaneously developing single-phase flows. The numerical code was validated by comparison with previous experimental and numerical results for the same micro-channel dimensions and classical correlations based on conventional sized channels. High heat fluxes up to 130W/cm 2 were applied to investigate micro-channel thermal characteristics. The entire computational domain was discretized using a 120×160×100 grid for the micro-channel with an aspect ratio of (α=4.56) and examined for Reynolds numbers in the laminar range (Re 500-2000) using FLUENT. De-ionized water served as the cooling fluid while the micro-channel substrate used was made of copper. Validation results were found to be in good agreement with previous experimental and numerical data [1] with an average deviation of less than 4.2%. As the applied heat flux increased, an increase in heat transfer coefficient values was observed. Also, the Reynolds number required for transition from single-phase fluid to two-phase was found to increase. A correlation is proposed for the results of average Nusselt numbers for the heat transfer characteristics in micro-channels with simultaneously developing, single-phase flows. © 2011 Elsevier Ltd.

Forced convection flow boiling and two-phase flow phenomena in a microchannel

Science.gov (United States)

Na, Yun Whan

2008-07-01

The present study was performed to numerically analyze the evaporation phenomena through the liquid-vapor interface and to investigate bubble dynamics and heat transfer behavior during forced convective flow boiling in a microchannel. Flow instabilities of two-phase flow boiling in a microchannel were studied as well. The main objective of this research is to investigate the fundamental mechanisms of two-phase flow boiling in a microchannel and provide predictive tools to design thermal management systems, for example, microchannel heat sinks. The numerical results obtained from this study were qualitatively and quantitatively compared with experimental results in the open literature. Physical and mathematical models, accounting for evaporating phenomena through the liquid-vapor interface in a microchannel at constant heat flux and constant wall temperature, have been developed, respectively. The heat transfer mechanism is affected by the dominant heat conduction through the thin liquid film and vaporization at the liquid-vapor interface. The thickness of the liquid film and the pressure of the liquid and vapor phases were simultaneously solved by the governing differential equations. The developed semi-analytical evaporation model that takes into account of the interfacial phenomena and surface tension effects was used to obtain solutions numerically using the fourth-order Runge-Kutta method. The effects of heat flux 19 and wall temperature on the liquid film were evaluated. The obtained pressure drops in a microchannel were qualitatively consistent with the experimental results of Qu and Mudawar (2004). Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation to investigate bubble dynamics, flow patterns, and heat transfer. The momentum and energy equations were solved using the finite volume method while the liquid-vapor interface of a bubble is captured using the VOF (Volume of Fluid

One-dimensional position readout from microchannel plates

International Nuclear Information System (INIS)

Connell, K.A.; Przybylski, M.M.

1982-01-01

The development of a one-dimensional position readout system with microchannel plates, is described, for heavy ion detectors for use in a particle time-of-flight telescope and as a position sensitive device in front of an ionisation counter at the Nuclear Structure Facility. (U.K.)

Cooling Performance of Additively Manufactured Microchannels and Film Cooling Holes

Science.gov (United States)

Stimpson, Curtis K.

Additive manufacturing (AM) enables fabrication of components that cannot be made with any other manufacturing method. Significant advances in metal-based AM systems have made this technology feasible for building production parts to be used use in commercial products. In particular, the gas turbine industry benefits from AM as a manufacturing technique especially for development of components subjected to high heat flux. It has been shown that the use of microchannels in high heat flux components can lead to more efficient cooling designs than those that presently exist. The current manufacturing methods have prevented the use of microchannels in such parts, but AM now makes them manufacturable. However, before such designs can become a reality, much research must be done to characterize impacts on flow and heat transfer of AM parts. The current study considers the effect on flow and heat transfer through turbine cooling features made with AM. Specifically, the performance of microchannels and film cooling holes made with laser powder bed fusion (L-PBF) is assessed. A number of test coupons containing microchannels were built from high temperature alloy powders on a commercially available L-PBF machine. Pressure drop and heat transfer experiments characterized the flow losses and convective heat transfer of air passing through the channels at various Reynolds numbers and Mach numbers. The roughness of the channels' surfaces was characterized in terms of statistical roughness parameters; the morphology of the roughness was examined qualitatively. Magnitude and morphology of surface roughness found on AM parts is unlike any form of roughness seen in the literature. It was found that the high levels of roughness on AM surfaces result in markedly augmented pressure loss and heat transfer at all Reynolds numbers, and conventional flow and heat transfer correlations produce erroneous estimates. The physical roughness measurements made in this study were correlated to

Numerical study of the bubbly flow regime in micro-channel flow boiling

Science.gov (United States)

Bhuvankar, Pramod; Dabiri, Sadegh

2017-11-01

Two-phase flow accompanied by boiling in micro-channel heat sinks is an effective means for heat removal from computer chips. We present a numerical study of flow boiling in micro-channels with conjugate heat transfer with a focus on the bubbly flow regime. The bubbles are assumed to nucleate at a pre-determined location and frequency. The Navier Stokes equations are solved using a single fluid formulation with the Front tracking method. Phase change is implemented using the deficit in heat flux across the bubble interface. The analytical solution for bubble growth in a superheated liquid is used as a benchmark to validate the mentioned numerical method. Water and FC-72 are studied as the operating fluids in a micro-channel made of Copper with a focus on hotspot mitigation. The micro-channel of cross-section 231 μm × 1000 μm , is used to study the effects of vertical up-flow, vertical down-flow and horizontal flow of the mentioned fluids on the heat transfer coefficients. A simple film model accounting for mass and energy conservation is applied wherever the bubble approaches closer than a cell width to the wall. The results of the simulation are compared with existing experimental data for bubble growth rates and heat transfer coefficients.

Flow and heat transfer behaviour of nanofluids in microchannels

Directory of Open Access Journals (Sweden)

James Bowers

2018-04-01

Full Text Available Flow and heat transfer of aqueous based silica and alumina nanofluids in microchannels were experimentally investigated. The measured friction factors were higher than conventional model predictions at low Reynolds numbers particularly with high nanoparticle concentrations. A decrease in the friction factor was observed with increasing Reynolds number, possibly due to the augmentation of nanoparticle aggregate shape arising from fluid shear and alteration of local nanoparticle concentration and nanofluid viscosity. Augmentation of the silica nanoparticle morphology by fluid shear may also have affected the friction factor due to possible formation of a core/shell structure of the particles. Measured thermal conductivities of the silica nanofluids were in approximate agreement with the Maxwell-Crosser model, whereas the alumina nanofluids only showed slight enhancements. Enhanced convective heat transfer was observed for both nanofluids, relative to their base fluids (water, at low particle concentrations. Heat transfer enhancement increased with increasing Reynolds number and microchannel hydraulic diameter. However, the majority of experiments showed a larger increase in pumping power requirements relative to heat transfer enhancements, which may hinder the industrial uptake of the nanofluids, particularly in confined environments, such as Micro Electro-Mechanical Systems (MEMS. Keywords: Nanofluid, Microchannel, Heat transfer, Pressure drop, Friction factor, Thermal conductivity, Viscosity

Effect of supersaturation on L-glutamic acid polymorphs under droplet-based microchannels

Science.gov (United States)

Jiang, Nan; Wang, Zhanzhong; Dang, Leping; Wei, Hongyuan

2016-07-01

Supersaturation is an important controlling factor for crystallization process and polymorphism. Droplet-based microchannels and conventional crystallization were used to investigate polymorphs of L-gluatamic acid in this work. The results illustrate that it is easy to realize the accurate and rapid control of the crystallization temperature in the droplets, which is especially beneficial to heat and mass transfer during crystallization. It is also noted that higher degree of supersaturation favors the nucleation of α crystal form, while lower degree of supersaturation favors the nucleation of β crystal form under droplet-based microchannels for L-gluatamic acid. In addition, there is a different nucleation behavior to be found under droplet-based microchannels both for the β form and α form of L-glutamic acid. This new finding can provide important insight into the development and design of investigation meanings for drug polymorph.

Comparison of heat pump performance using fin-and-tube and microchannel heat exchangers under frost conditions

International Nuclear Information System (INIS)

Shao, Liang-Liang; Yang, Liang; Zhang, Chun-Lu

2010-01-01

Vapor compression heat pumps are drawing more attention in energy saving applications. Microchannel heat exchangers can provide higher performance via less core volume and reduce system refrigerant charge, but little is known about their performance in heat pump systems under frosting conditions. In this study, the system performance of a commercial heat pump using microchannel heat exchangers as evaporator is compared with that using conventional finned-tube heat exchangers numerically and experimentally. The microchannel and finned-tube heat pump system models used for comparison of the microchannel and finned-tube evaporator performance under frosting conditions were developed, considering the effect of maldistribution on both refrigerant and air sides. The quasi-steady-state modeling results are in reasonable agreement with the test data under frost conditions. The refrigerant-side maldistribution is found remarkable impact on the microchannel heat pump system performance under the frost conditions. Parametric study on the fan speed and the fin density under frost conditions are conducted as well to figure out the best trade-off in the design of frost tolerant evaporators. (author)

Transition from annular flow to plug/slug flow in condensation of steam in microchannels

Energy Technology Data Exchange (ETDEWEB)

Quan, Xiaojun; Cheng, Ping; Wu, Huiying [School of Mechanical and Power Engineering, Shanghai Jiaotong University, 800 Dong Chuan Road, Shanghai 200240 (China)

2008-02-15

A visualization study has been conducted to investigate the transition from annular flow to plug/slug flow in the condensation of steam in two different sets of parallel microchannels, having hydraulic diameters of 90 {mu}m and 136 {mu}m, respectively. The steam in the parallel microchannels was cooled on the bottom by forced convection of water and by natural convection of air from the top. It is found that the location, where the transition from annular flow to plug/slug flow takes place, depends on mass flux and cooling rate of steam. The effects of mass flux and cooling rate on the occurrence frequency of the injection flow in a single microchannel, having a hydraulic diameter of 120 {mu}m and 128 {mu}m, respectively, are investigated. It is found that two different shapes of injection flow occur in the smooth annular flow in microchannels: injection flow with unsteady vapor ligament occurring at low mass flux (or high cooling rate) and injection flow with steady vapor ligament occurring at high mass flux (or low cooling rate). It is also found that increase of steam mass flux, decrease of cooling rate, or decrease of the microchannel diameter tends to enhance instability of the condensate film on the wall, resulting in occurrence of the injection flow further toward the outlet with an increase in occurrence frequency. (author)

In vitro blood flow in a rectangular PDMS microchannel: experimental observations using a confocal micro-PIV system.

Science.gov (United States)

Lima, Rui; Wada, Shigeo; Tanaka, Shuji; Takeda, Motohiro; Ishikawa, Takuji; Tsubota, Ken-ichi; Imai, Yohsuke; Yamaguchi, Takami

2008-04-01

Progress in microfabricated technologies has attracted the attention of researchers in several areas, including microcirculation. Microfluidic devices are expected to provide powerful tools not only to better understand the biophysical behavior of blood flow in microvessels, but also for disease diagnosis. Such microfluidic devices for biomedical applications must be compatible with state-of-the-art flow measuring techniques, such as confocal microparticle image velocimetry (PIV). This confocal system has the ability to not only quantify flow patterns inside microchannels with high spatial and temporal resolution, but can also be used to obtain velocity measurements for several optically sectioned images along the depth of the microchannel. In this study, we investigated the ability to obtain velocity measurements using physiological saline (PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel (300 microm wide, 45 microm deep) using a confocal micro-PIV system. Applying this combination, measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re = 0.02). Velocity profiles were acquired by successive measurements at different depth positions to obtain three-dimensional (3-D) information on the behavior of both fluid flows. Generally, the velocity profiles were found to be markedly blunt in the central region, mainly due to the low aspect ratio (h/w = 0.15) of the rectangular microchannel. Predictions using a theoretical model for the rectangular microchannel corresponded quite well with the experimental micro-PIV results for the PS fluid. However, for the in vitro blood with 20% hematocrit, small fluctuations were found in the velocity profiles. The present study clearly shows that confocal micro-PIV can be effectively integrated with a PDMS microchannel and used to obtain blood velocity profiles along the full depth of the microchannel because of its unique 3-D optical sectioning ability

Real field mission profile oriented design of a SiC-based PV-inverter application

DEFF Research Database (Denmark)

Sintamarean, Nicolae Christian; Blaabjerg, Frede; Wang, Huai

2013-01-01

This paper introduces a real field mission profile oriented design tool for the new generation of grid connected PV-inverters applications based on SiC-devices. The proposed design tool consists of a grid connected PV-inverter model, an ElectroThermal model, a converter safe operating area (SOA...... Zth_H in order to perform in a safe mode for the whole operating range. Furthermore, the proposed design tool considers the mission profile (the measured solar irradiance and ambient temperature) from the real field where the converter will operate. Thus, a realistic loading of the converter devices......) model, a mission profile model and an the evaluation block. The PV-system model involves a three level bipolar switch neutral point clamped (3L-BS NPC) inverter connected to the three phase grid through a LCL-filter. Moreover, the SOA model calculates the required converter heatsink thermal impedance...

Optimization of porous microchannel heat exchanger

Science.gov (United States)

Kozhukhov, N. N.; Konovalov, D. A.

2017-11-01

The technical progress in information and communication sphere leads to a sharp increase in the use of radio electronic devices. Functioning of radio electronics is accompanied by release of thermal energy, which must be diverted from the heat-stressed element. Moreover, using of electronics at negative temperatures, on the contrary, requires supply of a certain amount of heat to start the system. There arises the task of creating a system that allows both to supply and to divert the necessary amount of thermal energy. The development of complex thermostabilization systems for radio electronic equipment is due to increasing the efficiency of each of its elements separately. For more efficient operation of a heat exchanger, which directly affects the temperature of the heat-stressed element, it is necessary to calculate the mode characteristics and to take into account the effect of its design parameters. The results of optimizing the microchannel heat exchanger are presented in the article. The target optimization functions are the mass, pressure drop and temperature. The parameters of optimization are the layout of porous fins, their geometric dimensions and coolant flow. For the given conditions, the optimum variant of porous microchannel heat exchanger is selected.

Oscillatory electroosmotic flow in a parallel-plate microchannel under asymmetric zeta potentials

Science.gov (United States)

Peralta, M.; Arcos, J.; Méndez, F.; Bautista, O.

2017-06-01

In this work, we conduct a theoretical analysis of the start-up of an oscillatory electroosmotic flow (EOF) in a parallel-plate microchannel under asymmetric zeta potentials. It is found that the transient evolution of the flow field is controlled by the parameters {R}ω , {R}\\zeta , and \\bar{κ }, which represent the dimensionless frequency, the ratio of the zeta potentials of the microchannel walls, and the electrokinetic parameter, which is defined as the ratio of the microchannel height to the Debye length. The analysis is performed for both low and high zeta potentials; in the former case, an analytical solution is derived, whereas in the latter, a numerical solution is obtained. These solutions provide the fundamental characteristics of the oscillatory EOFs for which, with suitable adjustment of the zeta potential and the dimensionless frequency, the velocity profiles of the fluid flow exhibit symmetric or asymmetric shapes.

Novel dense CO2 technique for beta-galactosidase immobilization in polystyrene microchannels.

Science.gov (United States)

Leclair Ellis, Jeffrey; Tomasko, David L; Dehghani, Fariba

2008-03-01

In this study we design new fabrication techniques and demonstrate the potential of using dense CO2 for facilitating crucial steps in the fabrication of polymeric lab-on-a-chip microdevices by embedding biomolecules at temperatures well below the polymer's glass transition temperature (T(g)). These new techniques are environmentally friendly and done without the use of a clean room. Carbon dioxide at 40 degrees C and between 4.48 and 6.89 MPa was used to immobilize the biologically active molecule, beta-galactosidase (beta-gal), on the surface of polystyrene microchannels. To our knowledge, this is the first time dense CO2 has been used to directly immobilize an enzyme in a microchannel. beta-gal activity was maintained and shown via a fluorescent reaction product, after enzyme immobilization and microchannel capping by the designed fabrication steps at 40 degrees C and pressures up to 6.89 MPa.

Flow and Heat Transfer in Cooling Microchannels with Phase-Change

Energy Technology Data Exchange (ETDEWEB)

Peles, Y P; Yarin, L P; Hetsroni, G [Technion, Israel Institute of Technology, Haifa (Israel) Faculty of Engineering

1998-05-19

The subject of the present work is the parametrical investigation of hydrodynamic and thermal characteristics of laminar flow with phase-change in a heating microchannels. The study is based on the quasi-one-dimensional model of non-isothermal capillary flow. This model takes into account the evolution of flow, heating and evaporation of the liquid, as well as the influence of capillary, inertia, friction and gravity forces. The effect of various parameters (sizes of microchannel, initial temperature of cooling liquid, wall heat flux etc.) on hydrodynamic and thermal structures of the flow, the length of heating, evaporation and superheat regions is studied. Thc specific features of the phenomena is discussed.

Flow and Heat Transfer in Cooling Microchannels with Phase-Change

International Nuclear Information System (INIS)

Peles, Y.P.; Yarin, L.P.; Hetsroni, G.

1998-01-01

The subject of the present work is the parametrical investigation of hydrodynamic and thermal characteristics of laminar flow with phase-change in a heating microchannels. The study is based on the quasi-one-dimensional model of non-isothermal capillary flow. This model takes into account the evolution of flow, heating and evaporation of the liquid, as well as the influence of capillary, inertia, friction and gravity forces. The effect of various parameters (sizes of microchannel, initial temperature of cooling liquid, wall heat flux etc.) on hydrodynamic and thermal structures of the flow, the length of heating, evaporation and superheat regions is studied. Thc specific features of the phenomena is discussed

Measuring the 3D motion of particles in microchannel acoustophoresis using astigmatism particle tracking velocimetry

DEFF Research Database (Denmark)

Augustsson, P.; Barnkob, Rune; Bruus, Henrik

2012-01-01

We introduce full three-dimensional tracking of particles in an acoustophoresis microchannel using Astigmatism Particle Tracking Velocimetry (APTV) [1]. For the first time the interaction between acoustic streaming and the primary acoustic radiation force in microchannel acoustophoresis are exami...... relative to the influence from the acoustic radiation force. The current study opens the route to optimized acoustophoretic system design and operation to enable manipulation of small biological components such as spores, bacteria and viruses.......We introduce full three-dimensional tracking of particles in an acoustophoresis microchannel using Astigmatism Particle Tracking Velocimetry (APTV) [1]. For the first time the interaction between acoustic streaming and the primary acoustic radiation force in microchannel acoustophoresis...... are examined in three dimensions. We have quantified the velocity of particles driven by the primary acoustic radiation force and acoustic streaming, respectively, using 0.5-μm and 5-μm particles. Increased ultrasound frequency and lowered viscosity of the medium reduced the influence of acoustic streaming...

Continuous particle focusing in a waved microchannel using negative dc dielectrophoresis

KAUST Repository

Li, Ming

2012-07-26

We present a waved microchannel for continuous focusing of microparticles and cells using negative direct current (dc) dielectrophoresis. The waved channel is composed of consecutive s-shaped curved channels in series to generate an electric field gradient required for the dielectrophoretic effect. When particles move electrokinetically through the channel, the experienced negative dielectrophoretic forces alternate directions within two adjacent semicircular microchannels, leading to a focused continuous-flow stream along the channel centerline. Both the experimentally observed and numerically simulated results of the focusing performance are reported, which coincide acceptably in proportion to the specified dimensions (i.e. inlet and outlet of the waved channel). How the applied electric field, particle size and medium concentration affect the performance was studied by focusing polystyrene microparticles of varying sizes. As an application in the field of biology, the focusing of yeast cells in the waved mcirochannel was tested. This waved microchannel shows a great potential for microflow cytometry applications and is expected to be widely used before different processing steps in lab-on-A-chip devices with integrated functions. © 2012 IOP Publishing Ltd.

Fabrication of rectangular cross-sectional microchannels on PMMA with a CO2 laser and underwater fabricated copper mask

Science.gov (United States)

Prakash, Shashi; Kumar, Subrata

2017-09-01

CO2 lasers are commonly used for fabricating polymer based microfluidic devices. Despite several key advantages like low cost, time effectiveness, easy to operate and no requirement of clean room facility, CO2 lasers suffer from few disadvantages like thermal bulging, improper dimensional control, difficulty to produce microchannels of other than Gaussian cross sectional shapes and inclined surface walls. Many microfluidic devices require square or rectangular cross-sections which are difficult to produce using normal CO2 laser procedures. In this work, a thin copper sheet of 40 μm was used as a mask above the PMMA (Polymethyl-methacrylate) substrate while fabricating the microchannels utilizing the raster scanning feature of the CO2 lasers. Microchannels with different width dimensions were fabricated utilizing a CO2 laser in with mask and without-mask conditions. A comparison of both the fabricating process has been made. It was found that microchannels with U shape cross section and rectangular cross-section can efficiently be produced using the with mask technique. In addition to this, this technique can provide perfect dimensional control and better surface quality of the microchannel walls. Such a microchannel fabrication process do not require any post-processing. The fabrication of mask using a nanosecond fiber laser has been discussed in details. An underwater laser fabrication method was adopted to overcome heat related defects in mask preparation. Overall, the technique was found to be easy to adopt and significant improvements were observed in microchannel fabrication.

Non-Photolithographic Manufacturing Processes for Micro-Channels Functioned by Micro-Contact-Printed SAMs

Science.gov (United States)

Saigusa, Hiroki; Suga, Yasuo; Miki, Norihisa

In this paper we propose non-photolithographic fabrication processes of micro-fluid channels with patterned SAMs (Self-Assembled-Monolayers). SAMs with a thiol group are micro-contact printed on a patterned Au/Ti layer, which is vapor-deposited through a shadow mask. Ti is an adhesion layer. Subsequently, the micro-channels are formed by bonding surface-activated PDMS onto the silicon substrate via a silanol group, producing a SAMs-functioned bottom wall of the micro-channel. No photolithographic processes are necessary and thus, the proposed processes are very simple, quick and low cost. The micro-reactors can have various functions associated with the micro-contact-printed SAMs. We demonstrate successful manufacturing of micro-reactors with two types of SAMs. The micro-reactor with patterned AUT (11-amino-1-undecanethiol) successfully trapped nano-particles with a carboxylic acid group, indicating that micro-contact-printed SAMs remain active after the manufacturing processes of the micro-reactor. AUT -functioned micro-channels are applicable to bioassay and to immobilize proteins for DNA arrays. ODT (1-octadecanethiol) makes surfaces hydrophobic with the methyl terminal group. When water was introduced into the micro-reactor with ODT-patterned surfaces, water droplets remained only in the hydrophilic areas where ODT was not patterned. ODT -functioned micro-channels are applicable to fluid handling.

Application of two-phase flow for cooling of hybrid microchannel PV cells: A comparative study

International Nuclear Information System (INIS)

Valeh-e-Sheyda, Peyvand; Rahimi, Masoud; Karimi, Ebrahim; Asadi, Masomeh

2013-01-01

Highlights: ► Showing cooling potential of gas–liquid two-phase flow in microchannels for PV cell. ► Introducing the concept of using slug flow in microchannels for cooling of PV cells. ► In single-phase flow, increasing the liquid flow rate enhances the PV power. ► Showing that in two-phase flow the output power related the fluid flow regime. ► By coupling PV and microchannel an increase up to 38% in output power was observed. - Abstract: This paper reports the experimental data from performance of two-phase flows in a small hybrid microchannel solar cell. Using air and water as two-phase fluid, the experiments were conducted at indoor condition in an array of rectangular microchannels with a hydraulic diameter of 0.667 mm. The gas superficial velocity ranges were between 0 and 3.27 m s −1 while liquid flow rate was 0.04 m s −1 . The performance analysis of the PV cell at slug and transitional slug/annular flow regimes are the focus of this study. The influence of two-phase working fluid on PV cell cooling was compared with single-phase. In addition, the great potential of slug flow for heat removal enhancement in PV/T panel was investigated. The obtained data showed the proposed hybrid system could substantially increases the output power of PV solar cells

Micro-channel plate photon detector studies for the TORCH detector

Energy Technology Data Exchange (ETDEWEB)

Castillo García, L., E-mail: lucia.castillo.garcia@cern.ch [CERN, PH Department, CH-1211, Geneva 23 (Switzerland); Laboratory for High Energy Physics, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); Brook, N.; Cowie, E.N.; Cussans, D. [H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom); Forty, R.; Frei, C. [CERN, PH Department, CH-1211, Geneva 23 (Switzerland); Gao, R. [Department of Physics, University of Oxford, Oxford OXI 3RH (United Kingdom); Gys, T. [CERN, PH Department, CH-1211, Geneva 23 (Switzerland); Harnew, N. [Department of Physics, University of Oxford, Oxford OXI 3RH (United Kingdom); Piedigrossi, D. [CERN, PH Department, CH-1211, Geneva 23 (Switzerland); Van Dijk, M. [H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)

2015-07-01

The Time Of internally Reflected Cherenkov light (TORCH) detector is under development. Charged particle tracks passing through a 1 cm plate of quartz will generate the Cherenkov photons, and their arrival will be timed by an array of micro-channel plate photon detectors. As part of the TORCH R&D studies, commercial and custom-made micro-channel plate detectors are being characterized. The final photon detectors for this application are being produced in a three-phase program in collaboration with industry. Custom-made single-channel devices with extended lifetime have been manufactured and their performance is being systematically investigated in the laboratory. Optical studies for the preparation of beam and laboratory tests of a TORCH prototype are also underway.

Experimental investigation of Cu-based, double-layered, microchannel heat exchangers

International Nuclear Information System (INIS)

Lu, Bin; Meng, W J; Mei, Fanghua

2013-01-01

Cu-based, single- and double-layered, microchannel heat exchangers (MHEs) were fabricated and assembled. Comparative measurements on liquid flow characteristics and heat transfer performance were conducted on these devices. Results were compared at the individual microchannel level as well as at the device level. The present results demonstrate that double-layered MHEs exhibit similar heat transfer performance while suffering a much lower pressure drop penalty compared to single-layered MHEs. Another Cu-based, double-layered, liquid–liquid counter-flow MHE was fabricated, assembled and tested. Results show that a low-volume, multilayered, high-performance, liquid-to-liquid MHE is achievable following the manufacturing protocols of the present double-layered, liquid–liquid counter-flow MHE. (paper)

Development of a Microchannel In Situ Propellant Production System

Energy Technology Data Exchange (ETDEWEB)

Brooks, Kriston P.; Rassat, Scot D.; TeGrotenhuis, Ward E.

2005-09-01

An in situ propellant production (ISPP) plant on future Mars robotic missions can produce oxygen (O2) and methane (CH4) that can be used for propellant for the return voyage. By producing propellants from Mars atmospheric carbon dioxide (CO2) and hydrogen (H2) brought from Earth, the initial mass launched in low Earth orbit can be reduced by 20% to 45%, as compared to carrying all of the propellant for a round-trip mission to the Mars surface from Earth. Pacific Northwest National Laboratory used microchannel architecture to develop a Mars-based In Situ Propellant Production (ISPP) system. This three year research and development effort focused on process intensification and system miniaturization of three primary subsystems: a thermochemical compressor, catalytic reactors, and components for separating gas phases from liquid phases. These systems were designed based on a robotic direct return mission scenario, but can be scaled up to human flight missions by simply numbering up the microchannel devices. The thermochemical compression was developed both using absorption and adsorption. A multichannel adsorption system was designed to meet the full-scale CO2 collection requirements using temperature swing adsorption. Each stage is designed to achieve a 10x compression of CO2. A compression ratio to collect Martian atmospheric CO2 at ~0.8 kPa and compress it to at least 100 kPa can be achieved with two adsorption stages in series. A compressor stage incorporates eight thermally coupled adsorption cells at various stages in the adsorption/desorption cycle to maximize the recuperation of thermal energy and provide a nearly continuous flow of CO2 to the downstream reactors. The thermochemically compressed CO2 is then mixed with hydrogen gas and fed to two reactors: a Sabatier Reaction unit and a Reverse Water/Gas Shift unit. The microchannel architecture allows better heat control than is possible in an adiabatic system, resulting in significantly higher conversion. The

Direct simulation Monte Carlo method for gas flows in micro-channels with bends with added curvature

Directory of Open Access Journals (Sweden)

Tisovský Tomáš

2017-01-01

Full Text Available Gas flows in micro-channels are simulated using an open source Direct Simulation Monte Carlo (DSMC code dsmcFOAM for general application to rarefied gas flow written within the framework of the open source C++ toolbox called OpenFOAM. Aim of this paper is to investigate the flow in micro-channel with bend with added curvature. Results are compared with flows in channel without added curvature and equivalent straight channel. Effects of micro-channel bend was already thoroughly investigated by White et al. Geometry proposed by White is also used here for refference.

Microchannel Reactors for ISRU Applications Using Nanofabricated Catalysts, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Makel Engineering, Inc. (MEI) and USRA propose to develop microchannel reactors for In-Situ Resources Utilization (ISRU) using nanofabricated catalysts. The proposed...

A simple process to achieve microchannels geometries able to produce hydrodynamic cavitation

Science.gov (United States)

Qiu, X.; Cherief, W.; Colombet, D.; Ayela, F.

2017-04-01

We present a simple process to perform microchannels in which cavitating two phase flows are easily producible. Up to now, hydrodynamic cavitation ‘on a chip’ was reached with small flow rates inside microchannels whose micromachining had involved a deep reactive ion etching (D-RIE). The process we present here does not require a D-RIE reactor, as it is only funded on a wet etching of silicon. It leads to a so-called microstep profile, and large cavitating flow rates become possible together with moderate pressure drops.

A simple process to achieve microchannels geometries able to produce hydrodynamic cavitation

International Nuclear Information System (INIS)

Qiu, X; Cherief, W; Colombet, D; Ayela, F

2017-01-01

We present a simple process to perform microchannels in which cavitating two phase flows are easily producible. Up to now, hydrodynamic cavitation ‘on a chip’ was reached with small flow rates inside microchannels whose micromachining had involved a deep reactive ion etching (D-RIE). The process we present here does not require a D-RIE reactor, as it is only funded on a wet etching of silicon. It leads to a so-called microstep profile, and large cavitating flow rates become possible together with moderate pressure drops. (technical note)

Fluid flow and heat transfer of nanofluids in microchannel heat sink with V-type inlet/outlet arrangement

Directory of Open Access Journals (Sweden)

Ayoub Abdollahi

2017-03-01

Full Text Available The fluid flow and heat transfer characteristics of laminar nanofluid flow in microchannel heat sink (MCHS with V-Type inlet/outlet arrangement are numerically studied. A constant heat flux boundary condition is applied on the base plate of MCHS and all the other surfaces of MCHS are insulated. Four different kinds of nanofluids are utilized as working fluids which are SiO2, Al2O3, ZnO and CuO dispersed in pure water as a base fluid. Three different volume fractions of 1%, 1.5% and 2% and three distinctive nanoparticle diameters of 30 nm, 40 nm and 60 nm were employed. The results specify that the SiO2 nanofluid has the uppermost heat transfer rate compared to other tested nanofluids. Increasing the nanoparticles volume fraction together with decreasing the nanoparticles diameter enhances the Nusselt number value. The pressure drop coefficient did not change significantly by using nanofluid with various volume fractions and varied nanoparticle diameters. Moreover, the results indicate that nanofluid can enhance the performance of MCHS with V-shaped inlet/outlet arrangement.

Experimental and numerical investigations on spray structure under the effect of cavitation phenomenon in a microchannel

International Nuclear Information System (INIS)

Ghorbani, Morteza; Sadaghiani, Abdolali Khalili; Yidiz, Mehmet; Kosar, Ali

2017-01-01

In this study, the effect of upstream pressure on cavitation flows inside a microchannel with an inner diameter of 152 μm and resulting spray structure were experimentally and numerically investigated. The effects of bubble number density on two-phase flow hydrodynamics were studied using the numerical approach, where transient model was utilized to obtain the changes in vapor quality inside the microchannel and velocity field near the inlet and outlet of the nozzle. Spray visualization was carried out at a distance of 4.5 mm from the tip of the microchannel using the high speed visualization system. The experimental results showed that the spray cone angle increased with upstream pressure, and beyond the upstream pressure of 50 bar, the liquid jet flow changed to the cloudy spray flow. The bubble collapse was recorded at upstream pressures of 100 and 120 bar, where the cavitation bubbles extended to the outlet of the microchannel, and their collapse took place around the spray

Flow boiling in expanding microchannels

CERN Document Server

Alam, Tamanna

2017-01-01

This Brief presents an up to date summary of details of the flow boiling heat transfer, pressure drop and instability characteristics; two phase flow patterns of expanding microchannels. Results obtained from the different expanding microscale geometries are presented for comparison and addition to that, comparison with literatures is also performed. Finally, parametric studies are performed and presented in the brief. The findings from this study could help in understanding the complex microscale flow boiling behavior and aid in the design and implementation of reliable compact heat sinks for practical applications.

Photon counting with small pore microchannel plates

International Nuclear Information System (INIS)

Martindale, A.; Lapington, J.S.; Fraser, G.W.

2007-01-01

We describe the operation of microchannel plates (MCPs) with 3.2μm diameter channels as photon counting detectors of soft X-rays. Gain and temporal resolution measurements are compared with theoretical scaling laws for channel diameter. A minimum pulse width of 264ps is observed for a two stage multiplier at a total bias voltage of ∼1930V

EXPERIMENTAL PERFORMANCE OF R134a AND R152a USING MICROCHANNEL CONDENSER

OpenAIRE

Bhatkar, V. W.

2018-01-01

An experimental performance study on vapour compression refrigeration system with R134a and drop in substitute R152a with aluminium microchannel condenser was carried out for condensation temperature of 48°C while evaporation temperature varied from -10 to 15°C. Refrigerant charge of R152a was reduced by 40% over R134a with the microchannel condenser. Performance parameters like work input to the compressor, coefficient of performance, refrigerating capacity, condenser capacity and the produc...

Self-separation of blood plasma from whole blood during the capillary flow in microchannel

Science.gov (United States)

Nunna, Bharath Babu; Zhuang, Shiqiang; Lee, Eon Soo

2017-11-01

Self-separation of blood plasma from whole blood in microchannels is of great importance due to the enormous range of applications in healthcare and diagnostics. Blood is a multiphase complex fluid, composed of cells suspended in blood plasma. RBCs are the suspended particles whose shape changes during the flow of blood. The primary constituents of blood are erythrocytes or red blood cells (RBCs), leukocytes or white blood cells (WBCs), thrombocytes or platelets and blood plasma. The existence of RBCs in blood makes the blood a non-Newtonian fluid. The current study of separation of blood plasma from whole blood during self-driven flows in a single microchannel without bifurcation, by enhancing the capillary effects. The change in the capillary effect results in a change in contact angle which directly influences the capillary flow. The flow velocity directly influences the net force acting on the RBCs and influence the separation process. The experiments are performed on the PDMS microchannels with different contact angles by altering the surface characteristics using plasma treatment. The change in the separation length is studied during the capillary flow of blood in microchannel. Bharath Babu Nunna is a researcher in mechanical engineering and implementing the novel and innovative technologies in the biomedical devices to enhance the sensitivity of the disease diagnosis.

Magnetic Control of Fe3O4 Nanomaterial for Fat Ablation in Microchannel

Directory of Open Access Journals (Sweden)

Ming Chang

2015-11-01

Full Text Available In this study, surface modification of iron (II, III oxide Fe3O4 nanoparticles by oleic acid (OA coating is investigated for the microablation of fat in a microchannel. The nanoparticles are synthesized by the co-precipitation method and then dispersed in organic solvent prior to mixing with the OA. The magnetization, agglomeration, and particle size distribution properties of the OA-coated Fe3O4 nanoparticles are characterized. The surface modification of the Fe3O4 nanoparticles reveals that upon injection into a microchannel, the lipophilicity of the OA coating influences the movement of the nanoparticles across an oil-phase barrier. The motion of the nanoparticles is controlled using an AC magnetic field to induce magnetic torque and a static gradient field to control linear translation. The fat microablation process in a microchannel is demonstrated using an oscillating driving field of less than 1200 Am−1.

'Zero-time' detectors using microchannel plates for charged particle detection

International Nuclear Information System (INIS)

Girard, J.

1977-01-01

The mass identification of the reaction products detected in heavy ion nuclear reactions is generally obtained by the time-of-flight method. This method requires a device giving first the 'start' signal (zero time at the passage of the particle) and then the stop 'signal'. The interest lying in 'zero-time' detectors using a secondary electron emission has been considerably increased with using microchannel electron multipliers. Nevertheless such a device was shown to induce either fluctuations in the distance of flight or the use of detectors of different type in the 'start' and 'stop' channels respectively. In both cases, it remains an ambiguity as the access to time resolution, in the channel including the electron multiplier, is not direct and the effect of the different parameters on this resolution are masked. To palliate this drawback and study the qualities of microchannel plate multipliers in time measurement field, some devices mechanically and electronically symmetric have been developed. The resolution measurement in time of flight is obtained for electrons generated by the same particle and emitted from either side of a thin film. The distances of flight of the electrons on each side of the film are same, and so are the accelerating potentials. The microchannel electron multipliers and the processing electronic units are the same in each channel [fr

Measuring the local pressure amplitude in microchannel acoustophoresis

DEFF Research Database (Denmark)

Barnkob, Rune; Augustsson, Per; Laurell, Thomas

2010-01-01

/glass microchannels. The system is actuated by a PZT piezo transducer attached beneath the chip and driven by an applied ac voltage near its eigenfrequency of 2 MHz. For a given frequency a number of particle tracks are recorded by a CCD camera and fitted to a theoretical expression for the acoustophoretic motion...

Lattice Boltzmann Simulation of the Hydrodynamic Entrance Region of Rectangular Microchannels in the Slip Regime

Directory of Open Access Journals (Sweden)

Niya Ma

2018-02-01

Full Text Available Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 < Re < 1000, channel aspect ratio (0 < ε < 1, and Knudsen number (0.001 < Kn < 0.1 on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime.

Numerical study on fabricating rectangle microchannel in microfluidic chips by glass molding process

Science.gov (United States)

Wang, Tao; Chen, Jing; Zhou, Tianfeng

2017-09-01

This paper studied the glass molding process (GMP) for fabricating a typical microstructure of glass microfluidic chips, i. e., rectangle microchannel, on soda-lime glass by finite element method. More than 100 models were established on the platform of Abaqus/Standard. The influence of parameters, i. e., temperature, aspect ratio, side wall angle and friction coefficient on deformation were studied, and the predicted morphology of the molded microchannel were presented as well. The research could provide fundamental experience for optimizing GMP process in the future.

Photochemical immobilization of protein on the inner wall of a microchannel and Its application in a glucose sensor

International Nuclear Information System (INIS)

Nakajima, Hizuru; Ishino, Satomi; Masuda, Hironori; Nakagama, Tatsuro; Shimosaka, Takuya; Uchiyama, Katsumi

2006-01-01

A new protein immobilization technique has been developed for patterning enzymes in a specific position inside a microchannel. First, bovine serum albumin (BSA) was adsorbed onto the internal surface of a polydimethylsiloxane microchannel. The microchannel was then filled with the conjugate solution of a photoreactive cross-linker, 4-azido-2,3,5,6-tetrafluorobenzoic acid succinimidyl ester (ATFB-SE), and an enzyme, horseradish peroxidase (HRP). An irradiation by a He-Cd laser activated the azido group of the conjugates and these conjugates became covalently attached to the adsorbed BSA on the microchannel. The enzyme turnover was observed from only the HRP zone. This technique was successfully applied to the enzymatic glucose sensor. Glucose oxidase (GOD) and HRP were sequentially patterned in a single microchannel, i.e., the HRP zone was located downstream from the GOD zone. The calibration curve of a glucose standard solution was linear over the range of 0-128 μM with a correlation coefficient of 0.993. Compared to the traditional method using a 96-well microtiter plate, the present technique on the microchip shortened the reaction time from 30 min to 4.8 s, i.e., to 1/375

An adhesive bonding method with microfabricating micro pillars to prevent clogging in a microchannel

International Nuclear Information System (INIS)

Chen, Pin-Chuan; Liu, Yu-Min; Chou, Huang-Chieh

2016-01-01

Thermoplastics are widely used in the fabrication of microfluidic chips, due to their low cost, flexibility in manufacturing, and applicability in large-scale production. This paper presents a novel bonding method for the assembly of thermoplastic microfluidic chips, with the aim of preventing the flow of UV adhesive into microchannels during the bonding process. The proposed bonding methodology depends primarily on controlling the thickness of the UV adhesive, which is achieved by using spin-coating for the uniform UV adhesive in conjunction with the microfabrication of short pillars for keeping a uniform gap between the two bonded surfaces. In this study, two devices with serpentine microchannels (cross-sectional area of 500 μm  ×  500 μm and 200 μm  ×  200 μm) were fabricated on PMMA substrates using a micromilling machine, whereupon a hydrophobic coating was applied to the walls of 200 μm  ×  200 μm microchannels in order to prevent clogging, which might otherwise be caused by the seepage of UV adhesive into the channels. A variety of experiments were used to characterize the quality of bonding, the results of which reveal the following: (1) no leakage was observed in either of the microfluidic chips; (2) the hydrophobic coating proved highly effective in preventing the flow of UV adhesive into the smaller microchannels; (3) the average amount of clogging inside 500 μm  ×  500 μm microchannels was 1.13% with standard deviation of 0.55%, while the average amount of clogging inside 200 μm  ×  200 μm microchannels was 1.65% with standard deviation of 0.92%; (4) the average thickness of the UV adhesive in a 500 μm  ×  500 μm microfluidic chip was 32 μm with standard deviation of 2 μm, whereas the average thickness of the UV adhesive in a 200 μm  ×  200 μm microfluidic chip was 31 μm with standard deviation of 1.2 μm; (5) the two chips possess sufficient bonding strength to withstand

Entropy generation minimization of a MHD (magnetohydrodynamic) flow in a microchannel

Energy Technology Data Exchange (ETDEWEB)

Ibanez, Guillermo [Universidad de Ciencias y Artes de Chiapas, Tuxtla Gutierrez, Chiapas 29000 (Mexico); Cuevas, Sergio [Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico A.P. 34, Temixco, Mor. 62580 (Mexico)

2010-10-15

The dissipative processes that arise in a microchannel flow subjected to electromagnetic interactions, as occurs in a MHD (magnetohydrodynamic) micropump, are analyzed. The entropy generation rate is used as a tool for the assessment of the intrinsic irreversibilities present in the microchannel owing to viscous friction, heat flow and electric conduction. The flow in a parallel plate microchannel produced by a Lorentz force created by a transverse magnetic field and an injected electric current is considered assuming a thermally fully developed flow and conducting walls of finite thickness. The conjugate heat transfer problem in the fluid and solid walls is solved analytically using thermal boundary conditions of the third kind at the outer surfaces of the walls and continuity of temperature and heat flux across the fluid-wall interfaces. Velocity, temperature and current density fields in the fluid and walls are used to calculate the global entropy generation rate. Conditions under which this quantity is minimized are determined for specific values of the geometrical and physical parameters of the system. The Nusselt number is also calculated and explored for different conditions. Results can be used to determine optimized conditions that lead to a minimum dissipation consistent with the physical constraints demanded by the microdevice. (author)

Hydrophilic Surface Modification of PDMS Microchannel for O/W and W/O/W Emulsions

Directory of Open Access Journals (Sweden)

Shazia Bashir

2015-09-01

Full Text Available A surface modification method for bonded polydimethylsiloxane (PDMS microchannels is presented herein. Polymerization of acrylic acid was performed on the surface of a microchannel using an inline atmospheric pressure dielectric barrier microplasma technique. The surface treatment changes the wettability of the microchannel from hydrophobic to hydrophilic. This is a challenging task due to the fast hydrophobic recovery of the PDMS surface after modification. This modification allows the formation of highly monodisperse oil-in-water (O/W droplets. The generation of water-in-oil-in-water (W/O/W double emulsions was successfully achieved by connecting in series a hydrophobic microchip with a modified hydrophilic microchip. An original channel blocking technique to pattern the surface wettability of a specific section of a microchip using a viscous liquid comprising a mixture of honey and glycerol, is also presented for generating W/O/W emulsions on a single chip.

Two-phase pressure drop and flow visualization of FC-72 in a silicon microchannel heat sink

International Nuclear Information System (INIS)

Megahed, Ayman; Hassan, Ibrahim

2009-01-01

The rapid development of two-phase microfluidic devices has triggered the demand for a detailed understanding of the flow characteristics inside microchannel heat sinks to advance the cooling process of micro-electronics. The present study focuses on the experimental investigation of pressure drop characteristics and flow visualization of a two-phase flow in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 276 μm, width of 225 μm, and a length of 16 mm. Experiments are carried out for mass fluxes ranging from 341 to 531 kg/m 2 s and heat fluxes from 60.4 to 130.6 kW/m 2 using FC-72 as the working fluid. Bubble growth and flow regimes are observed using high speed visualization. Three major flow regimes are identified: bubbly, slug, and annular. The frictional two-phase pressure drop increases with exit quality for a constant mass flux. An assessment of various pressure drop correlations reported in the literature is conducted for validation. A new general correlation is developed to predict the two-phase pressure drop in microchannel heat sinks for five different refrigerants. The experimental pressure drops for laminar-liquid laminar-vapor and laminar-liquid turbulent-vapor flow conditions are predicted by the new correlation with mean absolute errors of 10.4% and 14.5%, respectively.

Effect of junction configurations on microdroplet formation in a T-junction microchannel

Science.gov (United States)

Lih, F. L.; Miao, J. M.

2015-03-01

This study investigates the dynamic formation process of water microdroplets in a silicon oil flow in a T-junction microchannel. Segmented water microdroplets are formed at the junction when the water flow is perpendicularly injected into the silicon oil flow in a straight rectangular microchannel. This study further presents the effects of the water flow inlet geometry on hydrodynamic characteristics of water microdroplet formation. A numerical multiphase volume of fluid (VOF) scheme is coupled to solve the unsteady three-dimensional laminar Navier-Stokes equations to depict the droplet formation phenomena at the junction. Predicted results on the length and generated frequency of the microdroplets agree well with experimental results in a T-junction microchannel with straight and flat inlets (the base model) for both fluid flows. Empirical correlations are reported between the volumetric flow ratio and the dimensionless microdroplet length or dimensionless frequency of droplet generation at a fixed capillary number of 4.7 · 10-3. The results of this study indicate a reduction in the droplet length of approximately 21% if the straight inlet for the water flow is modified to a downstream sudden contraction inlet for the water flow.

The measurements of water flow rates in the straight microchannel based on the scanning micro-PIV technique

Science.gov (United States)

Wang, H. L.; Han, W.; Xu, M.

2011-12-01

Measurement of the water flow rate in microchannel has been one of the hottest points in the applications of microfluidics, medical, biological, chemical analyses and so on. In this study, the scanning microscale particle image velocimetry (scanning micro-PIV) technique is used for the measurements of water flow rates in a straight microchannel of 200μm width and 60μm depth under the standard flow rates ranging from 2.481μL/min to 8.269μL/min. The main effort of this measurement technique is to obtain three-dimensional velocity distribution on the cross sections of microchannel by measuring velocities of the different fluid layers along the out-of-plane direction in the microchannel, so the water flow rates can be evaluated from the discrete surface integral of velocities on the cross section. At the same time, the three-dimensional velocity fields in the measured microchannel are simulated numerically using the FLUENT software in order to verify the velocity accuracy of measurement results. The results show that the experimental values of flow rates are well consistent to the standard flow rates input by the syringe pump and the compared results between numerical simulation and experiment are consistent fundamentally. This study indicates that the micro-flow rate evaluated from three-dimensional velocity by the scanning micro-PIV technique is a promising method for the micro-flow rate research.

Entropy generation of nanofluid flow in a microchannel heat sink

Science.gov (United States)

Manay, Eyuphan; Akyürek, Eda Feyza; Sahin, Bayram

2018-06-01

Present study aims to investigate the effects of the presence of nano sized TiO2 particles in the base fluid on entropy generation rate in a microchannel heat sink. Pure water was chosen as base fluid, and TiO2 particles were suspended into the pure water in five different particle volume fractions of 0.25%, 0.5%, 1.0%, 1.5% and 2.0%. Under laminar, steady state flow and constant heat flux boundary conditions, thermal, frictional, total entropy generation rates and entropy generation number ratios of nanofluids were experimentally analyzed in microchannel flow for different channel heights of 200 μm, 300 μm, 400 μm and 500 μm. It was observed that frictional and total entropy generation rates increased as thermal entropy generation rate were decreasing with an increase in particle volume fraction. In microchannel flows, thermal entropy generation could be neglected due to its too low rate smaller than 1.10e-07 in total entropy generation. Higher channel heights caused higher thermal entropy generation rates, and increasing channel height yielded an increase from 30% to 52% in thermal entropy generation. When channel height decreased, an increase of 66%-98% in frictional entropy generation was obtained. Adding TiO2 nanoparticles into the base fluid caused thermal entropy generation to decrease about 1.8%-32.4%, frictional entropy generation to increase about 3.3%-21.6%.

Experimental study on frosting control of mobile air conditioning system with microchannel evaporator

International Nuclear Information System (INIS)

Qu Xiaohua; Shi Junye; Qi Zhaogang; Chen Jiangping

2011-01-01

In this paper, a newly developed frost control system is proposed. System bench tests and vehicle test in wind tunnel have been carried out to explore the anti-frosting performance of automotive air conditioning system with microchannel evaporator. The experimental results are compared with the baseline conventional laminated evaporator system. The test results show that the installation position of temperature sensor can dramatically affect the anti-frosting performance. The clutch switching on/off temperature range of the microchannel evaporator is also experimentally studied. The test results show that, with a proper installation position and on/off temperature range, the system COP can be improved, and meanwhile the panel vents' air off temperature can be reduced, and temperature swing can be reduced. - Highlights: → The frost control systems were tested with microchannel and laminated evaporators separately. → The installation position of temperature sensor affects the anti-frosting performance. → Temperature control range affects the anti-frosting performance. → The panel vents' air off temperature and swing can be reduced by proper control parameters. → The system COP can be improved by proper control parameters.

Effect of patterned micro-magnets on superparamagnetic beads in microchannels

International Nuclear Information System (INIS)

Guo, S S; Deng, Y L; Zhao, L B; Zhao, X-Z; Chan, H L W

2008-01-01

The trapping response of patterned micro-magnets (PMMs) was studied based on the parameters affecting superparamagnetic beads in microfluidic channels. Using replica moulding and electroplating technologies, the PMMs were fabricated on the microchannel bottom, which generated sufficient magnetic forces to bias the moments of magnetic particles in a flowing stream. A simplified physical principle was used to analyse the relative velocity of the magnetic particle in the confined space of a microchannel. The results revealed that the magnetic force contributed to the fluidic flow rate as well as to the hydrodynamic drag force. The relative velocity of magnetic particles was dependent on the frequency under an external magnetic field driven by an alternate current (ac) source. It showed that the magnetic gradient induced hysteresis characteristics of the transmission spectrum, associated with the interaction of superparamagnetic beads and magnetic field

The flow field around a micropillar confined in a microchannel

International Nuclear Information System (INIS)

Jung, Junkyu; Kuo, C.-J.; Peles, Yoav; Amitay, Michael

2012-01-01

The flow field over a low aspect ratio (AR) circular pillar (L/D = 1.5) in a microchannel was studied experimentally. Microparticle image velocimetry (μPIV) was employed to quantify flow parameters such as flow field, spanwise vorticity, and turbulent kinetic energy (TKE) in the microchannel. Flow regimes of cylinder-diameter-based Reynolds number at 100 ⩽ Re D ⩽ 700 (i.e., steady, transition from quasi-steady to unsteady, and unsteady flow) were elucidated at the microscale. In addition, active flow control (AFC), via a steady control jet (issued from the pillar itself in the downstream direction), was implemented to induce favorable disturbances to the flow in order to alter the flow field, promote turbulence, and increase mixing. Together with passive flow control (i.e., a circular pillar), turbulent kinetic energy was significantly increased in a controllable manner throughout the flow field.

