bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of Thermal Conductivity for Silicon Dioxide
Authors: Yao Da-Jeng , Lai Wei-Chih , Chien Heng-Chieh
Published: June 2009

Heat transport of dielectric thin films in 30–300 nm thick is characterized in the temperature range of 74–300 K using the 3ω method, which is a simple method to measure the cross-plane thermal conductivity of dielectric thin films. Dielectric film samples of two kinds, deposited on Si substrates using plasma enhanced chemical vapor deposition (PECVD) and grown by thermal oxidation, were measured. In order to broaden the application of 3ω method, 3ω method system was combined with cryogenics system to measure temperature dependent material property. SiO2 films, prepared by thermal oxidation and PECVD, have been put and measured in the cryogenics system. The apparent thermal conductivity, intrinsic thermal conductivity, and interface resistance have been analyzed in different temperature. For this experiment, we discovered the thermal conductivity of PECVD SiO2 films is smaller than the thermal conductivity of SiO2 grown by thermal oxidation, because the porosity of thermal SiO2 is smaller than PECVD SiO2. The apparent thermal conductivity of SiO2 film decreases with film thickness. The thickness dependent thermal conductivity is interpreted in terms of a small interface thermal resistance RI. For SiO2 films, the thermal conductivity decreases if the temperature decreases, because the mean free path of heater carriers increases.
Estimation and Measurement of Pressure Drop in the Microchannel
Authors: Yao Da-Jeng , Tseng Di-Nung
Published: June 2009

In this paper, an innovation approach was used to estimate the pressure drops in the microchannel. The approach took a simple way to calculate the pressure drops, which could reduce the necessity of an embedded pressure sensor inside microchannel. The concept was to design the rectangular branch-channel along the side wall of main flow in the microchannel. When the fluidic flowed through the microchannel, the bubbles would be formed inside the branch-channel. By observing the changes of the bubbles sizes, the pressure drops around the particular sites of the branch-channel could be estimated. As the experiment results, we could indirectly obtain the pressure drops of the micro fluidic around the micro channel by the changes of the bubbles sizes. In addition to demonstrate the estimating of the pressure drops and the concept of the branch-channel design, it has also supported a frame of the channel sizes and the pressure drops to design the proper microchannel.
Fabrication of Nanochannels in Silicon and Polymers
Authors: Nguyen Nam-Trung , Abgrall Patrick
Published: June 2009

This paper reports the fabrication of planar nanochannels in silicon and thermoplastic. Conventional technologies such as reactive ion etching (RIE) and anodic bonding were used for fabricating the silicon-based nanochannels, while hot embossing and thermal bonding were used for polymer-based nanochannels. Due to the limit of photolithography, the lateral dimension of the channels are kept on the order of micrometers. The depth can be controlled precisely by etch rate or deposition rate. While fabrication technologies for nanochannels in silicon and glass are established and straightforward to implement, fabrication of planar nanochannels in a plastic is challenging because of the more severe collapsing of the structure during bonding. Besides the silicon technology, we demonstrate a simple and low-cost fabrication technology of planar nanochannels by hot-embossing in a thermoplastic and bonding below the glass transition temperature.
Thermal Characterization of Micro/Nanoscale Conductive and Nonconductive Wires by Transient Photo-Electro-Thermal Technique
Authors: Wang Tao , Wang Xinwei , Guo Jiaqi , Luo Zhongyang , Cen Kefa
Published: June 2009

In this work, a transient photon-electro-thermal (TPET) technique based on step laser heating and electrical thermal sensing is developed to characterize the thermophysical properties of one-dimensional micro/nanoscale conductive and nonconductive wires. In this method, the to-be-measured thin wire/tube is suspended over two electrodes and is irradiated with a step CW laser beam. The laser beam induces a transient temperature rise in the wire/tube, which will lead to a transient change of its electrical resistance. A DC current is applied to the sample, and the resulting transient voltage variation over the wire is measured and used to extract the thermophysical properties of the sample. A 25.4-μm thick Pt wire is used as the reference sample to verify this technique. Sound agreement is obtained between the measured thermal diffusivity and the reference value. Applying the TPET technique, the thermal diffusivity of conductive single-wall carbon nanotube (SWCNT) bundles and nonconductive cloth fibers is measured. For nonconductive wires, a thin (∼nm) metallic film is coated on the outside of the wire for electrical thermal sensing. The measured thermal diffusivity for the SWCNT bundle is 2.53×10−5 m2/s, much less than the thermal diffusivity of graphite in the layer direction. For microscale cloth fibers, our experiment shows its thermal diffusivity is at the level of 10−7 m2/s.
CFD Simulations of Viscous Heating in a Spiral-Channel Micropump
Authors: Al-Halhouli A. T. , Kilani M. I. , Bu¨ttgenbach S.
Published: June 2009