Does Artificial Ascites Induce the Heat-Sink Phenomenon during Percutaneous Radiofrequency Ablation of the Hepatic Subcapsular Area?: an in vivo Experimental Study Using a Rabbit Model

International Nuclear Information System (INIS)

Kim, Young Sun; Rhim, Hyun Chul; Choi, Dong Il; Lim, Hyo K.

2009-01-01

To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model. A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05). One rabbit from the 'W' group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups 'W' and 'R' throughout the procedures (39.2± 0.4 .deg. C in group W and 33.4±4.3 .deg. C in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4±237.3 mL in group C, 1,172.0±468.9 mL in group R, and 1,030.6±665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group 'C' rabbits (p = 0.030). Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region

Does artificial ascites induce the heat-sink phenomenon during percutaneous radiofrequency ablation of the hepatic subcapsular area?: an in vivo experimental study using a rabbit model.

Science.gov (United States)

Kim, Young Sun; Rhim, Hyunchul; Choi, Dongil; Lim, Hyo K

2009-01-01

To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model. A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05). One rabbit from the "W" group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups "W" and "R" throughout the procedures (39.2+/-0.4 degrees C in group W and 33.4+/-4.3 degrees C in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4+/-237.3 mL in group C, 1,172.0+/-468.9 mL in group R, and 1,030.6+/-665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group "C" rabbits (p = 0.030). Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region.

Batch production of microchannel plate photo-multipliers

Energy Technology Data Exchange (ETDEWEB)

Frisch, Henry J.; Wetstein, Matthew; Elagin, Andrey

2018-03-06

In-situ methods for the batch fabrication of flat-panel micro-channel plate (MCP) photomultiplier tube (PMT) detectors (MCP-PMTs), without transporting either the window or the detector assembly inside a vacuum vessel are provided. The method allows for the synthesis of a reflection-mode photocathode on the entrance to the pores of a first MCP or the synthesis of a transmission-mode photocathode on the vacuum side of a photodetector entrance window.

Convective boiling in a parallel microchannel heat sink with a diverging cross-section design and artificial nucleation sites

International Nuclear Information System (INIS)

Lu, Chun Ting; Pan, Chin

2009-01-01

To develop a highly stable boiling heat transfer microchannel heat sink, the three types of diverging microchannels, namely Type-1, Type-2 and Type-3, were designed to explore experimentally the effect of different distribution of artificial nucleation sites on enhancing boiling heat transfer in 10 parallel diverging microchannels with a mean hydraulic diameter of 120 μm. The Type-1 system is with no cavities, Type-2 is with cavities distributed uniformly along the downstream half of the channel, while Type-3 is with cavities distributed uniformly along the whole channel. The artificial nucleation sites are laser-etched pits on the channel bottom wall with a mouth diameter of about 20-22 μm based on the heterogeneous nucleation theory. The results of the present study reveal the presence of the artificial nucleation sites for flow boiling in parallel diverging microchannel significantly reduces the wall superheat and enhances the boiling heat transfer performance. Additionally, the Type-3 design demonstrates the best boiling heat transfer performance. (author)

Diamond Microchannel Heat Sink Designs For High Heat Flux Thermal Control

National Research Council Canada - National Science Library

Corbin, Michael

2002-01-01

.... Many investigators have suggested the use of diamond heat spreaders to reduce flux levels at or near to its source, and some have suggested that diamond microchannel heat sinks ultimately may play...

Evaluation of Superficial and Dimensional Quality Features in Metallic Micro-Channels Manufactured by Micro-End-Milling

Directory of Open Access Journals (Sweden)

Claudio Giardini

2013-04-01

Full Text Available Miniaturization encourages the development of new manufacturing processes capable of fabricating features, like micro-channels, in order to use them for different applications, such as in fuel cells, heat exchangers, microfluidic devices and micro-electromechanical systems (MEMS. Many studies have been conducted on heat and fluid transfer in micro-channels, and they appeared significantly deviated from conventional theory, due to measurement errors and fabrication methods. The present research, in order to deal with this opportunity, is focused on a set of experiments in the micro-milling of channels made of aluminum, titanium alloys and stainless steel, varying parameters, such as spindle speed, depth of cut per pass (ap, channel depth (d, feed per tooth (fz and coolant application. The experimental results were analyzed in terms of dimensional error, channel profile shape deviation from rectangular and surface quality (burr and roughness. The micro-milling process was capable of offering quality features required on the micro-channeled devices. Critical phenomena, like run-out, ploughing, minimum chip thickness and tool wear, were encountered as an explanation for the deviations in shape and for the surface quality of the micro-channels. The application of coolant and a low depth of cut per pass were significant to obtain better superficial quality features and a smaller dimensional error. In conclusion, the integration of superficial and geometrical features on the study of the quality of micro-channeled devices made of different metallic materials contributes to the understanding of the impact of calibrated cutting conditions in MEMS applications.

Cavitation in flow through a micro-orifice inside a silicon microchannel

Science.gov (United States)

Mishra, Chandan; Peles, Yoav

2005-01-01

Hydrodynamic cavitation in flows through a micro-orifice entrenched in a microchannel has been detected and experimentally investigated. Microfabrication techniques have been employed to design and develop a microfluidic device containing an 11.5μm wide micro-orifice inside a 100.2μm wide and 101.3μm deep microchannel. The flow of de-ionized water through the micro-orifice reveals the presence of multifarious cavitating flow regimes. This investigation divulges both similarities and differences between cavitation in micro-orifices and cavitation in their macroscale counterparts. The low incipient cavitation number obtained from the current experiments suggests a dominant size scale effect. Choking cavitation is observed to be independent of any pressure or velocity scale effects. However, choking is significantly influenced by the small stream nuclei residence time at such scales. Flow rate choking leads to the establishment of a stationary cavity. Large flow and cavitation hysteresis have been detected at the microscale leading to very high desinent cavitation numbers. The rapid transition from incipient bubbles to choking cavitation and subsequent supercavitation suggests the presence of radically different flow patterns at the microscale. Supercavitation results in a thick cavity, which extends throughout the microchannel, and is encompassed by the liquid. Cavitation at the microscale is expected to considerably influence the design of innovative high-speed microfluidic systems.

Pressure and partial wetting effects on superhydrophobic friction reduction in microchannel flow

Science.gov (United States)

Kim, Tae Jin; Hidrovo, Carlos

2012-11-01

Friction reduction in microchannel flows can help alleviate the inherently taxing pumping power requirements associated with the dimensions involved. One possible way of achieving friction reduction is through the introduction of surface microtexturing that can lead to a superhydrophobic Cassie-Baxter state. The Cassie-Baxter state is characterized by the presence of air pockets within the surface microtexturing believed to act as an effective "shear free" (or at least shear reduced) layer, decreasing the overall friction characteristics of the surface. Most work in this area has concentrated on optimizing the surface microtexturing geometry to maximize the friction reduction effects and overall stability of the Cassie-Baxter state. However, less attention has been paid to the effects of partially wetted conditions induced by pressure and the correlation between the liquid-gas interface location within the surface microtexturing and the microchannel flow characteristics. This is mainly attributed to the difficulty in tracking the interface shape and location within the microtexturing in the typical top-down view arrangements used in most studies. In this paper, a rectangular microchannel with regular microtexturing on the sidewalls is used to visualize and track the location of the air-water interface within the roughness elements. While visually tracking the wetting conditions in the microtextures, pressure drops versus flow rates for each microchannel are measured and analyzed in terms of the non-dimensional friction coefficient. The frictional behavior of the Poiseuille flow suggests that (1) the air-water interface more closely resembles a no-slip boundary rather than a shear-free one, (2) the friction is rather insensitive to the degree of microtexturing wetting, and (3) the fully wetted (Wenzel state) microtexturing provides lower friction than the non-wetted one (Cassie state), in corroboration with observations (1) and (2).

The application of μPIV technique in the study of magnetic flows in a micro-channel

International Nuclear Information System (INIS)

Nguyen, N.T.; Wu, Z.G.; Huang, X.Y.; Wen, C.-Y..

2005-01-01

In this preliminary experimental study, micro-scale particle image velocimetry (μPIV) was adopted for the first time to get the quantitative information of magnetic flows in a micro-channel. The μPIV consists of an inverted florescent microscope, a Q-switch Nd:YAG laser and a CCD camera. The florescent liquid with particles of 3 μm diameter was blended homogeneously with the prepared magnetic fluid. A permanent magnet approached and left one end of the micro-channel. The response of the magnetic fluid was recorded with the μPIV simultaneously. The flow features validate the feasibility of using μPIV technique in the study of magnetic flows in a micro-channel. μPIV provides a promising experimental tool for visualization and quantitative measurement of magnetic micro-flows

Pattern analysis of aligned nanowires in a microchannel

International Nuclear Information System (INIS)

Jeon, Young Jin; Kang, Hyun Wook; Ko, Seung Hwan; Sung, Hyung Jin

2013-01-01

An image processing method for evaluating the quality of nanowire alignment in a microchannel is described. A solution containing nanowires flowing into a microchannel will tend to deposit the nanowires on the bottom surface of the channel via near-wall shear flows. The deposited nanowires generally form complex directional structures along the direction of flow, and the physical properties of these structures depend on the structural morphology, including the alignment quality. A quantitative analysis approach to characterizing the nanowire alignment is needed to estimate the useful features of the nanowire structures. This analysis consists of several image processing methods, including ridge detection, texton analysis and autocorrelation function (ACF) calculation. The ridge detection method improved the ACF by extracting nanowire frames 1–2 pixels in width. Dilation filters were introduced to permit a comparison of the ACF results calculated from different images, regardless of the nanowire orientation. An ACF based on the FFT was then calculated over a square interrogation window. The alignment angle probability distribution was obtained using texton analysis. Monte Carlo simulations of artificially generated images were carried out, and the new algorithm was applied to images collected using two types of microscopy. (paper)

Osmotically driven flows in microchannels separated by a semipermeable membrane

DEFF Research Database (Denmark)

Jensen, Kåre Hartvig; Lee, J.; Bohr, Tomas

2009-01-01

We have fabricated lab-on-a-chip systems with microchannels separated by integrated membranes allowing for osmotically driven microflows. We have investigated these flows experimentally by studying the dynamics and structure of the front of a sugar solution travelling in 200 mu m wide and 50-200 mu...... m deep microchannels. We find that the sugar front travels at a constant speed, and that this speed is proportional to the concentration of the sugar solution and inversely proportional to the depth of the channel. We propose a theoretical model, which, in the limit of low axial flow resistance......, predicts that the sugar front should indeed travel with a constant velocity. The model also predicts an inverse relationship between the depth of the channel and the speed, and a linear relation between the sugar concentration and the speed. We thus find good qualitative agreement between the experimental...

Heat transfer and pressure drop in microchannels with random roughness

NARCIS (Netherlands)

Pelevic, N.; van der Meer, Theodorus H.

2016-01-01

The effect of surface roughness on heat transfer and fluid flow phenomena within a microchannel has been investigated by using the lattice Boltzmann method. The surface roughness has been generated by using Gaussian function. Gaussian function is an efficient and convenient method to create surface

Variation of microchannel plate resistance with temperature and applied voltage

International Nuclear Information System (INIS)

Pearson, J.F.; Fraser, G.W.; Whiteley, M.J.

1987-01-01

The resistance of microchannel plate electron multiplier is well known to be a function of both applied voltage and detector temperature. We show that the apparent variation of resistance with bias voltage is simply due to plate temperature increases resulting from resistive heating. (orig.)

Continuous particle focusing in a waved microchannel using negative dc dielectrophoresis

KAUST Repository

Li, Ming; Li, Shunbo; Cao, Wenbin; Li, Weihua; Wen, Weijia; Alici, Gursel

2012-01-01

We present a waved microchannel for continuous focusing of microparticles and cells using negative direct current (dc) dielectrophoresis. The waved channel is composed of consecutive s-shaped curved channels in series to generate an electric field

Air-side performance of a micro-channel heat exchanger in wet surface conditions

Directory of Open Access Journals (Sweden)

Srisomba Raviwat

2017-01-01

Full Text Available The effects of operating conditions on the air-side heat transfer, and pressure drop of a micro-channel heat exchanger under wet surface conditions were studied experimentally. The test section was an aluminum micro-channel heat exchanger, consisting of a multi-louvered fin and multi-port mini-channels. Experiments were conducted to study the effects of inlet relative humidity, air frontal velocity, air inlet temperature, and refrigerant temperature on air-side performance. The experimental data were analyzed using the mean enthalpy difference method. The test run was performed at relative air humidities ranging between 45% and 80%; air inlet temperature ranges of 27, 30, and 33°C; refrigerant-saturated temperatures ranging from 18 to 22°C; and Reynolds numbers between 128 and 166. The results show that the inlet relative humidity, air inlet temperature, and the refrigerant temperature had significant effects on heat transfer performance and air-side pressure drop. The heat transfer coefficient and pressure drop for the micro-channel heat exchanger under wet surface conditions are proposed in terms of the Colburn j factor and Fanning f factor.

Development of New Correlation and Assessment of Correlations for Two-Phase Pressure Drop in Rectangular Microchannels

International Nuclear Information System (INIS)

Choi, Chi Woong; Yu, Dong In; Kim, Moo Hwan

2010-01-01

There are two kinds of models in two-phase pressured drop; homogeneous flow model and separated flow model. Many previous researchers have developed correlations for two-phase pressure drop in a microchannel. Most correlations were modified Lockhart and Martinelli's correlation, which was based on the separated flow model. In this study, experiments for adiabatic liquid water and nitrogen gas flow in rectangular microchannels were conducted to investigate two-phase pressure drop in the rectangular microchannels. Two-phase frictional pressure drop in the rectangular microchannels is highly related with flow regime. Homogeneous model with six two-phase viscosity models: Owen(21)'s, MacAdams(22)'s, Cicchitti et al.(23)'s, Dukler et al.(24)'s, Beattie and Whalley(25)'s, Lin et al.(26)'s models and six separated flow models: Lockhart and Martinelli(27)'s, Chisholm(31)'s, Zhang et al.(15)'s, Lee and Lee(5)'s, Moriyama and Inue(4)'s, Qu and Mudawar(8)'s models were assessed with our experimental data. The best two-phase viscosity model is Beattie and Whalley's model. The best separated flow model is Qu and Mudawar's correlation. Flow regime dependency in both homogeneous and separated flow models was observed. Therefore, new flow pattern based correlations for both homogeneous and separated flow models were individually proposed

Theoretical modeling of electroosmotic flow in soft microchannels: A variational approach applied to the rectangular geometry

Science.gov (United States)

Sadeghi, Arman

2018-03-01

Modeling of fluid flow in polyelectrolyte layer (PEL)-grafted microchannels is challenging due to their two-layer nature. Hence, the pertinent studies are limited only to circular and slit geometries for which matching the solutions for inside and outside the PEL is simple. In this paper, a simple variational-based approach is presented for the modeling of fully developed electroosmotic flow in PEL-grafted microchannels by which the whole fluidic area is considered as a single porous medium of variable properties. The model is capable of being applied to microchannels of a complex cross-sectional area. As an application of the method, it is applied to a rectangular microchannel of uniform PEL properties. It is shown that modeling a rectangular channel as a slit may lead to considerable overestimation of the mean velocity especially when both the PEL and electric double layer (EDL) are thick. It is also demonstrated that the mean velocity is an increasing function of the fixed charge density and PEL thickness and a decreasing function of the EDL thickness and PEL friction coefficient. The influence of the PEL thickness on the mean velocity, however, vanishes when both the PEL thickness and friction coefficient are sufficiently high.

An experimental analysis of process parameters to manufacture micro-channels in AISI H13 tempered steel by laser micro-milling

Science.gov (United States)

Teixidor, D.; Ferrer, I.; Ciurana, J.

2012-04-01

This paper reports the characterization of laser machining (milling) process to manufacture micro-channels in order to understand the incidence of process parameters on the final features. Selection of process operational parameters is highly critical for successful laser micromachining. A set of designed experiments is carried out in a pulsed Nd:YAG laser system using AISI H13 hardened tool steel as work material. Several micro-channels have been manufactured as micro-mold cavities varying parameters such as scanning speed (SS), pulse intensity (PI) and pulse frequency (PF). Results are obtained by evaluating the dimensions and the surface finish of the micro-channel. The dimensions and shape of the micro-channels produced with laser-micro-milling process exhibit variations. In general the use of low scanning speeds increases the quality of the feature in both surface finishing and dimensional.

Laser-Driven Ion Acceleration from Plasma Micro-Channel Targets

Science.gov (United States)

Zou, D. B.; Pukhov, A.; Yi, L. Q.; Zhou, H. B.; Yu, T. P.; Yin, Y.; Shao, F. Q.

2017-02-01

Efficient energy boost of the laser-accelerated ions is critical for their applications in biomedical and hadron research. Achiev-able energies continue to rise, with currently highest energies, allowing access to medical therapy energy windows. Here, a new regime of simultaneous acceleration of ~100 MeV protons and multi-100 MeV carbon-ions from plasma micro-channel targets is proposed by using a ~1020 W/cm2 modest intensity laser pulse. It is found that two trains of overdense electron bunches are dragged out from the micro-channel and effectively accelerated by the longitudinal electric-field excited in the plasma channel. With the optimized channel size, these “superponderomotive” energetic electrons can be focused on the front surface of the attached plastic substrate. The much intense sheath electric-field is formed on the rear side, leading to up to ~10-fold ionic energy increase compared to the simple planar geometry. The analytical prediction of the optimal channel size and ion maximum energies is derived, which shows good agreement with the particle-in-cell simulations.

An analytical model for annular flow boiling heat transfer in microchannel heat sinks

International Nuclear Information System (INIS)

Megahed, A.; Hassan, I.

2009-01-01

An analytical model has been developed to predict flow boiling heat transfer coefficient in microchannel heat sinks. The new analytical model is proposed to predict the two-phase heat transfer coefficient during annular flow regime based on the separated model. Opposing to the majority of annular flow heat transfer models, the model is based on fundamental conservation principles. The model considers the characteristics of microchannel heat sink during annular flow and eliminates using any empirical closure relations. Comparison with limited experimental data was found to validate the usefulness of this analytical model. The model predicts the experimental data with a mean absolute error 8%. (author)

Pressure Drop and Catalytic Dehydrogenation of NaBH{sub 4} Solution Across Pin Fin Structures in a Microchannel Reactor

Energy Technology Data Exchange (ETDEWEB)

Jung, Ki Moon [Korea Institute of Industrial Technology, Cheonan (Korea, Republic of); Choi, Seok Hyun [Key Valve Technologies Ltd., Siheung (Korea, Republic of); Lee, Hee Joon [Kookmin Univ., Seoul (Korea, Republic of)

2017-06-15

Dehydrogenation from the hydrolysis of a sodium borohydride (NaBH{sub 4}) solution has been of interest owing to its high theoretical hydrogen storage capacity (10.8 wt.%) and potentially safe operation. An experimental study has been performed on the catalytic reaction rate and pressure drop of a NaBH4 solution over both a single microchannel with a hydraulic diameter of 300 μm and a staggered array of micro pin fins in the microchannel with hydraulic diameter of 50 μm. The catalytic reaction rates and pressure drops were obtained under Reynolds numbers from 1 to 60 and solution concentrations from 5 to 20 wt.%. Moreover, reacting flows were visualized using a high-speed camera with a macro zoom lens. As a result, both the amount of hydrogenation and pressure drop are 2.45 times and 1.5 times larger in a pin fin microchannel array than in a single microchannel, respectively.

Induced- and alternating-current electro-osmotic control of the diffusion layer growth in a microchannel-membrane interface device

Science.gov (United States)

Park, Sinwook; Yossifon, Gilad

2014-11-01

The passage of an electric current through an ionic permselective medium under an applied electric field is characterized by the formation of ionic concentration gradients, which result in regions of depleted and enriched ionic concentration at opposite ends of the medium. Induced-current electro-osmosis (ICEO) and alternating-current-electro-osmosis (ACEO) are shown to control the growth of the diffusion layer (DL) which, in turn, controls the diffusion limited ion transport through the microchannel-membrane system. We fabricated and tested devices made of a Nafion membrane connecting two opposite PDMS microchannels. An interdigitated electrode array was embedded within the microchannel with various distances from the microchannel-membrane interface. The induced ICEO (floating electrodes) / ACEO (active electrodes) vortices formed at the electrode array stir the fluid and thereby suppress the growth of the DL. The intensity of the ACEO vortices is controlled by either varying the voltage amplitude or the frequency, each having its own unique effect. Enhancement of the limiting current by on-demand control of the diffusion length is of importance in on-chip electro-dialysis, desalination and preconcentration of analytes.

Self-Sealed Bionic Long Microchannels with Thin Walls and Designable Nanoholes Prepared by Line-Contact Capillary-Force Assembly.

Science.gov (United States)

Lao, Zhao-Xin; Hu, Yan-Lei; Pan, Deng; Wang, Ren-Yan; Zhang, Chen-Chu; Ni, Jin-Cheng; Xu, Bing; Li, Jia-Wen; Wu, Dong; Chu, Jia-Ru

2017-06-01

Long microchannels with thin walls, small width, and nanoholes or irregular shaped microgaps, which are similar to capillaries or cancerous vessels, are urgently needed to simulate the physiological activities in human body. However, the fabrication of such channels remains challenging. Here, microchannels with designable holes are manufactured by combining laser printing with line-contact capillary-force assembly. Two microwalls are first printed by femtosecond laser direct-writing, and subsequently driven to collapse into a channel by the capillary force that arises in the evaporation of developer. The channel can remain stable in solvent due to the enhanced Van der Waals' force caused by the line-contact of microwalls. Microchannels with controllable nanoholes and almost arbitrary patterns can be fabricated without any bonding or multistep processes. As-prepared microchannels, with wall thicknesses less than 1 µm, widths less than 3 µm, lengths more than 1 mm, are comparable with human capillaries. In addition, the prepared channels also exhibit the ability to steer the flow of liquid without any external pump. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Crossflow type silicon microchannel substrate monodispersion oil-in-water emulsion manufacture; Kurosufuro gata shirikon maikuro chaneru kiban wo mochiita tanbunsan suchuyu emarushon no sakusei

Energy Technology Data Exchange (ETDEWEB)

Kawakatsu, Takahiro [Tohoku University, Miyagi (Japan). Graduate School; Komori, Hideai; Najima, Mitsutashi; Kikuchi, Yuji; Yonemoto, Toshikuni

1999-05-05

The new technique, which continuously produced the monodispersion oil-in-water (0/W) emulsion using the crossflow type silicon microchannel substrate, was developed. On the silicon monocrystal substrate, the watercourse as the liquid of the continuous phase flowed was produced, and the column of the equal slit of the size in both walls of the watercourse was precisely processed. By closing the upper part in the slit by the clamp of the flat glass board in the microchannel substrate, the microchannel column was formed. Through the microchannel, the oil droplet in which the size was even was formed by sending out the oil (triolein) in the water (0.3wt% sodium lauryl sulfate aqueous solution) of continuous phase which is flowing in respect of the watercourse. The size of the oil droplet is greatly dependent on the structure of the microchannel regulated by microchannel width, microchannel height and terrace length (the even part of which the microchannel exit was equipped). Monodispersion emulsion of 16,20 and 48 {mu}m at the average droplet diameter was formed by using microchannel substrate of the three types of which the structure differs. Droplet diameter decreased, when the substrate which formed large droplet of 48 {mu}m in which the water current quantity is 1.4x10{sup -2}mLmin{sup -1} was used, when the flow rate increased. However, there was no a flow rate at droplet diameter, even if it was made to change from 1.4x10{sup -2} to 2.4mLmin{sup -1}, 16 {mu}m 20 {mu}m small change. In all cases, the droplet size distribution was narrow, and the geometry standard deviation was under 1.03. (translated by NEDO)

A dimensional comparison between embedded 3D-printed and silicon microchannels

International Nuclear Information System (INIS)

O'Connor, J; Punch, J; Jeffers, N; Stafford, J

2014-01-01

The subject of this paper is the dimensional characterization of embedded microchannel arrays created using contemporary 3D-printing fabrication techniques. Conventional microchannel arrays, fabricated using deep reactive ion etching techniques (DRIE) and wet-etching (KOH), are used as a benchmark for comparison. Rectangular and trapezoidal cross-sectional shapes were investigated. The channel arrays were 3D-printed in vertical and horizontal directions, to examine the influence of print orientation on channel characteristics. The 3D-printed channels were benchmarked against Silicon channels in terms of the following dimensional characteristics: cross-sectional area (CSA), perimeter, and surface profiles. The 3D-printed microchannel arrays demonstrated variances in CSA of 6.6-20% with the vertical printing approach yielding greater dimensional conformity than the horizontal approach. The measured CSA and perimeter of the vertical channels were smaller than the nominal dimensions, while the horizontal channels were larger in both CSA and perimeter due to additional side-wall roughness present throughout the channel length. This side-wall roughness caused significant shape distortion. Surface profile measurements revealed that the base wall roughness was approximately the resolution of current 3D-printers. A spatial periodicity was found along the channel length which appeared at different frequencies for each channel array. This paper concludes that vertical 3D-printing is superior to the horizontal printing approach, in terms of both dimensional fidelity and shape conformity and can be applied in microfluidic device applications.

Flow analysis for efficient design of wavy structured microchannel mixing devices

Science.gov (United States)

Kanchan, Mithun; Maniyeri, Ranjith

2018-04-01

Microfluidics is a rapidly growing field of applied research which is strongly driven by demands of bio-technology and medical innovation. Lab-on-chip (LOC) is one such application which deals with integrating bio-laboratory on micro-channel based single fluidic chip. Since fluid flow in such devices is restricted to laminar regime, designing an efficient passive modulator to induce chaotic mixing for such diffusion based flow is a major challenge. In the present work two-dimensional numerical simulation of viscous incompressible flow is carried out using immersed boundary method (IBM) to obtain an efficient design for wavy structured micro-channel mixing devices. The continuity and Navier-Stokes equations governing the flow are solved by fractional step based finite volume method on a staggered Cartesian grid system. IBM uses Eulerian co-ordinates to describe fluid flow and Lagrangian co-ordinates to describe solid boundary. Dirac delta function is used to couple both these co-ordinate variables. A tether forcing term is used to impose the no-slip boundary condition on the wavy structure and fluid interface. Fluid flow analysis by varying Reynolds number is carried out for four wavy structure models and one straight line model. By analyzing fluid accumulation zones and flow velocities, it can be concluded that straight line structure performs better mixing for low Reynolds number and Model 2 for higher Reynolds number. Thus wavy structures can be incorporated in micro-channels to improve mixing efficiency.

A dimensional comparison between embedded 3D-printed and silicon microchannels

Science.gov (United States)

O'Connor, J.; Punch, J.; Jeffers, N.; Stafford, J.

2014-07-01

The subject of this paper is the dimensional characterization of embedded microchannel arrays created using contemporary 3D-printing fabrication techniques. Conventional microchannel arrays, fabricated using deep reactive ion etching techniques (DRIE) and wet-etching (KOH), are used as a benchmark for comparison. Rectangular and trapezoidal cross-sectional shapes were investigated. The channel arrays were 3D-printed in vertical and horizontal directions, to examine the influence of print orientation on channel characteristics. The 3D-printed channels were benchmarked against Silicon channels in terms of the following dimensional characteristics: cross-sectional area (CSA), perimeter, and surface profiles. The 3D-printed microchannel arrays demonstrated variances in CSA of 6.6-20% with the vertical printing approach yielding greater dimensional conformity than the horizontal approach. The measured CSA and perimeter of the vertical channels were smaller than the nominal dimensions, while the horizontal channels were larger in both CSA and perimeter due to additional side-wall roughness present throughout the channel length. This side-wall roughness caused significant shape distortion. Surface profile measurements revealed that the base wall roughness was approximately the resolution of current 3D-printers. A spatial periodicity was found along the channel length which appeared at different frequencies for each channel array. This paper concludes that vertical 3D-printing is superior to the horizontal printing approach, in terms of both dimensional fidelity and shape conformity and can be applied in microfluidic device applications.

Pool boiling visualization on open microchannel surfaces

Directory of Open Access Journals (Sweden)

Kaniowski Robert

2017-01-01

Full Text Available The paper presents visualization investigations into pool boiling heat transfer for open minichannel surfaces. The experiments were carried out wih saturated water at atmospheric pressure. Parallel microchannels fabricated by machining were about 0.3 mm wide and 0.2 to 0.4 mm deep. High-speed videos were used as an aid to understanding the heat transfer mechanism. The visualization study aimed at identifying nucleation sites of the departing bubbles and determining their diameters and frequency at various superheats.

Two-phase flow regimes in a horizontal microchannel with the height of 50 μm and width of 10 mm

Science.gov (United States)

Fina, V. P.; Ronshin, F. V.

2017-11-01

Two-phase flows of distilled deionized nanofiltered water and nitrogen gas in a microchannel with a height of 50 μm and a width of 10 mm have been investigated experimentally. The schlieren method has been used to determine main features of the two-phase flow in the microchannel. This method allows detecting the liquid film on the lower and upper walls of the microchannel as well as droplets of various shapes and sizes or vertical liquid bridges. Two-phase flow regimes have been observed, and their boundaries precisely determined using post-processing of the recordings. The following flow regimes have been distinguished: bubble, churn, jet, stratified and annular. Comparison of regime maps for channels of different widths has been carried out, and this parameter showed to have a significant impact on the boundaries between the regimes in microchannels of a height of less than 100 μm.

Fabrication of Super-Hydrophobic Microchannels via Strain-Recovery Deformations of Polystyrene and Oxygen Reactive Ion Etch.

Science.gov (United States)

Chakraborty, Anirban; Xiang, Mingming; Luo, Cheng

2013-08-19

In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles) on the inner surfaces of polystyrene (PS) microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations of the PS and oxygen reactive ion etch (ORIE). Using this approach, two types of micropillar-covered microchannels are fabricated. Their widths range from 118 μm to 132 μm, depths vary from 40 μm to 44 μm, and the inclined angles of their sidewalls are from 53° to 64°. The micropillars enable these microchannels to have super-hydrophobic properties. The contact angles observed on the channel-structured surfaces are above 162°, and the tilt angles to make water drops roll off from these channel-structured substrates can be as small as 1°.

Fabrication of Super-Hydrophobic Microchannels via Strain-Recovery Deformations of Polystyrene and Oxygen Reactive Ion Etch

Directory of Open Access Journals (Sweden)

Anirban Chakraborty

2013-08-01

Full Text Available In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles on the inner surfaces of polystyrene (PS microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations of the PS and oxygen reactive ion etch (ORIE. Using this approach, two types of micropillar-covered microchannels are fabricated. Their widths range from 118 μm to 132 μm, depths vary from 40 μm to 44 μm, and the inclined angles of their sidewalls are from 53° to 64°. The micropillars enable these microchannels to have super-hydrophobic properties. The contact angles observed on the channel-structured surfaces are above 162°, and the tilt angles to make water drops roll off from these channel-structured substrates can be as small as 1°.

Thermal and hydrodynamic studies for micro-channel cooling for large area silicon sensors in high energy physics experiments

Energy Technology Data Exchange (ETDEWEB)

Flaschel, Nils; Ariza, Dario; Diez, Sergio; Gregor, Ingrid-Maria; Tackmann, Kerstin [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Gerboles, Marta; Jorda, Xavier; Mas, Roser; Quirion, David; Ullan, Miguel [Centro Nacional de Microelectronica, Barcelona (Spain)

2017-01-15

Micro-channel cooling initially aiming at small-sized high-power integrated circuits is being transferred to the field of high energy physics. Today's prospects of micro-fabricating silicon opens a door to a more direct cooling of detector modules. The challenge in high energy physics is to save material in the detector construction and to cool large areas. In this paper, we are investigating micro-channel cooling as a candidate for a future cooling system for silicon detectors in a generic research and development approach. The work presented in this paper includes the production and the hydrodynamic and thermal testing of a micro-channel equipped prototype optimized to achieve a homogeneous flow distribution. Furthermore, the device was simulated using finite element methods.

Thermal and hydrodynamic studies for micro-channel cooling for large area silicon sensors in high energy physics experiments

International Nuclear Information System (INIS)

Flaschel, Nils; Ariza, Dario; Diez, Sergio; Gregor, Ingrid-Maria; Tackmann, Kerstin; Gerboles, Marta; Jorda, Xavier; Mas, Roser; Quirion, David; Ullan, Miguel

2017-01-01

Micro-channel cooling initially aiming at small-sized high-power integrated circuits is being transferred to the field of high energy physics. Today's prospects of micro-fabricating silicon opens a door to a more direct cooling of detector modules. The challenge in high energy physics is to save material in the detector construction and to cool large areas. In this paper, we are investigating micro-channel cooling as a candidate for a future cooling system for silicon detectors in a generic research and development approach. The work presented in this paper includes the production and the hydrodynamic and thermal testing of a micro-channel equipped prototype optimized to achieve a homogeneous flow distribution. Furthermore, the device was simulated using finite element methods.

Neural growth into a microchannel network: towards a regenerative neural interface

NARCIS (Netherlands)

Wieringa, P.A.; Wiertz, Remy; le Feber, Jakob; Rutten, Wim

2009-01-01

We propose and validated a design for a highly selective 'endcap' regenerative neural interface towards a neuroprosthesis. In vitro studies using rat cortical neurons determine if a branching microchannel structure can counter fasciculated growth and cause neurites to separte from one another,

Numerical study on drag reduction and heat transfer enhancement in microchannels with superhydrophobic surfaces for electronic cooling

International Nuclear Information System (INIS)

Cheng, Yongpan; Xu, Jinliang; Sui, Yi

2015-01-01

Microchannels with superhydrophobic surfaces are a promising candidate for electric cooling with mild frictional penalty. Frictional and thermal performance of laminar liquid-water flow in such microchannels is numerically investigated for various shear-free fractions and Reynolds numbers. The structures on superhydrophobic surfaces include square posts and holes, transverse and longitudinal grooves. Combined frictional and thermal performance of microchannels is evaluated by a goodness factor, and is compared with that of smooth plain channels. It is found that with increasing shear-free fractions, both friction factor and average Nusselt number deteriorate for four surface patterns; however, goodness factor is improved significantly over smooth plain channels. In general, superhydrophobic surfaces containing longitudinal and transverse grooves exhibit the lowest and highest frictional and thermal performance, respectively; however, combined performance of these two are on opposite. Among four surface patterns, longitudinal grooves have the highest goodness factors, except at high shear-free fractions or high Reynolds numbers where overall performance is surpassed by square posts. At very low or high shear-free fractions, frictional and thermal performance of two-dimensional square posts and holes approaches that of one-dimensional longitudinal or transverse grooves. Our study suggests microchannels with superhydrophobic surfaces as promising candidates for efficient cooling devices.

Behaviour and design considerations for continuous flow closed-open-closed liquid microchannels.

Science.gov (United States)

Melin, Jessica; van der Wijngaart, Wouter; Stemme, Göran

2005-06-01

This paper introduces a method of combining open and closed microchannels in a single component in a novel way which couples the benefits of both open and closed microfluidic systems and introduces interesting on-chip microfluidic behaviour. Fluid behaviour in such a component, based on continuous pressure driven flow and surface tension, is discussed in terms of cross sectional flow behaviour, robustness, flow-pressure performance, and its application to microfluidic interfacing. The closed-open-closed microchannel possesses the versatility of upstream and downstream closed microfluidics along with open fluidic direct access. The device has the advantage of eliminating gas bubbles present upstream when these enter the open channel section. The unique behaviour of this device opens the door to applications including direct liquid sample interfacing without the need for additional and bulky sample tubing.

Evaluation of a X-ray imaging method in micro-fluidics: the case of T-shaped micro-channels filling up

International Nuclear Information System (INIS)

Vabre, A.; Legoupil, S.; Manach, E.; Gal, O.; Colin, St.; Geoffroy, S.; Gue, A.M.

2006-01-01

X-rays methods assessment in micro-fluidics: case of 'T' shaped microchannels filling. Fluid flows within 'T' or 'Y' shaped microchannels are deeply studied in order to develop adapted modeling approaches and experimental techniques. Our technological choice lies on the attenuation measurement of X-ray in matter. The main advantage of this non-intrusive technique is to be implemented on media opaque to visible light. Moreover, X-rays methods may achieve better spatial resolutions as compared to optical methods because of their much lower wavelength. In order to validate this X-ray method, measurements obtained by this technique are compared with direct measurements carried out on similar microchannels. Finally, experimental results are compared with a theoretical model. (author)

Surface cell immobilization within perfluoroalkoxy microchannels

Energy Technology Data Exchange (ETDEWEB)

Stojkovič, Gorazd; Krivec, Matic [Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana (Slovenia); Vesel, Alenka [Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana (Slovenia); Marinšek, Marjan [Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana (Slovenia); Žnidaršič-Plazl, Polona, E-mail: polona.znidarsic@fkkt.uni-lj.si [Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana (Slovenia)

2014-11-30

Graphical abstract: - Highlights: • A very efficient approach for immobilization of cells into microreactors is presented. • It is applicable to various materials, including PFA and cyclic olefin (co)polymers. • It was used to immobilize different prokaryotic and eukaryotic microbes. • Cells were immobilized on the surface in high density and showed good stability. • Mechanisms of APTES interactions with target materials are proposed. - Abstract: Perfluoroalkoxy (PFA) is one of the most promising materials for the fabrication of cheap, solvent resistant and reusable microfluidic chips, which have been recently recognized as effective tools for biocatalytic process development. The application of biocatalysts significantly depends on efficient immobilization of enzymes or cells within the reactor enabling long-term biocatalyst use. Functionalization of PFA microchannels by 3-aminopropyltriethoxysilane (ATPES) and glutaraldehyde was used for rapid preparation of microbioreactors with surface-immobilized cells. X-ray photoelectron spectroscopy and scanning electron microscopy were used to accurately monitor individual treatment steps and to select conditions for cell immobilization. The optimized protocol for Saccharomyces cerevisiae immobilization on PFA microchannel walls comprised ethanol surface pretreatment, 4 h contacting with 10% APTES aqueous solution, 10 min treatment with 1% glutaraldehyde and 20 min contacting with cells in deionized water. The same protocol enabled also immobilization of Escherichia coli, Pseudomonas putida and Bacillus subtilis cells on PFA surface in high densities. Furthermore, the developed procedure has been proved to be very efficient also for surface immobilization of tested cells on other materials that are used for microreactor fabrication, including glass, polystyrene, poly (methyl methacrylate), polycarbonate, and two olefin-based polymers, namely Zeonor{sup ®} and Topas{sup ®}.

Stability Analysis of Reactive Multiphase Slug Flows in Microchannels

Directory of Open Access Journals (Sweden)

Alejandro A. Munera Parra

2014-05-01

Full Text Available Conducting multiphase reactions in micro-reactors is a promising strategy for intensifying chemical and biochemical processes. A major unresolved challenge is to exploit the considerable benefits offered by micro-scale operation for industrial scale throughputs by numbering-up whilst retaining the underlying advantageous flow characteristics of the single channel system in multiple parallel channels. Fabrication and installation tolerances in the individual micro-channels result in different pressure losses and, thus, a fluid maldistribution. In this work, an additional source of maldistribution, namely the flow multiplicities, which can arise in a multiphase reactive or extractive flow in otherwise identical micro-channels, was investigated. A detailed experimental and theoretical analysis of the flow stability with and without reaction for both gas-liquid and liquid-liquid slug flow has been developed. The model has been validated using the extraction of acetic acid from n-heptane with the ionic liquid 1-Ethyl-3-methylimidazolium ethyl sulfate. The results clearly demonstrate that the coupling between flow structure, the extent of reaction/extraction and pressure drop can result in multiple operating states, thus, necessitating an active measurement and control concept to ensure uniform behavior and optimal performance.

Preliminary studies of microchannel plate photomultiplier tube neutron detectors for flight test applications

International Nuclear Information System (INIS)

Dolan, K.W.

1978-10-01

Electrical, mechanical, thermal, and neutron response data indicate that microchannel plate photomultiplier tubes are viable candidates as miniature, ruggedized neutron detectors for flight test applications in future weapon systems

Theoretical study of time-dependent, ultrasound-induced acoustic streaming in microchannels

DEFF Research Database (Denmark)

Muller, Peter Barkholt; Bruus, Henrik

2015-01-01

Based on first- and second-order perturbation theory, we present a numerical study of the temporal buildup and decay of unsteady acoustic fields and acoustic streaming flows actuated by vibrating walls in the transverse cross-sectional plane of a long straight microchannel under adiabatic...

Optical fibre cavity ring down measurement of refractive index with a microchannel drilled by femtosecond laser

Science.gov (United States)

Zhou, Kaiming; Webb, David; Mou, Chengbo; Farries, Mark; Hayes, Neil; Bennion, Ian

2009-10-01

μA microchannel was inscribed in the fibre of a ring cavity which was constructed from two 0.1%:99.9% couplers and a 10m fibre loop. Cavity ring down spectroscopy (CRDS) was used to measure the refractive index (RI) of gels infused into the microchannel with high resolution. The ring down time discloses a nonlinear increase with respect to the RI of the gel and sensitivity up to 300μs/RI unit (RIU) and resolution of 5×10-4 were obtained.

Flow Investigation in a Microchannel with a Flow Disturbing Rib

Czech Academy of Sciences Publication Activity Database

Stogiannis, I.A.; Passos, A.D.; Mouza, A.A.; Paras, S.V.; Pěnkavová, Věra; Tihon, Jaroslav

2014-01-01

Roč. 119, NOV 8 (2014), s. 65-76 ISSN 0009-2509 R&D Projects: GA ČR(CZ) GAP101/12/0585; GA MŠk 7AMB12GR018 Institutional support: RVO:67985858 Keywords : microchannel * wall shear stress * micro-PIV Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.337, year: 2014

Experimental investigation of thermoelectric power generation versus coolant pumping power in a microchannel heat sink

DEFF Research Database (Denmark)

Kolaei, Alireza Rezania; Rosendahl, Lasse; Andreasen, Søren Juhl

2012-01-01

The coolant heat sinks in thermoelectric generators (TEG) play an important role in order to power generation in the energy systems. This paper explores the effective pumping power required for the TEGs cooling at five temperature difference of the hot and cold sides of the TEG. In addition......, the temperature distribution and the pressure drop in sample microchannels are considered at four sample coolant flow rates. The heat sink contains twenty plate-fin microchannels with hydraulic diameter equal to 0.93 mm. The experimental results show that there is a unique flow rate that gives maximum net-power...

Interferometric measurement and numerical comparisons of supersonic heat transfer flows in microchannel

International Nuclear Information System (INIS)

Takahashi, Yuya; Chen, Lin; Okajima, Junnosuke; Iga, Yuka; Komiya, Atsuki; Maruyama, Shigenao

2016-01-01

Highlights: • Effective cooling design by super-/sub-sonic air flow in microchannels is proposed. • Microscale supersonic flows is successfully generated and examined. • Microchannel flow density field were visualized quantitatively by interferometer. • The bump design shows great potential of heat transfer enhancement in microscale. - Abstract: With the fast development of electronic systems and the ever-increasing demand of thermally “smart” design in space and aeronautic engineering, the heat transfer innovations and high heat flux challenges have become a hot topic for decades. This study is aimed at the effective cooling heat transfer design by super-/sub-sonic air flow in microscale channels for high heat flux devices. The design is based on the low temperature flows with supersonic expansion in microscale, which yields a compact and simple design. By careful microelectromechanical process, microscale straight and bumped channels (with simple arc curve) are fabricated and experimentally tested in this study. The microscale flow field and density distributions under new designs are visualized quantitatively by an advanced phase-shifting interferometer system, which results are then compared carefully with numerical simulations. In this study, large differences between the two designs in density distribution and temperature changes (around 50 K) are found. The high heat flux potential for supersonic microchannel flows is realized and discussion into detail. It is confirmed that the bump design contributes significantly to the heat transfer enhancement, which shows potential for future application in novel system designs.

Determination of the Navier slip coefficient of microchannels exploiting the streaming potential.

Science.gov (United States)

Park, Hung Mok

2012-03-01

For most microchannels made of hydrophobic materials such as polymers, velocity slip occurs at the wall, affecting volumetric flow rate of electroosmotic flow Q(eof) and streaming potential (∂ϕ(str)/∂z). Since most techniques exploit Q(eof) or (∂ϕ(str)/∂z) to determine the zeta potential, ζ, it is very difficult to measure ζ of hydrophobic walls, if the slip coefficient b is not found a priori. Until now, Q(eof) and (∂ϕ(str)/∂z) are known to depend on ζ and b in a same functional form, which makes it impossible to estimate ζ or b separately using measurements of Q(eof) and (∂ϕ(str)/∂z). However, exploiting the analytic formula for Q(eof) and (∂ϕ(str)/∂z) derived in the present work, it is found that the effect of ζ and that of b on Q(eof) and (∂ϕ(str)/∂z) can be separated from each other by varying the bulk ionic concentration. Thus, the slip coefficient as well as the zeta potential of hydrophobic microchannels can be found with reasonable accuracy by means of a nonlinear curve fitting method using measured data of Q(eof) and (∂ϕ(str)/∂z) at various bulk ionic concentrations. The present method allows an accurate estimation of slip coefficient of hydrophobic microchannels, which is quite simple and cheap compared with methods employing microparticle velocimetry. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tunable hydrodynamic characteristics in microchannels with biomimetic superhydrophobic (lotus leaf replica) walls.

Science.gov (United States)

Dey, Ranabir; Raj M, Kiran; Bhandaru, Nandini; Mukherjee, Rabibrata; Chakraborty, Suman

2014-05-21

The present work comprehensively addresses the hydrodynamic characteristics through microchannels with lotus leaf replica (exhibiting low adhesion and superhydrophobic properties) walls. The lotus leaf replica is fabricated following an efficient, two-step, soft-molding process and is then integrated with rectangular microchannels. The inherent biomimetic, superhydrophobic surface-liquid interfacial hydrodynamics, and the consequential bulk flow characteristics, are critically analyzed by the micro-particle image velocimetry technique. It is observed that the lotus leaf replica mediated microscale hydrodynamics comprise of two distinct flow regimes even within the low Reynolds number paradigm, unlike the commonly perceived solely apparent slip-stick dominated flows over superhydrophobic surfaces. While the first flow regime is characterized by an apparent slip-stick flow culminating in an enhanced bulk throughput rate, the second flow regime exhibits a complete breakdown of the aforementioned laminar and uni-axial flow model, leading to a predominantly no-slip flow. Interestingly, the critical flow condition dictating the transition between the two hydrodynamic regimes is intrinsically dependent on the micro-confinement effect. In this regard, an energetically consistent theoretical model is also proposed to predict the alterations in the critical flow condition with varying microchannel configurations, by addressing the underlying biomimetic surface-liquid interfacial conditions. Hence, the present research endeavour provides a new design-guiding paradigm for developing multi-functional microfluidic devices involving biomimetic, superhydrophobic surfaces, by judicious exploitation of the tunable hydrodynamic characteristics in the two regimes.

Evaporative CO$_2$ microchannel cooling for the LHCb VELO pixel upgrade

CERN Document Server

de Aguiar Francisco, Oscar A; Collins, Paula; Dumps, Raphael; John, Malcolm; Mapelli, Alessandro; Romagnoli, Giulia

2015-01-01

The LHCb Vertex Detector (VELO) will be upgraded in 2018 to a lightweight pixel detector capable of 40 MHz readout and operation in very close proximity to the LHC beams. The thermal management of the system will be provided by evaporative CO$_2$ circulating in microchannels embedded within thin silicon plates. This solution has been selected due to the excellent thermal efficiency, the absence of thermal expansion mismatch with silicon ASICs and sensors, the radiation hardness of CO$_2$, and very low contribution to the material budget. Although microchannel cooling is gaining considerable attention for applications related to microelectronics, it is still a novel technology for particle physics experiments, in particular when combined with evaporative CO$_2$ cooling. The R&D effort for LHCb is focused on the design and layout of the channels together with a fluidic connector and its attachment which must withstand pressures up to 170 bar. Even distribution of the coolant is ensured by means of the use o...

A new miniature microchannel plate X-ray detector for synchrotron radiation

International Nuclear Information System (INIS)

Rosemeier, R.G.; Green, R.E. Jr.

1982-01-01

A state-of-the-art microchannel plate detector has been developed which allows real time X-ray imaging of X-ray diffraction as well as radiographic phenomenon. Advantages of the device include a 50 mm X-ray input, length less than 4'', and a weight of less than 1 lb. Since the use of synchrotron radiation is greatly facilitated by the capability of remote viewing of X-ray diffraction or radiographic images in real time, a prototype electro-optical system has been designed which couples the X-ray microchannel plate detector with a solid state television camera. Advantages of the miniature, lightweight, X-ray synchrotron camera include a large 50 mm X-ray input window, an output signal that is available in both analog format for display on a television monitor and in digital format for computer processing, and a completely modular design which allows all the components to be exchanged for other components optimally suited for the desired applications. (orig.)

Ferrofluid-in-oil two-phase flow patterns in a flow-focusing microchannel

Science.gov (United States)

Sheu, T. S.; Chen, Y. T.; Lih, F. L.; Miao, J. M.

This study investigates the two-phase flow formation process of water-based Fe3O4 ferrofluid (dispersed phase) in a silicon oil (continuous phase) flow in the microfluidic flow-focusing microchannel under various operational conditions. With transparent PDMS chip and optical microscope, four main two-phase flow patterns as droplet flow, slug flow, ring flow and churn flow are observed. The droplet shape, size, and formation mechanism were also investigated under different Ca numbers and intended to find out the empirical relations. The paper marks an original flow pattern map of the ferrofluid-in-oil flows in the microfluidic flow-focusing microchannels. The flow pattern transiting from droplet flow to slug flow appears for an operational conditions of QR < 1 and Lf / W < 1. The power law index that related Lf / W to QR was 0.36 in present device.

3D tomography of cells in micro-channels

Science.gov (United States)

Quint, S.; Christ, A. F.; Guckenberger, A.; Himbert, S.; Kaestner, L.; Gekle, S.; Wagner, C.

2017-09-01

We combine confocal imaging, microfluidics, and image analysis to record 3D-images of cells in flow. This enables us to recover the full 3D representation of several hundred living cells per minute. Whereas 3D confocal imaging has thus far been limited to steady specimens, we overcome this restriction and present a method to access the 3D shape of moving objects. The key of our principle is a tilted arrangement of the micro-channel with respect to the focal plane of the microscope. This forces cells to traverse the focal plane in an inclined manner. As a consequence, individual layers of passing cells are recorded, which can then be assembled to obtain the volumetric representation. The full 3D information allows for a detailed comparison with theoretical and numerical predictions unfeasible with, e.g., 2D imaging. Our technique is exemplified by studying flowing red blood cells in a micro-channel reflecting the conditions prevailing in the microvasculature. We observe two very different types of shapes: "croissants" and "slippers." Additionally, we perform 3D numerical simulations of our experiment to confirm the observations. Since 3D confocal imaging of cells in flow has not yet been realized, we see high potential in the field of flow cytometry where cell classification thus far mostly relies on 1D scattering and fluorescence signals.

Next Generation Microchannel Heat Exchangers

CERN Document Server

Ohadi, Michael; Dessiatoun, Serguei; Cetegen, Edvin

2013-01-01

In Next Generation Microchannel Heat Exchangers, the authors’ focus on the new generation highly efficient heat exchangers and presentation of novel data and technical expertise not available in the open literature.  Next generation micro channels offer record high heat transfer coefficients with pressure drops much less than conventional micro channel heat exchangers. These inherent features promise fast penetration into many mew markets, including high heat flux cooling of electronics, waste heat recovery and energy efficiency enhancement applications, alternative energy systems, as well as applications in mass exchangers and chemical reactor systems. The combination of up to the minute research findings and technical know-how make this book very timely as the search for high performance heat and mass exchangers that can cut costs in materials consumption intensifies.

High density gold nanoparticles immobilized on surface via plasma deposited APTES film for decomposing organic compounds in microchannels

Science.gov (United States)

Rao, Xi; Guyon, Cédric; Ognier, Stephanie; Da Silva, Bradley; Chu, Chenglin; Tatoulian, Michaël; Hassan, Ali Abou

2018-05-01

Immobilization of colloidal particles (e.g. gold nanoparticles (AuNps)) on the inner surface of micro-/nano- channels has received a great interest for catalysis. A novel catalytic ozonation setup using a gold-immobilized microchannel reactor was developed in this work. To anchor AuNps, (3-aminopropyl) triethoxysilane (APTES) with functional amine groups was deposited using plasma enhanced chemical vapor deposition (PECVD) process. The results clearly evidenced that PECVD processing exhibited relatively high efficiency for grafting amine groups and further immobilizing AuNPs. The catalytic activity of gold immobilized microchannel was evaluated by pyruvic acid ozonation. The decomposition rate calculated from High Performance Liquid Chromatography (HPLC) indicated a much better catalytic performance of gold in microchannel than that in batch. The results confirmed immobilizing gold nanoparticles on plasma deposited APTES for preparing catalytic microreactors is promising for the wastewater treatment in the future.

Shock wave attenuation in a micro-channel

Science.gov (United States)

Giordano, J.; Perrier, P.; Meister, L.; Brouillette, M.

2018-05-01

This work presents optical measurements of shock wave attenuation in a glass micro-channel. This transparent facility, with a cross section ranging from 1 mm× 150 μm to 1 mm× 500 μm, allowed for the use of high-speed schlieren videography to visualize the propagation of a shock wave within the entire micro-channel and to quantify velocity attenuation of the wave due to wall effects. In this paper, we present the experimental technique and the relevant data treatment we have used to increase the sensitivity of shock wave detection. Then, we compared our experimental results for different channel widths, lengths, and shock wave velocities with the analytical model for shock attenuation proposed by Russell (J Fluid Mech 27(2):305-314, 1967), which assumes laminar flow, and by Mirels (Attenuation in a shock tube due to unsteady-boundary-layer action, NACA Report 1333, 1957) for turbulent flow. We found that these models are inadequate to predict the observed data, owing to the presence of fully developed flow which violates the basic assumption of these models. The data are also compared with the empirical shock attenuation models proposed by Zeitoun (Phys Fluids 27(1):011701, 2015) and Deshpande and Puranik (Shock Waves 26(4):465-475, 2016), where better agreement is observed. Finally, we presented experimental data for the flow field behind the shock wave from measurements of the Mach wave angle which shows globally decreasing flow Mach numbers due to viscous wall effects.

Developing the laminar MHD forced convection flow of water/FMWNT carbon nanotubes in a microchannel imposed the uniform heat flux

Energy Technology Data Exchange (ETDEWEB)

Karimipour, Arash; Taghipour, Abdolmajid [Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad (Iran, Islamic Republic of); Malvandi, Amir, E-mail: amirmalvandi@aut.ac.ir [Department of Mechanical Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur (Iran, Islamic Republic of)

2016-12-01

This paper aims to investigate magnetic field and slip effects on developing laminar forced convection of nanofluids in the microchannels. A novel mixture of water and FMWNT carbon nanotubes is used as the working fluid. To do this, fluid flow and heat transfer through a microchannel is simulated by a computer code in FORTRAN language. The mixture of FMWNT carbon nanotubes suspended in water is considered as the nanofluid. Slip velocity is supposed as the hydrodynamic boundary condition while the microchannel's lower wall is insulated and the top wall is under the effect of a constant heat flux. Moreover, the flow field is subjected to a magnetic field with a constant strength. The results are presented as the velocity, temperature and Nusselt number profiles. It is observed that nanofluid composed of water and carbon nanotubes (FMWNT) can work well to increase the heat transfer rate along the microchannel walls. Furthermore, it is indicated that imposing the magnetic field is very effective at the thermally developing region. In contrast, the magnetic field effect at fully developed region is insignificant, especially at low values of Reynolds number. - Highlights: • Simulation of water/FMWNT carbon nanotubes flow in a microchannel. • The effects of magnetic field strength on nanofluid's slip velocity. • The effects of Ha, Re, ϕ and slip coefficient on averaged Nusselt number. • Magnetic field effect at developing flow region is significant.

Fast microchannel plate detector for particles

International Nuclear Information System (INIS)

Wurz, P.; Gubler, L.

1996-01-01

In this article we report on the timing capabilities of a new microchannel plate detector we designed and built. The detector assembly has an impedance-matched transition line (50 Ω line resistance) from anode to cable connector which is considerably smaller than other, commercially available solutions and at the same time has about four times the active area. The detector was tested with an alpha particle source and excellent time response was achieved. Using 10 μm pore size channel plates, a rise time of 300 ps and a pulse width of 520 ps are obtained. The details of the signal analysis are also given in the article. copyright 1996 American Institute of Physics

Investigating performance of microchannel evaporators for automobile air conditioning with different port structures

Directory of Open Access Journals (Sweden)

Guoliang Zhou

2017-08-01

Full Text Available Microchannel evaporator has been widely applied in automobile air conditioning, while it faces the problem of refrigerant maldistribution which deteriorates the thermal performance of evaporator. In this study, the performances of microchannel evaporators with different port structures are experimentally investigated for purpose of reducing evaporator pressure drop. Four evaporator samples with different port number and hydraulic diameter are made for this study. The performances of the evaporator samples are tested on a psychometric calorimeter test bench with the refrigerant R-134A at a real automobile air conditioning. The results on the variations of the evaporator pressure drop and evaporator surface temperature distribution are presented and analyzed. By studying the performance of an evaporator, seeking proper port structure is an approach to reduce refrigerant pressure drop as well as improve refrigerant distribution.

Activity and lifetime of urease immobilized using layer-by-layer nano self-assembly on silicon microchannels.

Science.gov (United States)

Forrest, Scott R; Elmore, Bill B; Palmer, James D

2005-01-01

Urease has been immobilized and layered onto the walls of manufactured silicon microchannels. Enzyme immobilization was performed using layer-by-layer nano self-assembly. Alternating layers of oppositely charged polyelectrolytes, with enzyme layers "encased" between them, were deposited onto the walls of the silicon microchannels. The polycations used were polyethylenimine (PEI), polydiallyldimethylammonium (PDDA), and polyallylamine (PAH). The polyanions used were polystyrenesulfonate (PSS) and polyvinylsulfate (PVS). The activity of the immobilized enzyme was tested by pumping a 1 g/L urea solution through the microchannels at various flow rates. Effluent concentration was measured using an ultraviolet/visible spectrometer by monitoring the absorbance of a pH sensitive dye. The architecture of PEI/PSS/PEI/urease/PEI with single and multiple layers of enzyme demonstrated superior performance over the PDDA and PAH architectures. The precursor layer of PEI/PSS demonstrably improved the performance of the reactor. Conversion rates of 70% were achieved at a residence time of 26 s, on d 1 of operation, and >50% at 51 s, on d 15 with a six-layer PEI/urease architecture.

Modeling of low-capillary number segmented flows in microchannels using OpenFOAM

NARCIS (Netherlands)

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

2012-01-01

Modeling of low-Capillary number segmented flows in microchannels is important for the design of microfluidic devices. We present numerical validations of microfluidic flow simulations using the volume-of-fluid (VOF) method as implemented in OpenFOAM. Two benchmark cases were investigated to ensure

Hydrogen production through aqueous-phase reforming of ethylene glycol in a washcoated microchannel

NARCIS (Netherlands)

Neira d'Angelo, M.F.; Ordomskiy, V.; Paunovic, V.; Schaaf, van der J.; Schouten, J.C.; Nijhuis, T.A.

2013-01-01

Aqueous-phase reforming (APR) of biocarbohydrates is conducted in a catalytically stable washcoated microreactor where multiphase hydrogen removal enhances hydrogen efficiency. Single microchannel experiments are conducted following a simplified model based on the microreactor concept. A coating

Technology Development of an Advanced Small-scale Microchannel-type Process Heat Exchanger (PHE) for Hydrogen Production in Iodine-sulfur Cycle

Energy Technology Data Exchange (ETDEWEB)

Sah, Injin; Kim, Chan Soo; Kim, Yong Wan; Park, Jae-Won; Kim, Eung-Seon; Kim, Min-Hwan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2015-10-15

In this study, ongoing manufacturing processes of the components employed in an advanced small-scale microchannel-type PHE are presented. The components, such as mechanically machined microchannels and a diffusion-bonded stack are introduced. Also, preliminary studies on surface treatment techniques for improving corrosion resistance from the corrosive sulfuric environment will be covered. Ongoing manufacturing process for an advanced small-size microchannel-type PHE in KAERI is presented. Through the preliminary studies for optimizing diffusion bonding condition of Hastelloy-X, a diffusion-bonded stack, consisting of primary and secondary side layer by layer, is scheduled to be fabricated in a few months. Also, surface treatment for enhancing the corrosion resistance from the sulfuric acid environment is in progress for the plates with microchannels. A massive production of hydrogen with electricity generation is expected in a Process Heat Exchanger (PHE) in a Very High Temperature gas-cooled Reactor (VHTR) system. For the application of hydrogen production, a small-scale gas loop for feasibility testing of a laboratory-scale has constructed and operated in Korea Atomic Energy Research Institute (KAERI) as a precursor to an experimental- and a pilot-scale gas loops.

Modelling and Pareto optimization of heat transfer and flow coefficients in microchannels using GMDH type neural networks and genetic algorithms

International Nuclear Information System (INIS)

Amanifard, N.; Nariman-Zadeh, N.; Borji, M.; Khalkhali, A.; Habibdoust, A.

2008-01-01

Three-dimensional heat transfer characteristics and pressure drop of water flow in a set of rectangular microchannels are numerically investigated using Fluent and compared with those of experimental results. Two metamodels based on the evolved group method of data handling (GMDH) type neural networks are then obtained for modelling of both pressure drop (ΔP) and Nusselt number (Nu) with respect to design variables such as geometrical parameters of microchannels, the amount of heat flux and the Reynolds number. Using such obtained polynomial neural networks, multi-objective genetic algorithms (GAs) (non-dominated sorting genetic algorithm, NSGA-II) with a new diversity preserving mechanism is then used for Pareto based optimization of microchannels considering two conflicting objectives such as (ΔP) and (Nu). It is shown that some interesting and important relationships as useful optimal design principles involved in the performance of microchannels can be discovered by Pareto based multi-objective optimization of the obtained polynomial metamodels representing their heat transfer and flow characteristics. Such important optimal principles would not have been obtained without the use of both GMDH type neural network modelling and the Pareto optimization approach

Effects of microchannel confinement on acoustic vaporisation of ultrasound phase change contrast agents

Science.gov (United States)

Lin, Shengtao; Zhang, Ge; Hau Leow, Chee; Tang, Meng-Xing

2017-09-01

The sub-micron phase change contrast agent (PCCA) composed of a perfluorocarbon liquid core can be activated into gaseous state and form stable echogenic microbubbles for contrast-enhanced ultrasound imaging. It has shown great promise in imaging microvasculature, tumour microenvironment, and cancer cells. Although PCCAs have been extensively studied for different diagnostic and therapeutic applications, the effect of biologically geometrical confinement on the acoustic vaporisation of PCCAs is still not clear. We have investigated the difference in PCCA-produced ultrasound contrast enhancement after acoustic activation with and without a microvessel confinement on a microchannel phantom. The experimental results indicated more than one-order of magnitude less acoustic vaporisation in a microchannel than that in a free environment taking into account the attenuation effect of the vessel on the microbubble scattering. This may provide an improved understanding in the applications of PCCAs in vivo.

Experimental and numerical investigations of ionic liquid-aqueous flow in microchannel

Science.gov (United States)

Li, Qi; Tsaoulidis, Dimitrios; Angeli, Panagiota

2015-11-01

The hydrodynamic characteristics of plug flow of an ionic liquid-aqueous two-phase system in a microchannel were studied experimentally and numerically. A mixture of 0.2M N-octyl(plenyl)-N,N-diisobutylcarbamoylmethyphosphine oxide (CMOP)- 1.2 M Tri-n-butylphosphate (TBP) in room temperature ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide ([C4min][NTf2]), and a nitric acid solution of 1M were chosen. These fluids are relevant Eu(III) separation by extraction from nitric acid solutions. The two liquid phases were introduced into microchannels of 0.2 and 0.5mm internal diameter through a T-junction inlet. The flow pattern was visualized during plug formation at the inlet section and further downstream by means by bright field planar micro-Particle Image Velocimetry. Key features of plug flow, such as plug velocity, film thickness, plug length and recirculation intensity were measured under various experimental conditions. To gain further understanding of the 3-D flow field, Computation Fluid Dynamics (CFD) simulations approach were also conducted.

Numerical simulation of electroosmotic flow in rough microchannels using the lattice Poisson-Nernst-Planck methods

Science.gov (United States)

Kamali, Reza; Soloklou, Mohsen Nasiri; Hadidi, Hooman

2018-05-01

In this study, coupled Lattice Boltzmann method is applied to solve the dynamic model for an electroosmotic flow and investigate the effects of roughness in a 2-D flat microchannel. In the present model, the Poisson equation is solved for the electrical potential, the Nernst- Planck equation is solved for the ion concentration. In the analysis of electroosmotic flows, when the electric double layers fully overlap or the convective effects are not negligible, the Nernst-Planck equation must be used to find the ionic distribution throughout the microchannel. The effects of surface roughness height, roughness interval spacing and roughness surface potential on flow conditions are investigated for two different configurations of the roughness, when the EDL layers fully overlap through the microchannel. The results show that in both arrangements of roughness in homogeneously charged rough channels, the flow rate decreases by increasing the roughness height. A discrepancy in the mass flow rate is observed when the roughness height is about 0.15 of the channel width, which its average is higher for the asymmetric configuration and this difference grows by increasing the roughness height. In the symmetric roughness arrangement, the mass flow rate increases until the roughness interval space is almost 1.5 times the roughness width and it decreases for higher values of the roughness interval space. For the heterogeneously charged rough channel, when the roughness surface potential ψr is less than channel surface potential ψs , the net charge density increases by getting far from the roughness surface, while in the opposite situation, when ψs is more than ψr , the net charge density decreases from roughness surface to the microchannel middle center. Increasing the roughness surface potential induces stronger electric driving force on the fluid which results in larger velocities in the flow.

The selective flow of volatile organic compounds in conductive polymer-coated microchannels

Science.gov (United States)

Hossein-Babaei, Faramarz; Hooshyar Zare, Ali

2017-02-01

Many gaseous markers of critical biological, physicochemical, or industrial occurrences are masked by the cross-sensitivity of the sensors to the other active components present at higher concentrations. Here, we report the strongly selective diffusion and drift of contaminant molecules in air-filled conductive polymer-coated microfluidic channels for the first time. Monitoring the passage of different target molecules through microchannels coated with Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) revealed that contaminants such as hexane, benzene, and CO pass through the channel unaffected by the coating while methanol, ethanol, and partly acetone are blocked. The observations are explained with reference to the selective interactions between the conductive polymer surface and target gas molecules amplified by the large wall/volume ratio in microchannels. The accumulated quantitative data point at the hydrogen bonding as the mechanism of wall adsorption; dipole-dipole interactions are relatively insignificant. The presented model facilitates a better understanding of how the conductive polymer-based chemical sensors operate.

Calculating and optimizing inter-electrode capacitances of charge division microchannel plate detectors

Energy Technology Data Exchange (ETDEWEB)

Xing, Yan [Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Chen, Bo, E-mail: chenb@ciomp.ac.cn [Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Zhang, Hong-Ji; Wang, Hai-Feng; He, Ling-Ping [Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Jin, Fang-Yuan [Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); University of Chinese Academy of Sciences, Beijing 100049 (China)

2016-04-01

Based on the principle of charge division microchannel plate detectors, the inter-electrode capacitances of charge division anodes which are related to electronic noise of the charge sensitive amplifier and crosstalk effect of the anode are presented. Under all the requirements of charge division microchannel plate detectors such as the imaging linearity and spatial resolution, decreasing the inter-electrode capacitances is one way to improve the imaging performance. In this paper, we illustrate the simulation process of calculating the inter-electrode capacitances. Moreover, a Wedge and Strip (WSZ) anode is fabricated with the picosecond laser micromachining process. Comparing the simulated capacitances and measured capacitances, the three-dimensional finite element method is proved to be valid. Furthermore, by adjusting the design parameters of the anode, the effects of the substrate permittivity, insulation width and the size of pitch on the inter-electrode capacitances have been analysed. The structure of the charge division anode has been optimized based on the simulation data.

Glucose Fuel Cells with a MicroChannel Fabricated on Flexible Polyimide Film

Science.gov (United States)

Sano, Ryohei; Fukushi, Yudai; Sasaki, Tsubasa; Mogi, Hiroshi; Koide, Syohei; Ikoma, Ryuta; Akatsuka, Wataru; Tsujimura, Seiya; Nishioka, Yasushiro

2013-12-01

In this work, a glucose fuel cell was fabricated using microfabrication processes assigned for microelectromechanical systems. The fuel cell was equipped with a microchannel to flow an aqueous solution of glucose. The cell was fabricated on a flexible polyimide substrate, and its porous carbon-coated aluminum (Al) electrodes of 2.8 mm in width and 11 mm in length were formed using photolithography and screen printing techniques. Porous carbon was deposited by screen printing of carbon black ink on the Al electrode surfaces in order to increase the effective electrode surface area and to absorb more enzymes on the electrode surfaces. The microchannel with a depth of 200 μm was fabricated using a hot embossing technique. A maximum power of 0.45 μW at 0.5 V that corresponds to a power density of 1.45 μW/cm2 was realized by introducing a 200 mM concentrated glucose solution at room temperature.

Glucose Fuel Cells with a MicroChannel Fabricated on Flexible Polyimide Film

International Nuclear Information System (INIS)

Sano, Ryohei; Fukushi, Yudai; Sasaki, Tsubasa; Mogi, Hiroshi; Koide, Syohei; Ikoma, Ryuta; Nishioka, Yasushiro; Akatsuka, Wataru; Tsujimura, Seiya

2013-01-01

In this work, a glucose fuel cell was fabricated using microfabrication processes assigned for microelectromechanical systems. The fuel cell was equipped with a microchannel to flow an aqueous solution of glucose. The cell was fabricated on a flexible polyimide substrate, and its porous carbon-coated aluminum (Al) electrodes of 2.8 mm in width and 11 mm in length were formed using photolithography and screen printing techniques. Porous carbon was deposited by screen printing of carbon black ink on the Al electrode surfaces in order to increase the effective electrode surface area and to absorb more enzymes on the electrode surfaces. The microchannel with a depth of 200 μm was fabricated using a hot embossing technique. A maximum power of 0.45 μW at 0.5 V that corresponds to a power density of 1.45 μW/cm 2 was realized by introducing a 200 mM concentrated glucose solution at room temperature

Distribution of Evaporating CO2 in Parallel Microchannels

DEFF Research Database (Denmark)

Brix, Wiebke; Elmegaard, Brian

2008-01-01

The impact on the heat exchanger performance due to maldistribution of evaporating CO2 in parallel channels is investigated numerically. A 1D steady state simulation model of a microchannel evaporator is built using correlations from the literature to calculate frictional pressure drop and heat...... transfer coefficients. For two channels in parallel two different cases of maldistribution are studied. Firstly, the impact of a non-uniform air flow is considered, and secondly the impact of maldistribution of the two phases in the inlet manifold is investigated. The results for both cases are compared...

Single-phase liquid flow forced convection under a nearly uniform heat flux boundary condition in microchannels

KAUST Repository

Lee, Man

2012-02-22

A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a waferbond-and-etch- back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number. © 2012 IOP Publishing Ltd.

Single-phase liquid flow forced convection under a nearly uniform heat flux boundary condition in microchannels

KAUST Repository

Lee, Man; Lee, Yi-Kuen; Zohar, Yitshak

2012-01-01

A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a waferbond-and-etch- back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number. © 2012 IOP Publishing Ltd.

Asymmetry of blood flow and cancer cell adhesion in a microchannel with symmetric bifurcation and confluence.

Science.gov (United States)

Ishikawa, Takuji; Fujiwara, Hiroki; Matsuki, Noriaki; Yoshimoto, Takefumi; Imai, Yohsuke; Ueno, Hironori; Yamaguchi, Takami

2011-02-01

Bifurcations and confluences are very common geometries in biomedical microdevices. Blood flow at microchannel bifurcations has different characteristics from that at confluences because of the multiphase properties of blood. Using a confocal micro-PIV system, we investigated the behaviour of red blood cells (RBCs) and cancer cells in microchannels with geometrically symmetric bifurcations and confluences. The behaviour of RBCs and cancer cells was strongly asymmetric at bifurcations and confluences whilst the trajectories of tracer particles in pure water were almost symmetric. The cell-free layer disappeared on the inner wall of the bifurcation but increased in size on the inner wall of the confluence. Cancer cells frequently adhered to the inner wall of the bifurcation but rarely to other locations. Because the wall surface coating and the wall shear stress were almost symmetric for the bifurcation and the confluence, the result indicates that not only chemical mediation and wall shear stress but also microscale haemodynamics play important roles in the adhesion of cancer cells to the microchannel walls. These results provide the fundamental basis for a better understanding of blood flow and cell adhesion in biomedical microdevices.

Mathematical modelling of liquid meniscus shape in cylindrical micro-channel for normal and micro gravity conditions

Science.gov (United States)

Marchuk, Igor; Lyulin, Yuriy

2017-10-01

Mathematical model of liquid meniscus shape in cylindrical micro-channel of the separator unit of condensing/separating system is presented. Moving liquid meniscus in the 10 μm cylindrical microchannel is used as a liquid lock to recover the liquid obtained by condensation from the separators. The main goal of the liquid locks to prevent penetration of a gas phase in the liquid line at the small flow rate of the condensate and because of pressure fluctuations in the vapor-gas-liquid loop. Calculation of the meniscus shape has been performed for liquid FC-72 at different values of pressure difference gas - liquid and under normal and micro gravity conditions.

Parametric Study on the Characteristics of Multiphase Laminar Flow with Density Difference in Various Microchannels

International Nuclear Information System (INIS)

Paek, Seung Ho; Kim, Dong Sung; Choi, Young Ki

2009-01-01

In this paper, we have performed a parametric study on the characteristics of multiphase laminar flow with density difference in various microchannels. The interface between multiphase fluids is rotated by the gravitational forces induced by density difference. The numerical simulations were carried out via commercial CFD package to study the characteristics of multiphase laminar flow. The results of the numerical simulations in this study were verified by comparing with the previously reported experimental results in the literature. We have also proposed a new dimensionless relationship between dimensionless rotation angle of interface and dimensionless parameters are proposed for square microchannels with various aspect ratios. The dimensionless relationship could be widely applied to the reliable design of various microfluidic devices dealing with multiphase laminar flow

A microchannel plate X-ray multiplier with rising-time less than 170 ps

International Nuclear Information System (INIS)

Zhao Shicheng; Ouyang Bin

1987-01-01

The time reponse of a microchannel plate X-ray multiplier has been improved considerably by using a coupling construction of coaxial tapers. The experimental calibration results with laser plasma X-ray source show that the rising-time of the multiplier is less than 170 ps

Improved lifetime of microchannel-plate PMTs

Energy Technology Data Exchange (ETDEWEB)

Lehmann, A., E-mail: lehmann@physik.uni-erlangen.de [Physikalisches Institut IV, Friedrich Alexander-University of Erlangen-Nuremberg, Erlangen (Germany); Britting, A.; Eyrich, W.; Uhlig, F. [Physikalisches Institut IV, Friedrich Alexander-University of Erlangen-Nuremberg, Erlangen (Germany); Dzhygadlo, R.; Gerhardt, A.; Götzen, K.; Höhler, R.; Kalicy, G.; Kumawat, H.; Lehmann, D.; Lewandowski, B.; Patsyuk, M.; Peters, K.; Schepers, G.; Schmitt, L.; Schwarz, C.; Schwiening, J.; Traxler, M.; Zühlsdorf, M. [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt (Germany); and others

2014-12-01

The charged particle identification at the PANDA experiment will be mainly performed with DIRC detectors. Because of their advantageous properties the preferred photon sensors are MCP-PMTs. However, until recently these devices showed serious aging problems which resulted in a diminishing quantum efficiency (QE) of the photo cathode. By applying innovative countermeasures against the aging causes, the manufacturers recently succeeded in drastically improving the lifetime of MCP-PMTs. Especially the application of an ALD coating technique to seal the material of the micro-channels proves very powerful and results in a lifetime of ≈6C/cm{sup 2} integrated anode charge without a substantial QE degradation for the latest PHOTONIS XP85112. This paper will present a comparative measurement of the lifetime of several older and recent MCP-PMTs demonstrating this progress.

Localized electric field induced transition and miniaturization of two-phase flow patterns inside microchannels.

Science.gov (United States)

Sharma, Abhinav; Tiwari, Vijeet; Kumar, Vineet; Mandal, Tapas Kumar; Bandyopadhyay, Dipankar

2014-10-01

Strategic application of external electrostatic field on a pressure-driven two-phase flow inside a microchannel can transform the stratified or slug flow patterns into droplets. The localized electrohydrodynamic stress at the interface of the immiscible liquids can engender a liquid-dielectrophoretic deformation, which disrupts the balance of the viscous, capillary, and inertial forces of a pressure-driven flow to engender such flow morphologies. Interestingly, the size, shape, and frequency of the droplets can be tuned by varying the field intensity, location of the electric field, surface properties of the channel or fluids, viscosity ratio of the fluids, and the flow ratio of the phases. Higher field intensity with lower interfacial tension is found to facilitate the oil droplet formation with a higher throughput inside the hydrophilic microchannels. The method is successful in breaking down the regular pressure-driven flow patterns even when the fluid inlets are exchanged in the microchannel. The simulations identify the conditions to develop interesting flow morphologies, such as (i) an array of miniaturized spherical or hemispherical or elongated oil drops in continuous water phase, (ii) "oil-in-water" microemulsion with varying size and shape of oil droplets. The results reported can be of significance in improving the efficiency of multiphase microreactors where the flow patterns composed of droplets are preferred because of the availability of higher interfacial area for reactions or heat and mass exchange. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Flow Boiling in a Micro-Channel Coated With Carbon Nanotubes

OpenAIRE

Khanikar, Vikash; Mudawar, Issam; Fisher, Timothy

2009-01-01

This study examines the heat transfer enhancement attributes of carbon nanotubes (CNTs) applied to the bottom wall of a shallow rectangular micro-channel. Using deionized water as working fluid, experiments were performed with both a bare copper bottom wall and a CNT-coated copper wall. Boiling curves were generated for both walls, aided by high-speed video analysis of interfacial features. CNT arrays promoted earlier, abundant and intense bubble nucleation at low mass velocities, consistent ...

Optimal Design of Silicon-based Chips for Piezo-induced Ultrasound Resonances in Embedded Microchannels

DEFF Research Database (Denmark)

Garofalo, F.; Laurell, T.; Bruus, Henrik

2015-01-01

constituting the device (the piezo transducer, the silicon walls, the fluid-filled microchannel, and the glass lid) allows for the introduction of the weak formulation used in the finite element discretization of the equations describing the system in its oscillatory regime. Additionally, the knowledge...... of the Lagrangian density leads to the derivation of the correct structure of the Hamiltonian density, i.e. the energy density, which is important for the quantification of the energy content of the whole system and its individual parts. Specifically, the energy content of the embedded microchannel is quantified...... by means of the acoustofluidic yield η defined as the ratio between the energy in the channel and the total energy. From the standpoint of acoustophoretic application, the introduction of the acoustophoretic mean orientation allows us to identify the frequencies for which an acoustophoretic effect, i...

Hydrodynamic dispersion in a combined magnetohydrodynamic- electroosmotic-driven flow through a microchannel with slowly varying wall zeta potentials

Science.gov (United States)

Vargas, C.; Arcos, J.; Bautista, O.; Méndez, F.

2017-09-01

The effective dispersion coefficient of a neutral solute in the combined electroosmotic (EO) and magnetohydrodynamic (MHD)-driven flow of a Newtonian fluid through a parallel flat plate microchannel is studied. The walls of the microchannel are assumed to have modulated and low zeta potentials that vary slowly in the axial direction in a sinusoidal manner. The flow field required to obtain the dispersion coefficient is solved using the lubrication approximation theory. The solution of the electrical potential is based on the Debye-Hückel approximation for a symmetric (Z :Z ) electrolyte solution. The EO and MHD effects, together with the variations in the zeta potentials of the walls, are observed to notably modify the axial distribution of the effective dispersion coefficient. The problem is formulated for two cases of the zeta potential function. Note that the dispersion coefficient primarily depends on the Hartmann number, on the ratio of the half height of the microchannel to the Debye length, and on the assumed variation in the zeta potentials of the walls.

Synthesis of Rh/Macro-Porous Alumina Over Micro-Channel Plate and Its Catalytic Activity Tests for Diesel Reforming.

Science.gov (United States)

Seong, Yeon Baek; Kim, Yong Sul; Park, No-Kuk; Lee, Tae Jin

2015-11-01

Macro-porous Al2O3 as the catalytic support material was synthesized using colloidal polystyrene spheres over a micro-channel plate. The colloidal polystyrene spheres were used as a template for the production of an ordered macro porous material using an alumina nitrate solution as the precursor for Al2O3. The close-packed colloidal crystal array template method was applied to the formulation of ordered macro-porous Al2O3 used as a catalytic support material over a micro-channel plate. The solvent in the mixture solution, which also contained the colloidal polystyrene solution, aluminum nitrate solution and the precursor of the catalytic active materials (Rh), was evaporated in a vacuum oven at 50 degrees C. The ordered polystyrene spheres and aluminum salt of the solid state were deposited over a micro channel plate, and macro-porous Al2O3 was formed after calcination at 600 degrees C to remove the polystyrene spheres. The catalytic activity of the Rh/macro-porous alumina supported over the micro-channel plate was tested for diesel reforming.

VOF Modeling and Analysis of the Segmented Flow in Y-Shaped Microchannels for Microreactor Systems

Directory of Open Access Journals (Sweden)

Xian Wang

2013-01-01

Full Text Available Microscaled devices receive great attention in microreactor systems for producing high renewable energy due to higher surface-to-volume, higher transport rates (heat or/and mass transfer rates, and other advantages over conventional-size reactors. In this paper, the two-phase liquid-liquid flow in a microchannel with various Y-shaped junctions has been studied numerically. Two kinds of immiscible liquids were injected into a microchannel from the Y-shaped junctions to generate the segment flow mode. The segment length was studied. The volume of fluid (VOF method was used to track the liquid-liquid interface and the piecewise-liner interface construction (PLIC technique was adopted to get a sharp interface. The interfacial tension was simulated with continuum surface force (CSF model and the wall adhesion boundary condition was taken into consideration. The simulated flow pattern presents consistence with our experimental one. The numerical results show that a segmented flow mode appears in the main channel. Under the same inlet velocities of two liquids, the segment lengths of the two liquids are the same and depend on the inclined angles of two lateral channels. The effect of inlet velocity is studied in a typical T-shaped microchannel. It is found that the ratio between the lengths of two liquids is almost equal to the ratio between their inlet velocities.

A Flexible Ascorbic Acid Fuel Cell with a Microchannel Fabricated using MEMS Techniques

Science.gov (United States)

Mogi, Hiroshi; Fukushi, Yudai; Koide, Syohei; Sano, Ryohei; Sasaki, Tsubasa; Nishioka, Yasushiro

2013-12-01

We fabricated a miniature ascorbic acid fuel cells equipped with a microchannel for the circulation of ascorbic acid (AA) solution using micro electronic mechanical system techniques. The fuel cell was fabricated on a flexible polyimide substrate, and its porous carbon-coated aluminium (Al) electrodes of 2.8 mm in width and 11 mm in length were formed using photolithography and screen-printing techniques. The porous carbon was deposited by screen-printing of carbon-black ink on the Al electrode surfaces in order to increase the effective electrode surface area and to absorb more enzymes on the cathode surface. The microchannel with a depth of 200 μm was fabricated using a hot-embossing technique. A maximum power of 0.60 μW at 0.58 V that corresponds to a power density of 1.83 μW/cm2 was realized by introducing a 200 mM concentrated AA solution at room temperature.

Continuous particle separation in a serpentine microchannel via negative and positive dielectrophoretic focusing

International Nuclear Information System (INIS)

Church, Christopher; Zhu, Junjie; Nieto, Juan; Keten, Gyunay; Ibarra, Erl; Xuan, Xiangchun

2010-01-01

Dielectrophoresis (DEP) has been widely used to focus and separate cells and particles in microfluidic devices. This work first demonstrates negative and positive dielectrophoretic focusing of particles in a serpentine microchannel by changing only the electric conductivity of the suspending fluid. Due to the channel turn-induced dielectrophoretic force, particles are focused to either the centerline or the sidewalls of the channel when their electric conductivity is lower (i.e. negative DEP) or higher (i.e. positive DEP) than that of the fluid. These distinctive dielectrophoretic focusing phenomena in a serpentine microchannel are then combined to implement a continuous separation between particles of different sizes and electric conductivities. Such separation eliminates the fabrication of in-channel microelectrodes or micro-insulators that are typically required in DEP-based separation techniques. A numerical model is also developed to predict the particle motion, and the simulation results agree reasonably with the observed particle focusing and separation behaviors.

Three-dimensional particle-in-cell simulation on gain saturation effect of microchannel plate

Energy Technology Data Exchange (ETDEWEB)

Wang, Qiangqiang; Yuan, Zheng; Cao, Zhurong, E-mail: cao33jin@aliyun.com; Deng, Bo; Chen, Tao; Deng, Keli [Research Center of Laser Fusion, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621900 (China)

2016-07-15

We present here the results of the simulation work, using the three-dimensional particle-in-cell method, on the performance of the lead glass microchannel plate under saturated state. We calculated the electron cascade process with different DC bias voltages under both self-consistent condition and non-self-consistent condition. The comparative results have demonstrated that the strong self-consistent field can suppress the cascade process and make the microchannel plate saturated. The simulation results were also compared to the experimental data and good agreement was obtained. The simulation results also show that the electron multiplication process in the channel is accompanied by the buildup process of positive charges in the channel wall. Though the interactions among the secondary electron cloud in the channel, the positive charges in the channel wall, and the external acceleration field can make the electron-surface collision more frequent, the collision energy will be inevitably reduced, thus the electron gain will also be reduced.

Numerical Study of Surfactant Dynamics during Emulsification in a T-Junction Microchannel.

Science.gov (United States)

Riaud, Antoine; Zhang, Hao; Wang, Xueying; Wang, Kai; Luo, Guangsheng

2018-04-18

Microchannel emulsification requires large amounts of surfactant to prevent coalescence and improve emulsions lifetime. However, most numerical studies have considered surfactant-free mixtures as models for droplet formation in microchannels, without taking into account the distribution of surfactant on the droplet surface. In this paper, we investigate the effects of nonuniform surfactant coverage on the microfluidic flow pattern using an extended lattice-Boltzmann model. This numerical study, supported by micro-particle image velocimetry experiments, reveals the likelihood of uneven distribution of surfactant during the droplet formation and the appearance of a stagnant cap. The Marangoni effect affects the droplet breakup by increasing the shear rate. According to our results, surfactant-free and surfactant-rich droplet formation processes are qualitatively different, such that both the capillary number and the Damköhler number should be considered when modeling the droplet generation in microfluidic devices. The limitations of traditional volume and pressure estimation methods for determining the dynamic interfacial tension are also discussed on the basis of the simulation results.

Antiproton, positron, and electron imaging with a microchannel plate/phosphor detector

CERN Document Server

Andresen, G B; Bowe, P D; Bray, C; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Gill, D R; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Humphries, A J; Hydomako, R; Jørgensen, L V; Kerrigan, S J; Kurchaninov, L; Lambo, R; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Sarid, E; Seif El Nasr, S; Silveira, D M; Storey, J W; Thompson, R I; van der Werf, D P; Yamazaki, Y

2009-01-01

A microchannel plate (MCP)/phosphor screen assembly has been used to destructively measure the radial profile of cold, confined antiprotons, electrons, and positrons in the ALPHA experiment, with the goal of using these trapped particles for antihydrogen creation and confinement. The response of the MCP to low energy (10-200 eV, <1 eV spread) antiproton extractions is compared to that of electrons and positrons.

Coupling between electroosmotically driven flow and bipolar faradaic depolarization processes in electron-conducting microchannels

NARCIS (Netherlands)

Qian, S.Z.; Duval, J.F.L.

2006-01-01

A quantitative theory is proposed for the analysis of steady electroosmotically driven flows within conducting cylindrical microchannels. Beyond a threshold value of the electric field applied in the electrolyte Solution and parallel to the conducting surface, electrochemical oxidation and reduction

Modelling refrigerant distribution in microchannel evaporators

DEFF Research Database (Denmark)

Brix, Wiebke; Kærn, Martin Ryhl; Elmegaard, Brian

2009-01-01

of the refrigerant distribution is carried out for two channels in parallel and for two different cases. In the first case maldistribution of the inlet quality into the channels is considered, and in the second case a non-uniform airflow on the secondary side is considered. In both cases the total mixed superheat...... out of the evaporator is kept constant. It is shown that the cooling capacity of the evaporator is reduced significantly, both in the case of unevenly distributed inlet quality and for the case of non-uniform airflow on the outside of the channels.......The effects of refrigerant maldistribution in parallel evaporator channels on the heat exchanger performance are investigated numerically. For this purpose a 1D steady state model of refrigerant R134a evaporating in a microchannel tube is built and validated against other evaporator models. A study...

Eulerian-Eulerian two-phase numerical simulation of nanofluid laminar forced convection in a microchannel

International Nuclear Information System (INIS)

Kalteh, Mohammad; Abbassi, Abbas; Saffar-Avval, Majid; Harting, Jens

2011-01-01

In this paper, laminar forced convection heat transfer of a copper-water nanofluid inside an isothermally heated microchannel is studied numerically. An Eulerian two-fluid model is considered to simulate the nanofluid flow inside the microchannel and the governing mass, momentum and energy equations for both phases are solved using the finite volume method. For the first time, the detailed study of the relative velocity and temperature of the phases are presented and it has been observed that the relative velocity and temperature between the phases is very small and negligible and the nanoparticle concentration distribution is uniform. However, the two-phase modeling results show higher heat transfer enhancement in comparison to the homogeneous single-phase model. Also, the heat transfer enhancement increases with increase in Reynolds number and nanoparticle volume concentration as well as with decrease in the nanoparticle diameter, while the pressure drop increases only slightly.

Method for producing components with internal architectures, such as micro-channel reactors, via diffusion bonding sheets

Science.gov (United States)

Alman, David E [Corvallis, OR; Wilson, Rick D [Corvallis, OR; Davis, Daniel L [Albany, OR

2011-03-08

This invention relates to a method for producing components with internal architectures, and more particularly, this invention relates to a method for producing structures with microchannels via the use of diffusion bonding of stacked laminates. Specifically, the method involves weakly bonding a stack of laminates forming internal voids and channels with a first generally low uniaxial pressure and first temperature such that bonding at least between the asperites of opposing laminates occurs and pores are isolated in interfacial contact areas, followed by a second generally higher isostatic pressure and second temperature for final bonding. The method thereby allows fabrication of micro-channel devices such as heat exchangers, recuperators, heat-pumps, chemical separators, chemical reactors, fuel processing units, and combustors without limitation on the fin aspect ratio.

X-ray focusing with Wolter microchannel plate optics

CERN Document Server

Price, G J; Beijersbergen, M W; Fraser, G W; Bavdaz, M; Boutot, J P; Fairbend, R; Flyckt, S O; Peacock, A; Tomaselli, E

2002-01-01

Square-pore microchannel plate (MCP) X-ray optics of the 'lobster-eye' geometry have frequently been described in the literature. We have now investigated the use of a radial channel packing geometry which, in the context of an MCP pair slumped to the correct radii of curvature, can form a conic approximation to the Wolter Type I grazing incidence X-ray optic. Such an optic can provide a large effective area with very low mass and may be ideally suited for use in applications such as planetary imaging X-ray fluorescence. We present here the results of X-ray illumination of the first such optic, fabricated by Photonis SAS, France.

Heater Chip with Different Microchannels Geometries for a Low Pressure Free Molecular Micro-Resistojet

NARCIS (Netherlands)

Cordeiro Guerrieri, D.; de Athayde Costa e Silva, M.; Zandbergen, B.T.C.; Cervone, A.

2016-01-01

This paper presents a dynamic system approach for the modeling of fluid flow in microchannels to be used in thrust control applications. A micro-resistojet fabricated using MEMS (Microelectromechanical Systems) technology has been selected for the analysis. The device operates by vaporizing a liquid

Enhancing heat transfer in microchannel heat sinks using converging flow passages

International Nuclear Information System (INIS)

Dehghan, Maziar; Daneshipour, Mahdi; Valipour, Mohammad Sadegh; Rafee, Roohollah; Saedodin, Seyfolah

2015-01-01

Highlights: • The fluid flow and conjugate heat transfer in microchannel heat sinks are studied. • The Poiseuille and Nusselt numbers are presented for width-tapered MCHS. • Converging walls are found to enhance the thermal performance of MCHS. • The optimum performance of MCHS for fixed inlet and outlet pressures is discussed. • For the optimum configuration, the pumping power is reduced up to 75%. - Abstract: Constrained fluid flow and conjugate heat transfer in microchannel heat sinks (MCHS) with converging channels are investigated using the finite volume method (FVM) in the laminar regime. The maximum pressure of the MCHS loop is assumed to be limited due to constructional or operational conditions. Results show that the Poiseuille number increases with increased tapering, while the required pumping power decreases. Meanwhile, the Nusselt number increases with tapering as well as the convection heat transfer coefficient. The MCHS having the optimum heat transfer performance is found to have a width-tapered ratio equal to 0.5. For this tapering configuration and at the maximum pressure constraint of 3000 Pa, the pumping power reduces by a factor of 4 while the overall heat removal rate is kept fixed in comparison with a straight channel

Slow waves in microchannel metal waveguides and application to particle acceleration

Directory of Open Access Journals (Sweden)

L. C. Steinhauer

2003-06-01

Full Text Available Conventional metal-wall waveguides support waveguide modes with phase velocities exceeding the speed of light. However, for infrared frequencies and guide dimensions of a fraction of a millimeter, one of the waveguide modes can have a phase velocity equal to or less than the speed of light. Such a metal microchannel then acts as a slow-wave structure. Furthermore, if it is a transverse magnetic mode, the electric field has a component along the direction of propagation. Therefore, a strong exchange of energy can occur between a beam of charged particles and this slow-waveguide mode. Moreover, the energy exchange can be sustained over a distance limited only by the natural damping of the wave. This makes the microchannel metal waveguide an attractive possibility for high-gradient electron laser acceleration because the wave can be directly energized by a long-wavelength laser. Indeed the frequency of CO_{2} lasers lies at a fortuitous wavelength that produces a strong laser-particle interaction in a channel of reasonable macroscopic size (e.g., ∼0.6  mm. The dispersion properties including phase velocity and damping for the slow wave are developed. The performance and other issues related to laser accelerator applications are discussed.

Slow waves in microchannel metal waveguides and application to particle acceleration

Science.gov (United States)

Steinhauer, L. C.; Kimura, W. D.

2003-06-01

Conventional metal-wall waveguides support waveguide modes with phase velocities exceeding the speed of light. However, for infrared frequencies and guide dimensions of a fraction of a millimeter, one of the waveguide modes can have a phase velocity equal to or less than the speed of light. Such a metal microchannel then acts as a slow-wave structure. Furthermore, if it is a transverse magnetic mode, the electric field has a component along the direction of propagation. Therefore, a strong exchange of energy can occur between a beam of charged particles and this slow-waveguide mode. Moreover, the energy exchange can be sustained over a distance limited only by the natural damping of the wave. This makes the microchannel metal waveguide an attractive possibility for high-gradient electron laser acceleration because the wave can be directly energized by a long-wavelength laser. Indeed the frequency of CO2 lasers lies at a fortuitous wavelength that produces a strong laser-particle interaction in a channel of reasonable macroscopic size (e.g., ˜0.6 mm). The dispersion properties including phase velocity and damping for the slow wave are developed. The performance and other issues related to laser accelerator applications are discussed.

Optimum thermal design of microchannel heat sink with triangular reentrant cavities

International Nuclear Information System (INIS)

Xia Guodong; Chai Lei; Wang Haiyan; Zhou Mingzheng; Cui Zhenzhen

2011-01-01

The effect of geometric parameters on water flow and heat transfer characteristics in microchannel heat sink with triangular reentrant cavities is numerically investigated. A three-dimensional laminar flow model, consisting of Navier-Stokes equations and energy conservation equation, with the conjugate heat transfer between the silicon base and water taken into consideration is solved numerically. In order to find the optimum geometric parameters, four variables, representing the distance and geometry of the triangular reentrant cavity, are designed. It is found that the vortices in the triangular reentrant cavities lead to chaotic advection and can greatly enhance the convective fluid mixing. The thermal and hydraulic boundary layers are interrupted and the repeated developing flow enhances heat transfer in the constant cross-section segment. Furthermore, the effects of the four design variables on heat transfer augmentation and pressure drop penalty are investigated depending on different Reynolds numbers by using the simulated annealing method. Based on the thermal enhancement factor performance maps, the optimal geometric parameters are obtained in principle. - Research highlights: → The microchannels with different triangular reentrant cavities are numerically investigated. → The heat transfer enhancement attributes to fluid mixing and redeveloped thermal boundary layers. → The optimal distance and geometry of the triangular reentrant cavity are obtained in principle.

Investigation of high frequency external perturbation effects on flow in a T-shape microchannel by μLIF technique

Science.gov (United States)

Kravtsova, A. Yu; Meshalkin, Yu E.; Bilsky, A. V.

2017-11-01

Investigation of high frequency external perturbation effect on flow inside T-shape microchannel was examined. In-phase pulsations of different frequencies were added to both inlets of the T-shaped microchannel to study mixing by means of Micro Laser Induced Fluorescence (μLIF) technique. For all flow regimes studied, mixing enhancement was obtained. Significant enhancement can be achieved at the beginning of the outlet channel operating in steady asymmetric regime (Re=186) by forcing at certain frequency ranges (f = 500Hz, f = 800Hz). Mixing suppression was also observed for two flow regimes (Re = 400, f = 1000Hz) and (Re = 120, f = 700Hz).

Coaxial nozzle-assisted 3D bioprinting with built-in microchannels for nutrients delivery.

Science.gov (United States)

Gao, Qing; He, Yong; Fu, Jian-zhong; Liu, An; Ma, Liang

2015-08-01

This study offers a novel 3D bioprinting method based on hollow calcium alginate filaments by using a coaxial nozzle, in which high strength cell-laden hydrogel 3D structures with built-in microchannels can be fabricated by controlling the crosslinking time to realize fusion of adjacent hollow filaments. A 3D bioprinting system with a Z-shape platform was used to realize layer-by-layer fabrication of cell-laden hydrogel structures. Curving, straight, stretched or fractured filaments can be formed by changes to the filament extrusion speed or the platform movement speed. To print a 3D structure, we first adjusted the concentration and flow rate of the sodium alginate and calcium chloride solution in the crosslinking process to get partially crosslinked filaments. Next, a motorized XY stages with the coaxial nozzle attached was used to control adjacent hollow filament deposition in the precise location for fusion. Then the Z stage attached with a Z-shape platform moved down sequentially to print layers of structure. And the printing process always kept the top two layers fusing and the below layers solidifying. Finally, the Z stage moved down to keep the printed structure immersed in the CaCl2 solution for complete crosslinking. The mechanical properties of the resulting fused structures were investigated. High-strength structures can be formed using higher concentrations of sodium alginate solution with smaller distance between adjacent hollow filaments. In addition, cell viability of this method was investigated, and the findings show that the viability of L929 mouse fibroblasts in the hollow constructs was higher than that in alginate structures without built-in microchannels. Compared with other bioprinting methods, this study is an important technique to allow easy fabrication of lager-scale organs with built-in microchannels. Copyright © 2015 Elsevier Ltd. All rights reserved.

Heat Transfer and Pressure Drop Characteristics in Straight Microchannel of Printed Circuit Heat Exchangers

Directory of Open Access Journals (Sweden)

Jang-Won Seo

2015-05-01

Full Text Available Performance tests were carried out for a microchannel printed circuit heat exchanger (PCHE, which was fabricated with micro photo-etching and diffusion bonding technologies. The microchannel PCHE was tested for Reynolds numbers in the range of 100‒850 varying the hot-side inlet temperature between 40 °C–50 °C while keeping the cold-side temperature fixed at 20 °C. It was found that the average heat transfer rate and heat transfer performance of the countercurrrent configuration were 6.8% and 10%‒15% higher, respectively, than those of the parallel flow. The average heat transfer rate, heat transfer performance and pressure drop increased with increasing Reynolds number in all experiments. Increasing inlet temperature did not affect the heat transfer performance while it slightly decreased the pressure drop in the experimental range considered. Empirical correlations have been developed for the heat transfer coefficient and pressure drop factor as functions of the Reynolds number.

Performance enhancement of PV cells through micro-channel cooling

Directory of Open Access Journals (Sweden)

Muzaffar Ali

2015-11-01

Full Text Available Efficiency of a PV cell is strongly dependent on its surface temperature. The current study is focused to achieve maximum efficiency of PV cells even in scorching temperatures in hot climates like Pakistan where the cell surface temperatures can even rise up to around 80 ℃. The study includes both the CFD and real time experimental investigations of a solar panel using micro channel cooling. Initially, CFD analysis is performed by developing a 3D model of a Mono-Crystalline cell with micro-channels to analyze cell surface temperature distribution at different irradiance and water flow rates. Afterwards, an experimental setup is developed for performance investigations under the real conditions of an open climate of a Pakistan's city, Taxila. Two 35W panels are manufactured for the experiments; one is based on the standard manufacturing procedure while other cell is developed with 4mm thick aluminum sheet having micro-channels of cross-section of 1mm by 1mm. The whole setup also includes different sensors for the measurement of solar irradiance, cell power, surface temperature and water flow rates. The experimental results show that PV cell surface temperature drop of around 15 ℃ is achieved with power increment of around 14% at maximum applied water flow rate of 3 LPM. Additionally, a good agreement is also found between CFD and experimental results. Therefore, that study clearly shows that a significant performance improvement of PV cells can be achieved through the proposed cell cooling technique.

Ionizing device comprising a microchannel electron multiplier with secondary electron emission

International Nuclear Information System (INIS)

Chalmeton, Vincent.