In this work, the influence of viscous heating on the flow performance of a spiral-channel viscous micropump was investigated numerically using finite volume method (FVM). A number of 3D models for the spiral-channel micropump boundary conditions and using different working fluids (Glycerin, and water) were built and analyzed by considering the change of the fluid viscosity as a function of temperature. Results showed that significant temperature rises due to viscous heating are obtained, and the error in calculating the volumetric flow rate by considering viscous heating term is increased with increasing Re.Eu, and reaches 10% for the spiral wall condition and 40% for the single wall condition at Re.Eu = 1.5. Also, it was found that large deviations from the analytical predictions are obtained for high viscous fluids, and that viscous heating and temperature rise in the stationary wall condition is higher than that in the spiral wall condition. As a conclusion, viscous heating in the spiral-channel micropump is too significant to be neglected and affects the temperature, pressure, and velocity distribution of the flow field.
Simulation of Electromagnetic Field Distribution at a Nanowire Probe for Near Field Scanning Optical Microscopy
Authors: Malcolm Nathan P. , Heltzel Alex J. , Shi Li , Howell John R.
Published: June 2009

This work studies a new design of a near field scanning optical microscopy (NSOM) probe based on a ZnO nanowire sub-wavelength waveguide terminated with a plasmonic gold nanoparticle. Three-dimensional finite difference time domain (FDTD) simulation is used to visualize light guiding in the nanowire and near field coupling between the plasmonic nanoparticle and the substrate. The simulation results reveal local field enhancement at the gap between the nanoparticle and a gold substrate when the nanowire axis is tilted from the substrate normal by a small angle. The enhancement occurs only along the cross section plane that is parallel to the polarization of the excitation laser beam. The regime of field enhancement is much smaller than the diameter of the 100 nm plasmonic particle, making the nanowire probe well suited for NSOM with superior spatial resolution and signal to noise ratio compared to the state of the art.
Analysis and Design of Thermal Double-Cantilever Bimorph Actuators for Rotating-Type Micromirrors
Authors: Kim DongHyun , Oh Kyung Su , Park Seungho , Kwon Ohmyoung , Choi Young Ki , Lee Joon Sik
Published: June 2009

This paper reports the design and simulation of thermal double-cantilever bimorph (TDCB) actuators that can be used to drive micromirrors efficiently. A TDCB actuator combines two paralleled bimorph actuators acting in opposite directions for rotational control of micromirrors. Each actuator is structured by nickel and silicon dioxide thin films with an embedded polysilicon line as a heat source. With a size of only 20 μm width and 100 μm length, TDCB actuators result in vertical displacement of 28 μm at 11 volts DC which is a significant improvement, comparing to the conventional thermal bimorph actuators.
Biological Micro/Nanofluidics
Authors: Takayama Shuichi , Tung Yi-Chung , Chueh Bor-Han
Published: June 2009

Many biological studies, drug screening methods, and cellular therapies require culture and manipulation of living cells outside of their natural environment in the body. The gap between the cellular microenvironment in vivo and in vitro, however, poses challenges for obtaining physiologically relevant responses from cells used in basic biological studies or drug screens and for drawing out the maximum functional potential from cells used therapeutically. One of the reasons for this gap is because the fluidic environment of mammalian cells in vivo is microscale and dynamic whereas typical in vitro cultures are macroscopic and static. This presentation will give an overview of efforts in our laboratory to develop programmable microfluidic systems that enable spatio-temporal control of both the chemical and fluid mechanical environment of cells. The technologies and methods close the physiology gap to provide biological information otherwise unobtainable and to enhance cellular performance in therapeutic applications. Specific biomedical topics that will be discussed include subcellular signalling in normal and cancer cells, in vitro fertilization on a chip, studies of the effect of physiological and pathological fluid mechanical stresses on endothelial and epithelial cells, and microfluidic stem cell engineering. In the nanoscale regime, tunable nanochannels that can manipulate single DNA molecules will be discussed.
Two-Phase Heat Transfer Performance of Dielectric Fluid HFE-7100 Within Multiport Microchannel
Authors: Lin Lung-Yi , Jeng Yeau-Ren , Wang Chi-Chuan
Published: June 2009