1974-01-01

The present invention relates to a ionizing device comprising a microchannel electron multiplier involving secondary electron emission as a means of ionization. A system of electrodes is used to accelerate said electrons, ionize the gas and extract the ions from thus created plasma. Said ionizer is suitable for bombarding the target in neutron sources (target of the type of nickel molybdenum coated with tritiated titanium or with a tritium deuterium mixture) [fr

Experimental study on flame pattern formation and combustion completeness in a radial microchannel

Science.gov (United States)

Fan, Aiwu; Minaev, Sergey; Kumar, Sudarshan; Liu, Wei; Maruta, Kaoru

2007-12-01

Combustion behavior in a radial microchannel with a gap of 2.0 mm and a diameter of 50 mm was experimentally investigated. In order to simulate the heat recirculation, which is an essential strategy in microscale combustion devices, positive temperature gradients along the radial flow direction were given to the microchannel by an external heat source. A methane-air mixture was supplied from the center of the top plate through a 4.0 mm diameter delivery tube. A variety of flame patterns, including a stable circular flame and several unstable flame patterns termed unstable circular flame, single and double pelton-like flames, traveling flame and triple flame, were observed in the experiments. The regime diagram of all these flame patterns is presented in this paper. Some characteristics of the various flame patterns, such as the radii of stable and unstable circular flames, major combustion products and combustion efficiencies of all these flame patterns, were also investigated. Furthermore, the effect of the heat recirculation on combustion stability was studied by changing the wall temperature levels.

A novel ZVS high voltage power supply for micro-channel plate photomultiplier tubes

International Nuclear Information System (INIS)

Pei, Chengquan; Tian, Jinshou; Liu, Zhen; Qin, Hong; Wu, Shengli

2017-01-01

A novel resonant high voltage power supply (HVPS) with zero voltage switching (ZVS), to reduce the voltage stress on switching devices and improve conversion efficiency, is proposed. The proposed HVPS includes a drive circuit, a transformer, several voltage multiplying circuits, and a regulator circuit. The HVPS contains several secondary windings that can be precisely regulated. The proposed HVPS performed better than the traditional resistor voltage divider, which requires replacing matching resistors resulting in resistor dispersibility in the Micro-Channel Plate (MCP). The equivalent circuit of the proposed HVPS was established and the operational principle analyzed. The entire switching element can achieve ZVS, which was validated by a simulation and experiments. The properties of this HVPS were tested including minimum power loss (240 mW), maximum power loss (1 W) and conversion efficiency (85%). The results of this research are that the proposed HVPS was suitable for driving the micro-channel plate photomultiplier tube (MCP-PMT). It was therefore adopted to test the MCP-PMT, which will be used in Daya Bay reactor neutrino experiment II in China.

A novel ZVS high voltage power supply for micro-channel plate photomultiplier tubes

Energy Technology Data Exchange (ETDEWEB)

Pei, Chengquan [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi' an Jiaotong University, Xi’an 710049 (China); Tian, Jinshou [Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi' an 710119 (China); Liu, Zhen [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi' an Jiaotong University, Xi’an 710049 (China); Qin, Hong [School of Computer Science and Technology, Xi' an University of Science and Technology, Xi' an 710054 (China); Wu, Shengli, E-mail: slwu@mail.xjtu.edu.cn [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi' an Jiaotong University, Xi’an 710049 (China)

2017-04-11

A novel resonant high voltage power supply (HVPS) with zero voltage switching (ZVS), to reduce the voltage stress on switching devices and improve conversion efficiency, is proposed. The proposed HVPS includes a drive circuit, a transformer, several voltage multiplying circuits, and a regulator circuit. The HVPS contains several secondary windings that can be precisely regulated. The proposed HVPS performed better than the traditional resistor voltage divider, which requires replacing matching resistors resulting in resistor dispersibility in the Micro-Channel Plate (MCP). The equivalent circuit of the proposed HVPS was established and the operational principle analyzed. The entire switching element can achieve ZVS, which was validated by a simulation and experiments. The properties of this HVPS were tested including minimum power loss (240 mW), maximum power loss (1 W) and conversion efficiency (85%). The results of this research are that the proposed HVPS was suitable for driving the micro-channel plate photomultiplier tube (MCP-PMT). It was therefore adopted to test the MCP-PMT, which will be used in Daya Bay reactor neutrino experiment II in China.

In-channel electrochemical detection in the middle of microchannel under high electric field.

Science.gov (United States)

Kang, Chung Mu; Joo, Segyeong; Bae, Je Hyun; Kim, Yang-Rae; Kim, Yongseong; Chung, Taek Dong

2012-01-17

We propose a new method for performing in-channel electrochemical detection under a high electric field using a polyelectrolytic gel salt bridge (PGSB) integrated in the middle of the electrophoretic separation channel. The finely tuned placement of a gold working electrode and the PGSB on an equipotential surface in the microchannel provided highly sensitive electrochemical detection without any deterioration in the separation efficiency or interference of the applied electric field. To assess the working principle, the open circuit potentials between gold working electrodes and the reference electrode at varying distances were measured in the microchannel under electrophoretic fields using an electrically isolated potentiostat. In addition, "in-channel" cyclic voltammetry confirmed the feasibility of electrochemical detection under various strengths of electric fields (∼400 V/cm). Effective separation on a microchip equipped with a PGSB under high electric fields was demonstrated for the electrochemical detection of biological compounds such as dopamine and catechol. The proposed "in-channel" electrochemical detection under a high electric field enables wider electrochemical detection applications in microchip electrophoresis.

Effect of Induced Magnetic Field on MHD Mixed Convection Flow in Vertical Microchannel

Science.gov (United States)

Jha, B. K.; Aina, B.

2017-08-01

The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.

Static response of deformable microchannels

Science.gov (United States)

Christov, Ivan C.; Sidhore, Tanmay C.

2017-11-01

Microfluidic channels manufactured from PDMS are a key component of lab-on-a-chip devices. Experimentally, rectangular microchannels are found to deform into a non-rectangular cross-section due to fluid-structure interactions. Deformation affects the flow profile, which results in a nonlinear relationship between the volumetric flow rate and the pressure drop. We develop a framework, within the lubrication approximation (l >> w >> h), to self-consistently derive flow rate-pressure drop relations. Emphasis is placed on handling different types of elastic response: from pure plate-bending, to half-space deformation, to membrane stretching. The ``simplest'' model (Stokes flow in a 3D rectangular channel capped with a linearly elastic Kirchhoff-Love plate) agrees well with recent experiments. We also simulate the static response of such microfluidic channels under laminar flow conditions using ANSYSWorkbench. Simulations are calibrated using experimental flow rate-pressure drop data from the literature. The simulations provide highly resolved deformation profiles, which are difficult to measure experimentally. By comparing simulations, experiments and our theoretical models, we show good agreement in many flow/deformation regimes, without any fitting parameters.

Simulation of Micro-Channel and Micro-Orifice Flow Using Lattice Boltzmann Method with Langmuir Slip Model

Directory of Open Access Journals (Sweden)

A. R. Rahmati

2016-12-01

Full Text Available Because of its kinetic nature and computational advantages, the Lattice Boltzmann method (LBM has been well accepted as a useful tool to simulate micro-scale flows. The slip boundary model plays a crucial role in the accuracy of solutions for micro-channel flow simulations. The most used slip boundary condition is the Maxwell slip model. The results of Maxwell slip model are affected by the accommodation coefficient significantly, but there is not an explicitly relationship between properties at wall and accommodation coefficient. In the present wok, Langmuir slip model is used beside LBM to simulate micro-channel and micro-orifice flows. Slip velocity and nonlinear pressure drop profiles are presented as two major effects in such flows. The results are in good agreement with existing results in the literature.

Process for making unsaturated hydrocarbons using microchannel process technology

Science.gov (United States)

Tonkovich, Anna Lee [Dublin, OH; Yuschak, Thomas [Lewis Center, OH; LaPlante, Timothy J [Columbus, OH; Rankin, Scott [Columbus, OH; Perry, Steven T [Galloway, OH; Fitzgerald, Sean Patrick [Columbus, OH; Simmons, Wayne W [Dublin, OH; Mazanec, Terry Daymo, Eric

2011-04-12

The disclosed invention relates to a process for converting a feed composition comprising one or more hydrocarbons to a product comprising one or more unsaturated hydrocarbons, the process comprising: flowing the feed composition and steam in contact with each other in a microchannel reactor at a temperature in the range from about 200.degree. C. to about 1200.degree. C. to convert the feed composition to the product, the process being characterized by the absence of catalyst for converting the one or more hydrocarbons to one or more unsaturated hydrocarbons. Hydrogen and/or oxygen may be combined with the feed composition and steam.

Regulating the Emission Spectrum of CsPbBr₃ from Green to Blue via Controlling the Temperature and Velocity of Microchannel Reactor.

Science.gov (United States)

Tang, Yong; Lu, Hanguang; Rao, Longshi; Li, Zongtao; Ding, Xinrui; Yan, Caiman; Yu, Binhai

2018-03-02

The ability to precisely obtain tunable spectrum of lead halide perovskite quantum dots (QDs) is very important for applications, such as in lighting and display. Herein, we report a microchannel reactor method for synthesis of CsPbBr₃ QDs with tunable spectrum. By adjusting the temperature and velocity of the microchannel reactor, the emission peaks of CsPbBr₃ QDs ranging from 520 nm to 430 nm were obtained, which is wider than that of QDs obtained in a traditional flask without changing halide component. The mechanism of photoluminescence (PL) spectral shift of CsPbBr₃ QDs was investigated, the result shows that the supersaturation control enabled by the superior mass and heat transfer performance in the microchannel is the key to achieve the wide range of PL spectrum, with only a change in the setting of the temperature controller required. The wide spectrum of CsPbBr₃ QDs can be applied to light-emitting diodes (LEDs), photoelectric sensors, lasers, etc.

Automated and temperature-controlled micro-PIV measurements enabling long-term-stable microchannel acoustophoresis characterization

DEFF Research Database (Denmark)

Augustsson, Per; Barnkob, Rune; Wereley, Steven T.

2011-01-01

We present a platform for micro particle image velocimetry (μPIV), capable of carrying out full-channel, temperature-controlled, long-term-stable, and automated μPIV-measurement of microchannel acoustophoresis with uncertainties below 5% and a spatial resolution in the order of 20 μm. A method to...

Hydrodynamic shrinkage of liquid CO2 Taylor drops in a straight microchannel

Science.gov (United States)

Qin, Ning; Wen, John Z.; Ren, Carolyn L.

2018-03-01

Hydrodynamic shrinkage of liquid CO2 drops in water under a Taylor flow regime is studied using a straight microchannel (length/width ~100). A general form of a mathematical model of the solvent-side mass transfer coefficient (k s) is developed first. Based on formulations of the surface area (A) and the volume (V) of a general Taylor drop in a rectangular microchannel, a specific form of k s is derived. Drop length and speed are experimentally measured at three specified positions of the straight channel, namely, immediately after drop generation (position 1), the midpoint of the channel (position 2) and the end of the channel (position 3). The reductions of drop length (L x , x  =  1, 2, 3) from position 1 to 2 and down to 3 are used to quantify the drop shrinkage. Using the specific model, k s is calculated mainly based on L x and drop flowing time (t). Results show that smaller CO2 drops produced by lower flow rate ratios ({{Q}LC{{O2}}}/{{Q}{{H2}O}} ) are generally characterized by higher (nearly three times) k s and Sherwood numbers than those produced by higher {{Q}LC{{O2}}}/{{Q}{{H2}O}} , which is essentially attributed to the larger effective portion of the smaller drop contributing in the mass transfer under same levels of the flowing time and the surface-to-volume ratio (~104 m-1) of all drops. Based on calculated pressure drops of the segmented flow in microchannel, the Peng-Robinson equation of state and initial pressures of drops at the T-junction in experiments, overall pressure drop (ΔP t) in the straight channel as well as the resulted drop volume change are quantified. ΔP t from position 1-3 is by average 3.175 kPa with a ~1.6% standard error, which only leads to relative drop volume changes of 0.3‰ to 0.52‰.

Hydrodynamic shrinkage of liquid CO2 Taylor drops in a straight microchannel.

Science.gov (United States)

Qin, Ning; Wen, John; Ren, Carolyn L

2018-01-16

Hydrodynamic shrinkage of liquid CO2 drops in water under a Taylor flow regime is studied using a straight microchannel (length/width ~ 100). A general form of a mathematical model of the solvent-side mass transfer coefficient (ks) is developed first. Based on formulations of the surface area (A) and the volume (V) of a general Taylor drop in a rectangular microchannel, a specific form of ks is derived. Drop length and speed are experimentally measured at three specified positions of the straight channel, namely, immediately after drop generation (position 1), the midpoint of the channel (position 2) and the end of the channel (position 3). The reductions of drop length (Lx, x = 1, 2, 3) from position 1 to 2 and down to 3 are used to quantify the drop shrinkage. Using the specific model, ks is calculated mainly based on Lx and drop flowing time (t). Results show that smaller CO2 drops produced by lower flow rate ratios (QLCO2/QH2O) are generally characterized by higher (nearly three times) ks and Sherwood numbers than those produced by higher QLCO2/QH2O, which is essentially attributed to the larger effective portion of the smaller drop contributing in the mass transfer under same levels of the flowing time and the surface-to-volume ratio (~ 104 m-1) of all drops. Based on calculated pressure drops of the segmented flow in microchannel, the Peng-Robinson equation of state (EOS) and initial pressures of drops at the T-junction in experiments, overall pressure drop (ΔPt) in the straight channel as well as the resulted drop volume change are quantified. ΔPt from position 1 to 3 is by average 3.175 kPa with a ~1.6% standard error, which only leads to relative drop volume changes of 0.3‰ to 0.52‰. © 2018 IOP Publishing Ltd.

Measuring density and compressibility of white blood cells and prostate cancer cells by microchannel acoustophoresis

DEFF Research Database (Denmark)

Barnkob, Rune; Augustsson, Per; Magnusson, Cecilia

2011-01-01

We present a novel method for the determination of density and compressibility of individual particles and cells undergoing microchannel acoustophoresis in an arbitrary 2D acoustic field. Our method is a critical advancement within acoustophoretic separation of biological cells, as the ability to...

Microchannel laminated mass exchanger and method of making

Science.gov (United States)

Martin, Peter M.; Bennett, Wendy D.; Matson, Dean W.; Stewart, Donald C.; Drost, Monte K.; Wegeng, Robert S.; Perez, Joseph M.; Feng, Xiangdong; Liu, Jun

2000-01-01

The present invention is a microchannel mass exchanger having a first plurality of inner thin sheets and a second plurality of outer thin sheets. The inner thin sheets each have a solid margin around a circumference, the solid margin defining a slot through the inner thin sheet thickness. The outer thin sheets each have at least two header holes on opposite ends and when sandwiching an inner thin sheet. The outer thin sheets further have a mass exchange medium. The assembly forms a closed flow channel assembly wherein fluid enters through one of the header holes into the slot and exits through another of the header holes after contacting the mass exchange medium.

Detailed measurements and shaping of gate profiles for microchannel-plate-based X-ray framing cameras

International Nuclear Information System (INIS)

Landen, O.L.; Hammel, B.A.; Bell, P.M.; Abare, A.; Bradley, D.K.; Univ. of Rochester, NY

1994-01-01

Gated, microchannel-plate-based (MCP) framing cameras are increasingly used worldwide for x-ray imaging of subnanosecond laser-plasma phenomena. Large dynamic range (> 1,000) measurements of gain profiles for gated microchannel plates (MCP) are presented. Temporal profiles are reconstructed for any point on the microstrip transmission line from data acquired over many shots with variable delay. No evidence for significant pulse distortion by voltage reflections at the ends of the microstrip is observed. The measured profiles compare well to predictions by a time-dependent discrete dynode model down to the 1% level. The calculations do overestimate the contrast further into the temporal wings. The role of electron transit time dispersion in limiting the minimum achievable gate duration is then investigated by using variable duration flattop gating pulses. A minimum gate duration of 50 ps is achieved with flattop gating, consistent with a fractional transit time spread of ∼ 15%

COMPUTER PROGRAM FOR CALCULATION MICROCHANNEL HEAT EXCHANGERS FOR AIR CONDITIONING SYSTEMS

Directory of Open Access Journals (Sweden)

Olga V. Olshevska

2016-08-01

Full Text Available Creating a computer program to calculate microchannel air condensers to reduce design time and carrying out variant calculations. Software packages for thermophysical properties of the working substance and the coolant, the correlation equation for calculating heat transfer, aerodynamics and hydrodynamics, the thermodynamic equations for the irreversible losses and their minimization in the heat exchanger were used in the process of creating. Borland Delphi 7 is used for creating software package.

Experimental investigation of the liquid volumetric mass transfer coefficient for upward gas-liquid two-phase flow in rectangular microchannels

Directory of Open Access Journals (Sweden)

X. Y. Ji

2010-12-01

Full Text Available The gas-liquid two-phase mass transfer process in microchannels is complicated due to the special dynamical characteristics. In this work, a novel method was explored to measure the liquid side volumetric mass transfer coefficient kLa. Pressure transducers were utilized to measure the pressure variation of upward gas-liquid two-phase flow in three vertical rectangular microchannels and the liquid side volumetric mass transfer coefficient kLa was calculated through the Pressure-Volume-Temperature correlation of the gas phase. Carbon dioxide-water, carbon dioxide-ethanol and carbon dioxide-n-propanol were used as working fluids, respectively. The dimensions of the microchannels were 40 µm×240 µm (depth×width, 100 µm×800 µm and 100 µm×2000 µm, respectively. Results showed that the channel diameter and the capillary number influence kLa remarkably and that the maximum value of kLa occurs in the annular flow regime. A new correlation of kLa was proposed based on the Sherwood number, Schmidt number and the capillary number. The predicted values of kLa agreed well with the experimental data.

Fabrication and Characterization of Silicon Micro-Funnels and Tapered Micro-Channels for Stochastic Sensing Applications

Directory of Open Access Journals (Sweden)

Frances S. Ligler

2008-06-01

Full Text Available We present a simplified, highly reproducible process to fabricate arrays of tapered silicon micro-funnels and micro-channels using a single lithographic step with a silicon oxide (SiO2 hard mask on at a wafer scale. Two approaches were used for the fabrication. The first one involves a single wet anisotropic etch step in concentrated potassium hydroxide (KOH and the second one is a combined approach comprising Deep Reactive Ion Etch (DRIE followed by wet anisotropic etching. The etching is performed through a 500 mm thick silicon wafer, and the resulting structures are characterized by sharp tapered ends with a sub-micron cross-sectional area at the tip. We discuss the influence of various parameters involved in the fabrication such as the size and thickness variability of the substrate, dry and wet anisotropic etching conditions, the etchant composition, temperature, diffusion and micro-masking effects, the quality of the hard mask in the uniformity and reproducibility of the structures, and the importance of a complete removal of debris and precipitates. The presence of apertures at the tip of the structures is corroborated through current voltage measurements and by the translocation of DNA through the apertures. The relevance of the results obtained in this report is discussed in terms of the potential use of these structures for stochastic sensing.

Low temperature catalytic combustion of propane over Pt-based catalyst with inverse opal microstructure in microchannel reactor

NARCIS (Netherlands)

Guan, G.; Zapf, R.; Kolb, G.A.; Men, Y.; Hessel, V.; Löwe, H.; Ye, J.; Zentel, R.

2007-01-01

novel Pt-based catalyst with highly regular, periodic inverse opal microstructure was fabricated in a microchannel reactor, and catalytic testing revealed excellent conversion and stable activity for propane combustion at low temperatures

Two-fluid mixing in a microchannel

International Nuclear Information System (INIS)

Liu Yingzheng; Kim, Byoung Jae; Sung, Hyung Jin

2004-01-01

A numerical study of the mixing of two fluids (pure water and a solution of glycerol in water) in a microchannel was carried out. By varying the glycerol content of the glycerol/water solution, the variation in mixing behavior with changes in the difference in the properties of the two fluids (e.g., viscosity, density and diffusivity) was investigated. The mixing phenomena were tested for three micromixers: a squarewave mixer, a three-dimensional serpentine mixer and a staggered herringbone mixer. The governing equations of continuity, momentum and solute mass fraction were solved numerically. To evaluate mixing performance, a criterion index of mixing uniformity was proposed. In the systems considered, the Reynolds number based on averaged properties was Re=1 and 10. For low Reynolds number (Re=1), the mixing performance varied inversely with mass fraction of glycerol due to the dominance of molecular diffusion. The mixing performance deteriorated due to a significant reduction in the residence time of the fluid inside the mixers

Simulation, Fabrication and Analysis of Silver Based Ascending Sinusoidal Microchannel (ASMC for Implant of Varicose Veins

Directory of Open Access Journals (Sweden)

Muhammad Javaid Afzal

2017-09-01

Full Text Available Bioengineered veins can benefit humans needing bypass surgery, dialysis, and now, in the treatment of varicose veins. The implant of this vein in varicose veins has significant advantages over the conventional treatment methods. Deep vein thrombosis (DVT, vein patch repair, pulmonary embolus, and tissue-damaging problems can be solved with this implant. Here, the authors have proposed biomedical microdevices as an alternative for varicose veins. MATLAB and ANSYS Fluent have been used for simulations of blood flow for bioengineered veins. The silver based microchannel has been fabricated by using a micromachining process. The dimensions of the silver substrates are 51 mm, 25 mm, and 1.1 mm, in length, width, and depth respectively. The dimensions of microchannels grooved in the substrates are 0.9 mm in width and depth. The boundary conditions for pressure and velocity were considered, from 1.0 kPa to 1.50 kPa, and 0.02 m/s to 0.07 m/s, respectively. These are the actual values of pressure and velocity in varicose veins. The flow rate of 5.843 (0.1 nL/s and velocity of 5.843 cm/s were determined at Reynolds number 164.88 in experimental testing. The graphs and results from simulations and experiments are in close agreement. These microchannels can be inserted into varicose veins as a replacement to maintain the excellent blood flow in human legs.

Pressure loss in two-phase flow through a microchannel rod bundle

International Nuclear Information System (INIS)

Smith, A.C.; Hamm, L.L.; Qureshi, Z.; Steeper, T.J.

1998-01-01

The purpose of the microchannel rod bundle two-phase flow test described here was to provide data for benchmarking safety analyses for the accelerator production of tritium (APT). The objective was to obtain pressure loss data for a typical accelerator target rod bundle over a wide range of two-phase flow conditions. The test rod bundle assembly was fabricated for single-phase pressure drop tests conducted at Los Alamos National Laboratory (LANL) and subsequently used for the two-phase flow testing described here. The results for a typical case are given. These results fall generally in the slug flow regime for the horizontal flow results of Fukano and Kariyasaki for a 1.0-mm circular channel. Fukano and Kariyasaki found that surface tension effects were dominant in the 1-mm channel and report no churn regime. The results were also compared with the flow regime maps given by Triplett et al. for flow in discrete microchannels. Triplett employed both circular and trapezoidal channels, the latter to approximate the rod bundle interstitial flow channel shape. It was found that the rod bundle flow fell across the slug-to-churn flow regime transition reported by Triplett. This is consistent with the expectation that cross flow among channels would result in turbulent mixing and would suppress the formation of large discrete bubbles

Continuous Size-Dependent Sorting of Ferromagnetic Nanoparticles in Laser-Ablated Microchannel

Directory of Open Access Journals (Sweden)

Yiqiang Fan

2016-01-01

Full Text Available This paper reports a low-cost method of continuous size-dependent sorting of magnetic nanoparticles in polymer-based microfluidic devices by magnetic force. A neodymium permanent magnet was used to generate a magnetic field perpendicular to the fluid flow direction. Firstly, FeNi3 magnetic nanoparticles were chemically synthesized with diameter ranges from 80 nm to 200 nm; then, the solution of magnetic nanoparticles and a buffer were passed through the microchannel in laminar flow; the magnetic nanoparticles were deflected from the flow direction under the applied magnetic field. Nanoparticles in the microchannel will move towards the direction of high-gradient magnetic fields, and the degree of deflection depends on their sizes; therefore, magnetic nanoparticles of different sizes can be separated and finally collected from different output ports. The proposed method offers a rapid and continuous approach of preparing magnetic nanoparticles with a narrow size distribution from an arbitrary particle size distribution. The proposed new method has many potential applications in bioanalysis field since magnetic nanoparticles are commonly used as solid support for biological entities such as DNA, RNA, virus, and protein. Other than the size sorting application of magnetic nanoparticles, this approach could also be used for the size sorting and separation of naturally magnetic cells, including blood cells and magnetotactic bacteria.

Custom ceramic microchannel-cooled array for high-power fiber-coupled application

Science.gov (United States)

Junghans, Jeremy; Feeler, Ryan; Stephens, Ed

2018-03-01

A low-SWaP (Size, Weight and Power) diode array has been developed for a high-power fiber-coupled application. High efficiency ( 65%) diodes enable high optical powers while minimizing thermal losses. A large amount of waste heat is still generated and must be extracted. Custom ceramic microchannel-coolers (MCCs) are used to dissipate the waste heat. The custom ceramic MCC was designed to accommodate long cavity length diodes and micro-lenses. The coolers provide similar thermal performance as copper MCCs however they are not susceptible to erosion and can be cooled with standard filtered water. The custom ceramic micro-channel cooled array was designed to be a form/fit replacement for an existing copperbased solution. Each array consisted of three-vertically stacked MCCs with 4 mm CL, 976 nm diodes and beamshaping micro-optics. The erosion and corrosion resistance of ceramic array is intended to mitigate the risk of copperbased MCC corrosion failures. Elimination of the water delivery requirements (pH, resistivity and dissolved oxygen control) further reduces the system SWaP while maintaining reliability. The arrays were fabricated and fully characterized. This work discusses the advantages of the ceramic MCC technology and describes the design parameters that were tailored for the fiber-coupled application. Additional configuration options (form/fit, micro-lensing, alternate coolants, etc.) and on-going design improvements are also discussed.

Regulating the Emission Spectrum of CsPbBr3 from Green to Blue via Controlling the Temperature and Velocity of Microchannel Reactor

Science.gov (United States)

Tang, Yong; Lu, Hanguang; Rao, Longshi; Ding, Xinrui; Yan, Caiman; Yu, Binhai

2018-01-01

The ability to precisely obtain tunable spectrum of lead halide perovskite quantum dots (QDs) is very important for applications, such as in lighting and display. Herein, we report a microchannel reactor method for synthesis of CsPbBr3 QDs with tunable spectrum. By adjusting the temperature and velocity of the microchannel reactor, the emission peaks of CsPbBr3 QDs ranging from 520 nm to 430 nm were obtained, which is wider than that of QDs obtained in a traditional flask without changing halide component. The mechanism of photoluminescence (PL) spectral shift of CsPbBr3 QDs was investigated, the result shows that the supersaturation control enabled by the superior mass and heat transfer performance in the microchannel is the key to achieve the wide range of PL spectrum, with only a change in the setting of the temperature controller required. The wide spectrum of CsPbBr3 QDs can be applied to light-emitting diodes (LEDs), photoelectric sensors, lasers, etc. PMID:29498710

Thermal analysis of a multi-layer microchannel heat sink for cooling concentrator photovoltaic (CPV) cells

Science.gov (United States)

Siyabi, Idris Al; Shanks, Katie; Mallick, Tapas; Sundaram, Senthilarasu

2017-09-01

Concentrator Photovoltaic (CPV) technology is increasingly being considered as an alternative option for solar electricity generation. However, increasing the light concentration ratio could decrease the system output power due to the increase in the temperature of the cells. The performance of a multi-layer microchannel heat sink configuration was evaluated using numerical analysis. In this analysis, three dimensional incompressible laminar steady flow model was solved numerically. An electrical and thermal solar cell model was coupled for solar cell temperature and efficiency calculations. Thermal resistance, solar cell temperature and pumping power were used for the system efficiency evaluation. An increase in the number of microchannel layers exhibited the best overall performance in terms of the thermal resistance, solar cell temperature uniformity and pressure drop. The channel height and width has no effect on the solar cell maximum temperature. However, increasing channel height leads to a reduction in the pressure drop and hence less fluid pumping power.

Slow waves in microchannel metal waveguides and application to particle acceleration

OpenAIRE

L. C. Steinhauer; W. D. Kimura

2003-01-01

Conventional metal-wall waveguides support waveguide modes with phase velocities exceeding the speed of light. However, for infrared frequencies and guide dimensions of a fraction of a millimeter, one of the waveguide modes can have a phase velocity equal to or less than the speed of light. Such a metal microchannel then acts as a slow-wave structure. Furthermore, if it is a transverse magnetic mode, the electric field has a component along the direction of propagation. Therefore, a strong ex...

Systematic studies of micro-channel plate PMTs

International Nuclear Information System (INIS)

Lehmann, A.; Britting, A.; Cowie, E.; Dodokhof, V.Kh.; Dueren, M.; Dutta, D.; Eyrich, W.; Foehl, K.; Glazier, D.I.; Hayrapetyan, A.; Hoek, M.; Hohler, R.; Kaiser, R.; Keri, T.; Koch, P.; Kroeck, B.; Lehmann, D.; Marton, J.; Merle, O.; Montgomery, R.

2011-01-01

DIRC Cherenkov detectors will be the main devices for π/K separation at the PANDA experiment at FAIR. Due to their advantageous properties in terms of time resolution and especially inside magnetic fields micro-channel plate photo multipliers (MCP-PMTs) are very attractive sensor candidates. In this paper we present the investigation of several types of multi-anode MCP-PMTs. The darkcount rate, the behavior inside a magnetic field of up to 2 T, the time resolution, the gain homogeneity and crosstalk of multi-pixel MCP-PMTs were found to be well suitable for the PANDA requirements. Even the rate capability of the latest models from Burle-Photonis and Hamamatsu is satisfactory. Although a big step forward was accomplished with these recently available MCP-PMTs, the lifetime is still not sufficient for the photon densities expected for the PANDA DIRCs.

Regulating the Emission Spectrum of CsPbBr3 from Green to Blue via Controlling the Temperature and Velocity of Microchannel Reactor

OpenAIRE

Yong Tang; Hanguang Lu; Longshi Rao; Zongtao Li; Xinrui Ding; Caiman Yan; Binhai Yu

2018-01-01

The ability to precisely obtain tunable spectrum of lead halide perovskite quantum dots (QDs) is very important for applications, such as in lighting and display. Herein, we report a microchannel reactor method for synthesis of CsPbBr3 QDs with tunable spectrum. By adjusting the temperature and velocity of the microchannel reactor, the emission peaks of CsPbBr3 QDs ranging from 520 nm to 430 nm were obtained, which is wider than that of QDs obtained in a traditional flask without changing hal...

Optimization of Dimples in Microchannel Heat Sink with Impinging Jets — Part A: Mathematical Model and the Influence of Dimple Radius

Science.gov (United States)

Ming, Tingzhen; Cai, Cunjin; Yang, Wei; Shen, Wenqing; Gan, Ting

2018-06-01

With increasing heat fluxes caused by electronic components, dimples have attracted wide attention by researchers and have been applied to microchannel heat sink in modern advanced cooling technologies. In this work, the combination of dimples, impinging jets and microchannel heat sink was proposed to improve the heat transfer performance on a cooling surface with a constant heat flux 500 W/cm2. A mathematical model was advanced for numerically analyzing the fluid flow and heat transfer characteristics of a microchannel heat sink with impinging jets and dimples (MHSIJD), and the velocity distribution, pressure drop, and thermal performance of MHSIJD were analyzed by varying the radii of dimples. The results showed that the combination of dimples and MHSIJ can achieve excellent heat transfer performance; for the MHSIJD model in this work, the maximum and average temperatures can be as low as 320 K and 305 K, respectively when mass flow rate is 30 g/s; when dimple radius is larger than 0.195 mm, both the heat transfer coefficient and the overall performance h/ΔP of MHSIJD are higher than those of MHSIJ.

Single-phase flow and flow boiling of water in horizontal rectangular microchannels

OpenAIRE

Mirmanto

2013-01-01

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University The current study is part of a long term experimental project devoted to investigating single-phase flow pressure drop and heat transfer, flow boiling pressure drop and heat transfer, flow boiling instability and flow visualization of de-ionized water flow in microchannels. The experimental facility was first designed and constructed by S. Gedupudi (2009) and in the present study; ...

Features of two-phase flow in a microchannel of 0.05×20 mm

Science.gov (United States)

Ronshin, Fedor

2017-10-01

We have studied the two-phase flow in a microchannel with cross-section of 0.05×20 mm2. The following two-phase flow regimes have been registered: jet, bubble, stratified, annular, and churn ones. The main features of flow regimes in this channel such as formation of liquid droplets in all two-phase flows have been distinguished.

Bubble splitting under gas–liquid–liquid three-phase flow in a double T-junction microchannel

NARCIS (Netherlands)

Liu, Yanyan; Yue, Jun; Zhao, Shuainan; Yao, Chaoqun; Chen, Guangwen

Gas–aqueous liquid–oil three-phase flow was generated in a microchannel with a double T-junction. Under the squeezing of the dispersed aqueous phase at the second T-junction (T2), the splitting of bubbles generated from the first T-junction (T1) was investigated. During the bubble splitting process,

Developments in microchannel plate detectors for imaging x-ray astronomy

International Nuclear Information System (INIS)

Fraser, G.W.; Whiteley, M.J.; Pearson, J.F.

1985-01-01

The authors present new results in four areas of microchannel plate (MCP) X-ray detector operation. The performance in pulse counting mode of MCPs with 8 micron channel diameters is reported. The effects on MCP quantum detection efficiency and energy discrimination of multiple CsI coatings are described. A new mode of operation of two-stage multipliers is evaluated. Replacing the conventional electron-accelerating inter-plate potential difference by a retarding field is shown to result in definite advantages with regard to X-ray energy discrimination and detector lifetime. The source of the MCP internal background is discussed

Effects of carbon nanotube coating on flow boiling in a micro-channel

OpenAIRE

Khanikar, Vikash; Mudawar, Issam; Fisher, Timothy

2009-01-01

Experiments were performed to assess the heat transfer enhancement benefits of coating the bottom wall of a shallow rectangular micro-channel with carbon nanotubes (CNTs). Using water as working fluid, tests were performed with a bare copper surface and three separate, yet identical CNT-coated surfaces. Each of the CNT-coated surfaces was tested repeatedly at the same mass velocity to explore any time dependence of heat transfer performance parameters, especially critical heat flux (CHIF). Ap...

Measurements of tangential momentum accommodation coefficient for various gases in plane microchannel

OpenAIRE

Graur , I; Perrier , Pierre; Ghozlani , W ,; Méolans , J.Gilbert

2009-01-01

International audience; Mass flow rate measurements in a single silicon microchannel were carried out for various gases in isothermal steady flows. The results obtained from hydrodynamic to near free molecular regime by using a powerful experimental platform allowed us to deduce interesting information, notably about the reflection/accommodation process at the wall. In the 0–0.3 Knudsen range, a continuum analytic approach was derived from the NS equations, associated with first or second ord...

Mixing in wicking structures and the use of enhanced mixing within wicks in microchannel devices

Science.gov (United States)

Stenkamp, Victoria S [Richland, WA; TeGrotenhuis, Ward E [Kennewick, WA; Wegeng, Robert S [Alexandria, VA

2009-06-02

Advanced wicking structures and methods utilizing these structures are described. The use of advanced wicking structures can promote rapid mass transfer while maintaining high capillary pressure through the use of small pores. Particularly improved results in fluid contacting processes can be achieved by enhanced mixing within a wicking layer within a microchannel.

Regulating the Emission Spectrum of CsPbBr3 from Green to Blue via Controlling the Temperature and Velocity of Microchannel Reactor

Directory of Open Access Journals (Sweden)

Yong Tang

2018-03-01

Full Text Available The ability to precisely obtain tunable spectrum of lead halide perovskite quantum dots (QDs is very important for applications, such as in lighting and display. Herein, we report a microchannel reactor method for synthesis of CsPbBr3 QDs with tunable spectrum. By adjusting the temperature and velocity of the microchannel reactor, the emission peaks of CsPbBr3 QDs ranging from 520 nm to 430 nm were obtained, which is wider than that of QDs obtained in a traditional flask without changing halide component. The mechanism of photoluminescence (PL spectral shift of CsPbBr3 QDs was investigated, the result shows that the supersaturation control enabled by the superior mass and heat transfer performance in the microchannel is the key to achieve the wide range of PL spectrum, with only a change in the setting of the temperature controller required. The wide spectrum of CsPbBr3 QDs can be applied to light-emitting diodes (LEDs, photoelectric sensors, lasers, etc.

Features of two-phase flow in a microchannel of 0.05×20 mm

Directory of Open Access Journals (Sweden)

Ronshin Fedor

2017-01-01

Full Text Available We have studied the two-phase flow in a microchannel with cross-section of 0.05×20 mm2. The following two-phase flow regimes have been registered: jet, bubble, stratified, annular, and churn ones. The main features of flow regimes in this channel such as formation of liquid droplets in all two-phase flows have been distinguished.

A bio-inspired, microchanneled hydrogel with controlled spacing of cell adhesion ligands regulates 3D spatial organization of cells and tissue.

Science.gov (United States)

Lee, Min Kyung; Rich, Max H; Lee, Jonghwi; Kong, Hyunjoon

2015-07-01

Bioactive hydrogels have been extensively studied as a platform for 3D cell culture and tissue regeneration. One of the key desired design parameters is the ability to control spatial organization of biomolecules and cells and subsequent tissue in a 3D matrix. To this end, this study presents a simple but advanced method to spatially organize microchanneled, cell adherent gel blocks and non-adherent ones in a single construct. This hydrogel system was prepared by first fabricating a bimodal hydrogel in which the microscale, alginate gel blocks modified with cell adhesion peptides containing Arg-Gly-Asp sequence (RGD peptides), and those free of RGD peptides, were alternatingly presented. Then, anisotropically aligned microchannels were introduced by uniaxial freeze-drying of the bimodal hydrogel. The resulting gel system could drive bone marrow stromal cells to adhere to and differentiate into neuron and glial cells exclusively in microchannels of the alginate gel blocks modified with RGD peptides. Separately, the bimodal gel loaded with microparticles releasing vascular endothelial growth factor stimulated vascular growth solely into microchannels of the RGD-alginate gel blocks in vivo. These results were not attained by the bimodal hydrogel fabricated to present randomly oriented micropores. Overall, the bimodal gel system could regulate spatial organization of nerve-like tissue or blood vessels at sub-micrometer length scale. We believe that the hydrogel assembly demonstrated in this study will be highly useful in developing a better understanding of diverse cellular behaviors in 3D tissue and further improve quality of a wide array of engineered tissues. Copyright © 2015 Elsevier Ltd. All rights reserved.

Use of Large Surface MicroChannel Plates for the Tagging of Intermediate Energy Exotic Beams

Energy Technology Data Exchange (ETDEWEB)

Lombardo, I., E-mail: ilombardo@lns.infn.it [Dipartimento di Fisica, Universita di Catania, Catania (Italy); INFN Laboratori Nazionali del Sud, Catania (Italy); Amorini, F. [INFN Laboratori Nazionali del Sud, Catania (Italy); Cardella, G. [INFN, Sezione di Catania, Catania (Italy); Cavallaro, S. [Dipartimento di Fisica, Universita di Catania, Catania (Italy); INFN Laboratori Nazionali del Sud, Catania (Italy); De Filippo, E. [INFN, Sezione di Catania, Catania (Italy); Geraci, E.; Grassi, L. [Dipartimento di Fisica, Universita di Catania, Catania (Italy); INFN, Sezione di Catania, Catania (Italy); La Guidara, E. [INFN, Sezione di Catania, Catania (Italy); Centro Siciliano di Fisica Nucleare e Struttura della Materia, Catania (Italy); Lanzalone, G. [INFN Laboratori Nazionali del Sud, Catania (Italy); Libera Universita Kore, Enna (Italy); Pagano, A.; Papa, M.; Pirrone, S. [INFN, Sezione di Catania, Catania (Italy); Politi, G. [Dipartimento di Fisica, Universita di Catania, Catania (Italy); INFN, Sezione di Catania, Catania (Italy); Porto, F.; Rizzo, F.; Russotto, P. [Dipartimento di Fisica, Universita di Catania, Catania (Italy); INFN Laboratori Nazionali del Sud, Catania (Italy); Verde, G. [INFN, Sezione di Catania, Catania (Italy); Vigilante, M. [INFN, Sezione di Napoli and Dipartimento di Fisica, Universita Federico II di Napoli (Italy)

2011-06-15

We show the properties of the tagging system for exotic beams coupled to the CHIMERA detector. In particular, the characteristics of a newly developed large surface MicroChannel Plate will be discussed. Timing and efficiency of this instrument have been investigated. Preliminary results of tests performed with radioactive beams and alpha sources are presented.

Numerical investigation of fluid flow and heat transfer under high heat flux using rectangular micro-channels

KAUST Repository

Mansoor, Mohammad M.; Wong, Kokcheong; Siddique, Mansoor M.

2012-01-01

computational domain was discretized using a 120×160×100 grid for the micro-channel with an aspect ratio of (α=4.56) and examined for Reynolds numbers in the laminar range (Re 500-2000) using FLUENT. De-ionized water served as the cooling fluid while the micro

Experimental demonstration of a tailored-width microchannel heat exchanger configuration for uniform wall temperature

International Nuclear Information System (INIS)

Riera, S; Barrau, J; Rosell, J I; Omri, M; Fréchette, L G

2013-01-01

In this work, an experimental study of a novel microfabricated heat sink configuration that tends to uniform the wall temperature, even with increasing flow temperature, is presented. The design consists of a series of microchannel sections with stepwise varying width. This scheme counteracts the flow temperature increase by reducing the local thermal resistance along the flow path. A test apparatus with uniform heat flux and distributed wall temperature measurements was developed for microchannel heat exchanger characterisation. The energy balance is checked and the temperature distribution is analysed for each test. The results show that the wall temperature decreases slightly along the flow path while the fluid temperature increases, highlighting the strong impact of this approach. For a flow rate of 16 ml/s, the mean thermal resistance of the heat sink is 2,35·10 −5 m 2 ·K/W which enhances the results compared to the millimeter scale channels nearly three-fold. For the same flow rate and a heat flux of 50 W/cm 2 , the temperature uniformity, expressed as the standard deviation of the wall temperature, is around 6 °C

Mixing enhancement of low-Reynolds electro-osmotic flows in microchannels with temperature-patterned walls.

Science.gov (United States)

Alizadeh, A; Zhang, L; Wang, M

2014-10-01

Mixing becomes challenging in microchannels because of the low Reynolds number. This study aims to present a mixing enhancement method for electro-osmotic flows in microchannels using vortices caused by temperature-patterned walls. Since the fluid is non-isothermal, the conventional form of Nernst-Planck equation is modified by adding a new migration term which is dependent on both temperature and internal electric potential gradient. This term results in the so-called thermo-electrochemical migration phenomenon. The coupled Navier-Stokes, Poisson, modified Nernst-Planck, energy and advection-diffusion equations are iteratively solved by multiple lattice Boltzmann methods to obtain the velocity, internal electric potential, ion distribution, temperature and species concentration fields, respectively. To enhance the mixing, three schemes of temperature-patterned walls have been considered with symmetrical or asymmetrical arrangements of blocks with surface charge and temperature. Modeling results show that the asymmetric arrangement scheme is the most efficient scheme and enhances the mixing of species by 39% when the Reynolds number is on the order of 10(-3). Current results may help improve the design of micro-mixers at low Reynolds number. Copyright © 2014 Elsevier Inc. All rights reserved.

Direct measurement of erythrocyte deformability in diabetes mellitus with a transparent microchannel capillary model and high-speed video camera system.

Science.gov (United States)

Tsukada, K; Sekizuka, E; Oshio, C; Minamitani, H

2001-05-01

To measure erythrocyte deformability in vitro, we made transparent microchannels on a crystal substrate as a capillary model. We observed axisymmetrically deformed erythrocytes and defined a deformation index directly from individual flowing erythrocytes. By appropriate choice of channel width and erythrocyte velocity, we could observe erythrocytes deforming to a parachute-like shape similar to that occurring in capillaries. The flowing erythrocytes magnified 200-fold through microscopy were recorded with an image-intensified high-speed video camera system. The sensitivity of deformability measurement was confirmed by comparing the deformation index in healthy controls with erythrocytes whose membranes were hardened by glutaraldehyde. We confirmed that the crystal microchannel system is a valuable tool for erythrocyte deformability measurement. Microangiopathy is a characteristic complication of diabetes mellitus. A decrease in erythrocyte deformability may be part of the cause of this complication. In order to identify the difference in erythrocyte deformability between control and diabetic erythrocytes, we measured erythrocyte deformability using transparent crystal microchannels and a high-speed video camera system. The deformability of diabetic erythrocytes was indeed measurably lower than that of erythrocytes in healthy controls. This result suggests that impaired deformability in diabetic erythrocytes can cause altered viscosity and increase the shear stress on the microvessel wall. Copyright 2001 Academic Press.

Streaming potential of superhydrophobic microchannels.

Science.gov (United States)

Park, Hung Mok; Kim, Damoa; Kim, Se Young

2017-03-01

For the purpose of gaining larger streaming potential, it has been suggested to employ superhydrophobic microchannels with a large velocity slip. There are two kinds of superhydrophobic surfaces, one having a smooth wall with a large Navier slip coefficient caused by the hydrophobicity of the wall material, and the other having a periodic array of no- shear slots of air pockets embedded in a nonslip wall. The electrokinetic flows over these two superhydrophobic surfaces are modelled using the Navier-Stokes equation and convection-diffusion equations of the ionic species. The Navier slip coefficient of the first kind surfaces and the no-shear slot ratio of the second kind surfaces are similar in the sense that the volumetric flow rate increases as these parameter values increase. However, although the streaming potential increases monotonically with respect to the Navier slip coefficient, it reaches a maximum and afterward decreases as the no-shear ratio increases. The results of the present investigation imply that the characterization of superhydrophobic surfaces employing only the measurement of volumetric flow rate against pressure drop is not appropriate and the fine structure of the superhydrophobic surfaces must be verified before predicting the streaming potential and electrokinetic flows accurately. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spinning and tumbling of micron-sized triangles in a micro-channel shear flow

Science.gov (United States)

Fries, J.; Kumar, M. Vijay; Mihiretie, B. Mekonnen; Hanstorp, D.; Mehlig, B.

2018-03-01

We report on measurements of the angular dynamics of micron-sized equilaterally triangular platelets suspended in a micro-channel shear flow. Our measurements confirm that such particles spin and tumble like a spheroid in a simple shear. Since the triangle has corners, we can observe the spinning directly. In general, the spinning frequency is different from the tumbling frequency and the spinning is affected by tumbling. This gives rise to doubly periodic angular dynamics.

Varying the agglomeration position of particles in a micro-channel using Acoustic Radiation Force beyond the resonance condition.

Science.gov (United States)

Dron, Olivier; Aider, Jean-Luc

2013-09-01

It is well-known that particles can be focused at mid-height of a micro-channel using Acoustic Radiation Force (ARF) tuned at the resonance frequency (h=λ/2). The resonance condition is a strong limitation to the use of acoustophoresis (particles manipulation using acoustic force) in many applications. In this study we show that it is possible to focus the particles anywhere along the height of a micro-channel just by varying the acoustic frequency, in contradiction with the resonance condition. This result has been thoroughly checked experimentally. The different physical properties as well as wall materials have been changed. The wall materials is finally the only critical parameters. One of the specificity of the micro-channel is the thickness of the carrier and reflector layer. A preliminary analysis of the experimental results suggests that the acoustic focusing beyond the classic resonance condition can be explained in the framework of the multilayered resonator proposed by Hill [1]. Nevertheless, further numerical studies are needed in order to confirm and fully understand how the acoustic pressure node can be moved over the entire height of the micro channel by varying the acoustic frequency. Despite some uncertainties about the origin of the phenomenon, it is robust and can be used for improved acoustic sorting or manipulation of particles or biological cells in confined set-ups. Copyright © 2013 Elsevier B.V. All rights reserved.

Microchannel-connected SU-8 honeycombs by single-step projection photolithography for positioning cells on silicon oxide nanopillar arrays

International Nuclear Information System (INIS)

Larramendy, Florian; Paul, Oliver; Blatche, Marie Charline; Mazenq, Laurent; Laborde, Adrian; Temple-Boyer, Pierre

2015-01-01

We report on the fabrication, functionalization and testing of SU-8 microstructures for cell culture and positioning over large areas. The microstructure consists of a honeycomb arrangement of cell containers interconnected by microchannels and centered on nanopillar arrays designed for promoting cell positioning. The containers have been dimensioned to trap single cells and, with a height of 50 µm, prevent cells from escaping. The structures are fabricated using a single ultraviolet photolithography exposure with focus depth in the lower part of the SU-8 resist. With optimized process parameters, microchannels of various aspect ratios are thus produced. The cell containers and microchannels serve for the organization of axonal growth between neurons. The roughly 2 µm-high and 500 nm-wide nanopillars are made of silicon oxide structured by deep reactive ion etching. In future work, beyond their cell positioning purpose, the nanopillars could be functionalized as sensors. The proof of concept of the novel microstructure for organized cell culture is given by the successful growth of interconnected PC12 cells. Promoted by the honeycomb geometry, a dense network of interconnections between the cells has formed and the intended intimate contact of cells with the nanopillar arrays was observed by scanning electron microscopy. This proves the potential of these new devices as tools for the controlled cell growth in an interconnected container system with well-defined 3D geometry. (paper)

Two-Phase Flow in High-Heat-Flux Micro-Channel Heat Sink for Refrigeration Cooling Applications. Part 1: Micro-Channel Heat Sink for Direct Refrigeration Cooling

Science.gov (United States)

2008-09-01

the two-phase mixture exiting the condenser. Throttling from high to low pressure was achieved by a manual metering valve situated upstream of the micro...channel et al. htp N4hsP) correlation (2002) kh sp = Nu kf dh’ Nuta, = const (Refer to Eqs. (1.4.6) and (1.4.7)), = 0.023Re" Prf4 f f E=1.0+6Bol6 +f(Bo)x...12.26% (318 data points) 0Id" +30%OND A ~’AAK - -30%",A- / A’ A* 10 " , , , htp ,&xp [W/M 2 K] Figure 1.4.8 Comparison of heat transfer coefficient

Implementation of 40-ps high-speed gated-microchannel-plate based x-ray framing cameras on reentrant SIM's for Nova

International Nuclear Information System (INIS)

Bell, P.M.; Kilkenny, J.D.; Landen, O.; Bradley, D.K.

1994-01-01

Gated framing cameras used in diagnosing laser produced plasmas have been used on the Nova laser system since 1987. There have been many variations of these systems implemented. All of these cameras have been ultimately limited in response time for two reasons. One being the electrical gating amplitude verses the gate width, this has always limited the detectable gain in the system. The second being the length to diameter (l/d) ratio of standard off the shelf microchannel plates (MCP). This sets the minimum electrical gate pulse that will give detectable gain from a given microchannel plate. The authors have implemented two different types of 40 ps framing camera configurations on the Nova laser system. They will describe the configurations of both systems as well as discuss the advantages of each

Flame dynamics in a micro-channeled combustor

International Nuclear Information System (INIS)

Hussain, Taaha; Balachandran, Ramanarayanan; Markides, Christos N.

2015-01-01

The increasing use of Micro-Electro-Mechanical Systems (MEMS) has generated a significant interest in combustion-based power generation technologies, as a replacement of traditional electrochemical batteries which are plagued by low energy densities, short operational lives and low power-to-size and power-to-weight ratios. Moreover, the versatility of integrated combustion-based systems provides added scope for combined heat and power generation. This paper describes a study into the dynamics of premixed flames in a micro-channeled combustor. The details of the design and the geometry of the combustor are presented in the work by Kariuki and Balachandran [1]. This work showed that there were different modes of operation (periodic, a-periodic and stable), and that in the periodic mode the flame accelerated towards the injection manifold after entering the channels. The current study investigates these flames further. We will show that the flame enters the channel and propagates towards the injection manifold as a planar flame for a short distance, after which the flame shape and propagation is found to be chaotic in the middle section of the channel. Finally, the flame quenches when it reaches the injector slots. The glow plug position in the exhaust side ignites another flame, and the process repeats. It is found that an increase in air flow rate results in a considerable increase in the length (and associated time) over which the planar flame travels once it has entered a micro-channel, and a significant decrease in the time between its conversion into a chaotic flame and its extinction. It is well known from the literature that inside small channels the flame propagation is strongly influenced by the flow conditions and thermal management. An increase of the combustor block temperature at high flow rates has little effect on the flame lengths and times, whereas at low flow rates the time over which the planar flame front can be observed decreases and the time of

Flame dynamics in a micro-channeled combustor

Energy Technology Data Exchange (ETDEWEB)

Hussain, Taaha; Balachandran, Ramanarayanan, E-mail: r.balachandran@ucl.ac.uk [Department of Mechanical Engineering, University College London, London (United Kingdom); Markides, Christos N. [Clean Energy Processes Laboratory, Department of Chemical Engineering, Imperial College London, London (United Kingdom)

2015-01-22

The increasing use of Micro-Electro-Mechanical Systems (MEMS) has generated a significant interest in combustion-based power generation technologies, as a replacement of traditional electrochemical batteries which are plagued by low energy densities, short operational lives and low power-to-size and power-to-weight ratios. Moreover, the versatility of integrated combustion-based systems provides added scope for combined heat and power generation. This paper describes a study into the dynamics of premixed flames in a micro-channeled combustor. The details of the design and the geometry of the combustor are presented in the work by Kariuki and Balachandran [1]. This work showed that there were different modes of operation (periodic, a-periodic and stable), and that in the periodic mode the flame accelerated towards the injection manifold after entering the channels. The current study investigates these flames further. We will show that the flame enters the channel and propagates towards the injection manifold as a planar flame for a short distance, after which the flame shape and propagation is found to be chaotic in the middle section of the channel. Finally, the flame quenches when it reaches the injector slots. The glow plug position in the exhaust side ignites another flame, and the process repeats. It is found that an increase in air flow rate results in a considerable increase in the length (and associated time) over which the planar flame travels once it has entered a micro-channel, and a significant decrease in the time between its conversion into a chaotic flame and its extinction. It is well known from the literature that inside small channels the flame propagation is strongly influenced by the flow conditions and thermal management. An increase of the combustor block temperature at high flow rates has little effect on the flame lengths and times, whereas at low flow rates the time over which the planar flame front can be observed decreases and the time of

The effects of different nano particles of Al2O3 and Ag on the MHD nano fluid flow and heat transfer in a microchannel including slip velocity and temperature jump

Science.gov (United States)

Karimipour, Arash; D'Orazio, Annunziata; Shadloo, Mostafa Safdari

2017-02-01

The forced convection of nanofluid flow in a long microchannel is studied numerically according to the finite volume approach and by using a developed computer code. Microchannel domain is under the influence of a magnetic field with uniform strength. The hot inlet nanofluid is cooled by the heat exchange with the cold microchannel walls. Different types of nanoparticles such as Al2O3 and Ag are examined while the base fluid is considered as water. Reynolds number are chosen as Re=10 and Re=100. Slip velocity and temperature jump boundary conditions are simulated along the microchannel walls at different values of slip coefficient for different amounts of Hartmann number. The investigation of magnetic field effect on slip velocity and temperature jump of nanofluid is presented for the first time. The results are shown as streamlines and isotherms; moreover the profiles of slip velocity and temperature jump are drawn. It is observed that more slip coefficient corresponds to less Nusselt number and more slip velocity especially at larger Hartmann number. It is recommended to use Al2O3-water nanofluid instead of Ag-water to increase the heat transfer rate from the microchannel walls at low values of Re. However at larger amounts of Re, the nanofluid composed of nanoparticles with higher thermal conductivity works better.

Recent developments with microchannel-plate PMTs

Science.gov (United States)

Lehmann, A.; Böhm, M.; Britting, A.; Eyrich, W.; Pfaffinger, M.; Uhlig, F.; Belias, A.; Dzhygadlo, R.; Gerhardt, A.; Götzen, K.; Kalicy, G.; Krebs, M.; Lehmann, D.; Nerling, F.; Patsyuk, M.; Peters, K.; Schepers, G.; Schmitt, L.; Schwarz, C.; Schwiening, J.; Traxler, M.; Zühlsdorf, M.; Düren, M.; Etzelmüller, E.; Föhl, K.; Hayrapetyan, A.; Kröck, B.; Merle, O.; Rieke, J.; Schmidt, M.; Wasem, T.; Cowie, E.; Keri, T.; Achenbach, P.; Cardinali, M.; Hoek, M.; Lauth, W.; Schlimme, S.; Sfienti, C.; Thiel, M.

2017-12-01

Microchannel-plate (MCP) PMTs are the favored photon sensors for the DIRC detectors of the PANDA experiment at FAIR. Until recently the main drawback of MCP-PMTs were serious aging effects which led to a limited lifetime due to a rapidly decreasing quantum efficiency (QE) of the photo cathode (PC) as the integrated anode charge (IAC) increased. In the latest models of PHOTONIS and Hamamatsu an innovative atomic layer deposition (ALD) technique is applied to overcome these limitations. During the last five years comprehensive aging tests with ALD coated MCP-PMTs were performed and the results were compared to tubes treated with other techniques. The QE in dependence of the IAC was measured as a function of the wavelength and the position across the PC. For the best performing tubes the lifetime improvement in comparison to the older MCP-PMTs is a factor of > 50 based on an IAC of meanwhile > 10 C /cm2 . In addition, the performance results of a new 2-in. ALD coated MCP-PMT prototype from Hamamatsu with a very high position resolution (128×6 anode pixels) is presented and the first conclusions from investigations concerning the PC aging mechanism will be discussed.

Functionalized Nano-Film Microchannel Plate: A Single High Aspect Ratio Device for High Resolution, Low Noise Astronomical Imaging, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — The proposed innovation is to apply proven nano-film technology to enable Microchannel plate (MCP) devices to be manufactured on a range of insulating substrates and...

The effects of viscosity, surface tension, and flow rate on gasoil-water flow pattern in microchannels

Energy Technology Data Exchange (ETDEWEB)

Boogar, Rahman Sadeghi; Gheshlaghi, Reza; Mahdavi, Mahmood Akhavan [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

2013-01-15

A microchannel was fabricated with glass tubes to investigate the effect of viscosity, surface tension, and flow rate on the liquid-liquid two-phase flow regime. Water and gasoil were selected as aqueous and organic working fluids, respectively. The two fluids were injected into the microchannel and created either slug or parallel profile depending on the applied conditions. The range of Reynolds and capillary numbers was chosen in such a way that neither inertia nor interfacial tension forces were negligible. Xanthan gum was used to increase viscosity and Triton X-100 (TX-100) and Sodium Dodecyl Sulfate (SDS) were used to reduce the interfacial tension. The results demonstrated that higher value of viscosity and flow rate increased interfacial area, but slug flow regime remained unchanged. The two surfactants showed different effects on the flow regime and interfacial area. Addition of TX-100 did not change the slug flow but decreased the interfacial area. In contrast, addition of SDS increased interfacial area by decreasing the slug’s length in the low concentrations and by switching from slug to parallel regime at high concentrations.

Numerical simulation of the droplet formation in a cross-junction microchannel using the Lattice Boltzmann Method

International Nuclear Information System (INIS)

Li, Zilu; Kang, Jinfen; Park, Jae Hyun; Suh, Yong Kweon

2007-01-01

This study describes the numerical simulation of two-dimensional droplet formation and the following motion by using the Lattice Boltzmann Method (LBM) with the phase field equation. The free energy model is used to treat the interfacial force and the deformation of a binary fluid system, drawn into a cross-junction microchannel. While one fluid is introduced through the central inlet channel, the other fluid is drawn into the main channel through the two vertical inlet channels. Due to the effect of surface tension on the interface between the two fluids, the droplets of the first fluid are formed near the cross-junction. The aim in this investigation is to examine the applicability of LBM to the numerical analysis of the droplet formation and its motion in the microchannel. It was found from comparison with the experimentally visualized patterns that LBM with the free energy model can reproduce the droplet formation successfully. However because of the stability problem which is intrinsic for high surface-tension cases, it requires a very long computational time. This issue is to be resolved in the future.

Numerical simulation of the droplet formation in a cross-junction microchannel using the Lattice Boltzmann Method

International Nuclear Information System (INIS)

Li, Zi Lu; Kang, Jin Fen; Park, Jae Hyun; Suh, Yong Kweon

2007-01-01

This study describes the numerical simulation of two-dimensional droplet formation and the following motion by using the Lattice Boltzmann Method (LBM) with the phase field equation. The free energy model is used to treat the interfacial force and the deformation of a binary fluid system, drawn into a cross-junction microchannel. While one fluid is introduced through the central inlet channel, the other fluid is drawn into the main channel through the two vertical inlet channels. Due to the effect of surface tension on the interface between the two fluids, the droplets of the first fluid are formed near the cross-junction. The aim in this investigation is to examine the applicability of LBM to the numerical analysis of the droplet formation and its motion in the microchannel. It was found from comparison with the experimentally visualized patterns that LBM with the free energy model can reproduce the droplet formation successfully. However because of the stability problem which is intrinsic for high surface-tension cases, it requires a very long computational time. This issue is to be resolved in the future

Degradation of the performance of microchannel heat exchangers due to flow maldistribution

DEFF Research Database (Denmark)

Nielsen, Kaspar Kirstein; Engelbrecht, Kurt; Christensen, Dennis

2012-01-01

The effect of flow maldistribution on the performance of microchannel parallel plate heat exchangers is investigated using an established single blow numerical model and cyclic steady-state regenerator experiments. It is found that as the variation of the individual channel thickness...... in a particular stack (heat exchanger) increases the actual performance of the heat exchanger decreases significantly, deviating from the expected nominal performance. We show that this is due to both the varying fluid flow velocities in each individual channel and the thermal cross talk between the channels...

Increasing heat transfer of non-Newtonian nanofluid in rectangular microchannel with triangular ribs

Science.gov (United States)

Shamsi, Mohammad Reza; Akbari, Omid Ali; Marzban, Ali; Toghraie, Davood; Mashayekhi, Ramin

2017-09-01

In this study, computational fluid dynamics and the laminar flow of the non-Newtonian fluid have been numerically studied. The cooling fluid includes water and 0.5 wt% Carboxy methyl cellulose (CMC) making the non-Newtonian fluid. In order to make the best of non-Newtonian nanofluid in this simulation, solid nanoparticles of Aluminum Oxide have been added to the non-Newtonian fluid in volume fractions of 0-2% with diameters of 25, 45 and 100 nm. The supposed microchannel is rectangular and two-dimensional in Cartesian coordination. The power law has been used to speculate the dynamic viscosity of the cooling nanofluid. The field of numerical solution is simulated in the Reynolds number range of 5 nanoparticles as well as the use for nanoparticles with smaller diameters lead to greater heat transfer. Among all the studied forms, the triangular rib from with an angle of attack 30° has the biggest Nusselt number and the smallest pressure drop along the microchannel. Also, an increase in the angle of attack and as a result of a sudden contact between the fluid and the ribs and also a reduction in the coflowing length (length of the rib) cause a cut in heat transfer by the fluid in farther parts from the solid wall (tip of the rib).

High-Throughput Particle Manipulation Based on Hydrodynamic Effects in Microchannels

Directory of Open Access Journals (Sweden)

Chao Liu

2017-03-01

Full Text Available Microfluidic techniques are effective tools for precise manipulation of particles and cells, whose enrichment and separation is crucial for a wide range of applications in biology, medicine, and chemistry. Recently, lateral particle migration induced by the intrinsic hydrodynamic effects in microchannels, such as inertia and elasticity, has shown its promise for high-throughput and label-free particle manipulation. The particle migration can be engineered to realize the controllable focusing and separation of particles based on a difference in size. The widespread use of inertial and viscoelastic microfluidics depends on the understanding of hydrodynamic effects on particle motion. This review will summarize the progress in the fundamental mechanisms and key applications of inertial and viscoelastic particle manipulation.

Proton beam micromachined buried microchannels in negative tone resist materials

International Nuclear Information System (INIS)

Rajta, I.; Chatzichristidi, M.; Baradacs, E.; Cserhati, C.; Raptis, I.; Manoli, K.; Valamontes, E.S.

2007-01-01

In the present work the Atomki, Debrecen microprobe facility has been used to write long tilted structures by 2 MeV protons. For the formation of the structures, two exposures have been carried out at +20 o and -20 o using a goniometer stage sample holder. The tilted structures were resolved in the negative tone resist materials SU-8 and ADEPR (an aqueous base developable chemically amplified resist). The length of the microchannels was varied between 100 μm and 1000 μm, the wall thickness was less than 10 μm. By applying the developed methodology it was possible to resolve the desired layout through the whole length of the channel

Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow.

Science.gov (United States)

Song, Hongjun; Wang, Yi; Pant, Kapil

2013-01-01

This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space.

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

Science.gov (United States)

Malekzadeh, Shima; Roohi, Ehsan

2015-06-01

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

Effect of laser beam conditioning on fabrication of clean micro-channel on stainless steel 316L using second harmonic of Q-switched Nd:YAG laser

Science.gov (United States)

Singh, Sanasam Sunderlal; Baruah, Prahlad Kr; Khare, Alika; Joshi, Shrikrishna N.

2018-02-01

Laser micromachining of metals for fabrication of micro-channels generate ridge formation along the edges accompanied by ripples along the channel bed. The ridge formation is due to the formation of interference pattern formed by back reflections from the beam splitter and other optical components involved before focusing on the work piece. This problem can be curtailed by using a suitable aperture or Iris diaphragm so as to cut the unwanted portion of the laser beam before illuminating the sample. This paper reports an experimental investigation on minimizing this problem by conditioning the laser beam using an Iris diaphragm and using optimum process parameters. In this work, systematic experiments have been carried out using the second harmonic of a Q-switched Nd:YAG laser to fabricate micro-channels. Initial experiments revealed that formation of ridges along the sides of micro-channel can easily be minimized with the help of Iris diaphragm. Further it is noted that a clean micro-channel of depth 43.39 μm, width up to 64.49 μm and of good surface quality with average surface roughness (Ra) value of 370 nm can be machined on stainless steel (SS) 316L by employing optimum process condition: laser beam energy of 30 mJ/pulse, 11 number of laser scans and scan speed of 169.54 μm/s with an opening of 4 mm diameter of Iris diaphragm in the path of the laser beam.

Observation of Ultra-Slow Antiprotons using Micro-channel Plate

Science.gov (United States)

Imao, H.; Torii, H. A.; Nagata, Y.; Toyoda, H.; Shimoyama, T.; Enomoto, Y.; Higaki, H.; Kanai, Y.; Mohri, A.; Yamazaki, Y.

2008-08-01

Our group ASACUSA-MUSASHI has succeeded in accumulating several million antiprotons and extracting them as monochromatic ultra-slow antiproton beams (10 eV-1 keV) at CERN AD. We have observed ultra-slow antiprotons using micro-channel plates (MCP). The integrated pulse area of the output signals generated when the MCP was irradiated by ultra-slow antiprotons was 6 times higher than that by electrons. As a long-term effect, we also observed an increase in the background rate presumably due to the radioactivation of the MCP surface. Irradiating the antiproton beams on the MCP induces antiproton-nuclear annihilations only on the first layer of the surface. Low-energy and short-range secondary particles like charged nuclear fragments caused by the "surface nuclear reactions" would be the origin of our observed phenomena.

Investigating performance of microchannel evaporators with different manifold structures

Energy Technology Data Exchange (ETDEWEB)

Shi, Junye; Qu, Xiaohua; Qi, Zhaogang; Chen, Jiangping [Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, No. 800, Dongchuan Rd, Shanghai 200240 (China)

2011-01-15

In this paper, the performances of microchannel evaporators with different manifold structures are experimentally investigated. Eight evaporator samples with 7 different designs of the I/O manifold and 5 different designs of the return manifold are made for this study. The performances of the evaporator samples are tested on a psychometric calorimeter test bench with the refrigerant 134A at a real automotive AC condition. The results on the variations of the cooling capacity and air temperature distribution of the evaporator due to the deflector designs in the I/O manifold and flow hole arrangements in the return manifold are presented and analyzed. By studying the KPI's for the performance of an evaporator, the design trade-off for an evaporator designer is summarized and discussed. (author)

A performance evaluation of a microchannel reactor for the production of hydrogen from formic acid for electrochemical energy applications

CSIR Research Space (South Africa)

Ndlovu, IM

2017-12-01

Full Text Available An experimental evaluation of a microchannel reactor was completed to assess the reactor performance for the catalytic decomposition of vaporised formic acid (FA) for H2 production. Initially, X-ray powder diffraction (XRD), elemental mapping using...

Cooling high heat flux micro-electronic systems using refrigerants in high aspect ratio multi-microchannel evaporators

International Nuclear Information System (INIS)

Costa-Patry, E.

2011-11-01

Improving the energy efficiency of cooling systems can contribute to reduce the emission of greenhouse gases. Currently, most microelectronic applications are air-cooled. Switching to two-phase cooling systems would decrease power consumption and allow for the reuse of the extracted heat. For this type of application, multi-microchannel evaporators are thought to be well adapted. However, such devices have not been tested for a wide range of operating conditions, such that their thermal response to the high non-uniform power map typically generated by microelectronics has not been studied. This research project aims at clarifying these gray areas by investigating the behavior of the two-phase flow of different refrigerants in silicon and copper multi-microchannel evaporators under uniform, non-uniform and transient heat fluxes operating conditions. The test elements use as a heat source a pseudo-chip able to mimic the behavior of a CPU. It is formed by 35 independent sub-heaters, each having its own temperature sensor, such that 35 temperature and 35 heat flux measurements can be made simultaneously. Careful measurements of each pressure drop component (inlet, microchannels and outlet) found in the micro-evaporators showed the importance of the inlet and outlet restriction pressure losses. The overall pressure drop levels found in the copper test section were low enough to possibly be driven by a thermosyphon system. The heat transfer coefficients measured for uniform heat flux conditions were very high and typically followed a V-shape curve. The first branch was associated to the slug flow regime and the second to the annular flow regime. By tracking the minimum level of heat transfer, a transition criteria between the regimes was established, which included the effect of heat flux on the transition. Then for each branch, a different prediction method was used to form the first flow pattern-based prediction method for two-phase heat transfer in microchannels. A

Experimental study of gas-liquid flow local characteristics in rectangular microchannel

Directory of Open Access Journals (Sweden)

Bartkus German

2017-01-01

Full Text Available Using high-speed video recording and the method of dual laser scanning the gas-liquid flow was investigated in a rectangular microchannel with an aspect ratio of 0.74 (cross section 269×362 μm. The T-mixer was used at the channel’s inlet for the two-phase flow formation. The peculiarity of this work is using a number of liquids (ethanol, distilled water, 40% aqueous ethanol with different physical properties, including surface tension, viscosity, and density, with nitrogen. Experiments were carried out for the vertically upward and horizontal flow. Using laser scanning method the maps of flow patterns were obtained for all mixtures.

Numerical investigation of non-Newtonian nanofluid flow in a converging microchannel

Energy Technology Data Exchange (ETDEWEB)

Mohsenian, S.; Ramiar, A.; Ranjbar, A. A. [Faculty of Mechanical Engineering, Babol Noshirvani University of Technology, Babol (Iran, Islamic Republic of)

2017-01-15

In the present study the flow of non-Newtonian nanofluid through a converging microchannel is investigated numerically. TiO{sub 2} nanoparticles with 10 nm diameter are dispersed in an aqueous solution of 0.5 %.wt Carboxymethyl cellulose (CMC) to produce the nanofluid. Both nanofluid and the base fluid show pseudoplastic behavior. The equations have been solved with finite volume approach using collocated grid. It has been found that by increasing the volume fraction and Reynolds number and the convergence angle, the Nusselt number increases. Also, it has been observed that by increasing convergence angle and decreasing aspect ratio of the channel, the velocity of the channel increases.

A Neutron Sensitive Microchannel Plate Detector with Cross Delay Line Readout

International Nuclear Information System (INIS)

Berry, Kevin D.; Bilheux, Hassina Z.; Crow, Lowell; Diawara, Yacouba; Feller, W. Bruce; Iverson, Erik B.; Martin, Adrian; Robertson, J. Lee

2012-01-01

Microchannel plates containing neutron absorbing elements such as boron and gadolinium in the bulk glass are used as the sensing element in high spatial resolution, high rate neutron imaging systems. In this paper we describe one such device, using both 10 B and natural Gd, which employs cross delay line signal readout, with time-of-flight capability. This detector has a measured spatial resolution under 40 m FWHM, thermal neutron efficiency of 19%, and has recorded rates in excess of 500 kHz. A physical and functional description is presented, followed by a discussion of measurements of detector performance and a brief survey of some practical applications.

Steam conversion of liquefied petroleum gas and methane in microchannel reactor

Science.gov (United States)

Dimov, S. V.; Gasenko, O. A.; Fokin, M. I.; Kuznetsov, V. V.

2018-03-01

This study presents experimental results of steam conversion of liquefied petroleum gas and methane in annular catalytic reactor - heat exchanger. The steam reforming was done on the Rh/Al2O3 nanocatalyst with the heat applied through the microchannel gap from the outer wall. Concentrations of the products of chemical reactions in the outlet gas mixture are measured at different temperatures of reactor. The range of channel wall temperatures at which the ratio of hydrogen and carbon oxide in the outlet mixture grows substantially is determined. Data on the composition of liquefied petroleum gas conversion products for the ratio S/C = 5 was received for different GHVS.

Flow near the meniscus of a pressure-driven water slug in microchannels

International Nuclear Information System (INIS)

Kim, Sung Wook; Jin, Song Wan; Yoo, Jung Yul

2006-01-01

Micro-PIV system with a high speed CCD camera is used to measure the flow field near the advancing meniscus of a water slug in microchannels. Image shifting technique combined with meniscus detecting technique is proposed to measure the relative velocity of the liquid near the meniscus in a moving reference frame. The proposed method is applied to an advancing front of a slug in microchannels with rectangular cross section. In the case of hydrophilic channel, strong flow from the center to the side wall along the meniscus occurs, while in the case of the hydrophobic channel, the fluid flows in the opposite direction. Further, the velocity near the side wall is higher than the center region velocity, exhibiting the characteristics of a strong shear-driven flow. This phenomenon is explained to be due to the existence of small gaps between the slug and the channel wall at each capillary corner so that the gas flows through the gaps inducing high shear on the slug surface. Simulation of the shape of a static droplet inside a cubic cell obtained by using the Surface Evolver program is supportive of the existence of the gap at the rectangular capillary corners. The flow fields in the circular capillary, in which no such gap exists, are also measured. The results show that a similar flow pattern to that of the hydrophilic rectangular capillary (i.e., center-to-wall flow) is always exhibited regardless of the wettability of the channel wall, which is also indicative of the validity of the above-mentioned assertion

Membrane-based microchannel device for continuous quantitative extraction of dissolved free sulfide from water and from oil.

Science.gov (United States)

Toda, Kei; Ebisu, Yuki; Hirota, Kazutoshi; Ohira, Shin-Ichi

2012-09-05

Underground fluids are important natural sources of drinking water, geothermal energy, and oil-based fuels. To facilitate the surveying of such underground fluids, a novel microchannel extraction device was investigated for in-line continuous analysis and flow injection analysis of sulfide levels in water and in oil. Of the four designs investigated, the honeycomb-patterned microchannel extraction (HMCE) device was found to offer the most effective liquid-liquid extraction. In the HMCE device, a thin silicone membrane was sandwiched between two polydimethylsiloxane plates in which honeycomb-patterned microchannels had been fabricated. The identical patterns on the two plates were accurately aligned. The extracted sulfide was detected by quenching monitoring of fluorescein mercuric acetate (FMA). The sulfide extraction efficiencies from water and oil samples of the HMCE device and of three other designs (two annular and one rectangular channel) were examined theoretically and experimentally. The best performance was obtained with the HMCE device because of its thin sample layer (small diffusion distance) and large interface area. Quantitative extraction from both water and oil could be obtained using the HMCE device. The estimated limit of detection for continuous monitoring was 0.05 μM, and sulfide concentrations in the range of 0.15-10 μM could be determined when the acceptor was 5 μM FMA alkaline solution. The method was applied to natural water analysis using flow injection mode, and the data agreed with those obtained using headspace gas chromatography-flame photometric detection. The analysis of hydrogen sulfide levels in prepared oil samples was also performed. The proposed device is expected to be used for real time survey of oil wells and groundwater wells. Copyright © 2012 Elsevier B.V. All rights reserved.

Atomic layer deposition of alternative glass microchannel plates

Energy Technology Data Exchange (ETDEWEB)

O' Mahony, Aileen, E-mail: aom@incomusa.com; Craven, Christopher A.; Minot, Michael J.; Popecki, Mark A.; Renaud, Joseph M.; Bennis, Daniel C.; Bond, Justin L.; Stochaj, Michael E.; Foley, Michael R.; Adams, Bernhard W. [Incom, Inc., 294 Southbridge Road, Charlton, Massachusetts 01507 (United States); Mane, Anil U.; Elam, Jeffrey W. [Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439 (United States); Ertley, Camden; Siegmund, Oswald H. W. [Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, California 94720 (United States)

2016-01-15

The technique of atomic layer deposition (ALD) has enabled the development of alternative glass microchannel plates (MCPs) with independently tunable resistive and emissive layers, resulting in excellent thickness uniformity across the large area (20 × 20 cm), high aspect ratio (60:1 L/d) glass substrates. Furthermore, the use of ALD to deposit functional layers allows the optimal substrate material to be selected, such as borosilicate glass, which has many benefits compared to the lead-oxide glass used in conventional MCPs, including increased stability and lifetime, low background noise, mechanical robustness, and larger area (at present up to 400 cm{sup 2}). Resistively stable, high gain MCPs are demonstrated due to the deposition of uniform ALD resistive and emissive layers on alternative glass microcapillary substrates. The MCP performance characteristics reported include increased stability and lifetime, low background noise (0.04 events cm{sup −2} s{sup −1}), and low gain variation (±5%)

Numerical Investigation of Effect of Surface Roughness in a Microchannel

Energy Technology Data Exchange (ETDEWEB)

Shin, Myung Seob; Byun, Sung Jun; Yoon, Joon Yong [Hanyang University, Seoul (Korea, Republic of)

2010-05-15

In this paper, lattice Boltzmann method(LBM) results for a laminar flow in a microchannel with rough surface are presented. The surface roughness is modeled as an array of rectangular modules placed on the top and bottom surface of a parallel-plate channel. The effects of relative surface roughness, roughness distribution, and roughness size are presented in terms of the Poiseuille number. The roughness distribution characterized by the ratio of the roughness height to the spacing between the modules has a negligible effect on the flow and friction factors. Finally, a significant increase in the Poiseuille number is observed when the surface roughness is considered, and the effects of roughness on the microflow field mainly depend on the surface roughness.

A micro fuel reformer integrated with a combustor and a microchannel evaporator

Science.gov (United States)

Yoshida, Kazushi; Tanaka, Shuji; Hiraki, Hisashi; Esashi, Masayoshi

2006-09-01

This paper describes the development of a micro fuel reformer integrated with a combustor and an evaporator. Fuel reforming tests were performed by using a mixture of methanol and water as reforming fuel and hydrogen as combustion fuel. It was found that the design of the microchannel evaporator is critical to obtain larger hydrogen output. Hydrogen output and CO concentration were investigated by varying the input combustion power at different fuel feeding rates. 32.9 sccm of hydrogen, which is equivalent to 5.9 W in lower heating value, was produced, when input combustion power was 11 W.

Study of droplet flow in a T-shape microchannel with bottom wall fluctuation

Science.gov (United States)

Pang, Yan; Wang, Xiang; Liu, Zhaomiao

2018-03-01

Droplet generation in a T-shape microchannel, with a main channel width of 50 μm , side channel width of 25 μm, and height of 50 μm, is simulated to study the effects of the forced fluctuation of the bottom wall. The periodic fluctuations of the bottom wall are applied on the near junction part of the main channel in the T-shape microchannel. Effects of bottom wall's shape, fluctuation periods, and amplitudes on the droplet generation are covered in the research of this protocol. In the simulation, the average size is affected a little by the fluctuations, but significantly by the fixed shape of the deformed bottom wall, while the droplet size range is expanded by the fluctuations under most of the conditions. Droplet sizes are distributed in a periodic pattern with small amplitude along the relative time when the fluctuation is forced on the bottom wall near the T-junction, while the droplet emerging frequency is not varied by the fluctuation. The droplet velocity is varied by the bottom wall motion, especially under the shorter period and the larger amplitude. When the fluctuation period is similar to the droplet emerging period, the droplet size is as stable as the non-fluctuation case after a development stage at the beginning of flow, while the droplet velocity is varied by the moving wall with the scope up to 80% of the average velocity under the conditions of this investigation.

Time resolution of Burle 85001 micro-channel plate photo-multipliers in comparison with Hamamatsu R2083

Energy Technology Data Exchange (ETDEWEB)

V. Baturin; V. Burkert; W. Kim; S. Majewsky; D. Nekrasov; K. Park; V. Popov; E. S. Smith; D. Son; S. S. Stepanyan; C. Zorn

2005-06-01

The CLAS detector will require improvements in its particle identification system to take advantage of the higher energies provided by the Jefferson Laboratory accelerator upgrade to 12 GeV. To this end, we have studied the timing characteristics of the micro-channel plate photo-multiplier 85001 from Burle, which can be operated in a high magnetic field environment. For reference and comparison, measurements were also made using the standard PMT R2083 from Hamamatsu using two timing methods. The cosmic ray method, which utilizes three identical scintillating counters 2cm x 3cm x 50cm with PMs at the ends, yields 59.1(0.7)ps. The location method of particles from radiative source with known coordinates has been used to compare timing resolutions of R2083 and Burle-85001. This ''coordinate method'' requires only one counter instrumented with two PMs and it yields 59.5(0.7)ps. For the micro-channel plate photomultiplier from Burle with an external amplification of 10 to the signals, the co ordinate method yields 130(4)ps. This method also makes it possible to estimate the number of primary photo-electrons.

A PLIC-VOF-Based Simulation of Water-Organic Slug Flow Characteristics in a T-Shaped Microchannel

Directory of Open Access Journals (Sweden)

Xian Wang

2013-01-01

Full Text Available A water-organic slug flow in a T-shaped microchannel was numerically studied due to its importance in the microreactor system. Various factors affecting the flow mode were studied, for example, channel width, fluid viscosity, interfacial tension, and inlet velocity. The volume of fluid (VOF method was used to track the liquid-liquid interface, and the piecewise-liner interface construction (PLIC technique was adopted to get a sharp interface. The interfacial tension was simulated with continuum surface force (CSF, model and the wall adhesion boundary condition was taken into consideration. The results show that strong vortexes appear in both phases at the meeting sites of main and lateral channels where an organic slug is producing. Inlet velocity influences the slug length and flow mode greatly. The ratio between the slug lengths of two phases in the main channel is almost equal to the ratio between their inlet velocities. If the slug is produced, the interfacial tension and organic viscosity have less effect on the slug length for 200 μm microchannel. The slug producing rate is much higher in a narrow channel than that in a wide channel.

Pressure drop and heat transfer characteristics for single-phase developing flow of water in rectangular microchannels

International Nuclear Information System (INIS)

Mirmanto; Kenning, D B R; Lewis, J S; Karayiannis, T G

2012-01-01

Experiments were conducted to investigate the pressure drop and heat transfer characteristics of single-phase flow of de-ionized water in single copper microchannels of hydraulic diameters 0.438 mm, 0.561 mm and 0.635 mm. The channel length was 62 mm. The experimental conditions covered a range of mass flux from 500 to 5000 kg/m 2 s in the laminar, transitional and low Reynolds number turbulent regimes. Pressure drop was measured for adiabatic flows with fluid inlet temperatures of 30°C, 60°C and 90°C. In the heat transfer tests, the heat flux ranged from 256 kW/m 2 to 519 kW/m 2 . Friction factors and Nusselt numbers determined from the measurements were higher than for fully-developed conditions, but in reasonable agreement with predictions made using published solutions for hydrodynamically and thermally developing flow. When entrance effects, experimental uncertainties, heat losses, inlet and exit losses, thermal boundary conditions and departure from laminar flow were considered, the results indicate that equations developed for flow and heat transfer in conventional size channels are applicable for water flows in microchannels of these sizes.

Preconcentration and Separation of Mixed-Species Samples Near a Nano-Junction in a Convergent Microchannel

Directory of Open Access Journals (Sweden)

Ping-Hsien Chiu

2015-12-01

Full Text Available A fluidic microchip incorporating a convergent microchannel and a Nafion-nanoporous membrane is proposed for the preconcentration and separation of multi-species samples on a single platform. In the device, sample preconcentration is achieved by means of the ion concentration polarization effect induced at the micro/nano interface under the application of an external electric field, while species separation is achieved by exploiting the different electrophoretic mobilities of the sample components. The experimental results show that the device is capable of detecting C-reactive protein (CRP with an initial concentration as low as 9.50 × 10−6 mg/L given a sufficient preconcentration time and driving voltage. In addition, it is shown that a mixed-species sample consisting of three negatively-charged components (bovine serum albumin (BSA, tetramethylrhodamine(TAMRA isothiocyanate-Dextran and fluorescent polymer beads can be separated and preconcentrated within 20 min given a driving voltage of 100 V across 1 cm microchannel in length. In general, the present results confirm the feasibility of the device for the immunoassay or detection of various multi-species samples under low concentration in the biochemical and biomedical fields. The novel device can therefore improve the detection limit of traditional medical facilities.

The Viability of Single Cancer Cells after Exposure to Hydrodynamic Shear Stresses in a Spiral Microchannel: A Canine Cutaneous Mast Cell Tumor Model

Directory of Open Access Journals (Sweden)

Dettachai Ketpun

2017-12-01

Full Text Available Our laboratory has the fundamental responsibility to study cancer stem cells (CSC in various models of human and animal neoplasms. However, the major impediments that spike our accomplishment are the lack of universal biomarkers and cellular heterogeneity. To cope with these restrictions, we have tried to apply the concept of single cell analysis, which has hitherto been recommended throughout the world as an imperative solution pack for resolving such dilemmas. Accordingly, our first step was to utilize a predesigned spiral microchannel fabricated by our laboratory to perform size-based single cell separation using mast cell tumor (MCT cells as a model. However, the impact of hydrodynamic shear stresses (HSS on mechanical cell injury and viability in a spiral microchannel has not been fully investigated so far. Intuitively, our computational fluid dynamics (CFD simulation has strongly revealed the formations of fluid shear stress (FSS and extensional fluid stress (EFS in the sorting system. The panel of biomedical assays has also disclosed cell degeneration and necrosis in the model. Therefore, we have herein reported the combinatorically detrimental effect of FSS and EFS on the viability of MCT cells after sorting in our spiral microchannel, with discussion on the possibly pathogenic mechanisms of HSS-induced cell injury in the study model.

Features of two-phase flow patterns in horizontal rectangular microchannels of height 50 μm

Directory of Open Access Journals (Sweden)

Ron’shin Fedor

2016-01-01

Full Text Available The horizontal microchannel with the height of 50 micrometres and width of 40 mm of a rectangular cross-section has been used to study two-phase flow. The classical patterns of two-phase flow in the channel (bubble, stratified, churn, jet, and annular have been detected. Experimental information allows us to define the characteristics of the regimes and to determine precisely the boundaries between the patterns of the two-phase flows.

The size and spatial distribution of microchannel plate output electron clouds

International Nuclear Information System (INIS)

Lapington, J.S.; Edgar, M.L.

1989-01-01

An experimental technique for measuring the spatial distribution of the output charge cloud from a microchannel plate (MCP), using a planar, charge-division-type anode is discussed. The anode simultaneously measures, for each charge cloud, both the position of the charge centroid and the fractional charge falling to one side of the split in the pattern. The measurements from several thousand events have been combined to calculate the average spatial distribution of the electron cloud and the dominant factors influencing the charge cloud distribution have been found to be the MCP gain and the MCP-anode accelerating field and geometry. Experimental research on the two dominant factors with respect to ranges of distribution is presented. 10 refs

Calculation of Friction Coefficient and Analysis of Fluid Flow in a Stepped Micro-Channel for Wide Range of Knudsen Number Using Lattice Boltzmann (MRT Method

Directory of Open Access Journals (Sweden)

Y. Bakhshan

2015-01-01

Full Text Available Micro scale gas flows has attracted significant research interest in the last two decades. In this research, the fluid flow of gases in the stepped micro-channel at a wide range of Knudsen number has been analyzed with using the Lattice Boltzmann (MRT method. In the model, a modified second-order slip boundary condition and a Bosanquet-type effective viscosity are used to consider the velocity slip at the boundaries and to cover the slip and transition regimes of flow and to gain an accurate simulation of rarefied gases. It includes the slip and transition regimes of flow. The flow specifications such as pressure loss, velocity profile, streamline and friction coefficient at different conditions have been presented. The results show good agreement with available experimental data. The calculation shows that the friction coefficient decreases with increasing the Knudsen number and stepping the micro-channel has an inverse effect on the friction coefficient. Furthermore, a new correlation is suggested for calculation of the friction coefficient in the stepped micro-channel as below: C_f Re  = 3.113+2.915/(1 +2 Kn+ 0.641 exp⁡(3.203/(1 + 2 Kn

Flow map and measurement of void fraction and heat transfer coefficient using an image analysis technique for flow boiling of water in a silicon microchannel

International Nuclear Information System (INIS)

Singh, S G; Duttagupta, S P; Jain, A; Sridharan, A; Agrawal, Amit

2009-01-01

The present work focuses on the generation of the flow regime map for two-phase water flow in microchannels of a hydraulic diameter of 140 µm. An image analysis algorithm has been developed and utilized to obtain the local void fraction. The image processing technique is also employed to identify and estimate the percentage of different flow regimes and heat transfer coefficient, as a function of position, heat flux and mass flow rate. Both void fraction and heat transfer coefficient are found to increase monotonically along the length of the microchannel. At low heat flux and low flow rates, bubbly, slug and annular flow regimes are apparent. However, the flow is predominately annular at high heat flux and high flow rate. A breakup of the flow frequency suggests that the flow is bistable in the annular regime, in that at a fixed location, the flow periodically switches from single-phase liquid to annular and vice versa. Otherwise, the occurrence of three regimes—single-phase liquid, bubbly and slug are observed. These results provide several useful insights about two-phase flow in microchannels besides being of fundamental interest

Resolving Overlimiting Current Mechanisms in Microchannel-Nanochannel Interface Devices

Science.gov (United States)

Yossifon, Gilad; Leibowitz, Neta; Liel, Uri; Schiffbauer, Jarrod; Park, Sinwook

2015-11-01

We present results demonstrating the space charge-mediated transition between classical, diffusion-limited current and surface-conduction dominant over-limiting currents in a shallow micro-nanochannel device. The extended space charge layer develops at the depleted micro-nanochannel entrance at high current and is correlated with a distinctive maximum in the dc resistance. Experimental results for a shallow surface-conduction dominated system are compared with theoretical models, allowing estimates of the effective surface charge at high voltage to be obtained. Further, we extend the study to microchannels of moderate to large depths where the role of various electro-convection mechanisms becomes dominant. In particular, electro-osmotic of the second kind and electro-osmotic instability (EOI) which competes each other at geometrically heterogeneous (e.g. undulated nanoslot interface, array of nanoslots) nanoslot devices. Also, these effects are also shown to be strongly modulated by the non-ideal permselectivity of the nanochannel.

Multiple-photon disambiguation on stripline-anode Micro-Channel Plates

Energy Technology Data Exchange (ETDEWEB)

Jocher, Glenn R., E-mail: glenn.jocher@ultralytics.com [Ultralytics LLC, Arlington, VA 22203 (United States); Wetstein, Matthew J., E-mail: mwetstein@uchicago.edu [Iowa State University, Department of Physics and Astronomy, 12 Physics Hall, Ames, IA 50011 (United States); Adams, Bernhard, E-mail: badams@incomusa.com [Incom, Inc., 294 Southbridge Road, Charlton, MA 01507 (United States); Nishimura, Kurtis, E-mail: kurtis.nishimura@ultralytics.com [Ultralytics LLC, Arlington, VA 22203 (United States); Usman, Shawn M., E-mail: shawn.usman@nga.mil [Research Directorate, National Geospatial-Intelligence Agency, 7500 GEOINT Dr., Springfield, VA 22150 (United States); Department of Geography and Geoinformation Science, George Mason University, Fairfax, VA 22030 (United States)

2016-06-21

Large-Area Picosecond Photo-Detectors (LAPPDs) show great potential for expanding the performance envelope of Micro-Channel Plates (MCPs) to areas of up to 20×20 cm and larger. Such scaling introduces new challenges, including how to meet the electronics readout burden of ever larger area MCPs. One solution is to replace the traditional grid anode used for readout with a microwave stripline anode, thus allowing the channel count to scale with MCP width rather than area. However, stripline anodes introduce new issues not commonly dealt with in grid-anodes, especially as their length increases. One of these issues is the near simultaneous arrival of multiple photons on the detector, creating possible confusion about how to reconstruct their arrival times and positions. We propose a maximum a posteriori solution to the problem and verify its performance in simulated scintillator and water-Cherenkov detectors.

Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels

DEFF Research Database (Denmark)

Lafmejani, Saeed Sadeghi; Olesen, Anders Christian; Kær, Søren Knudsen

2016-01-01

and are fairly expensive. One means of increasing the hydrogen yield to cost ratio of such systems, is to increase the operating current density. However, at high current densities, management of heat and mass transfer in the anode current collector and channel becomes crucial. This entails that further...... understanding of the gas-liquid flow in both the porous media and the channel is necessary for insuring proper oxygen, water and heat management of the electrolysis cell. In this work, the patterns of vertical upward gas-liquid flow in a 5×1×94 mm micro-channel are experimentally analysed. A sheet of titanium...... felt is used as a permeable wall for permeation of air through a column of water similar to the phenomenon encountered at the anode. The transparent setup is operated ex-situ and the gas-liquid flow regimes are identified using a camera....

Hybrid method coupling molecular dynamics and Monte Carlo simulations to study the properties of gases in microchannels and nanochannels

NARCIS (Netherlands)

Nedea, S.V.; Frijns, A.J.H.; Steenhoven, van A.A.; Markvoort, Albert. J.; Hilbers, P.A.J.

2005-01-01

We combine molecular dynamics (MD) and Monte Carlo (MC) simulations to study the properties of gas molecules confined between two hard walls of a microchannel or nanochannel. The coupling between MD and MC simulations is introduced by performing MD near the boundaries for accuracy and MC in the bulk

Numerical study on the heat transfer performance of non-Newtonian fluid flow in a manifold microchannel heat sink

International Nuclear Information System (INIS)

Li, Si-Ning; Zhang, Hong-Na; Li, Xiao-Bin; Li, Qian; Li, Feng-Chen; Qian, Shizhi; Joo, Sang Woo

2017-01-01

Highlights: • Heat transfer performance of non-Newtonian fluid flow in a MHS is studied. • Pseudo-plastic fluid flow can clearly promote the heat transfer efficiency in MMC. • Heat transfer enhancement is attributed to the emergence of secondary flow. • The heat transfer uniformity can also be improved by pseudo-plastic fluid flow. - Abstract: As the miniaturization and integration become the leading trend of the micro-electro-mechanical systems, it is of great significance to improve the microscaled heat transfer performance. This paper presents a three-dimensional (3D) numerical simulation on the flow characteristics and heat transfer performance of non-Newtonian fluid flow in a manifold microchannel (MMC) heat sink and traditional microchannel (TMC) heat sink. The non-Newtonian fluid was described by the power-law model. The analyses concentrated on the non-Newtonian fluid effect on the heat transfer performance, including the heat transfer efficiency and uniformity of temperature distribution, as well as the influence of inlet/outlet configurations on fluid flow and heat transfer. Comparing with Newtonian fluid flow, pseudo-plastic fluid could reduce the drag resistance in both MMC and TMC, while the dilatant fluid brought in quite larger drag resistance. For the heat transfer performance, the introduction of pseudo-plastic fluid flow greatly improved the heat transfer efficiency owing to the generation of secondary flow due to the shear-thinning property. Besides, the temperature distribution in MMC was more uniform by using pseudo-plastic fluid. Moreover, the inlet/outlet configuration was also important for the design and arrangement of microchannel heat sinks, since the present work showed that the maximum temperature was prone to locating in the corners near the inlet and outlet. This work provides guidance for optimal design of small-scale heat transfer devices in many cooling applications, such as biomedical chips, electronic systems, and

Ordering at Si(111)/o-Si and Si(111)/SiO2 Interfaces

DEFF Research Database (Denmark)

Robinson, I. K.; Waskiewicz, W. K.; Tung, R. T.

1986-01-01

X-ray diffraction has been used to measure the intensity profile of the two-dimensional rods of scattering from a single interface buried inside a bulk material. In both Si(111)/a-Si and Si(111)/SiO2 examples there are features in the perpendicular-momentum-transfer dependence which are not expec...... are not expected from an ideal sharp interface. The diffraction profiles are explained by models with partially ordered layers extending into the amorphous region. In the Si(111)/a-Si case there is clear evidence of stacking faults which are attributed to residual 7×7 reconstruction....

Fabrication of polyester microchannel with functional surface for electro-chromatography - Incorporation of detection devices into the microchip -

International Nuclear Information System (INIS)

Uchiyama, Katsumi; Qiu, Jing Miao; Hobo, Toshiyuki

2001-01-01

In recent years, new analytical techniques using microchip devise have been extensively studied (micro-TAS). One of the most successful examples is capillary electrophoresis (CE) with glass plate fabricated by photolithography followed by the chemical or physical etching process. Micro CE one of the most excellent separation techniques, performs separations in microchannel formed in appreciate substrate material. We developed a fabrication method for polyester micro channels with aikene alcohol inside the wall of the channel and demonstrated the usefulness of the polymer microchip. Although many researchers have been studying microchannel or micro-devices for analytical use, miniaturization of the total system including sample introduction, separation, detection and data treatment is still under development. Especially, the miniaturization of the detection system will be a hard bar to be overcome. Our method, based upon the in situ polymerization of polyester resin on an appreciate template, can be exported to let some parts incorporated directly into the microchip during the polymerization process. In this paper, we will describe the incorporation of detection components (light emitting diode and optical fiber) into polyester microchip and the application of the microchip to the analysis of amino acids separated by electrophoresis.

Microchannel plate special nuclear materials sensor

International Nuclear Information System (INIS)

Feller, W.B.; White, P.L.; White, P.B.; Siegmund, O.H.W.; Martin, A.P.; Vallerga, J.V.

2011-01-01

Nova Scientific Inc., is developing for the Domestic Nuclear Detection Office (DNDO SBIR no. HSHQDC-08-C-00190), a solid-state, high-efficiency neutron detection alternative to 3 He gas tubes, using neutron-sensitive microchannel plates (MCPs) containing 10 B and/or Gd. This work directly supports DNDO development of technologies designed to detect and interdict nuclear weapons or illicit nuclear materials. Neutron-sensitized MCPs have been shown theoretically and more recently experimentally, to be capable of thermal neutron detection efficiencies equivalent to 3 He gas tubes. Although typical solid-state neutron detectors typically have an intrinsic gamma sensitivity orders of magnitude higher than that of 3 He gas detectors, we dramatically reduce gamma sensitivity by combining a novel electronic coincidence rejection scheme, employing a separate but enveloping gamma scintillator. This has already resulted in a measured gamma rejection ratio equal to a small 3 He tube, without in principle sacrificing neutron detection efficiency. Ongoing improvements to the MCP performance as well as the coincidence counting geometry will be described. Repeated testing and validation with a 252 Cf source has been underway throughout the Phase II SBIR program, with ongoing comparisons to a small commercial 3 He gas tube. Finally, further component improvements and efforts toward integration maturity are underway, with the goal of establishing functional prototypes for SNM field testing.

Numerical study of acoustophoretic motion of particles in a PDMS microchannel driven by surface acoustic waves.

Science.gov (United States)

Nama, Nitesh; Barnkob, Rune; Mao, Zhangming; Kähler, Christian J; Costanzo, Francesco; Huang, Tony Jun

2015-06-21

We present a numerical study of the acoustophoretic motion of particles suspended in a liquid-filled PDMS microchannel on a lithium niobate substrate acoustically driven by surface acoustic waves. We employ a perturbation approach where the flow variables are divided into first- and second-order fields. We use impedance boundary conditions to model the PDMS microchannel walls and we model the acoustic actuation by a displacement function from the literature based on a numerical study of piezoelectric actuation. Consistent with the type of actuation, the obtained first-order field is a horizontal standing wave that travels vertically from the actuated wall towards the upper PDMS wall. This is in contrast to what is observed in bulk acoustic wave devices. The first-order fields drive the acoustic streaming, as well as the time-averaged acoustic radiation force acting on suspended particles. We analyze the motion of suspended particles driven by the acoustic streaming drag and the radiation force. We examine a range of particle diameters to demonstrate the transition from streaming-drag-dominated acoustophoresis to radiation-force-dominated acoustophoresis. Finally, as an application of our numerical model, we demonstrate the capability to tune the position of the vertical pressure node along the channel width by tuning the phase difference between two incoming surface acoustic waves.

Electrokinetic Flow in Microchannels with Finite Reservoir Size Effects

International Nuclear Information System (INIS)

Yan, D; Yang, C; Nguyen, N-T; Huang, X

2006-01-01

In electrokinetically-driven microfluidic applications, reservoirs are indispensable and have finite sizes. During operation processes, as the liquid level difference in reservoirs keeps changing as time elapses, the flow characteristics in a microchannel exhibit a combination of the electroosmotic flow and the time-dependent induced backpressure-driven flow. In this work, an assessment of the finite reservoir size effect on electroosmotic flows is presented theoretically and experimentally. A model is developed to describe the timedependent electrokinetic flow with finite reservoir size effects. The theoretical analysis shows that under certain conditions the finite reservoir size effect is significant. The important parameters that describe the effect of finite reservoir size on the flow characteristics are discussed. A new concept denoted as 'effective pumping period' is introduced to characterize the reservoir size effect. The proposed model clearly identifies the mechanisms of the finitereservoir size effects and is further confirmed by using micro-PIV technique. The results of this study can be used for facilitating the design of microfluidic devices

Study of Si/Si, Si/SiO2, and metal-oxide-semiconductor (MOS) using positrons

International Nuclear Information System (INIS)

Leung, To Chi.