This study presents convective single-phase and boiling two-phase heat transfer performance of HFE-7100 coolant within multi-port microchannel heat sinks. The corresponding hydraulic diameters are 450 and 237 μm, respectively. For single-phase results, the presence of inlet/outlet locations inevitably gives rise to considerable increase of total pressure drop of a multi-port microchannel heat sink whereas has virtually no detectable influence on overall heat transfer performance provided that the effect of entrance has been accounted for. The convective boiling heat transfer coefficient for the HFE-7100 coolant shows a tremendous drop when vapor quality is above 0.6. For Dh = 450 μm, it is found that the mass flux effect on the convective heat transfer coefficient is rather small.
Thermal Lattice Boltzmann Simulation of Two-Phase Flow at the Anode Microchannel of Micro Direct Methanol Fuel Cells
Authors: Fei Kai , Chen Tzer-Shing , Hong Che-Wun
Published: June 2009

Carbon dioxide bubble removal in anode diffusion layer is a critical technique in micro direct methanol fuel cells (μDMFCs) [1, 2]. By deriving a thermal lattice-Boltzmann model, we investigate the hydrophilic, thermal and geometric effects on the two-phase flow (CO2 bubbles in methanol-water solution) in a microchannel of a μDMFC. The dimension of the example microchannel is similar to the diffusion layer. The length is 15.9 μm while the width (or height) is 1.5 μm, which are equivalent to the averaged pore size of the porous diffusion layer. A two-dimensional, nine-velocity (D2Q9) thermal lattice-Boltzmann model (TLBM) was derived in this paper.
Atomic Scale Three-Dimensional Phononic Crystals With Very Low Thermal Conductivities
Authors: Gillet Jean-Numa , Volz Sebastian , Chalopin Yann
Published: June 2009

Superlattices have been used to design thermoelectric materials with ultra-low thermal conductivities. Indeed, the thermoelectric figure of merit ZT varies as the inverse of the material thermal conductivity. However, the design of a thermoelectric material with ZT superior to the alloy limit usually fails with the superlattices because of two major drawbacks: First, a lattice mismatch can occur between the different layers of a superlattice as in a Si/Ge superlattice. This leads to the formation of defects and dislocations, which reduces the electrical conductivity and therefore avoids the increase of ZT compared to the alloy limit. On the other hand, the superlattices only affect heat transfer in one direction. To cancel heat conduction in the three spatial directions, we propose atomic-scale three-dimensional (3D) phononic crystals. Because the lattice constant of our phononic crystal is of the order of some nanometers, we obtain phonon confinement in the THz range and a nanomaterial with a very low thermal conductivity. This is not possible with the usual phononic crystals, which show band gaps in the sub-MHz range owing to their large lattice constant of the order of 1 mm. A period of our atomic-scale 3D phononic crystal is composed of a given number of diamond-like silicon cells forming a supercell. A periodic Si/Ge heterostructure is obtained since we substitute at each supercell center the Si atoms in a smaller number of cells by Ge atoms. The Ge atoms in the cells located at each supercell center form a box-like nanoparticle with a size that can be varied to obtain different atomic configurations of our nanomaterial. We also propose another design for our phononic crystal where we introduce a small number of diamond-like silicon cells at the center of a periodic supercell of diamond-like germanium cells. In this second design, we form box-like nanoparticles of Si atoms in a germanium matrix instead of boxlike nanoparticles of Ge atoms in a silicon matrix in the first design. With the dispersion curves computed by lattice dynamics and a general equation, we obtain the thermal conductivities of several atomic configurations of our phononic crystal. Compared to a bulk material, the thermal conductivity can be reduced by at least one order of magnitude in our phononic crystal. This reduction is only due to the phonon group velocities, and we expect a further decrease owing to the diminution of the phonon mean free path in our phononic crystal.
An Experimental Study of Micro Radially Rotating Heat Pipes With Water as the Working Fluid
Authors: Cao Yiding , Ling Jian
Published: June 2009

In this study, three copper-water rotating heat pipes having inner diameters of 1.5, 2, and 3 mm, respectively, are fabricated and tested. The effectiveness of the copper-water heat pipe is first validated by comparing its performance with that of a copper bar having the same inner and outer diameters. The heat pipes are then tested to prove their reliability, high effective thermal conductance, and critical working limitation. The experimental data shows that the critical limitation may be reached when the inner diameter of the heat pipe is below 1.5 mm under the condition of a low rotating speed. The tests of these water heat pipes could also explore potential applications of radially rotating heat pipes in disks/blades of a high-pressure compressor.
Effect of CuO Nanoparticle Concentration on R134A/Lubricant Pool Boiling Heat Transfer
Authors: Kedzierski Mark A.
Published: June 2009