1991-01-01

A variable-energy positron beam is used to study Si/Si, Si/SiO 2 , and metal-oxide-semiconductor (MOS) structures. The capability of depth resolution and the remarkable sensitivity to defects have made the positron annihilation technique a unique tool in detecting open-volume defects in the newly innovated low temperature (300C) molecular-beam-epitaxy (MBE) Si/Si. These two features of the positron beam have further shown its potential role in the study of the Si/SiO 2 . Distinct annihilation characteristics has been observed at the interface and has been studied as a function of the sample growth conditions, annealing (in vacuum), and hydrogen exposure. The MOS structure provides an effective way to study the electrical properties of the Si/SiO 2 interface as a function of applied bias voltage. The annihilation characteristics show a large change as the device condition is changed from accumulation to inversion. The effect of forming gas (FG) anneal is studied using positron annihilation and the result is compared with capacitance-voltage (C-V) measurements. The reduction in the number of interface states is found correlated with the changes in the positron spectra. The present study shows the importance of the positron annihilation technique as a non-contact, non-destructive, and depth-sensitive characterization tool to study the Si-related systems, in particular, the Si/SiO 2 interface which is of crucial importance in semiconductor technology, and fundamental understanding of the defects responsible for degradation of the electrical properties

Measurement of liquid film in microchannels using a laser focus displacement meter

Science.gov (United States)

Hazuku, Tatsuya; Fukamachi, Norihiro; Takamasa, Tomoji; Hibiki, Takashi; Ishii, Mamoru

2005-06-01

This paper presents a new method for measuring the interfacial displacement of a liquid film in microchannels using a laser focus displacement meter (LFD). The purpose of the study is to clarify the effectiveness of the new method for obtaining detailed information concerning interfacial displacement, especially in the case of a thin liquid film, in microchannels and minichannels. To prevent the tube wall signal from disturbing that of the gas liquid interface, a fluorocarbon tube with a water box was used; the refraction index of this device is the same as that for water. With this method, accurate instantaneous measurements of the interfacial displacement of the liquid film were achieved. The error caused by refraction of the laser beam passing through the acrylic water box and fluorocarbon tube was estimated analytically and experimentally. The formulated analytical equation can estimate the real interface displacement by using the measured displacement in a fluorocarbon tube of 25 μm to 2.0 mm I.D. A preliminary test using fluorocarbon tubes of 1 mm and 2 mm I.D. showed that the corrected interface displacement calculated by the equation agreed with the real displacement to within a 1% margin of error. It was also confirmed that the LFD in the system could measure a liquid film of 0.25 μm at the thinnest. We made simultaneous measurements of the interface in fluorocarbon tubes of 0.5 mm and 1 mm I.D. using the LFD and a high-speed video camera with a microscope. These showed that the LFD could measure the interface of a liquid film with high spatial and temporal resolution during annular, slug, and piston flow regimes. The data also clarified the existence of a thin liquid film of less than 1 μm in thickness in the slug and annular flow regimes.

Measurement of liquid film in microchannels using a laser focus displacement meter

Energy Technology Data Exchange (ETDEWEB)

Hazuku, Tatsuya; Fukamachi, Norihiro; Takamasa, Tomoji [Tokyo University of Marine Science and Technology, Faculty of Marine Technology, Etchujima, Koto, Tokyo (Japan); Hibiki, Takashi [Kyoto University, Research Reactor Institute, Kumatori, Sennan, Osaka (Japan); Ishii, Mamoru [Purdue University, School of Nuclear Engineering, West Lafayette, IN (United States)

2005-06-01

This paper presents a new method for measuring the interfacial displacement of a liquid film in microchannels using a laser focus displacement meter (LFD). The purpose of the study is to clarify the effectiveness of the new method for obtaining detailed information concerning interfacial displacement, especially in the case of a thin liquid film, in microchannels and minichannels. To prevent the tube wall signal from disturbing that of the gas-liquid interface, a fluorocarbon tube with a water box was used; the refraction index of this device is the same as that for water. With this method, accurate instantaneous measurements of the interfacial displacement of the liquid film were achieved. The error caused by refraction of the laser beam passing through the acrylic water box and fluorocarbon tube was estimated analytically and experimentally. The formulated analytical equation can estimate the real interface displacement by using the measured displacement in a fluorocarbon tube of 25 {mu}m to 2.0 mm I.D. A preliminary test using fluorocarbon tubes of 1 mm and 2 mm I.D. showed that the corrected interface displacement calculated by the equation agreed with the real displacement to within a 1% margin of error. It was also confirmed that the LFD in the system could measure a liquid film of 0.25 {mu}m at the thinnest. We made simultaneous measurements of the interface in fluorocarbon tubes of 0.5 mm and 1 mm I.D. using the LFD and a high-speed video camera with a microscope. These showed that the LFD could measure the interface of a liquid film with high spatial and temporal resolution during annular, slug, and piston flow regimes. The data also clarified the existence of a thin liquid film of less than 1 {mu}m in thickness in the slug and annular flow regimes. (orig.)

Single phase flow pressure drop and heat transfer in rectangular metallic microchannels

International Nuclear Information System (INIS)

Sahar, Amirah M.; Özdemir, Mehmed R.; Fayyadh, Ekhlas M.; Wissink, Jan; Mahmoud, Mohamed M.; Karayiannis, Tassos G.

2016-01-01

Numerical simulations were performed using Fluent 14.5 to investigate single phase flow and conjugate heat transfer in copper rectangular microchannels. Two different configurations were simulated: (1) single channel with hydraulic diameter of 0.561 mm and (2) multichannel configuration consisting of inlet and outlet manifolds and 25 channels with hydraulic diameter of 0.409 mm. In the single channel configuration, four numerical models were investigated namely, 2D thin-wall, 3D thin-wall (heated from the bottom), 3D thin-wall (three side heated) and 3D full conjugate models. In the multichannel configuration, only 3D full conjugate model was used. The simulation results of the single channel configuration were validated using experimental data of water as a test fluid while the results of the multichannel configuration were validated using experimental data of R134a refrigerant. In the multichannel configuration, flow distribution among the channels was also investigated. The 3D thin-wall model simulation was conducted at thermal boundary conditions similar to those assumed in the experimental data reduction (uniform heat flux) and showed excellent agreement with the experimental data. However, the results of the 3D full conjugate model demonstrated that there is a significant conjugate effect and the heat flux is not uniformly distributed along the channel resulting in significant deviation compared to the experimental data (more than 50%). Also, the results demonstrated that there is a significant difference between the 3D thin-wall and full conjugate models. The simulation of the multichannel configuration with an inlet manifold having gradual decrease in cross sectional area achieved very reasonable uniform flow distribution among the channels which will provide uniform heat transfer rates across the base of the microchannels.

Improved understanding of the acoustophoretic focusing of dense suspensions in a microchannel

Science.gov (United States)

Karthick, S.; Sen, A. K.

2017-11-01

We provide improved understanding of acoustophoretic focusing of a dense suspension (volume fraction φ >10 % ) in a microchannel subjected to an acoustic standing wave using a proposed theoretical model and experiments. The model is based on the theory of interacting continua and utilizes a momentum transport equation for the mixture, continuity equation, and transport equation for the solid phase. The model demonstrates the interplay between acoustic radiation and shear-induced diffusion (SID) forces that is critical in the focusing of dense suspensions. The shear-induced particle migration model of Leighton and Acrivos, coupled with the acoustic radiation force, is employed to simulate the continuum behavior of particles. In the literature, various closures for the diffusion coefficient Dφ* are available for rigid spheres at high concentrations and nonspherical deformable particles [e.g., red blood cells (RBCs)] at low concentrations. Here we propose a closure for Dφ* for dense suspension of RBCs and validate the proposed model with experimental data. While the available closures for Dφ* fail to predict the acoustic focusing of a dense suspension of nonspherical deformable particles like RBCs, the predictions of the proposed model match experimental data within 15%. Both the model and experiments reveal a competition between acoustic radiation and SID forces that gives rise to an equilibrium width w* of a focused stream of particles at some distance Leq* along the flow direction. Using different shear rates, acoustic energy densities, and particle concentrations, we show that the equilibrium width is governed by Péclet number Pe and Strouhal number Stas w*=1.4(PeSt) -0.5 while the length required to obtain the equilibrium-focused width depends on St as Leq*=3.8 /(St)0.6 . The proposed model and correlations would find significance in the design of microchannels for acoustic focusing of dense suspensions such as undiluted blood.

Photoluminescence of Er-doped Si-SiO2 and Al-Si-SiO2 sputtered thin films

International Nuclear Information System (INIS)

Rozo, C.; Fonseca, L.F.; Jaque, D.; Sole, J.Garcia

2008-01-01

Er-doped Si-SiO 2 and Al-Si-SiO 2 films have been deposited by rf-sputtering being annealed afterwards. Annealing behavior of the Er 3+ : 4 I 13/2 → 4 I 15/2 emission of Er-doped Si-SiO 2 yields a maximum intensity for annealing at 700-800 deg. C. 4 I 13/2 → 4 I 15/2 peak emission for Er-doped Al-Si-SiO 2 at 1525 nm is shifted from that for Er-doped Si-SiO 2 at 1530 nm and the bandwidth increases from 29 to 42 nm. 4 I 13/2 → 4 I 15/2 emission decays present a fast decaying component related to Er ions coupled to Si nanoparticles, defects, or other ions, and a slow decaying component related to isolated Er ions. Excitation wavelength dependence and excitation power dependence for the 4 I 13/2 → 4 I 15/2 emission correspond with energy transfer from Si nanoparticles. Populating of the 4 I 11/2 level in Er-doped Si-SiO 2 involves branching and energy transfer upconversion involving two or more Er ions. Addition of Al reduces the populating of this level to an energy transfer upconversion involving two ions

Experimental Study of Evaporative Heat Transfer Characteristics of R-134a with Channel-Bending Angle in Microchannel Heat Exchangers

International Nuclear Information System (INIS)

Lee, Hae Seung; Jeon, Dong Soon; Kim, Young Lyoul; Kim, Seon Chang

2010-01-01

Experimental investigations have been carried out to examine the evaporative heat transfer characteristics of R-134a with the channel-bending angle (CBA) in microchannel heat exchangers. In this study, we examined the effects of evaporation temperature and Reynolds number of R-134a on the evaporative heat transfer characteristics of R-134a in microchannel heat exchangers with CBAs of 120 .deg. , 150 .deg. , and 180 .deg. under counterflow conditions. Experimental results show that the evaporative heat transfer rate and evaporative heat transfer coefficient increased with an increase in the Reynolds number of R-134a. Further, the evaporative heat transfer rate corresponding to CBAs of 120 .deg. and 150 .deg. increased to values greater than the evaporative heat transfer rate corresponding to 180 .deg. by approximately 17.1% and 13.3%, respectively, for evaporating temperatures in the range 4.9-14.9 .deg. C. The evaporative heat transfer coefficient was affected by the channel angle with increasing evaporative heat transfer coefficient at small channel bending angle

Chaos analysis of viscoelastic chaotic flows of polymeric fluids in a micro-channel

Energy Technology Data Exchange (ETDEWEB)

Lim, C. P.; Lam, Y. C., E-mail: myclam@ntu.edu.sg [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 639798 (Singapore); BioSystems and Micromechanics (BioSyM) IRG, Singapore-MIT Alliance for Research and Technology (SMART) Centre, 138602 (Singapore); Han, J. [BioSystems and Micromechanics (BioSyM) IRG, Singapore-MIT Alliance for Research and Technology (SMART) Centre, 138602 (Singapore); Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2015-07-15

Many fluids, including biological fluids such as mucus and blood, are viscoelastic. Through the introduction of chaotic flows in a micro-channel and the construction of maps of characteristic chaos parameters, differences in viscoelastic properties of these fluids can be measured. This is demonstrated by creating viscoelastic chaotic flows induced in an H-shaped micro-channel through the steady infusion of a polymeric fluid of polyethylene oxide (PEO) and another immiscible fluid (silicone oil). A protocol for chaos analysis was established and demonstrated for the analysis of the chaotic flows generated by two polymeric fluids of different molecular weight but with similar relaxation times. The flows were shown to be chaotic through the computation of their correlation dimension (D{sub 2}) and the largest Lyapunov exponent (λ{sub 1}), with D{sub 2} being fractional and λ{sub 1} being positive. Contour maps of D{sub 2} and λ{sub 1} of the respective fluids in the operating space, which is defined by the combination of polymeric fluids and silicone oil flow rates, were constructed to represent the characteristic of the chaotic flows generated. It was observed that, albeit being similar, the fluids have generally distinct characteristic maps with some similar trends. The differences in the D{sub 2} and λ{sub 1} maps are indicative of the difference in the molecular weight of the polymers in the fluids because the driving force of the viscoelastic chaotic flows is of molecular origin. This approach in constructing the characteristic maps of chaos parameters can be employed as a diagnostic tool for biological fluids and, more generally, chaotic signals.

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

International Nuclear Information System (INIS)

Jiang, Xiaofan; Ma, Zhongyuan; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

2014-01-01

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN x /SiN y multilayers with high on/off ratio of 10 9 . High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

Science.gov (United States)

Jiang, Xiaofan; Ma, Zhongyuan; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

2014-09-01

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiNx/SiNy multilayers with high on/off ratio of 109. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

Development of a Microchannel High Temperature Recuperator for Fuel Cell Systems

Energy Technology Data Exchange (ETDEWEB)

Lukas, Michael [Fuelcell Energy, Inc., Danbury, CT (United States)

2014-03-24

This report summarizes the progress made in development of microchannel recuperators for high temperature fuel cell/turbine hybrid systems for generation of clean power at very high efficiencies. Both Solid Oxide Fuel Cell/Turbine (SOFC/T) and Direct FuelCell/Turbine (DFC/T) systems employ an indirectly heated Turbine Generator to supplement fuel cell generated power. The concept extends the high efficiency of the fuel cell by utilizing the fuel cell’s byproduct heat in a Brayton cycle. Features of the SOFC/T and DFC/T systems include: electrical efficiencies of up to 65% on natural gas, minimal emissions, reduced carbon dioxide release to the environment, simplicity in design, and potential cost competitiveness with existing combined cycle power plants. Project work consisted of candidate material selection from FuelCell Energy (FCE) and Pacific Northwest National Laboratory (PNNL) institutional databases as well as from industrial and academic literature. Candidate materials were then downselected and actual samples were tested under representative environmental conditions resulting in further downselection. A microchannel thermal-mechanical model was developed to calculate overall device cost to be later used in developing a final Tier 1 material candidate list. Specifications and operating conditions were developed for both SOFC/T and DFC/T systems. This development included system conceptualization and progression to process flow diagrams (PFD’s) including all major equipment. Material and energy balances were then developed for the two types of systems which were then used for extensive sensitivity studies that used high temperature recuperator (HTR) design parameters (e.g., operating temperature) as inputs and calculated overall system parameters (e.g., system efficiency). The results of the sensitivity studies determined the final HTR design temperatures, pressure drops, and gas compositions. The results also established operating conditions and

Microchannel plate detector technology potential for LUVOIR and HabEx

Science.gov (United States)

Siegmund, O. H. W.; Ertley, C.; Vallerga, J. V.; Schindhelm, E. R.; Harwit, A.; Fleming, B. T.; France, K. C.; Green, J. C.; McCandliss, S. R.; Harris, W. M.

2017-08-01

Microchannel plate (MCP) detectors have been the detector of choice for ultraviolet (UV) instruments onboard many NASA missions. These detectors have many advantages, including high spatial resolution (hardness, large formats (up to 20 cm), and ability for curved focal plane matching. Novel borosilicate glass MCPs with atomic layer deposition combine extremely low backgrounds, high strength, and tunable secondary electron yield. GaN and combinations of bialkali/alkali halide photocathodes show promise for broadband, higher quantum efficiency. Cross-strip anodes combined with compact ASIC readout electronics enable high spatial resolution over large formats with high dynamic range. The technology readiness levels of these technologies are each being advanced through research grants for laboratory testing and rocket flights. Combining these capabilities would be ideal for UV instruments onboard the Large UV/Optical/IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission (HABEX) concepts currently under study for NASA's Astrophysics Decadal Survey.

Micro-channel plate detector for ultra-fast relativistic electron diffraction

International Nuclear Information System (INIS)

Musumeci, P.; Moody, J.T.; Scoby, C.M.; Gutierrez, M.S.; Bender, H.A.; Hilko, B.; Kruschwitz, C.A.; Wilcox, N.S.

2011-01-01

Using relativistic ultra-short electron beams to obtain single-shot diffraction patterns holds the promise to yield real-time resolution of atomic motion in an easily accessible environment, such as a university laboratory, at a fraction of the cost of fourth-generation X-ray sources. One of the main issues in bringing this technique to full maturity is the development of efficient detector systems to record the diffraction pattern using a few MeV electron beams. Low noise, high spatial resolution, and single-electron detection capability are all characteristics of an ideal detector. In this paper, we compare the performances of a traditional fluorescent phosphor screen with a detection system based on the micro-channel plate (MCP). Since MCPs are typically used with lower energy electron beams, these tests constitute one of the few experimental data points available on the use of these devices with MeV energy beams.

Micro-channel plate detector for ultra-fast relativistic electron diffraction

Energy Technology Data Exchange (ETDEWEB)

Musumeci, P., E-mail: musumeci@physics.ucla.edu [UCLA Department of Physics and Astronomy, 475 Portola Plaza, Los Angeles, CA, 90095-1547 (United States); Moody, J.T.; Scoby, C.M.; Gutierrez, M.S. [UCLA Department of Physics and Astronomy, 475 Portola Plaza, Los Angeles, CA, 90095-1547 (United States); Bender, H.A.; Hilko, B.; Kruschwitz, C.A.; Wilcox, N.S. [National Security Technologies, LLC, Los Alamos Operations, Los Alamos, NM (United States)

2011-05-01

Using relativistic ultra-short electron beams to obtain single-shot diffraction patterns holds the promise to yield real-time resolution of atomic motion in an easily accessible environment, such as a university laboratory, at a fraction of the cost of fourth-generation X-ray sources. One of the main issues in bringing this technique to full maturity is the development of efficient detector systems to record the diffraction pattern using a few MeV electron beams. Low noise, high spatial resolution, and single-electron detection capability are all characteristics of an ideal detector. In this paper, we compare the performances of a traditional fluorescent phosphor screen with a detection system based on the micro-channel plate (MCP). Since MCPs are typically used with lower energy electron beams, these tests constitute one of the few experimental data points available on the use of these devices with MeV energy beams.

The effect of channel height on bubble nucleation in superhydrophobic microchannels due to subcritical heating

Science.gov (United States)

Cowley, Adam; Maynes, Daniel; Crockett, Julie; Iverson, Brian

2017-11-01

This work experimentally investigates the effects of heating on laminar flow in high aspect ratio superhydrophobic (SH) microchannels. When water that is saturated with dissolved air is used, the unwetted cavities of the SH surfaces act as nucleation sites and air effervesces out of solution onto the surfaces. The microchannels consist of a rib/cavity structured SH surface, that is heated, and a glass surface that is utilized for flow visualization. Two channel heights of nominally 183 and 366 μm are considered. The friction factor-Reynolds product (fRe) is obtained via pressure drop and volumetric flow rate measurements and the temperature profile along the channel is obtained via thermocouples embedded in an aluminum block below the SH surface. Five surface types/configurations are investigated: smooth hydrophilic, smooth hydrophobic, SH with ribs perpendicular to the flow, SH with ribs parallel to the flow, and SH with both ribs parallel to the flow and sparse ribs perpendicular to the flow. Depending on the surface type/configuration, large bubbles can form and adversely affect fRe and lead to higher temperatures along the channel. Once bubbles grow large enough, they are expelled from the channel. The channel size greatly effects the residence time of the bubbles and consequently fRe and the channel temperature. This research was supported by the National Science Foundation (NSF) (Grant No. CBET-1235881) and the Utah NASA Space Grant Consortium (NASA Grant NNX15A124H).

Inertial migrations of cylindrical particles in rectangular microchannels: Variations of equilibrium positions and equivalent diameters

Science.gov (United States)

Su, Jinghong; Chen, Xiaodong; Hu, Guoqing

2018-03-01

Inertial migration has emerged as an efficient tool for manipulating both biological and engineered particles that commonly exist with non-spherical shapes in microfluidic devices. There have been numerous studies on the inertial migration of spherical particles, whereas the non-spherical particles are still largely unexplored. Here, we conduct three-dimensional direct numerical simulations to study the inertial migration of rigid cylindrical particles in rectangular microchannels with different width/height ratios under the channel Reynolds numbers (Re) varying from 50 to 400. Cylindrical particles with different length/diameter ratios and blockage ratios are also concerned. Distributions of surface force with the change of rotation angle show that surface stresses acting on the particle end near the wall are the major contributors to the particle rotation. We obtain lift forces experienced by cylindrical particles at different lateral positions on cross sections of two types of microchannels at various Re. It is found that there are always four stable equilibrium positions on the cross section of a square channel, while the stable positions are two or four in a rectangular channel, depending on Re. By comparing the equilibrium positions of cylindrical particles and spherical particles, we demonstrate that the equivalent diameter of cylindrical particles monotonously increases with Re. Our work indicates the influence of a non-spherical shape on the inertial migration and can be useful for the precise manipulation of non-spherical particles.

The Use of an Electron Microchannel as a Self-Extracting and Focusing Plasma Cathode Electron Gun

International Nuclear Information System (INIS)

Cornish, S.; Khachan, J.

2016-01-01

A new and simple type of electron gun is presented. Unlike conventional electron guns, which require a heated filament or extractor, accelerator and focusing electrodes, this gun uses the collimated electron microchannels of an inertial electrostatic confinement (IEC) discharge to achieve the same outcome. A cylindrical cathode is placed coaxially within a cylindrical anode to create the discharge. Collimated beams of electrons and fast neutrals emerge along the axis of the cylindrical cathode. This geometry isolates one of the microchannels that emerge in a negatively biased IEC grid. The internal operating pressure range of the gun is 35-190 mTorr. A small aperture separates the gun from the main vacuum chamber in order to achieve a pressure differential. The chamber was operated at pressures of 4-12 mTorr. The measured current produced by the gun was 0.1-3 mA (0.2-14 mA corrected measurement) for discharge currents of 1-45 mA and discharge voltages of 0.5-12 kV. The collimated electron beam emerges from the aperture into the vacuum chamber. The performance of the gun is unaffected by the pressure differential between the vacuum chamber and the gun. This allows the aperture to be removed and the chamber pressure to be equal to the gun pressure if required. (paper)

The Use of an Electron Microchannel as a Self-Extracting and Focusing Plasma Cathode Electron Gun

Science.gov (United States)

Cornish, S.; Khachan, J.

2016-02-01

A new and simple type of electron gun is presented. Unlike conventional electron guns, which require a heated filament or extractor, accelerator and focusing electrodes, this gun uses the collimated electron microchannels of an inertial electrostatic confinement (IEC) discharge to achieve the same outcome. A cylindrical cathode is placed coaxially within a cylindrical anode to create the discharge. Collimated beams of electrons and fast neutrals emerge along the axis of the cylindrical cathode. This geometry isolates one of the microchannels that emerge in a negatively biased IEC grid. The internal operating pressure range of the gun is 35-190 mTorr. A small aperture separates the gun from the main vacuum chamber in order to achieve a pressure differential. The chamber was operated at pressures of 4-12 mTorr. The measured current produced by the gun was 0.1-3 mA (0.2-14 mA corrected measurement) for discharge currents of 1-45 mA and discharge voltages of 0.5-12 kV. The collimated electron beam emerges from the aperture into the vacuum chamber. The performance of the gun is unaffected by the pressure differential between the vacuum chamber and the gun. This allows the aperture to be removed and the chamber pressure to be equal to the gun pressure if required.

Anti-stiction coating of PDMS moulds for rapid microchannel fabrication by double replica moulding

DEFF Research Database (Denmark)

Zhuang, Guisheng; Kutter, Jörg Peter

2011-01-01

), which resulted in an anti-stiction layer for the improved release after PDMS casting. The deposition of FDTS on an O2 plasma-activated surface of PDMS produced a reproducible and well-performing anti-stiction monolayer of fluorocarbon, and we used the FDTS-coated moulds as micro-masters for rapid......In this paper, we report a simple and precise method to rapidly replicate master structures for fast microchannel fabrication by double replica moulding of polydimethylsiloxane (PDMS). A PDMS mould was surface-treated by vapour phase deposition of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS...

Electronic states at Si-SiO2 interface introduced by implantation of Si in thermal SiO2

International Nuclear Information System (INIS)

Kalnitsky, A.; Poindexter, E.H.; Caplan, P.J.

1990-01-01

Interface traps due to excess Si introduced into the Si-SiO 2 system by ion implantation are investigated. Implanted oxides are shown to have interface traps at or slightly above the Si conduction band edge with densities proportional to the density of off-stoichiometric Si at the Si-SiO 2 interface. Diluted oxygen annealing is shown to result in physical separation of interface traps and equilibrium substrate electrons, demonstrating that ''interface'' states are located within a 0.5 nm thick layer of SiO 2 . Possible charge trapping mechanisms are discussed and the effect of these traps on MOS transistor characteristics is described using a sheet charge model. (author)

Nonvolatile field effect transistors based on protons and Si/SiO2Si structures

International Nuclear Information System (INIS)

Warren, W.L.; Vanheusden, K.; Fleetwood, D.M.; Schwank, J.R.; Winokur, P.S.; Knoll, M.G.; Devine, R.A.B.

1997-01-01

Recently, the authors have demonstrated that annealing Si/SiO 2 /Si structures in a hydrogen containing ambient introduces mobile H + ions into the buried SiO 2 layer. Changes in the H + spatial distribution within the SiO 2 layer were electrically monitored by current-voltage (I-V) measurements. The ability to directly probe reversible protonic motion in Si/SiO 2 /Si structures makes this an exemplar system to explore the physics and chemistry of hydrogen in the technologically relevant Si/SiO 2 structure. In this work, they illustrate that this effect can be used as the basis for a programmable nonvolatile field effect transistor (NVFET) memory that may compete with other Si-based memory devices. The power of this novel device is its simplicity; it is based upon standard Si/SiO 2 /Si technology and forming gas annealing, a common treatment used in integrated circuit processing. They also briefly discuss the effects of radiation on its retention properties

Two-Dimensional Variable Property Conjugate Heat Transfer Simulation of Nanofluids in Microchannels

International Nuclear Information System (INIS)

Ramiar, A.; Ranjbar, A.A.

2013-01-01

Laminar two-dimensional forced convective heat transfer of CuO-water and Al 2 O 3 -water nanofluids in a horizontal microchannel has been studied numerically, considering axial conduction effects in both solid and liquid regions and variable thermal conductivity and dynamic viscosity. The results show that using nanoparticles with higher thermal conductivities will intensify enhancement of heat transfer characteristics and slightly increases shear stress on the wall. The obtained results show more steep changes in Nusselt number for lower diameters and also higher values of Nusselt number by decreasing the diameter of nanoparticles. Also, by utilizing conduction number as the criterion, it was concluded from the results that adding nanoparticles will intensify the axial conduction effect in the geometry considered.

The Effect of Micro-Channels in the MPL on the Predicted Membrane Water Content in a PEMFC – A Modeling Study

DEFF Research Database (Denmark)

Berning, Torsten

2014-01-01

The micro-porous layer (MPL) in a proton exchange membrane fuel cell is frequently believed to constitute a barrier for the liquid water owing to its low hydraulic permeability compared to the porous substrate. When micro-channels are carved into the MPL on the side facing the catalyst layer, liq...

Science of Water Leaks: Validated Theory for Moisture Flow in Microchannels and Nanochannels.

Science.gov (United States)

Lei, Wenwen; Fong, Nicole; Yin, Yongbai; Svehla, Martin; McKenzie, David R

2015-10-27

Water is ubiquitous; the science of its transport in micro- and nanochannels has applications in electronics, medicine, filtration, packaging, and earth and planetary science. Validated theory for water vapor and two-phase water flows is a "missing link"; completing it enables us to define and quantify flow in a set of four standard leak configurations with dimensions from the nanoscale to the microscale. Here we report the first measurements of water vapor flow rates through four silica microchannels as a function of humidity, including under conditions when air is present as a background gas. An important finding is that the tangential momentum accommodation coefficient (TMAC) is strongly modified by surface layers of adsorbed water molecules, in agreement with previous work on the TMAC for nitrogen molecules impacting a silica surface in the presence of moisture. We measure enhanced flow rates for two-phase flows in silica microchannels driven by capillary filling. For the measurement of flows in nanochannels we use heavy water mass spectrometry. We construct the theory for the flow rates of the dominant modes of water transport through each of the four standard configurations and benchmark it against our new measurements in silica and against previously reported measurements for nanochannels in carbon nanotubes, carbon nanopipes, and porous alumina. The findings show that all behavior can be described by the four standard leak configurations and that measurements of leak behavior made using other molecules, such as helium, are not reliable. Single-phase water vapor flow is overestimated by a helium measurement, while two-phase flows are greatly underestimated for channels larger than 100 nm or for all channels when boundary slip applies, to an extent that depends on the slip length for the liquid-phase flows.

Sub-barrier fusion of Si+Si systems

Science.gov (United States)

Colucci, G.; Montagnoli, G.; Stefanini, A. M.; Bourgin, D.; Čolović, P.; Corradi, L.; Courtin, S.; Faggian, M.; Fioretto, E.; Galtarossa, F.; Goasduff, A.; Haas, F.; Mazzocco, M.; Scarlassara, F.; Stefanini, C.; Strano, E.; Urbani, M.; Szilner, S.; Zhang, G. L.

2017-11-01

The near- and sub-barrier fusion excitation function has been measured for the system 30Si+30Si at the Laboratori Nazionali di Legnaro of INFN, using the 30Si beam of the XTU Tandem accelerator in the energy range 47 - 90 MeV. A set-up based on a beam electrostatic deflector was used for detecting fusion evaporation residues. The measured cross sections have been compared to previous data on 28Si+28Si and Coupled Channels (CC) calculations have been performed using M3Y+repulsion and Woods-Saxon potentials, where the lowlying 2+ and 3- excitations have been included. A weak imaginary potential was found to be necessary to reproduce the low energy 28Si+28Si data. This probably simulates the effect of the oblate deformation of this nucleus. On the contrary, 30Si is a spherical nucleus, 30Si+30Si is nicely fit by CC calculations and no imaginary potential is needed. For this system, no maximum shows up for the astrophysical S-factor so that we have no evidence for hindrance, as confirmed by the comparison with CC calculations. The logarithmic derivative of the two symmetric systems highlights their different low energy trend. A difference can also be noted in the two barrier distributions, where the high-energy peak present in 28Si+28Si is not observed for 30Si+30Si, probably due to the weaker couplings in last case.

Sub-barrier fusion of Si+Si systems

Directory of Open Access Journals (Sweden)

Colucci G.

2017-01-01

Full Text Available The near- and sub-barrier fusion excitation function has been measured for the system 30Si+30Si at the Laboratori Nazionali di Legnaro of INFN, using the 30Si beam of the XTU Tandem accelerator in the energy range 47 - 90 MeV. A set-up based on a beam electrostatic deflector was used for detecting fusion evaporation residues. The measured cross sections have been compared to previous data on 28Si+28Si and Coupled Channels (CC calculations have been performed using M3Y+repulsion and Woods-Saxon potentials, where the lowlying 2+ and 3− excitations have been included. A weak imaginary potential was found to be necessary to reproduce the low energy 28Si+28Si data. This probably simulates the effect of the oblate deformation of this nucleus. On the contrary, 30Si is a spherical nucleus, 30Si+30Si is nicely fit by CC calculations and no imaginary potential is needed. For this system, no maximum shows up for the astrophysical S-factor so that we have no evidence for hindrance, as confirmed by the comparison with CC calculations. The logarithmic derivative of the two symmetric systems highlights their different low energy trend. A difference can also be noted in the two barrier distributions, where the high-energy peak present in 28Si+28Si is not observed for 30Si+30Si, probably due to the weaker couplings in last case.

In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles.

Science.gov (United States)

Lima, Rui; Wada, Shigeo; Takeda, Motohiro; Tsubota, Ken-ichi; Yamaguchi, Takami

2007-01-01

A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-microm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number (Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements.

Nitric acid oxidation of Si (NAOS) method for low temperature fabrication of SiO{sub 2}/Si and SiO{sub 2}/SiC structures

Energy Technology Data Exchange (ETDEWEB)

Kobayashi, H., E-mail: koba771@ybb.ne.jp [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Imamura, K.; Kim, W.-B.; Im, S.-S.; Asuha [Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

2010-07-15

We have developed low temperature formation methods of SiO{sub 2}/Si and SiO{sub 2}/SiC structures by use of nitric acid, i.e., nitric acid oxidation of Si (or SiC) (NAOS) methods. By use of the azeotropic NAOS method (i.e., immersion in 68 wt% HNO{sub 3} aqueous solutions at 120 deg. C), an ultrathin (i.e., 1.3-1.4 nm) SiO{sub 2} layer with a low leakage current density can be formed on Si. The leakage current density can be further decreased by post-metallization anneal (PMA) at 200 deg. C in hydrogen atmosphere, and consequently the leakage current density at the gate bias voltage of 1 V becomes 1/4-1/20 of that of an ultrathin (i.e., 1.5 nm) thermal oxide layer usually formed at temperatures between 800 and 900 deg. C. The low leakage current density is attributable to (i) low interface state density, (ii) low SiO{sub 2} gap-state density, and (iii) high band discontinuity energy at the SiO{sub 2}/Si interface arising from the high atomic density of the NAOS SiO{sub 2} layer. For the formation of a relatively thick (i.e., {>=}10 nm) SiO{sub 2} layer, we have developed the two-step NAOS method in which the initial and subsequent oxidation is performed by immersion in {approx}40 wt% HNO{sub 3} and azeotropic HNO{sub 3} aqueous solutions, respectively. In this case, the SiO{sub 2} formation rate does not depend on the Si surface orientation. Using the two-step NAOS method, a uniform thickness SiO{sub 2} layer can be formed even on the rough surface of poly-crystalline Si thin films. The atomic density of the two-step NAOS SiO{sub 2} layer is slightly higher than that for thermal oxide. When PMA at 250 deg. C in hydrogen is performed on the two-step NAOS SiO{sub 2} layer, the current-voltage and capacitance-voltage characteristics become as good as those for thermal oxide formed at 900 deg. C. A relatively thick (i.e., {>=}10 nm) SiO{sub 2} layer can also be formed on SiC at 120 deg. C by use of the two-step NAOS method. With no treatment before the NAOS method

Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels (Poster)

DEFF Research Database (Denmark)

Lafmejani, Saeed Sadeghi; Olesen, Anders Christian; Kær, Søren Knudsen

One means of increasing the hydrogen yield to cost ratio of a PEM water electrolyser, is to increase the operating current density. However, at high current densities (higher than 1 A/cm2), management of heat and mass transfer in the anode current collector and channel becomes crucial and can lead...... to hot spots. Management of heat and fluid flow through the micro-channels play a great role in the capability of PEM water electrolysis when working at high current densities. Despite, many studies have been done on gas-liquid flows; still there is a lack of research on gas-liquid flows in micro......-sized channels (hydraulic diameter of 1 mm) of PEM water electrolysis. Precisely controlling all the parameters that affect the gas-liquid flow in a PEM water electrolysis cell is quite challenging, hence a simplified setup is constructed consisting of only a transparent channel with a sheet of titanium felt...

Hydraulic and thermal design of a gas microchannel heat exchanger

International Nuclear Information System (INIS)

Yang Yahui; Brandner, Juergen J; Morini, Gian Luca

2012-01-01

In this paper investigations on the design of a gas flow microchannel heat exchanger are described in terms of hydrodynamic and thermal aspects. The optimal choice for thermal conductivity of the solid material is discussed by analysis of its influences on the thermal performance of a micro heat exchanger. Two numerical models are built by means of a commercial CFD code (Fluent). The simulation results provide the distribution of mass flow rate, inlet pressure and pressure loss, outlet pressure and pressure loss, subjected to various feeding pressure values. Based on the thermal and hydrodynamic analysis, a micro heat exchanger made of polymer (PEEK) is designed and manufactured for flow and heat transfer measurements in air flows. Sensors are integrated into the micro heat exchanger in order to measure the local pressure and temperature in an accurate way. Finally, combined with numerical simulation, an operating range is suggested for the present micro heat exchanger in order to guarantee uniform flow distribution and best thermal and hydraulic performances.

Joining of SiC ceramics and SiC/SiC composites

Energy Technology Data Exchange (ETDEWEB)

Rabin, B.H. [Idaho National Engineering Lab., Idaho Falls, ID (United States)

1996-08-01

This project has successfully developed a practical and reliable method for fabricating SiC ceramic-ceramic joints. This joining method will permit the use of SiC-based ceramics in a variety of elevated temperature fossil energy applications. The technique is based on a reaction bonding approach that provides joint interlayers compatible with SiC, and excellent joint mechanical properties at temperatures exceeding 1000{degrees}C. Recent emphasis has been given to technology transfer activities, and several collaborative research efforts are in progress. Investigations are focusing on applying the joining method to sintered {alpha}-SiC and fiber-reinforced SiC/SiC composites for use in applications such as heat exchangers, radiant burners and gas turbine components.

Modeling and Experimentation of New Thermoelectric Cooler–Thermoelectric Generator Module

Directory of Open Access Journals (Sweden)

Khaled Teffah

2018-03-01

Full Text Available In this work, a modeling and experimental study of a new thermoelectric cooler–thermoelectric generator (TEC-TEG module is investigated. The studied module is composed of TEC, TEG and total system heatsink, all connected thermally in series. An input voltage (1–5 V passes through the TEC where the electrons by means of Peltier effect entrain the heat from the upper side of the module to the lower one creating temperature difference; TEG plays the role of a partial heatsink for the TEC by transferring this waste heat to the total system heatsink and converting an amount of this heat into electricity by a phenomenon called Seebeck effect, of the thermoelectric modules. The performance of the TEG as partial heatsink of TEC at different input voltages is demonstrated theoretically using the modeling software COMSOL Multiphysics. Moreover, the experiment validates the simulation result which smooths the path for a new manufacturing thermoelectric cascade model for the cooling and the immediate electric power generation.

Flipping interferometry and its application for quantitative phase microscopy in a micro-channel.

Science.gov (United States)

Roitshtain, Darina; Turko, Nir A; Javidi, Bahram; Shaked, Natan T

2016-05-15

We present a portable, off-axis interferometric module for quantitative phase microscopy of live cells, positioned at the exit port of a coherently illuminated inverted microscope. The module creates on the digital camera an interference pattern between the image of the sample and its flipped version. The proposed simplified module is based on a retro-reflector modification in an external Michelson interferometer. The module does not contain any lenses, pinholes, or gratings and its alignment is straightforward. Still, it allows full control of the off-axis angle and does not suffer from ghost images. As experimentally demonstrated, the module is useful for quantitative phase microscopy of live cells rapidly flowing in a micro-channel.

COOLING MICROELECTRONIC DEVICES USING OPTIMAL MICROCHANNEL HEAT SINKS: UNA COMPARACIÓN DE DOS ALGORITMOS DE OPTIMIZACIÓN GLOBAL

Directory of Open Access Journals (Sweden)

Jorge Mario Cruz Duarte

Full Text Available This article deals with the design of optimum microchannel heat sinks through Unified Particle Swarm Optimisation (UPSO and Harmony Search (HS. These heat sinks are used for the thermal management of electronic devices, and we analyse the performance of UPSO and HS in their design, both, systematically and thoroughly. The objective function was created using the entropy generation minimisation criterion. In this study, we fixed the geometry of the microchannel, the amount of heat to be removed, and the properties of the cooling fluid. Moreover, we calculated the entropy generation rate, the volume flow rate of air, the channel width, the channel height, and the Knudsen number. The results of several simulation optimizations indicate that both global optimisation strategies yielded similar results, about 0.032 W/K, and that HS required five times more iterations than UPSO, but only about a nineteenth of its computation time. In addition, HS revealed a greater chance (about three times of finding a better solution than UPSO, but with a higher dispersion rate (about five times. Nonetheless, both algorithms successfully optimised the design for different scenarios, even when varying the material of the heat sink, and for different heat transfer rates.

Comportamiento a la corrosión electroquímica de aleaciones MgAl con recubrimientos de materiales compuestos Al/SiCp mediante proyección térmica

Directory of Open Access Journals (Sweden)

Pardo, A.

2010-04-01

Full Text Available The corrosion protection of Mg-Al alloys by flame thermal spraying of Al/SiCp composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiC particles (SiCp varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of micro-channels, largely in the vicinity of the SiC particles, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5-30 vol.% SiCp compared with the unreinforced thermal spray aluminium coatings.

Se estudia, mediante espectroscopía de impedancia electroquímica en solución 3,5 % NaCl, la protección frente a la corrosión de aleaciones Mg-Al recubiertas por proyección térmica con materiales compuestos Al/SiCp. Se varió la fracción de volumen de las partículas de SiC (SiCp entre 5 y 30 %. Los recubrimientos efectuados por proyección térmica revelan un elevado número de microcanales, en la vecindad de las partículas de SiC, que facilitan la penetración del electrolito originando procesos de corrosión galvánica en los substratos de las aleaciones de magnesio. Un tratamiento posterior mediante la aplicación de una presión en frío reduce el grado de porosidad de los recubrimientos y mejora la unión, tanto entre el substrato y el recubrimiento como entre las partículas de aluminio y SiC, mejorando la resistencia a la corrosión de las aleaciones recubiertas. La efectividad de los recubrimientos disminuye ligeramente con la adición de SiCp cuando se comparan con los mismos recubrimientos de aluminio sin refuerzo.

Distinctive Capillary Action by Micro-channels in Bone-like Templates can Enhance Recruitment of Cells for Restoration of Large Bony Defect.

Science.gov (United States)

Oh, Daniel S; Koch, Alia; Eisig, Sidney; Kim, Sahng Gyoon; Kim, Yoon Hyuk; Kim, Do-Gyoon; Shim, Jae Hyuck

2015-09-11

Without an active, thriving cell population that is well-distributed and stably anchored to the inserted template, exceptional bone regeneration does not occur. With conventional templates, the absence of internal micro-channels results in the lack of cell infiltration, distribution, and inhabitance deep inside the templates. Hence, a highly porous and uniformly interconnected trabecular-bone-like template with micro-channels (biogenic microenvironment template; BMT) has been developed to address these obstacles. The novel BMT was created by innovative concepts (capillary action) and fabricated with a sponge-template coating technique. The BMT consists of several structural components: inter-connected primary-pores (300-400 µm) that mimic pores in trabecular bone, micro-channels (25-70 µm) within each trabecula, and nanopores (100-400 nm) on the surface to allow cells to anchor. Moreover, the BMT has been documented by mechanical test study to have similar mechanical strength properties to those of human trabecular bone (~3.8 MPa)12. The BMT exhibited high absorption, retention, and habitation of cells throughout the bridge-shaped (Π) templates (3 cm height and 4 cm length). The cells that were initially seeded into one end of the templates immediately mobilized to the other end (10 cm distance) by capillary action of the BMT on the cell media. After 4 hr, the cells homogenously occupied the entire BMT and exhibited normal cellular behavior. The capillary action accounted for the infiltration of the cells suspended in the media and the distribution (active migration) throughout the BMT. Having observed these capabilities of the BMT, we project that BMTs will absorb bone marrow cells, growth factors, and nutrients from the periphery under physiological conditions. The BMT may resolve current limitations via rapid infiltration, homogenous distribution and inhabitance of cells in large, volumetric templates to repair massive skeletal defects.

Microstructure and Mechanical Property of SiCf/SiC and Cf/SiC Composites

International Nuclear Information System (INIS)

Lee, S P; Cho, K S; Lee, H U; Lee, J K; Bae, D S; Byun, J H

2011-01-01

The mechanical properties of SiC based composites reinforced with different types of fabrics have been investigated, in conjunction with the detailed analyses of their microstructures. The thermal shock properties of SiC f /SiC composites were also examined. All composites showed a dense morphology in the matrix region. Carbon coated PW-SiC f /SiC composites had a good fracture energy, even if their strength was lower than that of PW-C f /SiC composites. SiC f /SiC composites represented a great reduction of flexural strength at the thermal shock temperature difference of 300 deg. C.

An efficient and cost-effective microchannel plate detector for slow neutron radiography

Science.gov (United States)

Wiggins, B. B.; Vadas, J.; Bancroft, D.; deSouza, Z. O.; Huston, J.; Hudan, S.; Baxter, D. V.; deSouza, R. T.

2018-05-01

A novel approach for efficiently imaging objects with slow neutrons in two dimensions is realized. Neutron sensitivity is achieved by use of a boron doped microchannel plate (MCP). The resulting electron avalanche is further amplified with a Z-stack MCP before being sensed by two orthogonally oriented wire planes. Coupling of the wire planes to delay lines efficiently encodes the position information as a time difference. To determine the position resolution, slow neutrons were used to illuminate a Cd-mask placed directly in front of the detector. Peaks in the resulting spectrum exhibited an average peak width of 329 μm FWHM, corresponding to an average intrinsic resolution of 216 μm. The center region of the detector exhibits a significantly better spatial resolution with an intrinsic resolution of <100 μm observed.

Testing micro-channel plate detectors for the particle identification upgrade of LHCb

CERN Document Server

Castillo Garcia, L

2012-01-01

The TORCH, Time of internally Reflected Cherenkov Light, is proposed for the high luminosity upgrade of the LHCb experiment. The detector combines Time-of-Flight and Cherenkov techniques to achieve positive pi/K/p separation on a >= 3 sigma level in the momentum range below 10 GeV/c. The required time resolution is <= 50 ps for single photon signal. In a preliminary R\\&D phase, we have shown that already commercially available micro-channel plate tubes with 8 x 8 channels fulfil the requirements. Timing properties of the tubes have been investigated with a pulsed laser diode in single photon regime. Key results from these laboratory tests are reported. An excellent timing resolution of <40 ps is achieved with an efficiency of similar to 90\\%. (C) 2011 Elsevier B.V. All rights reserved.

Magnetron-sputter epitaxy of β-FeSi2(220)/Si(111) and β-FeSi2(431)/Si(001) thin films at elevated temperatures

International Nuclear Information System (INIS)

Liu Hongfei; Tan Chengcheh; Chi Dongzhi

2012-01-01

β-FeSi 2 thin films have been grown on Si(111) and Si(001) substrates by magnetron-sputter epitaxy at 700 °C. On Si(111), the growth is consistent with the commonly observed orientation of [001]β-FeSi 2 (220)//[1-10]Si(111) having three variants, in-plane rotated 120° with respect to one another. However, on Si(001), under the same growth conditions, the growth is dominated by [-111]β-FeSi 2 (431)//[110]Si(001) with four variants, which is hitherto unknown for growing β-FeSi 2 . Photoelectron spectra reveal negligible differences in the valance-band and Fe2p core-level between β-FeSi 2 grown on Si(111) and Si(001) but an apparent increased Si-oxidization on the surface of β-FeSi 2 /Si(001). This phenomenon is discussed and attributed to the Si-surface termination effect, which also suggests that the Si/Fe ratio on the surface of β-FeSi 2 (431)/Si(001) is larger than that on the surface of β-FeSi 2 (220)/Si(111).

Giant magnetoimpedance-based microchannel system for quick and parallel genotyping of human papilloma virus type 16/18

Science.gov (United States)

Yang, Hao; Chen, Lei; Lei, Chong; Zhang, Ju; Li, Ding; Zhou, Zhi-Min; Bao, Chen-Chen; Hu, Heng-Yao; Chen, Xiang; Cui, Feng; Zhang, Shuang-Xi; Zhou, Yong; Cui, Da-Xiang

2010-07-01

Quick and parallel genotyping of human papilloma virus (HPV) type 16/18 is carried out by a specially designed giant magnetoimpedance (GMI) based microchannel system. Micropatterned soft magnetic ribbon exhibiting large GMI ratio serves as the biosensor element. HPV genotyping can be determined by the changes in GMI ratio in corresponding detection region after hybridization. The result shows that this system has great potential in future clinical diagnostics and can be easily extended to other biomedical applications based on molecular recognition.

A novel electro-thermal model for wide bandgap semiconductor based devices

DEFF Research Database (Denmark)

Sintamarean, Nicolae Christian; Blaabjerg, Frede; Wang, Huai

2013-01-01

This paper propose a novel Electro-Thermal Model for the new generation of power electronics WBG-devices (by considering the SiC MOSFET-CMF20120D from CREE), which is able to estimate the device junction and case temperature. The Device-Model estimates the voltage drop and the switching energies...... by considering the device current, the off-state blocking voltage and junction temperature variation. Moreover, the proposed Thermal-Model is able to consider the thermal coupling within the MOSFET and its freewheeling diode, integrated into the same package, and the influence of the ambient temperature...... variation. The importance of temperature loop feedback in the estimation accuracy of device junction and case temperature is studied. Furthermore, the Safe Operating Area (SOA) of the SiC MOSFET is determined for 2L-VSI applications which are using sinusoidal PWM. Thus, by considering the heatsink thermal...

Significantly increased lifetime of recent microchannel-plate photomultipliers

Energy Technology Data Exchange (ETDEWEB)

Britting, Alexander; Eyrich, Wolfgang; Lehmann, Albert; Uhlig, Fred [Physikalisches Institut, Universitaet Erlangen-Nuernberg (Germany)

2013-07-01

Micro-channel plate photo multipliers (MCP-PMT) are the favored sensors for the DIRC detectors (Detection of Internally Reflected Cherenkov Light) of the PANDA experiment. The main reasons for this are their usability in high magnetic fields of up to 2 T, a time resolution of better than σ = 50 ps and a rate capability high enough to withstand a detected photon rate of about 200 kHz cm{sup -2} at the MCP-PMTs surface, which is anticipated at the average luminosity of 2 . 10{sup 32} cm{sup -2}s{sup -1} in PANDA. Moreover, for the reconstruction of the Cherenkov angle using the planned optics for the barrel DIRC a spatial resolution of about 5 mm at the focal plane is needed. Until recently the major drawback of MCP-PMTs was their limited lifetime which was by far not sufficient to stand the integrated anode charge, which is ∼ 5 C/cm{sup 2} for the Barrel-DIRC and even more for the Disc-DIRC. However, the latest MCP prototype devices show a hugh step forward in this respect. The results of these lifetime measurements are presented. The achieved values are meanwhile close to the PANDA requirements for the Barrel-DIRC.

The parameterization of microchannel-plate-based detection systems

Science.gov (United States)

Gershman, Daniel J.; Gliese, Ulrik; Dorelli, John C.; Avanov, Levon A.; Barrie, Alexander C.; Chornay, Dennis J.; MacDonald, Elizabeth A.; Holland, Matthew P.; Giles, Barbara L.; Pollock, Craig J.

2016-10-01

The most common instrument for low-energy plasmas consists of a top-hat electrostatic analyzer (ESA) geometry coupled with a microchannel-plate-based (MCP-based) detection system. While the electrostatic optics for such sensors are readily simulated and parameterized during the laboratory calibration process, the detection system is often less well characterized. Here we develop a comprehensive mathematical description of particle detection systems. As a function of instrument azimuthal angle, we parameterize (1) particle scattering within the ESA and at the surface of the MCP, (2) the probability distribution of MCP gain for an incident particle, (3) electron charge cloud spreading between the MCP and anode board, and (4) capacitive coupling between adjacent discrete anodes. Using the Dual Electron Spectrometers on the Fast Plasma Investigation on NASA's Magnetospheric Multiscale mission as an example, we demonstrate a method for extracting these fundamental detection system parameters from laboratory calibration. We further show that parameters that will evolve in flight, namely, MCP gain, can be determined through application of this model to specifically tailored in-flight calibration activities. This methodology provides a robust characterization of sensor suite performance throughout mission lifetime. The model developed in this work is not only applicable to existing sensors but also can be used as an analytical design tool for future particle instrumentation.

Inertial effects on heat transfer in superhydrophobic microchannels

Science.gov (United States)

Cowley, Adam; Maynes, Daniel; Crockett, Julie; Iverson, Brian; BYU Fluids Team

2015-11-01

This work numerically studies the effects of inertia on thermal transport in superhydrophbic microchannels. An infinite parallel plate channel comprised of structured superhydrophbic walls is considered. The structure of the superhydrophobic surfaces consists of square pillars organized in a square array aligned with the flow direction. Laminar, fully developed flow is explored. The flow is assumed to be non-wetting and have an idealized flat meniscus. A shear-free, adiabatic boundary condition is used at the liquid/gas interface, while a no-slip, constant heat flux condition is used at the liquid/solid interface. A wide range of Peclet numbers, relative channel spacing distances, and relative pillar sizes are considered. Results are presented in terms of Poiseuille number, Nusselt number, hydrodynamic slip length, and temperature jump length. Interestingly, the thermal transport is varied only slightly by inertial effects for a wide range of parameters explored and compares well with other analytical and numerical work that assumed Stokes flow. It is only for very small relative channel spacing and large Peclet number that inertial effects exert significant influence. Overall, the heat transfer is reduced for the superhydrophbic channels in comparison to classic smooth walled channels. This research was supported by the National Science Foundation (NSF) - United States (Grant No. CBET-1235881).

Microchannel electrokinetics of charged analytes in buffered solutions near floating electrodes

DEFF Research Database (Denmark)

Andersen, Mathias Bækbo; Wolfcale, Trevor; Gregersen, Misha Marie

to accurately predict such behavior in these flow regimes. Experimentally, using conventional fluorescence microscopy, we investigated the concentration gradient (as well as the associated electroosmosis, induced-charge electro-osmosis, and electrophoresis) of the charged analyte near the floating electrode......We present both experimental and numerical studies of nonlinear electrokinetic flow of buffered solutions seeded with dilute analytes in a straight microchannel (0.6 μm high, 250 μm wide, and 9000 μm long) with a 0.15 μm high 60 μm wide electrode situated at the bottom center of the channel...... as a function of analyte (1 to 10 μM fluorescein and bodipy) and buffer (1 to 10 mM borate and posphate) concentrations and an externally applied voltage drop (50 to 100 V) along the channel. We have implemented a nonlinear continuum kinetics model of the system involving the electric potential, the buffer flow...

SiC Nanoparticles Toughened-SiC/MoSi2-SiC Multilayer Functionally Graded Oxidation Protective Coating for Carbon Materials at High Temperatures

Science.gov (United States)

Abdollahi, Alireza; Ehsani, Naser; Valefi, Zia; Khalifesoltani, Ali

2017-05-01

A SiC nanoparticle toughened-SiC/MoSi2-SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi2, α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi2-SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi2-SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10-2 g/cm3/h, respectively.

Reliability implications of defects in high temperature annealed Si/SiO2/Si structures

International Nuclear Information System (INIS)

Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S.; Devine, R.A.B.; Mathiot, D.; Wilson, I.H.; Xu, J.B.

1994-01-01

High-temperature post-oxidation annealing of poly-Si/SiO 2 /Si structures such as metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field effect transistors is known to result in enhanced radiation sensitivity, increased 1/f noise, and low field breakdown. The authors have studied the origins of these effects from a spectroscopic standpoint using electron paramagnetic resonance (EPR) and atomic force microscopy. One result of high temperature annealing is the generation of three types of paramagnetic defect centers, two of which are associated with the oxide close to the Si/SiO 2 interface (oxygen-vacancy centers) and the third with the bulk Si substrate (oxygen-related donors). In all three cases, the origin of the defects may be attributed to out-diffusion of O from the SiO 2 network into the Si substrate with associated reduction of the oxide. The authors present a straightforward model for the interfacial region which assumes the driving force for O out-diffusion is the chemical potential difference of the O in the two phases (SiO 2 and the Si substrate). Experimental evidence is provided to show that enhanced hole trapping and interface-trap and border-trap generation in irradiated high-temperature annealed Si/SiO 2 /Si systems are all related either directly, or indirectly, to the presence of oxygen vacancies

Fabrication and Mechanical Properties of SiCw(p/SiC-Si Composites by Liquid Si Infiltration using Pyrolysed Rice Husks and SiC Powders as Precursors

Directory of Open Access Journals (Sweden)

Dan Zhu

2014-03-01

Full Text Available Dense silicon carbide (SiC matrix composites with SiC whiskers and particles as reinforcement were prepared by infiltrating molten Si at 1550 °C into porous preforms composed of pyrolysed rice husks (RHs and extra added SiC powder in different ratios. The Vickers hardness of the composites showed an increase from 18.6 to 21.3 GPa when the amount of SiC added in the preforms was 20% (w/w, and then decreased to 17.3 GPa with the increase of SiC added in the preforms up to 80% (w/w. The values of flexural strength of the composites initially decreased when 20% (w/w SiC was added in the preform and then increased to 587 MPa when the SiC concentration reached 80% (w/w. The refinement of SiC particle sizes and the improvement of the microstructure in particle distribution of the composites due to the addition of external SiC played an effective role in improving the mechanical properties of the composites.

Oscillations in the fusion of the Si + Si systems; Oscilaciones en la fusion de sistemas de Si + Si

Energy Technology Data Exchange (ETDEWEB)

Aguilera R, E F; Kolata, J J; DeYoung, P A; Vega, J J [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico)

1986-02-15

Excitation functions for the yields of all the residual nuclei from the {sup 28} Si + {sup 28,30} and {sup 30} Si + {sup 30} Si reactions have been measured via the {gamma}-ray technique for center of mass energies in the region within one and two times the Coulomb barrier.Thirteen elements were identified for the first reaction and ten for the other two. While no structure is shown by the data for the {sup 28} + {sup 28} Si reaction, we have found evidence for intermediate width structure in the 2{alpha} and the {alpha}pn channels in {sup 28} Si + {sup 30} Si and for broad structure in the total fusion cross sections for {sup 30} Si + {sup 30} Si. Calculations using a barrier penetration model with one free parameter reproduce the experimental results quite well. Evaporation model calculations indicate that the individual structure of the nuclei involved in the respective decay chains might have an important influence upon the deexcitation process at the energies relevant to our experiments. (Author)

Effects of improved microchannel structures on the separation characteristics of microchip capillary electrophoresis

CERN Document Server

Utsumi, Y; Ozaki, M; Terabe, S

2003-01-01

We fabricated the electrophoresis microchips using the UV polymerization technique. We employed plastic substrates that were suitable for rapid prototyping instead of glass and quartz. A thick UV negative photo resist was used to form molds and poly-dimethylsilozane (PDMS) was polymerized by a thermal curing process on the mold to obtain replica microchips. Electroosmotic flow (EOF) was measured to evaluate the surface. Rhodamine B and sulforhodamine B are successfully separated using the microchip. Characteristic differences between UV-fabricated and SR-fabricated microchips were evaluated by EOF measurement. It was observed that accurately defined microchannels fabricated by synchrotron radiation (SR) lithography show constant peak heights and FWHMs. Thus the advantage of the application of SR lithography to the mold fabrication is also demonstrated. (author)

Power efficiency improvements of the industrial processes at application of thermochemical recuperation of heath of the leaving gases with use of microchannel reactors

Science.gov (United States)

Tararykov, A. V.; Garyaev, A. B.

2017-11-01

The possibility of increasing the energy efficiency of production processes by converting the initial fuel - natural gas to synthesized fuel using the heat of the exhaust gases of plants involved in production is considered. Possible applications of this technology are given. A mathematical model of the processes of heat and mass transfer occurring in a thermochemical reactor is developed taking into account the nonequilibrium nature of the course of chemical reactions of fuel conversion. The possibility of using microchannel reaction elements and facilities for methane conversion in order to intensify the process and reduce the overall dimensions of plants is considered. The features of the course of heat and mass transfer processes under flow conditions in microchannel reaction elements are described. Additions have been made to the mathematical model, which makes it possible to use it for microchannel installations. With the help of a mathematical model, distribution of the parameters of mixtures along the length of the reaction element of the reactor-temperature, the concentration of the reacting components, the velocity, and the values of the heat fluxes are obtained. The calculations take into account the change in the thermophysical properties of the mix-ture, the type of the catalytic element, the rate of the reactions, the heat exchange processes by radiation, and the lon-gitudinal heat transfer along the flow of the reacting mixture. The reliability of the results of the application of the mathematical model is confirmed by their comparison with the experimental data obtained by Grasso G., Schaefer G., Schuurman Y., Mirodatos C., Kuznetsov V.V., Vitovsky O.V. on similar installations.

Analyses of the As doping of SiO{sub 2}/Si/SiO{sub 2} nanostructures

Energy Technology Data Exchange (ETDEWEB)

Ruffino, Francesco; Miritello, Maria [CNR-IMM MATIS, via S. Sofia 64, 95123 Catania (Italy); Tomasello, Mario Vincenzo [Scuola Superiore di Catania, via San Nullo 5/i, 95123 Catania (Italy); De Bastiani, Riccardo; Grimaldi, Maria Grazia [Dipartimento di Fisica ed Astronomia, Universita di Catania, via S. Sofia 64, 95123 Catania (Italy); CNR-IMM MATIS, via S. Sofia 64, 95123 Catania (Italy); Nicotra, Giuseppe; Spinella, Corrado [Consiglio Nazionale delle Ricerche-Istituto per la Microelettronica e Microsistemi (CNR-IMM), VIII Strada 5, 95121 Catania (Italy)

2011-03-15

We illustrate the behaviour of As when it is confined, by the implantation technique, in a SiO{sub 2}(70nm)/Si(30nm)/SiO{sub 2}(70nm) multilayer and its spatial redistribution when annealing processes are performed. By Rutherford backscattering spectrometry and Z-contrast transmission electron microscopy we found an As accumulation at the Si/SiO{sub 2} interfaces and at the Si grain boundaries with no segregation of the As in the Si layer. Such an effect is in agreement with a model that assumes a traps distribution in the Si in the first 2-3 nm above the SiO{sub 2}/Si interfaces and along the Si grain boundaries. The traps concentration at the Si/SiO{sub 2} interfaces was estimated in 10{sup 14} traps/cm{sup 2}. The outlined results can open perspectives on the doping properties of As in Si nanocrystals, whose applications in nanoelectronics and optoelectronics are widely investigated (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiN{sub x}/SiN{sub y} multilayers

Energy Technology Data Exchange (ETDEWEB)

Jiang, Xiaofan; Ma, Zhongyuan, E-mail: zyma@nju.edu.cn; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan [National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory of Photonic Electronic Materials Sciences and Technology, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093 (China)

2014-09-28

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN{sub x}/SiN{sub y} multilayers with high on/off ratio of 10{sup 9}. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

Joule heating effects on electromagnetohydrodynamic flow through a peristaltically induced micro-channel with different zeta potential and wall slip

Science.gov (United States)

Ranjit, N. K.; Shit, G. C.

2017-09-01

This paper aims to develop a mathematical model for magnetohydrodynamic flow of biofluids through a hydrophobic micro-channel with periodically contracting and expanding walls under the influence of an axially applied electric field. The velocity slip effects have been taken into account at the channel walls by employing different slip lengths due to hydrophobic gating. Different temperature jump factors have also been used to investigate the thermomechanical interactions at the fluid-solid interface. The electromagnetohydrodynamic flow in a microchannel is simplified under the framework of Debye-Hückel linearization approximation. We have derived the closed-form solutions for the linearized dimensionless boundary value problem under the assumptions of long wave length and low Reynolds number. The axial velocity, temperature, pressure distribution, stream function, wall shear stress and the Nusselt number have been appraised for diverse values of the parameters approaching into the problem. Our main focus is to determine the effects of different zeta potential on the axial velocity and temperature distribution under electromagnetic environment. This study puts forward an important observation that the different zeta potential plays an important role in controlling fluid velocity. The study further reveals that the temperature increases significantly with the Joule heating parameter and the Brinkman number (arises due to the dissipation of energy).

Development of microchannel plates in advanced wind-tunnel instrumentation

Science.gov (United States)

Feller, W. Bruce

1990-01-01

Microchannel plate (MCP) electron multiplier dynamic range has been increased 3 to 4 orders of magnitude at ambient temperatures, through enhanced input count rate capability and reduced background or 'dark' noise. The previous upper limit of roughly 10(exp 7) - 10(exp 8) cm(exp -2)s(exp -1) at ambient has been extended to levels approach 10(exp 10) cm(exp -2)s(exp -1) under continuous dc operation. The lower limit, previously set by an irreducible background component (approximately 0.6 cm(exp -2)s(exp -1)), has been lowered to the cosmic ray limit of .01 cm(exp -2)s(exp -1). The high end improvement was achieved by conductively cooling a very low resistance MCP by bonding it to a heat sink, while maintaining pulse-counting operation with multianode readouts. The low-end improvement was achieved by removing all radioisotopes from the MCP matrix glass. The detectors will benefit optical and mass spectrometry, flow visualization, plasma diagnostics, magnetometry, and other high signal flux applications. Very low MCP background noise will benefit X-ray and UV astronomy, medical imaging, trace isotope mass spectrometry, and other applications where the signal flux is often extremely low.

Performance of a polymeric heat sink with circular microchannels

Energy Technology Data Exchange (ETDEWEB)

Barba, Alessandro; Musi, Barbara; Spiga, Marco [Department of Industrial Engineering, University of Parma, Parco Area delle Scienze 181, 43100 Parma (Italy)

2006-06-15

The object of this work is the thermal investigation of a polymeric microchannel heat sink designed for the active cooling of small flat surfaces. Its performance, pressure drop, temperature distribution, and thermal resistance are evaluated. A three-dimensional procedure is developed and applied to a geometrical configuration consisting of a circular microduct (with a gas running through it), embedded in a solid substrate with rectangular cross-section. The conjugate heat transfer problem is solved assuming fully developed laminar flow in forced convection. The bottom side of the heat sink receives a uniform heat flux, while the top side is adiabatic. Considering a gas flow with low Prandtl and Reynolds numbers, the temperature distribution is given by the sum of a linear function (in the stream direction) and a numerical solution obtained in 2-D coordinates resorting to a finite element software, based on the Rayleigh-Ritz-Galerkin method, with user-defined error tolerance. Rarefaction, compressibility and viscous dissipation are neglected, i.e., the Knudsen, Mach and Brinkman numbers are low. The theoretical results are shown in some graphs and compared with experimental data concerning helium and nitrogen flows in Nylon circular microducts. The agreement is quite satisfactory. [Author].

Feasibility investigations on a novel micro-manufacturing process for fabrication of fuel cell bipolar plates: Internal pressure-assisted embossing of micro-channels with in-die mechanical bonding

Energy Technology Data Exchange (ETDEWEB)

Koc, Muammer [NSF I/UCR Center for Precision Forming (CPF), Department of Mechanical Engineering, Virginia Commonwealth University (VCU), Richmond, VA (United States); Mahabunphachai, Sasawat [NSF I/UCR Center for Precision Forming (CPF), Department of Mechanical Engineering, Virginia Commonwealth University (VCU), Richmond, VA (United States); Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI (United States)

2007-10-25

In this paper, we present the results of our studies on conceptual design and feasibility experiments towards development of a novel hybrid manufacturing process to fabricate fuel cell bipolar plates that consists of multi-array micro-channels on a large surface area. The premises of this hybrid micro-manufacturing process stem from the use of an internal pressure-assisted embossing process (cold or warm) combined with mechanical bonding of double bipolar plates in a single-die and single-step operation. Such combined use of hydraulic and mechanical forming forces and in-process bonding will (a) enable integrated forming of micro-channels on both surfaces (as anode and cathode flow fields) and at the middle (as cooling channels), (b) reduce the process steps, (c) reduce variation in dimensional tolerances and surface finish, (d) increase the product quality, (e) increase the performance of fuel cell by optimizing flow-field designs and ensuring consistent contact resistance, and (f) reduce the overall stack cost. This paper explains two experimental investigations that were performed to characterize and evaluate the feasibility of the conceptualized manufacturing process. The first investigation involved hydroforming of micro-channels using thin sheet metals of SS304 with a thickness of 51 {mu}m. The width of the channels ranged from 0.46 to 1.33 mm and the height range was between 0.15 and 0.98 mm. Our feasibility experiments resulted in that different aspect ratios of micro-channels could be fabricated using internal pressure in a controllable manner although there is a limit to very sharp channel shapes (i.e., high aspect ratios with narrow channels). The second investigation was on the feasibility of mechanical bonding of thin sheet metal blanks. The effects of different process and material variables on the bond quality were studied. Successful bonding of various metal blanks (Ni201, Al3003, and SS304) was obtained. The experimental results from both

Influence of Dissipative Particle Dynamics parameters and wall models on planar micro-channel flows

Science.gov (United States)

Wang, Yuyi; She, Jiangwei; Zhou, Zhe-Wei; microflow Group Team

2017-11-01

Dissipative Particle Dynamics (DPD) is a very effective approach in simulating mesoscale hydrodynamics. The influence of solid boundaries and DPD parameters are typically very strong in DPD simulations. The present work studies a micro-channel Poisseuille flow. Taking the neutron scattering experiment and molecular dynamics simulation result as bench mark, the DPD results of density distribution and velocity profile are systematically studied. The influence of different levels of coarse-graining, the number densities of wall and fluid, conservative force coefficients, random and dissipative force coefficients, different wall model and reflective boundary conditions are discussed. Some mechanisms behind such influences are discussed and the artifacts in the simulation are identified with the bench mark. Chinese natural science foundation (A020405).

The effects of processing parameters on the properties of micro-scale porous surface for a micro-channel reactor

International Nuclear Information System (INIS)

Feng, Yanbing; Mei, Deqing; Qian, Miao; Yi, Zoudongyi; Chen, Zichen

2017-01-01

To improve the performance of hydrogen production via a microchannel reactor with a porous surface, the process of layered powder sintering and dissolution method is optimized, and the effects of processing parameters on the morphological and mechanical properties of the porous surface structure are studied. Based on the preliminary experiments, three key parameters in the process are the size of the NaCl particle, the compaction pressure, and the sintering temperature. Besides, the porous surface structures are evaluated by the specific surface area and compression strength to optimize the influencing variables. Results show that the specific surface area of porous surface structure is determined mainly by the size of NaCl particle, while the pressure and temperature have little influence unexpectedly within the range of experimental condition. With the increase of temperature and pressure, the compression strength will be enhanced, but the increase of the size of NaCl particles will cause the decrease of compression strength. The optimum compaction pressure, sintering temperature, and size of the NaCl particle are obtained respectively. Finally, the optimum parameters have been used to manufacture the micro-channel catalyst support with a porous surface, and its hydrogen production can be maximumly enhanced by 90% compared with the surface fabricated with NaCl particles of 125–150 µ m. (paper)

Strained Si/SiGe MOS transistor model

Directory of Open Access Journals (Sweden)

Tatjana Pešić-Brđanin

2009-06-01

Full Text Available In this paper we describe a new model of surfacechannel strained-Si/SiGe MOSFET based on the extension of non-quasi-static (NQS circuit model previously derived for bulk-Si devices. Basic equations of the NQS model have been modified to account for the new physical parameters of strained-Si and relaxed-SiGe layers. From the comparisons with measurements, it is shown that a modified NQS MOS including steady-state self heating can accurately predict DC characteristics of Strained Silicon MOSFETs.

Effect of hydrogen on passivation quality of SiNx/Si-rich SiNx stacked layers deposited by catalytic chemical vapor deposition on c-Si wafers

International Nuclear Information System (INIS)

Thi, Trinh Cham; Koyama, Koichi; Ohdaira, Keisuke; Matsumura, Hideki

2015-01-01

We investigate the role of hydrogen content and fixed charges of catalytic chemical vapor deposited (Cat-CVD) SiN x /Si-rich SiN x stacked layers on the quality of crystalline silicon (c-Si) surface passivation. Calculated density of fixed charges is on the order of 10 12 cm −2 , which is high enough for effective field effect passivation. Hydrogen content in the films is also found to contribute significantly to improvement in passivation quality of the stacked layers. Furthermore, Si-rich SiN x films deposited with H 2 dilution show better passivation quality of SiN x /Si-rich SiN x stacked layers than those prepared without H 2 dilution. Effective minority carrier lifetime (τ eff ) in c-Si passivated by SiN x /Si-rich SiN x stacked layers is as high as 5.1 ms when H 2 is added during Si-rich SiN x deposition, which is much higher than the case of using Si-rich SiN x films prepared without H 2 dilution showing τ eff of 3.3 ms. - Highlights: • Passivation mechanism of Si-rich SiN x /SiN x stacked layers is investigated. • H atoms play important role in passivation quality of the stacked layer. • Addition of H 2 gas during Si-rich SiN x film deposition greatly enhances effective minority carrier lifetime (τ eff ). • For a Si-rich SiN x film with refractive index of 2.92, τ eff improves from 3.3 to 5.1 ms by H 2 addition

U-Mo/Al-Si interaction: Influence of Si concentration

International Nuclear Information System (INIS)

Allenou, J.; Palancher, H.; Iltis, X.; Cornen, M.; Tougait, O.; Tucoulou, R.; Welcomme, E.; Martin, Ph.; Valot, C.; Charollais, F.; Anselmet, M.C.; Lemoine, P.

2010-01-01

Within the framework of the development of low enriched nuclear fuels for research reactors, U-Mo/Al is the most promising option that has however to be optimised. Indeed at the U-Mo/Al interfaces between U-Mo particles and the Al matrix, an interaction layer grows under irradiation inducing an unacceptable fuel swelling. Adding silicon in limited content into the Al matrix has clearly improved the in-pile fuel behaviour. This breakthrough is attributed to an U-Mo/Al-Si protective layer around U-Mo particles appeared during fuel manufacturing. In this work, the evolution of the microstructure and composition of this protective layer with increasing Si concentrations in the Al matrix has been investigated. Conclusions are based on the characterization at the micrometer scale (X-ray diffraction and energy dispersive spectroscopy) of U-Mo7/Al-Si diffusion couples obtained by thermal annealing at 450 deg. C. Two types of interaction layers have been evidenced depending on the Si content in the Al-Si alloy: the threshold value is found at about 5 wt.% but obviously evolves with temperature. It has been shown that for Si concentrations ranging from 2 to 10 wt.%, the U-Mo7/Al-Si interaction is bi-layered and the Si-rich part is located close to the Al-Si for low Si concentrations (below 5 wt.%) and close to the U-Mo for higher Si concentrations. For Si weight fraction in the Al alloy lower than 5 wt.%, the Si-rich sub-layer (close to Al-Si) consists of U(Al, Si) 3 + UMo 2 Al 20 , when the other sub-layer (close to U-Mo) is silicon free and made of UAl 3 and U 6 Mo 4 Al 43 . For Si weight concentrations above 5 wt.%, the Si-rich part becomes U 3 (Si, Al) 5 + U(Al, Si) 3 (close to U-Mo) and the other sub-layer (close to Al-Si) consists of U(Al, Si) 3 + UMo 2 Al 20 . On the basis of these results and of a literature survey, a scheme is proposed to explain the formation of different types of ILs between U-Mo and Al-Si alloys (i.e. different protective layers).

High spatial and temporal resolution cell manipulation techniques in microchannels.

Science.gov (United States)

Novo, Pedro; Dell'Aica, Margherita; Janasek, Dirk; Zahedi, René P

2016-03-21

The advent of microfluidics has enabled thorough control of cell manipulation experiments in so called lab on chips. Lab on chips foster the integration of actuation and detection systems, and require minute sample and reagent amounts. Typically employed microfluidic structures have similar dimensions as cells, enabling precise spatial and temporal control of individual cells and their local environments. Several strategies for high spatio-temporal control of cells in microfluidics have been reported in recent years, namely methods relying on careful design of the microfluidic structures (e.g. pinched flow), by integration of actuators (e.g. electrodes or magnets for dielectro-, acousto- and magneto-phoresis), or integrations thereof. This review presents the recent developments of cell experiments in microfluidics divided into two parts: an introduction to spatial control of cells in microchannels followed by special emphasis in the high temporal control of cell-stimulus reaction and quenching. In the end, the present state of the art is discussed in line with future perspectives and challenges for translating these devices into routine applications.

Inertia effects on bubble generation in thin T-junction microchannel

Science.gov (United States)

Sugiyama, Kazuyasu; Okubo, Hidehiko; Nabeshima, Seigo; Watamura, Tomoaki

2016-11-01

A numerical study on gas-liquid interface dynamics of bubble generation in a thin microchannel with a squeezed T-junction is performed. In consideration of liquid inertia, the basic equations consist of the Laplace law and the two-dimensional Euler-Darcy equation under the assumption of Hele-Shaw's flow owing to a large width-to-thickness aspect ratio of the channel cross-section. The velocity potential and the interface motion are numerically predicted by means of a boundary element method. The simulated results reasonably capture the experimentally observed behaviors that the interface pinches off at the channel junction and then a bubble forms. For a fixed liquid velocity, the generated bubble is likely to be smaller with decreasing the gas pressure, but the bubble is no longer generated at the gas pressure below a threshold. The bubble size minimized at the generation limit is arranged using the capillary, Reynolds and Weber numbers, and the results imply the significance of the liquid inertia in the bubble generation process in spite of the micrometer-scale phenomena.

Measurements of recent microchannel-plate photomultipliers with significantly increased lifetime

Energy Technology Data Exchange (ETDEWEB)

Uhlig, Fred; Eyrich, Wolfgang; Lehmann, Albert; Britting, Alexander [Universitaet Erlangen, Physikal. Institut IV (Germany); Collaboration: PANDA-Collaboration

2015-07-01

Microchannel-plate photomultipliers (MCP-PMTs) are the favored sensors for the DIRC detectors (Detection of Internally Reflected Cherenkov Light) of the PANDA experiment. They are usable in high magnetic fields of up to 2T and reach a time resolution of better than 50 ps (σ). The anticipated average luminosity of 2.10{sup 32} cm{sup -2} s{sup -1} in the detector requires a rate capability high enough to withstand a detected photon rate of about 200 kHz cm{sup -2} at the MCP-PMT surfaces. The major drawback until recently was the limited lifetime of MCP-PMTs, which appears to be solved for the latest generation of MCP-PMT prototype devices. The aging parameter is the quantum efficiency as a function of the integrated anode charge, which will be in the region of 5 C/cm{sup 2} for the Barrel- and the Disc-DIRC. We simultaneously measured the aging of several MCP-PMTs, which were treated with different methods to enhance the lifetime. Results of these measurements are presented.

Porous SiC/SiC composites development for industrial application

International Nuclear Information System (INIS)

Maeta, S.; Hinoki, T.

2014-01-01

Silicon carbide (SiC) is promising structural materials in nuclear fields due to an excellent irradiation resistance and low activation characteristics. Conventional SiC fibers reinforced SiC matrix (SiC/SiC composites) fabricated by liquid phase sintering (LPS-SiC/SiC composites) have been required high cost and long processing time. And microstructure and mechanical property data of finally obtained LPS-SiC/SiC composites are easily scattered, because quality of the composites depend on personal skill. Thus, conventional LPS-SiC/SiC composites are inadequate for industrial use. In order to overcome these issues, the novel “porous SiC/SiC composites” have been developed by means of liquid phase sintering fabrication process. The composites consist of porous SiC matrix and SiC fibers without conventional carbon interfacial layer. The composites don’t have concerns of the degradation interfacial layer at the severe accident. Porous SiC/SiC composites preform was prepared with a thin sheet shape of SiC, sintering additives and carbon powder mixture by tape casting process which was adopted because of productive and high yielding rate fabrication process. The preform was stacked with SiC fibers and sintered in hot-press at the high temperature in argon environment. The sintered preform was decarburized obtain porous matrix structure by heat-treatment in air. Moreover, mechanical property data scattering of the obtained porous SiC/SiC composites decreased. In the flexural test, the porous SiC/SiC composites showed pseudo-ductile behavior with sufficient strength even after heat treatment at high temperature in air. From these conclusions, it was proven that porous SiC/SiC composites were reliable material at severe environment such as high temperature in air, by introducing tape casting fabrication process that could produce reproducible materials with low cost and simple way. Therefore development of porous SiC/SiC composites for industrial application was

Quantifying the role of noise on droplet decisions in bifurcating microchannels

Science.gov (United States)

Norouzi Darabad, Masoud; Vaughn, Mark; Vanapalli, Siva

2017-11-01

While many aspects of path selection of droplets flowing through a bifurcating microchannel have been studied, there are still unaddressed issues in predicting and controlling droplet traffic. One of the more important is understanding origin of aperiodic patterns. As a new tool to investigate this phenomena we propose monitoring the continuous time response of pressure fluctuations at different locations. Then we use time-series analysis to investigate the dynamics of the system. We suggest that natural system noise is the cause of irregularity in the traffic patterns. Using a mathematical model, we investigate the effect of noise on droplet decisions at the junction. Noise can be derived from different sources including droplet size variation, droplet spacing, and pump induced velocity fluctuation. By analyzing different situations we explain system behavior. We also investigate the ``memory'' of a microfluidic system in terms of the resistance to perturbations that quantify the allowable deviation in operating condition before the system changes state.

Biomorphous SiSiC/Al-Si ceramic composites manufactured by squeeze casting: microstructure and mechanical properties

Energy Technology Data Exchange (ETDEWEB)

Zollfrank, C.; Travitzky, N.; Sieber, H.; Greil, P. [Department of Materials Science, Glass and Ceramics, University of Erlangen-Nuernberg (Germany); Selchert, T. [Advanced Ceramics Group, Technical University of Hamburg-Harburg (Germany)

2005-08-01

SiSiC/Al-Si composites were fabricated by pressure-assisted infiltration of an Al-Si alloy into porous biocarbon preforms derived from the rattan palm. Al-Si alloy was found in the pore channels of the biomorphous SiSiC preform, whereas SiC and carbon were present in the struts. The formation of a detrimental Al{sub 4}C{sub 3}-phase was not observed in the composites. A bending strength of 200 MPa was measured. The fractured surfaces showed pull-out of the Al-alloy. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

Reaction mechanisms at 4H-SiC/SiO2 interface during wet SiC oxidation

Science.gov (United States)

Akiyama, Toru; Hori, Shinsuke; Nakamura, Kohji; Ito, Tomonori; Kageshima, Hiroyuki; Uematsu, Masashi; Shiraishi, Kenji

2018-04-01

The reaction processes at the interface between SiC with 4H structure (4H-SiC) and SiO2 during wet oxidation are investigated by electronic structure calculations within the density functional theory. Our calculations for 4H-SiC/SiO2 interfaces with various orientations demonstrate characteristic features of the reaction depending on the crystal orientation of SiC: On the Si-face, the H2O molecule is stable in SiO2 and hardly reacts with the SiC substrate, while the O atom of H2O can form Si-O bonds at the C-face interface. Two OH groups are found to be at least necessary for forming new Si-O bonds at the Si-face interface, indicating that the oxidation rate on the Si-face is very low compared with that on the C-face. On the other hand, both the H2O molecule and the OH group are incorporated into the C-face interface, and the energy barrier for OH is similar to that for H2O. By comparing the calculated energy barriers for these reactants with the activation energies of oxide growth rate, we suggest the orientation-dependent rate-limiting processes during wet SiC oxidation.

Total Ionizing Dose Effects of Si Vertical Diffused MOSFET with SiO2 and Si3N4/SiO2 Gate Dielectrics

Directory of Open Access Journals (Sweden)

Jiongjiong Mo

2017-01-01

Full Text Available The total ionizing dose irradiation effects are investigated in Si vertical diffused MOSFETs (VDMOSs with different gate dielectrics including single SiO2 layer and double Si3N4/SiO2 layer. Radiation-induced holes trapping is greater for single SiO2 layer than for double Si3N4/SiO2 layer. Dielectric oxidation temperature dependent TID effects are also studied. Holes trapping induced negative threshold voltage shift is smaller for SiO2 at lower oxidation temperature. Gate bias during irradiation leads to different VTH shift for different gate dielectrics. Single SiO2 layer shows the worst negative VTH at VG=0 V, while double Si3N4/SiO2 shows negative VTH shift at VG=-5 V, positive VTH shift at VG=10 V, and negligible VTH shift at VG=0 V.

Nanocatalytic growth of Si nanowires from Ni silicate coated SiC nanoparticles on Si solar cell.

Science.gov (United States)

Parida, Bhaskar; Choi, Jaeho; Ji, Hyung Yong; Park, Seungil; Lim, Gyoungho; Kim, Keunjoo

2013-09-01

We investigated the nanocatalytic growth of Si nanowires on the microtextured surface of crystalline Si solar cell. 3C-SiC nanoparticles have been used as the base for formation of Ni silicate layer in a catalytic reaction with the Si melt under H2 atmosphere at an annealing temperature of 1100 degrees C. The 10-nm thick Ni film was deposited after the SiC nanoparticles were coated on the microtextured surface of the Si solar cell by electron-beam evaporation. SiC nanoparticles form a eutectic alloy surface of Ni silicate and provide the base for Si supersaturation as well as the Ni-Si alloy layer on Si substrate surface. This bottom reaction mode for the solid-liquid-solid growth mechanism using a SiC nanoparticle base provides more stable growth of nanowires than the top reaction mode growth mechanism in the absence of SiC nanoparticles. Thermally excited Ni nanoparticle forms the eutectic alloy and provides collectively excited electrons at the alloy surface, which reduces the activation energy of the nanocatalytic reaction for formation of nanowires.

Oxide Structure Dependence of SiO2/SiOx/3C-SiC/n-Type Si Nonvolatile Resistive Memory on Memory Operation Characteristics

Science.gov (United States)

Yamaguchi, Yuichiro; Shouji, Masatsugu; Suda, Yoshiyuki

2012-11-01

We have investigated the dependence of the oxide layer structure of our previously proposed metal/SiO2/SiOx/3C-SiC/n-Si/metal metal-insulator-semiconductor (MIS) resistive memory device on the memory operation characteristics. The current-voltage (I-V) measurement and X-ray photoemission spectroscopy results suggest that SiOx defect states mainly caused by the oxidation of 3C-SiC at temperatures below 1000 °C are related to the hysteresis memory behavior in the I-V curve. By restricting the SiOx interface region, the number of switching cycles and the on/off current ratio are more enhanced. Compared with a memory device formed by one-step or two-step oxidation of 3C-SiC, a memory device formed by one-step oxidation of Si/3C-SiC exhibits a more restrictive SiOx interface with a more definitive SiO2 layer and higher memory performances for both the endurance switching cycle and on/off current ratio.

Magnetic manipulation of particles and cells in ferrofluid flow through straight microchannels using two magnets

Science.gov (United States)

Zeng, Jian

Microfluidic devices have been increasingly used in the past two decades for particle and cell manipulations in many chemical and biomedical applications. A variety of force fields have been demonstrated to control particle and cell transport in these devices including electric, magnetic, acoustic, and optical forces etc. Among these particle handling techniques, the magnetic approach provides clear advantages over others such as low cost, noninvasive, and free of fluid heating issues. However, the current knowledge of magnetic control of particle transport is still very limited, especially lacking is the handling of diamagnetic particle. This thesis is focused on the magnetic manipulation of diamagnetic particles and cells in ferrofluid flow through the use of a pair of permanent magnets. By varying the configuration of the two magnets, diverse operations of particles and cells is implemented in a straight microchannel that can potentially be integrated into lab-on-a-chip devices for various applications. First, an approach for embedding two, symmetrically positioned, repulsive permanent magnets about a straight rectangular microchannel in a PDMS-based microfluidic device is developed for particle focusing. Focusing particles and cells into a tight stream is often required in order for continuous detection, counting, and sorting. The closest distance between the magnets is limited only by the size of the magnets involved in the fabrication process. The device is used to implement and investigate the three-dimensional magnetic focusing of polystyrene particles in ferrofluid microflow with both top-view and side-view visualizations. The effects of flow speed and particle size on the particle focusing effectiveness are studied. This device is also applied to magnetically focus yeast cells in ferrofluid, which proves to be biocompatible as verified by cell viability test. In addition, an analytical model is developed and found to be able to predict the experimentally

Interfacial characterization of CVI-SiC/SiC composites

International Nuclear Information System (INIS)

Yang, W.; Kohyama, A.; Noda, T.; Katoh, Y.; Hinoki, T.; Araki, H.; Yu, J.

2002-01-01

The mechanical properties of the interfaces of two families of chemical vapor infiltration SiC/SiC composites, advanced Tyranno-SA and Hi-Nicalon fibers reinforced SiC/SiC composites with various carbon and SiC/C interlayers, were investigated by single fiber push-out/push-back tests. Interfacial debonding and fibers sliding mainly occurred adjacent to the first carbon layer on the fibers. The interfacial debonding strengths and frictional stresses for both Tyranno-SA/SiC and Hi-Nicalon/SiC composites were correlated with the first carbon layer thickness. Tyranno-SA/SiC composites exhibited much larger interfacial frictional stresses compared to Hi-Nicalon/SiC composites. This was assumed to be mainly contributed by the rather rough surface of the Tyranno-SA fiber

Research on a Micro-Nano Si/SiGe/Si Double Heterojunction Electro-Optic Modulation Structure

Directory of Open Access Journals (Sweden)

Song Feng

2018-01-01

Full Text Available The electro-optic modulator is a very important device in silicon photonics, which is responsible for the conversion of optical signals and electrical signals. For the electro-optic modulator, the carrier density of waveguide region is one of the key parameters. The traditional method of increasing carrier density is to increase the external modulation voltage, but this way will increase the modulation loss and also is not conducive to photonics integration. This paper presents a micro-nano Si/SiGe/Si double heterojunction electro-optic modulation structure. Based on the band theory of single heterojunction, the barrier heights are quantitatively calculated, and the carrier concentrations of heterojunction barrier are analyzed. The band and carrier injection characteristics of the double heterostructure structure are simulated, respectively, and the correctness of the theoretical analysis is demonstrated. The micro-nano Si/SiGe/Si double heterojunction electro-optic modulation is designed and tested, and comparison of testing results between the micro-nano Si/SiGe/Si double heterojunction micro-ring electro-optic modulation and the micro-nano Silicon-On-Insulator (SOI micro-ring electro-optic modulation, Free Spectrum Range, 3 dB Bandwidth, Q value, extinction ratio, and other parameters of the micro-nano Si/SiGe/Si double heterojunction micro-ring electro-optic modulation are better than others, and the modulation voltage and the modulation loss are lower.

Low dose irradiation performance of SiC interphase SiC/SiC composites

International Nuclear Information System (INIS)

Snead, L.L.; Lowden, R.A.; Strizak, J.; More, K.L.; Eatherly, W.S.; Bailey, J.; Williams, A.M.; Osborne, M.C.; Shinavski, R.J.

1998-01-01

Reduced oxygen Hi-Nicalon fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carbide (SiC) matrix and interphases of either 'porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1 x 10 25 n m -2 (E>0.1 MeV) in the temperature range of 260 to 1060 C. The unirradiated properties of these composites are superior to previously studied ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress was observed after irradiation for the multilayer SiC interphase material and a slight reduction in matrix microcracking stress was observed for the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest irradiation temperature. The ultimate fracture stress (in four point bending) following irradiation for the multilayer SiC and porous SiC interphase materials was reduced by 15% and 30%, respectively, which is an improvement over the 40% reduction suffered by irradiated ceramic grade Nicalon fiber materials fabricated in a similar fashion, though with a carbon interphase. The degradation of the mechanical properties of these composites is analyzed by comparison with the irradiation behavior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (CVD) SiC. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation of fiber and hence composite is reduced for the newer low-oxygen fiber. (orig.)

Carbon redistribution and precipitation in high temperature ion-implanted strained Si/SiGe/Si multi-layered structures

DEFF Research Database (Denmark)

Gaiduk, Peter; Hansen, John Lundsgaard; Nylandsted Larsen, Arne

2014-01-01

Graphical abstract Carbon depth profiles after high temperature implantation in strained Si/SiGe/Si multilayered system and induced structural defects.......Graphical abstract Carbon depth profiles after high temperature implantation in strained Si/SiGe/Si multilayered system and induced structural defects....

High-dose MeV electron irradiation of Si-SiO2 structures implanted with high doses Si+

Science.gov (United States)

Kaschieva, S.; Angelov, Ch; Dmitriev, S. N.

2018-03-01

The influence was studied of 22-MeV electron irradiation on Si-SiO2 structures implanted with high-fluence Si+ ions. Our earlier works demonstrated that Si redistribution is observed in Si+-ion-implanted Si-SiO2 structures (after MeV electron irradiation) only in the case when ion implantation is carried out with a higher fluence (1016 cm-2). We focused our attention on the interaction of high-dose MeV electron irradiation (6.0×1016 cm-2) with n-Si-SiO2 structures implanted with Si+ ions (fluence 5.4×1016 cm-2 of the same order magnitude). The redistribution of both oxygen and silicon atoms in the implanted Si-SiO2 samples after MeV electron irradiation was studied by Rutherford back-scattering (RBS) spectroscopy in combination with a channeling technique (RBS/C). Our results demonstrated that the redistribution of oxygen and silicon atoms in the implanted samples reaches saturation after these high doses of MeV electron irradiation. The transformation of amorphous SiO2 surface into crystalline Si nanostructures (after MeV electron irradiation) was evidenced by atomic force microscopy (AFM). Silicon nanocrystals are formed on the SiO2 surface after MeV electron irradiation. The shape and number of the Si nanocrystals on the SiO2 surface depend on the MeV electron irradiation, while their size increases with the dose. The mean Si nanocrystals height is 16-20 nm after irradiation with MeV electrons at the dose of 6.0×1016 cm-2.

Applications of Si/SiGe heterostructures to CMOS devices

International Nuclear Information System (INIS)

Sidek, R.M.

1999-03-01

For more than two decades, advances in MOSFETs used in CMOS VLSI applications have been made through scaling to ever smaller dimensions for higher packing density, faster circuit speed and lower power dissipation. As scaling now approaches nanometer regime, the challenge for further scaling becomes greater in terms of technology as well as device reliability. This work presents an alternative approach whereby non-selectively grown Si/SiGe heterostructure system is used to improve device performance or to relax the technological challenge. SiGe is considered to be of great potential because of its promising properties and its compatibility with Si, the present mainstream material in microelectronics. The advantages of introducing strained SiGe in CMOS technology are examined through two types of device structure. A novel structure has been fabricated in which strained SiGe is incorporated in the source/drain of P-MOSFETs. Several advantages of the Si/SiGe source/drain P-MOSFETs over Si devices are experimentally, demonstrated for the first time. These include reduction in off-state leakage and punchthrough susceptibility, degradation of parasitic bipolar transistor (PBT) action, suppression of CMOS latchup and suppression of PBT-induced breakdown. The improvements due to the Si/SiGe heterojunction are supported by numerical simulations. The second device structure makes use of Si/SiGe heterostructure as a buried channel to enhance the hole mobility of P-MOSFETs. The increase in the hole mobility will benefit the circuit speed and device packing density. Novel fabrication processes have been developed to integrate non-selective Si/SiGe MBE layers into self-aligned PMOS and CMOS processes based on Si substrate. Low temperature processes have been employed including the use of low-pressure chemical vapor deposition oxide and plasma anodic oxide. Low field mobilities, μ 0 are extracted from the transfer characteristics, Id-Vg of SiGe channel P-MOSFETs with various Ge

Methods for applying microchannels to separate methane using liquid absorbents, especially ionic liquid absorbents from a mixture comprising methane and nitrogen

Science.gov (United States)

Tonkovich, Anna Lee Y [Dublin, OH; Litt, Robert D [Westerville, OH; Dongming, Qiu [Dublin, OH; Silva, Laura J [Plain City, OH; Lamont, Micheal Jay [Plain City, OH; Fanelli, Maddalena [Plain City, OH; Simmons, Wayne W [Plain city, OH; Perry, Steven [Galloway, OH

2011-10-04

Methods of using microchannel separation systems including absorbents to improve thermal efficiency and reduce parasitic power loss. Energy is typically added to desorb methane and then energy or heat is removed to absorb methane using a working solution. The working solution or absorbent may comprise an ionic liquid, or other fluids that demonstrate a difference in affinity between methane and nitrogen in a solution.

Irradiation effect on Nite-SiC/SiC composites

International Nuclear Information System (INIS)

Hinoki, T.; Choi, Y.B.; Kohyama, A.; Ozawa, K.

2007-01-01

Full text of publication follows: Silicon carbide (SiC) and SiC composites are significantly attractive materials for nuclear application in particular due to exceptional low radioactivity, excellent high temperature mechanical properties and chemical stability. Despite of the excellent potential of SiC/SiC composites, the prospect of industrialization has not been clear mainly due to the low productivity and the high material cost. Chemical vapor infiltration (CVI) method can produce the excellent SiC/SiC composites with highly crystalline and excellent mechanical properties. It has been reported that the high purity SiC/SiC composites reinforced with highly crystalline fibers and fabricated by CVI method is very stable to neutron irradiation. However the production cost is high and it is difficult to fabricate thick and dense composites by CVI method. The novel processing called Nano-powder Infiltration and Transient Eutectic Phase (NITE) Processing has been developed based on the liquid phase sintering (LPS) process modification. The NITE processing can achieve both the excellent material quality and the low processing cost. The productivity of the processing is also excellent, and various kinds of shape and size of SiC/SiC composites can be produced by the NITE processing. The NITE processing can form highly crystalline matrix, which is requirement for nuclear application. The objective of this work is to understand irradiation effect of the NITESiC/SiC composites. The SiC/SiC composites used were reinforced with high purity SiC fibers, Tyranno TM SA and fabricated by the NITE method. The NITE-SiC/SiC composite bars and reference monolithic SiC bars fabricated by CVI and NITE were irradiated at up to 1.0 dpa and 600-1000 deg. C at JMTR, Japan. Mechanical properties of non-irradiated and irradiated NITESiC/ SiC composites bars were evaluated by tensile tests. Monolithic SiC bars were evaluated by flexural tests. The fracture surface was examined by SEM. Ultimate

Centrifugal Separation Device Based on Two-Layer Laminar Flow in Microchannels for High-Throughput and Continuous Blood Cell/Plasma Separation

Science.gov (United States)

Taizo Kobayashi,; Taisuke Funamoto,; Makoto Hosaka,; Satoshi Konishi,

2010-07-01

This paper presents a novel type of centrifugation device that is based on the two-layer laminar flow in micro flow channels for continuous blood cell/plasma separation. We propose to rotate the flow channels which are arranged along the circumference around the rotational axis. Downsizing the channel width reduced both the cell sedimentation time and the required centrifugal force, because the channel width corresponds to the centrifugal sedimentation length. First, plasma and cells were continuously extracted from pig blood in each of the branch channels using a milled acrylic prototype device (channel width = 800 μm, volume = 150 μl). Next, the relationship between the channel width (125, 250, and 500 μm) and the sedimentation time taken for various centrifugal forces (2.3, 9, 36, and 145 G) was evaluated using the downsized microchannels fabricated by hot-embossing and thermal bonding technologies. Using downsized microchannels with a width of 125 μm successfully reduced the sedimentation time to 85 s as compared to the sedimentation time of 270 s for a channel of a width of 500 μm, when a centrifugal force of 2.3 G was applied. The use of the proposed device did not result in obvious hemolysis at the centrifugal forces lower than 335 G.

Stability analysis of SiO2/SiC multilayer coatings

International Nuclear Information System (INIS)

Fu Zhiqiang; Jean-Charles, R.

2006-01-01

The stability behaviours of SiC coatings and SiO 2 /SiC coatings in helium with little impurities are studied by HSC Chemistry 4.1, the software for analysis of Chemical reaction and equilibrium in multi-component complex system. It is found that in helium with a low partial pressure of oxidative impurities under different total pressure, the key influence factor controlling T cp of SiC depends is the partial pressure of oxidative impurities; T cp of SiC increases with the partial pressure of oxidative impurities. In helium with a low partial pressure of different impurities, the key influence factor of T cs of SiO 2 are both the partial pressure of impurities and the amount of impurities for l mol SiO 2 ; T cs of SiO 2 increases with the partial pressure of oxidative impurities at the same amount of the impurities for 1 mol SiO 2 while it decreases with the amount of the impurities for 1 mm SiO 2 at the same partial pressure of the impurities. The influence of other impurities on T cp of SiC in He-O 2 is studied and it is found that CO 2 , H 2 O and N-2 increase T cp of SiC in He-O 2 while H 2 , CO and CH 4 decrease T cp of SiC He-O 2 . When there exist both oxidative impurities and reductive impurities, their effect on T cs of SiO 2 can be suppressed by the other. In HTR-10 operation atmosphere, SiO 2 /SiC coatings can keep stable status at higher temperature than SiC coatings, so SiO 2 /SiC coatings is more suitable to improve the oxidation resistance of graphite in HTR-10 operation atmosphere compared with SiC coatings. (authors)

Si-O-Si bond-angle distribution in vitreous silica from first-principles 29Si NMR analysis

International Nuclear Information System (INIS)

Mauri, Francesco; Pasquarello, Alfredo; Pfrommer, Bernd G.; Yoon, Young-Gui; Louie, Steven G.

2000-01-01

The correlation between 29 Si chemical shifts and Si-O-Si bond angles in SiO 2 is determined within density-functional theory for the full range of angles present in vitreous silica. This relation closely reproduces measured shifts of crystalline polymorphs. The knowledge of the correlation allows us to reliably extract from the experimental NMR spectrum the mean (151 degree sign ) and the standard deviation (11 degree sign ) of the Si-O-Si angular distribution of vitreous silica. In particular, we show that the Mozzi-Warren Si-O-Si angular distribution is not consistent with the NMR data. This analysis illustrates the potential of our approach for structural determinations of silicate glasses. (c) 2000 The American Physical Society

Time response of fast-gated microchannel plates used as x-ray detectors

International Nuclear Information System (INIS)

Turner, R.E.; Bell, P.; Hanks, R.; Kilkenny, J.D.; Landen, N.; Power, G.; Wiedwald, J.; Meier, M.

1990-01-01

We report measurements of the time response of fast-gated, micro- channel plate (MCP) detectors, using a <10 ps pulsewidth ultra-violet laser and an electronic sampling system to measure time resolutions to better than 25 ps. The results show that framing times of less than 100 ps are attainable with high gain. The data is compared to a Monte Carlo calculation, which shows good agreement. We also measured the relative sensitivity as a function of DC bias, and saturation effects for large signal inputs. In part B, we briefly describe an electrical ''time-of-flight'' technique, which we have used to measure the response time of a fast-gated microchannel plate (MCP). Thinner MCP's than previously used have been tested, and, as expected, show fast gating times and smaller electron multiplication. A preliminary design for an x-ray pinhole camera, using a thin MCP, is presented. 7 refs., 6 figs

Interfacial microstructure of NiSi x/HfO2/SiO x/Si gate stacks

International Nuclear Information System (INIS)

Gribelyuk, M.A.; Cabral, C.; Gusev, E.P.; Narayanan, V.

2007-01-01

Integration of NiSi x based fully silicided metal gates with HfO 2 high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi x film. Ni content varies near the NiSi/HfO x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi x /HfO 2 interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi x /HfO x was found higher than that of poly-Si/HfO 2 , likely due to compositional non-uniformity of NiSi x . No intermixing between Hf, Ni and Si beyond interfacial roughness was observed

Downstream pressure and elastic wall reflection of droplet flow in a T-junction microchannel

Science.gov (United States)

Pang, Yan; Liu, Zhaomiao; Zhao, Fuwang

2016-08-01

This paper discusses pressure variation on a wall during the process of liquid flow and droplet formation in a T-junction microchannel. Relevant pressure in the channel, deformation of the elastic wall, and responses of the droplet generation are analyzed using a numerical method. The pressure difference between the continuous and dispersed phases can indicate the droplet-generation period. The pressure along the channel of the droplet flow is affected by the position of droplets, droplet-generation period, and droplet escape from the outlet. The varying pressures along the channel cause a nonuniform deformation of the wall when they are elastic. The deformation is a vibration and has the same period as the droplet generation arising from the process of droplet formation.

Luminescence properties of Si-capped β-FeSi{sub 2} nanodots epitaxially grown on Si(001) and (111) substrates

Energy Technology Data Exchange (ETDEWEB)

Amari, Shogo; Ichikawa, Masakazu [Department of Applied Physics, Graduate School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan); Nakamura, Yoshiaki, E-mail: nakamura@ee.es.osaka-u.ac.jp [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531 (Japan); PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)

2014-02-28

We studied the luminescence properties of Si-capped β-FeSi{sub 2} nanodots (NDs) epitaxially grown on Si substrates by using photoluminescence (PL) and electroluminescence (EL) spectroscopies. Codepositing Fe and Si on ultrathin SiO{sub 2} films induced the self-assembly of epitaxial β-FeSi{sub 2} NDs. The PL spectra of the Si/β-FeSi{sub 2} NDs/Si structure depended on the crystal orientation of the Si substrate. These structures exhibited a broad PL peak near 0.8 eV on both Si(001) and (111) substrates. The PL intensity depended on the shape of the β-FeSi{sub 2} NDs. For the flat NDs, which exhibited higher PL intensity, we also recorded EL spectra. We explained the luminescence properties of these structures by the presence of nanostructured Si offering radiative electronic states in the Si cap layers, generated by nano-stressors for upper Si layer: the strain-relaxed β-FeSi{sub 2} NDs.

Thermal shock properties of 2D-SiCf/SiC composites

International Nuclear Information System (INIS)

Lee, Sang Pill; Lee, Jin Kyung; Son, In Soo; Bae, Dong Su; Kohyama, Akira

2012-01-01

This paper dealt with the thermal shock properties of SiC f /SiC composites reinforced with two dimensional SiC fabrics. SiC f /SiC composites were fabricated by a liquid phase sintering process, using a commercial nano-size SiC powder and oxide additive materials. An Al 2 O 3 –Y 2 O 3 –SiO 2 powder mixture was used as a sintering additive for the consolidation of SiC matrix region. In this composite system, Tyranno SA SiC fabrics were also utilized as a reinforcing material. The thermal shock test for SiC f /SiC composites was carried out at the elevated temperature. Both mechanical strength and microstructure of SiC f /SiC composites were investigated by means of optical microscopy, SEM and three point bending test. SiC f /SiC composites represented a dense morphology with a porosity of about 8.2% and a flexural strength of about 160 MPs. The characterization of SiC f /SiC composites was greatly affected by the history of cyclic thermal shock. Especially, SiC f /SiC composites represented a reduction of flexural strength at the thermal shock temperature difference higher than 800 °C.

SiC/SiC Cladding Materials Properties Handbook

Energy Technology Data Exchange (ETDEWEB)

Snead, Mary A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koyanagi, Takaaki [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Singh, Gyanender P. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-08-01

When a new class of material is considered for a nuclear core structure, the in-pile performance is usually assessed based on multi-physics modeling in coordination with experiments. This report aims to provide data for the mechanical and physical properties and environmental resistance of silicon carbide (SiC) fiber–reinforced SiC matrix (SiC/SiC) composites for use in modeling for their application as accidenttolerant fuel cladding for light water reactors (LWRs). The properties are specific for tube geometry, although many properties can be predicted from planar specimen data. This report presents various properties, including mechanical properties, thermal properties, chemical stability under normal and offnormal operation conditions, hermeticity, and irradiation resistance. Table S.1 summarizes those properties mainly for nuclear-grade SiC/SiC composites fabricated via chemical vapor infiltration (CVI). While most of the important properties are available, this work found that data for the in-pile hydrothermal corrosion resistance of SiC materials and for thermal properties of tube materials are lacking for evaluation of SiC-based cladding for LWR applications.

Exceptional cracking behavior in H-implanted Si/B-doped Si0.70Ge0.30/Si heterostructures

Science.gov (United States)

Chen, Da; Wang, Dadi; Chang, Yongwei; Li, Ya; Ding, Rui; Li, Jiurong; Chen, Xiao; Wang, Gang; Guo, Qinglei

2018-01-01

The cracking behavior in H-implanted Si/B-doped Si0.70Ge0.30/Si structures after thermal annealing was investigated. The crack formation position is found to closely correlate with the thickness of the buried Si0.70Ge0.30 layer. For H-implanted Si containing a buried 3-nm-thick B-doped Si0.70Ge0.30 layer, localized continuous cracking occurs at the interfaces on both sides of the Si0.70Ge0.30 interlayer. Once the thickness of the buried Si0.70Ge0.30 layer increases to 15 and 70 nm, however, a continuous sharp crack is individually observed along the interface between the Si substrate and the B-doped Si0.70Ge0.30 interlayer. We attribute this exceptional cracking behavior to the existence of shear stress on both sides of the buried Si0.70Ge0.30 layer and the subsequent trapping of hydrogen, which leads to a crack in a well-controlled manner. This work may pave the way for high-quality Si or SiGe membrane transfer in a feasible manner, thus expediting its potential applications to ultrathin silicon-on-insulator (SOI) or silicon-germanium-on-insulator (SGOI) production.

A Microchannel Inlet to Reduce High-Velocity Impact Fragmentation of Molecules in Orbital and Fly-by Mass Spectrometers

Science.gov (United States)

Turner, Brandon; Anupriya, Anupriya; Sevy, Eric; Austin, Daniel E.

2017-10-01

Closed source neutral mass spectrometers are often used on flyby missions to characterize the molecular components of planetary exospheres. In a typical closed source, neutrals are thermalized as they deflect off the walls within a spherical antechamber prior to ionization and mass analysis. However, the high kinetic energy of each molecule as it impacts the chamber can lead to fragmentation before the ionization region is reached. Due to this fragmentation, the original composition of the molecule can be altered, leading to ambiguous identification.Even knowing the fragmentation pathways that occur may not allow deconvolution of data to give the correct composition. Only stable, volatile fragments will be observed in the subsequent mass spectrometer and different organic compounds likely give similar fragmentation products. Simply detecting these products will not lead to unambiguous identication of the precursor molecules. Here, we present a hardware solution to this problem—an inlet that reduces the fragmentation of molecules that impact at high velocities.We present a microchannel inlet that reduces the impact fragmentation by allowing the molecules to dissipate kinetic energy faster than their respective dissociation lifetimes. Preliminary calculations indicate that impact-induced fragmentation will be reduced up to three orders of magnitude compared with conventional closed sources by using this inlet. The benefits of such an inlet apply to any orbital or flyby velocity. The microchannel inlet enables detection of semi-volatile molecules that were previously undetectable due to impact fragmentation.

Mean secondary electron yield of avalanche electrons in the channels of a microchannel plate detector

International Nuclear Information System (INIS)

Funsten, H.O.; Suszcynsky, D.M.; Harper, R.W.

1996-01-01

By modeling the statistical evolution of an avalanche created by 20 keV protons impacting the input surface of a z-stack microchannel plate (MCP) detector, the mean secondary electron yield γ C of avalanche electrons propagating through a MCP channel is measured to equal 1.37 for 760 V per MCP in the z stack. This value agrees with other studies that used MCP gain measurements to infer γ C . The technique described here to measure γ C is independent of gain saturation effects and simplifying assumptions used in the segmented dynode model, both of which can introduce errors when inferring γ C through gain measurements. copyright 1996 American Institute of Physics

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process

Science.gov (United States)

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-01

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Erythorbic acid promoted formation of CdS QDs in a tube-in-tube micro-channel reactor

Energy Technology Data Exchange (ETDEWEB)

Liang, Yan; Tan, Jiawei; Wang, Jiexin; Chen, Jianfeng [State Key Laboratory of Organic–Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Research Center of the Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029 (China); Sun, Baochang, E-mail: sunbc@mail.buct.edu.cn [State Key Laboratory of Organic–Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Research Center of the Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029 (China); Shao, Lei, E-mail: shaol@mail.buct.edu.cn [State Key Laboratory of Organic–Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Research Center of the Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029 (China)

2014-12-15

Erythorbic acid assistant synthesis of CdS quantum dots (QDs) was conducted by homogeneous mixing of two continuous liquids in a high-throughput microporous tube-in-tube micro-channel reactor (MTMCR) at room temperature. The effects of the micropore size of the MTMCR, liquid flow rate, mixing time and reactant concentration on the size and size distribution of CdS QDs were investigated. It was found that the size and size distribution of CdS QDs could be tuned in the MTMCR. A combination of erythorbic acid promoted formation technique with the MTMCR may be a promising pathway for controllable mass production of QDs.

Avalanche transistor pulser for fast-gated operation of micro-channel plate image-intensifiers

International Nuclear Information System (INIS)

Lundy, A.; Parker, J.R.; Lunsford, J.S.; Martin, A.D.

1977-01-01

Transistors operated in the avalanche mode are employed to generate a 1000 volt 10 to 30 nsec wide pulse with less than 4 nsec rise and fall times. This pulse is resistively attenuated to approximately equal to 270 volts and drives the image intensifier tube which is a load of approximately equal to 200 pf. To reduce stray inductance and capacitance, transistor chips were assembled on a thick-film hybrid substrate. Circuit parameters, operating conditions, and coupling to the microchannel plate image-intensifier (MCPI 2 ) tube are described. To provide dc operating voltages and control of transient voltages on the MCPI 2 tube a resistance-capacitance network has been developed which (a) places the MCPI 2 output phosphor at ground, (b) provides programmable gains in ''f-stop'' steps, and (c) minimizes voltage transients on the MCPI 2 tube

Electrical properties of Si/Si1-xGex/Si inverted modulation doped structures

International Nuclear Information System (INIS)

Sadeghzadeh, M.A.

1998-12-01

This thesis is a report of experimental investigations of growth strategy and electrical properties of Si/Si 1-x Ge x /Si inverted Modulation Doped (MD) structures grown by solid source Molecular Beam Epitaxy (MBE). If the grown Si layer is B-doped at some distance (as spacer) before or after the alloy layer, this remote doping induces the formation of a quasi Two Dimensional Hole Gas (2-DHG) near to the inverted (SiGe on Si) or normal (Si on SiGe) heterointerfaces of the Si/Si 1-x Ge x /Si quantum well, respectively. The latter arrangement is the well known 'normal' MD structure but the former one is the so-called 'inverted' MD structure which is of great interest for Field Effect Transistor (FET) applications. A reproducible growth strategy was employed by the use of a thick (400nm) Si cap for inverted MD structures with Ge composition in the range of 16-23%. Boron segregation and cap surface charges are significant in these inverted structures with small ( 20nm) spacer layers, respectively. It was demonstrated by secondary ion mass spectroscopy (SIMS) that boron segregation, which causes a reduction in the effective spacer dimension, can be suppressed by growth interruption after boron doping. The enhancement in hole sheet density with increasing Si cap layer thickness, is attributed to a reduction in the influence of positive surface charges in these structures. Top-gated devices were fabricated using these structures and the hole sheet density could be varied by applying a voltage to the metal-semiconductor gate, and the maximum Hall mobility of 5550 cm 2 V -1 s -1 with 4.2x10 11 cm -2 was measured (at 1.6K) in these structures. Comparison of measured Hall mobility (at 4.2K) as a function of hole sheet density in normal and inverted MD structures implies that both 2-DHG confined at normal and/or inverted structures are subjected to very similar interface charge, roughness, and alloy scattering potentials. Low temperatures magnetotransport measurements (down to

Abrupt GaP/Si hetero-interface using bistepped Si buffer

Energy Technology Data Exchange (ETDEWEB)

Ping Wang, Y., E-mail: yanping.wang@insa-rennes.fr; Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O. [UMR FOTON, CNRS, INSA Rennes, Rennes F-35708 (France); Stodolna, J.; Ponchet, A. [CEMES-CNRS, Université de Toulouse, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 04 (France); Bahri, M.; Largeau, L.; Patriarche, G. [Laboratoire de Photonique et Nanostructures, CNRS UPR 20, Route de Nozay, Marcoussis 91460 (France); Magen, C. [LMA, INA-ARAID, and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza (Spain)

2015-11-09

We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth.

Abrupt GaP/Si hetero-interface using bistepped Si buffer

International Nuclear Information System (INIS)

Ping Wang, Y.; Kuyyalil, J.; Nguyen Thanh, T.; Almosni, S.; Bernard, R.; Tremblay, R.; Da Silva, M.; Létoublon, A.; Rohel, T.; Tavernier, K.; Le Corre, A.; Cornet, C.; Durand, O.; Stodolna, J.; Ponchet, A.; Bahri, M.; Largeau, L.; Patriarche, G.; Magen, C.

2015-01-01

We evidence the influence of the quality of the starting Si surface on the III-V/Si interface abruptness and on the formation of defects during the growth of III-V/Si heterogeneous crystal, using high resolution transmission electron microscopy and scanning transmission electron microscopy. GaP layers were grown by molecular beam epitaxy on vicinal Si (001). The strong effect of the Si substrate chemical preparation is first demonstrated by studying structural properties of both Si homoepitaxial layer and GaP/Si heterostructure. It is then shown that choosing adequate chemical preparation conditions and subsequent III-V regrowth conditions enables the quasi-suppression of micro-twins in the epilayer. Finally, the abruptness of GaP/Si interface is found to be very sensitive to the Si chemical preparation and is improved by the use of a bistepped Si buffer prior to III-V overgrowth

Synthesis and structural property of Si nanosheets connected to Si nanowires using MnCl{sub 2}/Si powder source

Energy Technology Data Exchange (ETDEWEB)

Meng, Erchao [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Ueki, Akiko [Toyota Central R& D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Meng, Xiang [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Suzuki, Hiroaki [Graduate School of Engineering, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Itahara, Hiroshi [Toyota Central R& D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192 (Japan); Tatsuoka, Hirokazu, E-mail: tatsuoka.hirokazu@shizuoka.ac.jp [Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johuku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan)

2016-08-15

Graphical abstract: Si nanosheets connected to Si nanowires synthesized using a MnCl{sub 2}/Si powder source with an Au catalyst avoid the use of air-sensitive SiH{sub 4} or SiCl{sub 4}. It was evident from these structural features of the nanosheets (leaf blade) with nanowires (petiole) that the nanosheets were formed by the twin-plane reentrant-edge mechanism. The feature of the observed lattice fringes of the Si(111) nanosheets was clearly explained by the interference with the extra diffraction spots that arose due to the reciprocal lattice streaking effect. - Highlights: • New Si nanosheets connected to Si nanowires were synthesized using MnCl{sub 2}/Si powders. • The synthesis method has benefits in terms of avoiding air sensitive SiH{sub 4} or SiCl{sub 4}. • Structural property and electron diffraction of the Si nanosheets were clarified. • Odd lattice fringes of the Si nanosheets observed by HRTEM were clearly explained. - Abstract: Si nanosheets connected to Si nanowires were synthesized using a MnCl{sub 2}/Si powder source with an Au catalyst. The synthesis method has benefits in terms of avoiding conventionally used air-sensitive SiH{sub 4} or SiCl{sub 4}. The existence of the Si nanosheets connected to the Si<111> nanowires, like sprouts or leaves with petioles, was observed, and the surface of the nanosheets was Si{111}. The nanosheets were grown in the growth direction of <211> perpendicular to that of the Si nanowires. It was evident from these structural features of the nanosheets that the nanosheets were formed by the twin-plane reentrant-edge mechanism. The feature of the observed lattice fringes, which do not appear for Si bulk crystals, of the Si(111) nanosheets obtained by high resolution transmission electron microscopy was clearly explained due to the extra diffraction spots that arose by the reciprocal lattice streaking effect.

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process.

Science.gov (United States)

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-25

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Understanding the dynamic performance of microchannel plates in pulsed mode

International Nuclear Information System (INIS)

Ray Thomas; Ming Wu; Nathan Joseph; Craig Kruschwitz; Gregroy A. Rochau

2007-01-01

The dynamic performance of a microchannel plate (MCP) is highly dependent on the high-voltage waveforms that are applied to it. Impedance mismatches in MCP detectors can significantly vary the waveforms on the MCP compared to the input pulses. High-voltage pulse waveforms launched onto surface coatings on the MCPs have historically been difficult and expensive to measure. Over the past few years, we have developed and tested techniques utilizing probes to measure the voltage propagation on the surface of MCPs. Square and Gaussian pulses with widths ranging from 200 ps to 2 ns have been applied. We have investigated the effects of coating thickness, microstrip width, and openended versus terminated strips. These data provide a wealth of knowledge that is enabling a better understanding of images recorded with these devices. This presentation discusses a method for measuring voltage profiles on the surface of the MCP and presents Monte Carlo simulations of the optical gate profiles based on the measured waveforms. Excellent agreement in the optical gate profiles have been achieved between the simulations and the experimental measurements using a short-pulse ultraviolet laser

Formation, structure, and phonon confinement effect of nanocrystalline Si1-xGex in SiO2-Si-Ge cosputtered films

International Nuclear Information System (INIS)

Yang, Y.M.; Wu, X.L.; Siu, G.G.; Huang, G.S.; Shen, J.C.; Hu, D.S.

2004-01-01

Using magnetron cosputtering of SiO 2 , Ge, and Si targets, Si-based SiO 2 :Ge:Si films were fabricated for exploring the influence of Si target proportion (P Si ) and annealing temperature (Ta) on formation, local structure, and phonon properties of nanocrystalline Si 1-x Ge x (nc-Si 1-x Ge x ). At low P Si and Ta higher than 800 deg. C, no nc-Si 1-x Ge x but a kind of composite nanocrystal consisting of a Ge core, GeSi shell, and amorphous Si outer shell is formed in the SiO 2 matrix. At moderate P Si , nc-Si 1-x Ge x begins to be formed at Ta=800 deg. C and coexists with nc-Ge at Ta=1100 deg. C. At high P Si , it was disclosed that both optical phonon frequency and lattice spacing of nc-Si 1-x Ge x increase with raising Ta. The possible origin of this phenomenon is discussed by considering three factors, the phonon confinement, strain effect, and composition variation of nc-Si 1-x Ge x . This work will be helpful in understanding the growth process of ternary GeSiO films and beneficial to further investigations on optical properties of nc-Ge 1-x Si x in the ternary matrix

Si/SiGe heterointerfaces in one-, two-, and three-dimensional nanostructures: their impact on SiGe light emission

Science.gov (United States)

Lockwood, David; Wu, Xiaohua; Baribeau, Jean-Marc; Mala, Selina; Wang, Xialou; Tsybeskov, Leonid

2016-03-01

Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide- semiconductor (CMOS) integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures, which can emit light at wavelengths within the important optical communication wavelength range of 1.3 - 1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1-xGex nanostructures have prevented the attainment of efficient light-emitting devices including the desired lasers. Thus, the engineering of Si/Si1-xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL) at energies in the range 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe nanostructures and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots), two dimensions (corresponding to quantum wires), and one dimension (corresponding to quantum wells). The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for nanostructure confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/Ge NW diameter in the range 50 - 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex nanostructures incorporated into a Si0.6Ge0.4 wavy

Experimental and thermodynamic assessments of substitutions in the AlFeSi, FeMnSi, FeSiZr and AlCaFeSi systems (65 wt % Si) - solidification simulation

International Nuclear Information System (INIS)

Gueneau, C.; Ansara, I.

1994-01-01

The substitutions of Al Si, Fe Mn and Fe Zr in some intermetallic compounds of the Al-Fe-Si, Fe-Mn-Si and Fe-Si-Zr systems are modelled in the Si-rich corner using a two sublattice model. The solidification paths of the studied alloys are determined at equilibrium. The ascalculated phase volume fractions of the alloys are compared to the experimental ones. Finally, a solidification simulation using the Gulliver-Scheil's model is performed in order to explain the formation of some precipitates experimentally observed. (authors). 14 figs., 19 refs

Ultrathin SiO{sub 2} layer formed by the nitric acid oxidation of Si (NAOS) method to improve the thermal-SiO{sub 2}/Si interface for crystalline Si solar cells

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, Taketoshi; Nakajima, Hiroki; Irishika, Daichi; Nonaka, Takaaki; Imamura, Kentaro; Kobayashi, Hikaru, E-mail: h.kobayashi@sanken.osaka-u.ac.jp

2017-02-15

Highlights: • The density of interface states at the SiO{sub 2}/Si interface is decreased by NAOS. • The minority carrier lifetime is increased by the NAOS treatment. • Great interfacial properties of the NAOS layer are kept after thermal oxidation. - Abstract: A combination of the nitric acid oxidation of Si (NAOS) method and post-thermal oxidation is found to efficiently passivate the SiO{sub 2}/n-Si(100) interface. Thermal oxidation at 925 °C and annealing at 450 °C in pure hydrogen atmosphere increases the minority carrier lifetime by three orders of magnitude, and it is attributed to elimination of Si dangling bond interface states. Fabrication of an ultrathin, i.e., 1.1 nm, NAOS SiO{sub 2} layer before thermal oxidation and H{sub 2} annealing further increases the minority carrier lifetime by 30% from 8.6 to 11.1 ms, and decreased the interface state density by 10% from 6.9 × 10{sup 9} to 6.3 × 10{sup 9}eV{sup −1} cm{sup −2}. After thermal oxidation at 800 °C, the SiO{sub 2} layer on the NAOS-SiO{sub 2}/Si(100) structure is 2.26 nm thick, i.e., 0.24 nm thicker than that on the Si(100) surface, while after thermal oxidation at 925 °C, it is 4.2 nm thick, i.e., 0.4 nm thinner than that on Si(100). The chemical stability results from the higher atomic density of a NAOS SiO{sub 2} layer than that of a thermal oxide layer as reported in Ref. [28] (Asuha et al., 2002). Higher minority carrier lifetime in the presence of the NAOS layer indicates that the NAOS-SiO{sub 2}/Si interface with a low interface state density is preserved after thermal oxidation, which supports out-diffusion oxidation mechanism, by which a thermal oxide layer is formed on the NAOS SiO{sub 2} layer.

Effect of microculture on cell metabolism and biochemistry: do cells get stressed in microchannels?

Science.gov (United States)

Su, Xiaojing; Theberge, Ashleigh B; January, Craig T; Beebe, David J

2013-02-05

Microfluidics is emerging as a promising platform for cell culture, enabling increased microenvironment control and potential for integrated analysis compared to conventional macroculture systems such as well plates and Petri dishes. To advance the use of microfluidic devices for cell culture, it is necessary to better understand how miniaturization affects cell behavior. In particular, microfluidic devices have significantly higher surface-area-to-volume ratios than conventional platforms, resulting in lower volumes of media per cell, which can lead to cell stress. We investigated cell stress under a variety of culture conditions using three cell lines: parental HEK (human embryonic kidney) cells and transfected HEK cells that stably express wild-type (WT) and mutant (G601S) human ether-a-go-go related gene (hERG) potassium channel protein. These three cell lines provide a unique model system through which to study cell-type-specific responses in microculture because mutant hERG is known to be sensitive to environmental conditions, making its expression a particularly sensitive readout through which to compare macro- and microculture. While expression of WT-hERG was similar in microchannel and well culture, the expression of mutant G601S-hERG was reduced in microchannels. Expression of the endoplasmic reticulum (ER) stress marker immunoglobulin binding protein (BiP) was upregulated in all three cell lines in microculture. Using BiP expression, glucose consumption, and lactate accumulation as readouts we developed methods for reducing ER stress including properly increasing the frequency of media replacement, reducing cell seeding density, and adjusting the serum concentration and buffering capacity of culture medium. Indeed, increasing the buffering capacity of culture medium or frequency of media replacement partially restored the expression of the G601S-hERG in microculture. This work illuminates how biochemical properties of cells differ in macro- and

Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

International Nuclear Information System (INIS)

Suvorova, N.A.; Lopez, C.M.; Irene, E.A.; Suvorova, A.A.; Saunders, M.

2004-01-01

(Ba,Sr)TiO 3 (BST) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO 2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO 2 on Si or 3.5 nm SiO 2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO 2 . Using the conductance method, capacitance-voltage measurements show a decrease in the interface trap density D it of an order of magnitude for oxidized Si substrates with a thicker SiO 2 underlayer. Further reduction of D it was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization

Comparison of interfaces for (Ba,Sr)TiO3 films deposited on Si and SiO2/Si substrates

Science.gov (United States)

Suvorova, N. A.; Lopez, C. M.; Irene, E. A.; Suvorova, A. A.; Saunders, M.

2004-03-01

(Ba,Sr)TiO3(BST) thin films were deposited by ion sputtering on both bare and oxidized Si. Spectroscopic ellipsometry results have shown that a SiO2 underlayer of nearly the same thickness (2.6 nm in average) is found at the Si interface for BST sputter depositions onto nominally bare Si, 1 nm SiO2 on Si or 3.5 nm SiO2 on Si. This result was confirmed by high-resolution electron microscopy analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO2. Using the conductance method, capacitance-voltage measurements show a decrease in the interface trap density Dit of an order of magnitude for oxidized Si substrates with a thicker SiO2 underlayer. Further reduction of Dit was achieved for the capacitors grown on oxidized Si and annealed in forming gas after metallization.

Mechanical behavior of SiCf/SiC composites with alternating PyC/SiC multilayer interphases

International Nuclear Information System (INIS)

Yu, Haijiao; Zhou, Xingui; Zhang, Wei; Peng, Huaxin; Zhang, Changrui

2013-01-01

Highlights: ► Superior combination of flexural strength and fracture toughness of the 3D SiC/SiC composite was achieved by interface tailoring. ► Resulted composite possesses a much higher flexural strength and fracture toughness than its counterparts in literatures. ► Mechanisms that PyC/SiC multilayer coatings improve the mechanical properties were illustrated. -- Abstract: In order to tailor the fiber–matrix interface of continuous silicon carbide fiber reinforced silicon carbide (SiC f /SiC) composites for improved fracture toughness, alternating pyrolytic carbon/silicon carbide (PyC/SiC) multilayer coatings were applied to the KD-I SiC fibers using chemical vapor deposition (CVD) method. Three dimensional (3D) KD-I SiC f /SiC composites reinforced by these coated fibers were fabricated using a precursor infiltration and pyrolysis (PIP) process. The interfacial characteristics were determined by the fiber push-out test and microstructural examination using scanning electron microscopy (SEM). The effect of interface coatings on composite mechanical properties was evaluated by single-edge notched beam (SENB) test and three-point bending test. The results indicate that the PyC/SiC multilayer coatings led to an optimum interfacial bonding between fibers and matrix and greatly improved the fracture toughness of the composites.

Analysis of Hydrodynamic Mechanism on Particles Focusing in Micro-Channel Flows

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Qikun Wang

2017-06-01

Full Text Available In this paper, the hydrodynamic mechanism of moving particles in laminar micro-channel flows was numerically investigated. A hydrodynamic criterion was proposed to determine whether particles in channel flows can form a focusing pattern or not. A simple formula was derived to demonstrate how the focusing position varies with Reynolds number and particle size. Based on this proposed criterion, a possible hydrodynamic mechanism was discussed as to why the particles would not be focused if their sizes were too small or the channel Reynolds number was too low. The Re-λ curve (Re, λ respectively represents the channel-based Reynolds number and the particle’s diameter scaled by the channel was obtained using the data fitting with a least square method so as to obtain a parameter range of the focusing pattern. In addition, the importance of the particle rotation to the numerical modeling for the focusing of particles was discussed in view of the hydrodynamics. This research is expected to deepen the understanding of the particle transport phenomena in bounded flow, either in micro or macro fluidic scope.

Oscillations in the fusion of the Si + Si systems

International Nuclear Information System (INIS)

Aguilera R, E.F.; Kolata, J.J.; DeYoung, P.A.; Vega, J.J.

1986-02-01

Excitation functions for the yields of all the residual nuclei from the 28 Si + 28,30 and 30 Si + 30 Si reactions have been measured via the γ-ray technique for center of mass energies in the region within one and two times the Coulomb barrier.Thirteen elements were identified for the first reaction and ten for the other two. While no structure is shown by the data for the 28 + 28 Si reaction, we have found evidence for intermediate width structure in the 2α and the αpn channels in 28 Si + 30 Si and for broad structure in the total fusion cross sections for 30 Si + 30 Si. Calculations using a barrier penetration model with one free parameter reproduce the experimental results quite well. Evaporation model calculations indicate that the individual structure of the nuclei involved in the respective decay chains might have an important influence upon the deexcitation process at the energies relevant to our experiments. (Author)

Flow characterization in periodic microchannels containing asymmetric grooves

Energy Technology Data Exchange (ETDEWEB)

Osorio-Nesme, A; Delgado, A, E-mail: anuhar.nesme@fau.de [Institute of Fluid Mechanics, Friedrich-Alexander Erlangen-Nuremberg University, Cauerstrasse 4, D-91058 Erlangen (Germany)

2017-10-15

Characterization of two-dimensional flows in microchannels with anisotropic periodic grooves is numerically carried out by using the lattice Boltzmann method. Periodically placed microstructures, consisting of novel nozzle-diffuser-like grooves are deliberately designed to introduce a flow-direction dependent resistance. Simulations were conducted for a low-to-moderate Reynolds number in the laminar-transition flow regime. Different channel geometries, defined by the half-angle ϕ of the periodic grooves are considered. The influence of the half-angle on both the flow field and the onset of oscillatory flow regime at different driving body forces is analyzed. At a low Reynolds number, the flow is observed stationary and fully reversible, regardless of the groove geometry. In this regime, higher Reynolds numbers were observed when the geometry acts as a diffuser (negative flow) than as a nozzle (positive flow) for a given driving body force. At sufficiently high Reynolds number the flow turns from a steady state to a time-dependent oscillatory regime through a Hopf bifurcation. Successive flow bifurcations lead the flow structure from a periodic regime to a quasi-chaotic regime with three-dimensional structures. The onset of unsteady flow occurs earlier for positive flows and geometries with small half-angles. For higher driving forces, there is a reduction in the volume flow rate due to the advected material in the transversal direction, causing consequently a decrease in the Reynolds number. (paper)

Structure of MnSi on SiC(0001)

Science.gov (United States)

Meynell, S. A.; Spitzig, A.; Edwards, B.; Robertson, M. D.; Kalliecharan, D.; Kreplak, L.; Monchesky, T. L.

2016-11-01

We report on the growth and magnetoresistance of MnSi films grown on SiC(0001) by molecular beam epitaxy. The growth resulted in a textured MnSi(111) film with a predominantly [1 1 ¯0 ] MnSi (111 )∥[11 2 ¯0 ] SiC(0001) epitaxial relationship, as demonstrated by transmission electron microscopy, reflection high energy electron diffraction, and atomic force microscopy. The 500 ∘C temperature required to crystallize the film leads to a dewetting of the MnSi layer. Although the sign of the lattice mismatch suggested the films would be under compressive stress, the films acquire an in-plane tensile strain likely driven by the difference in thermal expansion coefficients between the film and substrate during annealing. As a result, the magnetoresistive response demonstrates that the films possess a hard-axis out-of-plane magnetocrystalline anisotropy.

Analytical Solution of Electro-Osmotic Peristalsis of Fractional Jeffreys Fluid in a Micro-Channel

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Xiaoyi Guo

2017-11-01

Full Text Available The electro-osmotic peristaltic flow of a viscoelastic fluid through a cylindrical micro-channel is studied in this paper. The fractional Jeffreys constitutive model, including the relaxation time and retardation time, is utilized to describe the viscoelasticity of the fluid. Under the assumptions of long wavelength, low Reynolds number, and Debye-Hückel linearization, the analytical solutions of pressure gradient, stream function and axial velocity are explored in terms of Mittag-Leffler function by Laplace transform method. The corresponding solutions of fractional Maxwell fluid and generalized second grade fluid are also obtained as special cases. The numerical analysis of the results are depicted graphically, and the effects of electro-osmotic parameter, external electric field, fractional parameters and viscoelastic parameters on the peristaltic flow are discussed.

A new method to measure and increase the detection efficiency of a microchannel plate for 100 keV electrons

International Nuclear Information System (INIS)

Tornow, R.P.

1990-01-01

A new method is described which permits measurement of efficiency of a microchannel plate (MCP) simply by tracing the output current pulse in the saturated mode. The dependence of the detection efficiency on the gain of the input stages of a detector is calculated and the result is applied to a MCP. Furthermore, an enhancement of the detection efficiency of a MCP is presented for 100 keV electrons up to more than 90% by means of the field-enhanced secondary electron emission. (author)

Hydrostatic and Flow Measurements on Wrinkled Membrane Walls

Science.gov (United States)

Ozsun, Ozgur; Ekinci, Kamil

2013-03-01

In this study, we investigate structural properties of wrinkled silicon nitride (SiN) membranes, under both hydrostatic perturbations and flow conditions, through surface profile measurements. Rectangular SiN membranes with linear dimensions of 15 mm × 1 . 5 mm × 1 μ m are fabricated on a 500 - μ m-thick silicon substrate using standard lithography techniques. These thin, initially flat, tension-dominated membranes are wrinkled by bending the silicon substrate. The wrinkled membranes are subsequently incorporated as walls into rectangular micro-channels, which allow both hydrostatic and flow measurements. The structural response of the wrinkles to hydrostatic pressure provides a measure of the various energy scales in the problem. Flow experiments show that the elastic properties and the structural undulations on a compliant membrane completely dominate the flow, possibly providing drag reduction. These measurements pave the way for building and using compliant walls for drag reduction in micro-channels.

Laser-controlled stress of Si nanocrystals in a free-standing Si /SiO2 superlattice

Science.gov (United States)

Khriachtchev, Leonid; Räsänen, Markku; Novikov, Sergei

2006-01-01

We report laser manipulations with stress at the nanoscale level. The continuous-wave Ar+ laser radiation melts Si nanocrystals in a free-standing Si /SiO2 superlattice. Silicon crystallization from the liquid phase leads to a compressive stress, which can be accurately tuned in the 3GPa range using laser annealing below the Si melting temperature and then recovered by laser annealing above the melting temperature. This allows investigations of various phenomena as a function of stress and makes a case of Si-nanocrystal memory with very long retention time, which can be written, erased, and read by optical means.

Laser-controlled stress of Si nanocrystals in a free-standing Si/SiO2 superlattice

International Nuclear Information System (INIS)

Khriachtchev, Leonid; Raesaenen, Markku; Novikov, Sergei

2006-01-01

We report laser manipulations with stress at the nanoscale level. The continuous-wave Ar + laser radiation melts Si nanocrystals in a free-standing Si/SiO 2 superlattice. Silicon crystallization from the liquid phase leads to a compressive stress, which can be accurately tuned in the 3 GPa range using laser annealing below the Si melting temperature and then recovered by laser annealing above the melting temperature. This allows investigations of various phenomena as a function of stress and makes a case of Si-nanocrystal memory with very long retention time, which can be written, erased, and read by optical means

Isotopic effects in sub-barrier fusion of Si + Si systems

Science.gov (United States)

Colucci, G.; Montagnoli, G.; Stefanini, A. M.; Esbensen, H.; Bourgin, D.; Čolović, P.; Corradi, L.; Faggian, M.; Fioretto, E.; Galtarossa, F.; Goasduff, A.; Grebosz, J.; Haas, F.; Mazzocco, M.; Scarlassara, F.; Stefanini, C.; Strano, E.; Szilner, S.; Urbani, M.; Zhang, G. L.

2018-04-01

Background: Recent measurements of fusion cross sections for the 28Si+28Si system revealed a rather unsystematic behavior; i.e., they drop faster near the barrier than at lower energies. This was tentatively attributed to the large oblate deformation of 28Si because coupled-channels (CC) calculations largely underestimate the 28Si+28Si cross sections at low energies, unless a weak imaginary potential is applied, probably simulating the deformation. 30Si has no permanent deformation and its low-energy excitations are of a vibrational nature. Previous measurements of this system reached only 4 mb, which is not sufficient to obtain information on effects that should show up at lower energies. Purpose: The aim of the present experiment was twofold: (i) to clarify the underlying fusion dynamics by measuring the symmetric case 30Si+30Si in an energy range from around the Coulomb barrier to deep sub-barrier energies, and (ii) to compare the results with the behavior of 28Si+28Si involving two deformed nuclei. Methods: 30Si beams from the XTU tandem accelerator of the Laboratori Nazionali di Legnaro of the Istituto Nazionale di Fisica Nucleare were used, bombarding thin metallic 30Si targets (50 μ g /cm2) enriched to 99.64 % in mass 30. An electrostatic beam deflector allowed the detection of fusion evaporation residues (ERs) at very forward angles, and angular distributions of ERs were measured. Results: The excitation function of 30Si+30Si was measured down to the level of a few microbarns. It has a regular shape, at variance with the unusual trend of 28Si+28Si . The extracted logarithmic derivative does not reach the LCS limit at low energies, so that no maximum of the S factor shows up. CC calculations were performed including the low-lying 2+ and 3- excitations. Conclusions: Using a Woods-Saxon potential the experimental cross sections at low energies are overpredicted, and this is a clear sign of hindrance, while the calculations performed with a M3Y + repulsion

Self-aligned indium–gallium–zinc oxide thin-film transistors with SiNx/SiO2/SiNx/SiO2 passivation layers

International Nuclear Information System (INIS)

Chen, Rongsheng; Zhou, Wei; Zhang, Meng; Kwok, Hoi-Sing

2014-01-01

Self-aligned top-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with SiN x /SiO 2 /SiN x /SiO 2 passivation layers are developed in this paper. The resulting a-IGZO TFT exhibits high reliability against bias stress and good electrical performance including field-effect mobility of 5 cm 2 /Vs, threshold voltage of 2.5 V, subthreshold swing of 0.63 V/decade, and on/off current ratio of 5 × 10 6 . With scaling down of the channel length, good characteristics are also obtained with a small shift of the threshold voltage and no degradation of subthreshold swing. The proposed a-IGZO TFTs in this paper can act as driving devices in the next generation flat panel displays. - Highlights: • Self-aligned top-gate indium–gallium–zinc oxide thin-film transistor is proposed. • SiN x /SiO 2 /SiN x /SiO 2 passivation layers are developed. • The source/drain areas are hydrogen-doped by CHF3 plasma. • The devices show good electrical performance and high reliability against bias stress

Synthesis and characterization of laminated Si/SiC composites

Science.gov (United States)

Naga, Salma M.; Kenawy, Sayed H.; Awaad, Mohamed; Abd El-Wahab, Hamada S.; Greil, Peter; Abadir, Magdi F.

2012-01-01

Laminated Si/SiC ceramics were synthesized from porous preforms of biogenous carbon impregnated with Si slurry at a temperature of 1500 °C for 2 h. Due to the capillarity infiltration with Si, both intrinsic micro- and macrostructure in the carbon preform were retained within the final ceramics. The SEM micrographs indicate that the final material exhibits a distinguished laminar structure with successive Si/SiC layers. The produced composites show weight gain of ≈5% after heat treatment in air at 1300 °C for 50 h. The produced bodies could be used as high temperature gas filters as indicated from the permeability results. PMID:25685404

Synthesis and characterization of laminated Si/SiC composites

Directory of Open Access Journals (Sweden)

Salma M. Naga

2013-01-01

Full Text Available Laminated Si/SiC ceramics were synthesized from porous preforms of biogenous carbon impregnated with Si slurry at a temperature of 1500 °C for 2 h. Due to the capillarity infiltration with Si, both intrinsic micro- and macrostructure in the carbon preform were retained within the final ceramics. The SEM micrographs indicate that the final material exhibits a distinguished laminar structure with successive Si/SiC layers. The produced composites show weight gain of ≈5% after heat treatment in air at 1300 °C for 50 h. The produced bodies could be used as high temperature gas filters as indicated from the permeability results.

High power vertical stacked and horizontal arrayed diode laser bar development based on insulation micro-channel cooling (IMCC) and hard solder bonding technology

Science.gov (United States)

Wang, Boxue; Jia, Yangtao; Zhang, Haoyu; Jia, Shiyin; Liu, Jindou; Wang, Weifeng; Liu, Xingsheng

2018-02-01

An insulation micro-channel cooling (IMCC) has been developed for packaging high power bar-based vertical stack and horizontal array diode lasers, which eliminates many issues caused in its congener packaged by commercial copper formed micro-channel cooler(MCC), such as coefficient of thermal expansion (CTE) mismatch between cooler and diode laser bar, high coolant quality requirement (DI water) and channel corrosion and electro-corrosion induced by DI water if the DI-water quality is not well maintained The IMCC cooler separates water flow route and electrical route, which allows tap-water as coolant without electro-corrosion and therefore prolongs cooler lifetime dramatically and escalated the reliability of these diode lasers. The thickness of ceramic and copper in an IMCC cooler is well designed to minimize the CTE mismatch between laser bar and cooler, consequently, a very low "SMILE" of the laser bar can be achieved for small fast axis divergence after collimation. In additional, gold-tin hard solder bonding technology was also developed to minimize the risk of solder electromigration at high current density and thermal fatigue under hard-pulse operation mode. Testing results of IMCC packaged diode lasers are presented in this report.

Propagation of misfit dislocations from buffer/Si interface into Si

Science.gov (United States)

Liliental-Weber, Zuzanna [El Sobrante, CA; Maltez, Rogerio Luis [Porto Alegre, BR; Morkoc, Hadis [Richmond, VA; Xie, Jinqiao [Raleigh, VA

2011-08-30

Misfit dislocations are redirected from the buffer/Si interface and propagated to the Si substrate due to the formation of bubbles in the substrate. The buffer layer growth process is generally a thermal process that also accomplishes annealing of the Si substrate so that bubbles of the implanted ion species are formed in the Si at an appropriate distance from the buffer/Si interface so that the bubbles will not migrate to the Si surface during annealing, but are close enough to the interface so that a strain field around the bubbles will be sensed by dislocations at the buffer/Si interface and dislocations are attracted by the strain field caused by the bubbles and move into the Si substrate instead of into the buffer epi-layer. Fabrication of improved integrated devices based on GaN and Si, such as continuous wave (CW) lasers and light emitting diodes, at reduced cost is thereby enabled.

Tailoring of SiC nanoprecipitates formed in Si

Energy Technology Data Exchange (ETDEWEB)

Velisa, G., E-mail: gihan.velisa@cea.fr [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Magurele (Romania); Trocellier, P. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Thomé, L. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, UMR8609, Bât. 108, 91405 Orsay (France); Vaubaillon, S. [CEA, INSTN, UEPTN, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Miro, S.; Serruys, Y.; Bordas, É. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France); Meslin, E. [CEA, DEN, Service de Recherches de Métallurgie Physique, F-91191 Gif-sur-Yvette (France); Mylonas, S. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, UMR8609, Bât. 108, 91405 Orsay (France); Coulon, P.E. [Ecole Polytechnique, Laboratoire des Solides Irradiés, CEA/DSM/IRAMIS-CNRS, 91128 Palaiseau Cedex (France); Leprêtre, F.; Pilz, A.; Beck, L. [CEA, DEN, Service de Recherches de Métallurgie Physique, Laboratoire JANNUS, F-91191 Gif-sur-Yvette (France)

2013-07-15

The SiC synthesis through single-beam of C{sup +}, and simultaneous-dual-beam of C{sup +} and Si{sup +} ion implantations into a Si substrate heated at 550 °C has been studied by means of three complementary analytical techniques: nuclear reaction analysis (NRA), Raman, and transmission electron microscopy (TEM). It is shown that a broad distribution of SiC nanoprecipitates is directly formed after simultaneous-dual-beam (520-keV C{sup +} and 890-keV Si{sup +}) and single-beam (520-keV C{sup +}) ion implantations. Their shape appear as spherical (average size ∼4–5 nm) and they are in epitaxial relationship with the silicon matrix.

Dynamic Characterizations of an 8-frame, Half-Strip, High-speed X-ray Microchannel Plate Imager

International Nuclear Information System (INIS)

Ken Moy; Ming Wu; Craig Kruschwitz; Aric Tibbits; Matt Griffin; Greg Rochau

2008-01-01

High-speed microchannel plate (MCP)-based imagers are critical detectors for x-ray diagnostics employed on Z-experiments at Sandia National Laboratories (SNL) to measure time-resolved x-ray spectra and to image dynamic hohlraums. A multiframe design using eight half strips in one imager permits recordings of radiation events in discrete temporal snapshots to yield a time-evolved movie. We present data using various facilities to characterize the performance of this design. These characterization studies include DC and pulsed-voltage biased measurements in both saturated and linear operational regimes using an intense, short-pulsed UV laser. Electrical probe measurements taken to characterize the shape of the HV pulse propagating across the strips help to corroborate the spatial gain dependence

Numerical simulation of a backward-facing step flow in a microchannel with external electric field

Directory of Open Access Journals (Sweden)

Qing-He Yao

2015-03-01

Full Text Available A backward-facing step flow in the microchannel with external electric field was investigated numerically by a high-order accuracy upwind compact difference scheme in this work. The Poisson–Boltzmann and Navier–Stokes equations were computed by the high-order scheme, and the results confirmed the ability of the new solver in simulation of micro-scale electric double layer effects. The flow fields were displayed for different Reynolds numbers; the positions of the vortex saddle point of model with external electric field and model without external electric field were compared. The average velocity increases linearly with the electric field intensity; however, the Joule heating effects cannot be neglected when the electric field intensity increases to a certain level.

Uniform Si nano-dot fabrication using reconstructed structure of Si(110)

Science.gov (United States)

Yano, Masahiro; Uozumi, Yuki; Yasuda, Satoshi; Asaoka, Hidehito

2018-06-01

Si nano-dot (ND) formation on Si(110) is observed by means of a scanning tunneling microscope (STM). The initial Si-NDs are Si crystals that are continuous from the substrate and grow during the oxide layer desorption. The NDs fabricated on the flat surface of Si(110)-1 × 1 are surrounded by four types of facets with almost identical appearance probabilities. An increase in the size of the NDs increases the variety of its morphology. In contrast, most Si-NDs fabricated on straight-stepped surface of Si(110)-16 × 2 reconstructed structure are surrounded by only a single type of facet, namely the \\text{Si}(17,15,1)-2 × 1 plane. An appearance probability of the facet in which the base line is along the step of Si(110)-16 × 2 exceeds 75%. This finding provides a fabrication technique of uniformed structural Si-NDs by using the reconstructed structure of Si(110).

Neutron tolerance of advanced SiC-fiber/CVI-SiC composites

International Nuclear Information System (INIS)

Katoh, Y.; Kohyama, A.; Snead, L.L.; Hinoki, T.; Hasegawa, A.

2003-01-01

Fusion blankets employing a silicon carbide (SiC) fiber-reinforced SiC matrix composite (SiC/SiC composite) as the structural material provide attractive features represented by high cycle efficiency and extremely low induced radioactivity. Recent advancement in processing and utilization techniques and application studies in ceramic gas turbine and advanced transportation systems, SiC/SiC composites are steadily getting matured as industrial materials. Reference SiC/SiC composites for fusion structural applications have been produced by a forced-flow chemical vapor infiltration (FCVI) method using conventional and advanced near-stoichiometric SiC fibers and extensively evaluated primarily in Japan-US collaborative JUPITER program. In this work, effect of neutron irradiation at elevated temperatures on mechanical property of these composites is characterized. Unlike in conventional SiC/SiC composites, practically no property degradation was identified in advanced composites with a thin carbon interphase by a neutron fluence level of approximately 8dpa at 800C. (author)

Time-of-flight resolution of scintillating counters with Burle 85001 microchannel plate photomultipliers in comparison with Hamamatsu R2083

Energy Technology Data Exchange (ETDEWEB)

Baturin, V. [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Burkert, V. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Kim, W. [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of)]. E-mail: wooyoung@jlab.org; Majewsky, S. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Park, K. [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Popov, V. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Smith, E.S. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Son, D. [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Stepanyan, S.S. [Department of Physics, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Zorn, C. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)

2006-06-15

Improvements in the time resolution of the CEBAF Large Acceptance Spectrometer (CLAS) below {approx}50ps will be required for experiments using the planned upgraded accelerator facility at Jefferson Lab. The improved time resolution will allow particle identification using time-of-flight techniques to be used effectively up to the proposed operating energy of 12GeV. The challenge of achieving this time resolution over a relatively large area is compounded because the photomultipliers (PM) in the CLAS 'time-zero' scintillating counters must operate in very high magnetic fields. Therefore, we have studied the resolution of 'time-zero' prototypes with microchannel plate PMs 85001-501 from Burle. For reference and comparison, measurements were also made using the standard PMs R2083 from Hamamatsu using two timing methods. The cosmic ray method, which utilizes three identical scintillating counters (Bicron BC-408, 2x3x50cm{sup 3}) with PMs at the ends, yields {sigma}{sub R2083}=59.1+/-0.7ps. The location method of particles from a radiative source with known coordinates has been used to compare timing resolutions of R2083 and 85001-501. This method yields {sigma}{sub R2083}=59.5+/-0.7ps and it also provides an estimate of the number of primary photoelectrons. For the microchannel plate PM from Burle the method yields {sigma}{sub 85001}=130+/-4ps due to lower number of primary photoelectrons.

High thermal conductivity SiC/SiC composites for fusion applications -- 2

International Nuclear Information System (INIS)

Kowbel, W.; Tsou, K.T.; Withers, J.C.; Youngblood, G.E.

1998-01-01

This report covers material presented at the IEA/Jupiter Joint International Workshop on SiC/SiC Composites for Fusion Structural Applications held in conjunction with ICFRM-8, Sendai, Japan, Oct. 23--24, 1997. An unirradiated SiC/SiC composite made with MER-developed CVR SiC fiber and a hybrid PIP/CVI SiC matrix exhibited room temperature transverse thermal conductivity of 45 W/mK. An unirradiated SiC/SiC composite made from C/C composite totally CVR-converted to a SiC/SiC composite exhibited transverse thermal conductivity values of 75 and 35 W/mK at 25 and 1000 C, respectively. Both types of SiC/SiC composites exhibited non-brittle failure in flexure testing

Passivation of defect states in Si and Si/SiO2 interface states by cyanide treatment: improvement of characteristics of pin-junction amorphous Si and crystalline Si-based metal-oxide-semiconductor junction solar cells

International Nuclear Information System (INIS)

Fujiwara, N.; Fujinaga, T.; Niinobe, D.; Maida, O.; Takahashi, M.; Kobayashi, H.

2003-01-01

Defect states in Si can be passivated by cyanide treatment which simply involves immersion of Si materials in KCN solutions, followed by rinse. When the cyanide treatment is applied to pin-junction amorphous Si [a-Si] solar cells, the initial conversion efficiency increases. When the crown-ether cyanide treatment using a KCN solution of xylene containing 18-crown-6 is performed on i-a-Si films, decreases in the photo- and dark current densities with the irradiation time are prevented. The cyanide treatment can also passivate interface states present at Si/SiO 2 interfaces, leading to an increase in the conversion efficiency of 2 / Si (100)> solar cells.. Si-CN bonds formed by the reaction of defect states with cyanide ions have a high bond energy of about 4.5 eV and hence heat treatment at 800 0 C does not rupture the bonds, making thermal stability of the cyanide treatment.. When the cyanide treatment is applied to ultrathin SiO 2 /Si structure, the leakage current density is markedly decreased (Authors)