This paper quantifies the influence of copper (II) oxide (CuO) nanoparticle concentration on the boiling performance of R134a/polyolester mixtures on a roughened, horizontal flat surface. Nanofluids are liquids that contain dispersed nanosize particles. Two lubricant based nanofluids (nanolubricants) were made with a synthetic polyolester and 30 nm diameter CuO particles to a 4% and a 2% volume fraction, respectively. As reported in a previous study for the 4% volume fraction nanolubricant, a 0.5% nanolubricant mass fraction with R134a resulted in a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) of between 50% and 275%. The same study had shown that increasing the mass fraction of the 4% volume fraction nanolubricant resulted in smaller, but significant, boiling heat transfer enhancements. The present study shows that use of a nanolubricant with half the concentration of CuO nanoparticles (2% by volume) resulted in either no improvement or boiling heat transfer degradations with respect to the R134a/polyolester mixtures without nanoparticles. Consequently, significant refrigerant/lubricant boiling heat transfer enhancements are possible with nanoparticles; however, the nanoparticle concentration is an important determining factor. Further research with nanolubricants and refrigerants are required to establish a fundamental understanding of the mechanisms that control nanofluid heat transfer.
Microchannel Optimization for Heat Dissipation From a Solid Substrate
Authors: Sobhan C. B. , Anoop P. S. , Arimboor Kuriyan , Abraham Thomas , Peterson G. P.
Published: June 2009

A computational model was developed to analyze and optimize the convective heat transfer for water flowing through rectangular microchannels fabricated in a silicon substrate. A baseline case was analyzed by solving the nondimensional governing equations. Using a quasi three-dimensional computational model, the velocity and temperature distributions were obtained and the numerical results were then used to determine the overall dimensionless thermal resistance for the convective heat transfer from the substrate to the fluid. To validate the numerical model, the average Nusselt numbers as determined by the numerical model were compared with experimental results available in the literature, for channels with comparable hydraulic diameters. The procedure for arriving at an optimum geometric configuration and arrangement of microchannels on the substrate, subject to given design constraints, so that the thermal resistance is at a minimum, is described and demonstrated using the computational model.
Three-Dimensional Analysis of Fluid Flow and Heat Transfer in the Microchannel Heat Sink Using Additive-Correction Multigrid Technique
Authors: Asgari Omid , Saidi Mohammad Hassan
Published: June 2009

Heat generation from very large-scale integrated (VLSI) circuits increases with the advent of high-density integrated circuit technology. One of the promising techniques is liquid cooling by using microchannel heat sink. Numerical works on the microchannel heat sink in the literature are mostly two dimensional. The purpose of the present study is to develop a three-dimensional analysis procedure to investigate flow and conjugate heat transfer in the microchannel-based heat sink for electronic packaging applications. The micro-heat sink model consists of a 10 mm long silicon substrate, with rectangular microchannels, 57 μm wide and 180 μm deep, fabricated along the entire length. A finite volume numerical code with a multigrid technique, based on additive correction multigrid (AC-MG) scheme, that is a high-performance solver, was developed to solve the steady incompressible laminar Navier–Stokes (N–S) equations, over a colocated Cartesian grid arrangement. The results indicate that thermophysical properties of the liquid can significantly influence both the flow and heat transfer in the microchannel heat sink. Comparison of the numerical results with other published numerical results and experimental data available in the literature for Reynolds numbers less than 200 based on a hydraulic diameter of Dh = 86 μm and Dh/Lx<0.01, indicates that the assumption of hydrodynanmic, fully developed laminar flow is valid. The current research indicates that the AC-MG acceleration technique is highly efficient, reliable and robust, which makes it feasible for CPU-intensive computations, such as pressure Poisson equations. When compared to the discretized momentum equations, the pressure Poisson equations tend to be very stiff and ill-conditioned, i.e ap ≡ Σnb anb Because of these reasons, solving the pressure Poisson equation is usually the CPU bottle-neck for the incompressible N–S equation system and AC-MG technique is required. With this acceleration technique the residuals of the large-scale algebraic equation system are guaranteed to be continuously driven down to the level of the computer machine round-off error and warrants strong conservations of mass and momentum satisfied over all the control volumes. In this cell centered multigrid algorithm both restriction and prolongation operators are based on piecewise constant interpolation. The accuracy of the prediction has been verified by comparing the results obtained with the numerical and analytical results from the open literature.
Ionic Transport in Finite Length Nano-Sized Pores and Channels
Authors: Hung S. W. , Chen C. P. , Chieng C. C.
Published: June 2009

Surface-charge regulated ionic transport phenomena in nano-pores and nano-channels have important applications in bio molecular analyses and power conversion involving NEMS. In such devises, the surface-to-volume ratio increases significantly. In nanofluidics, one characteristic is the overlapping of the electrical double layer (EDL) and the disappearance of the electrically neutral zone. The configuration to be considered is a finite length nano pore/channel connected by two reservoirs. Multi-dimensional analyses based on solutions of the Poisson-Nernst-Planck (PNP) equation were performed for the configuration in this study. Numerical solutions show that the ionic transport process in such a configuration depends strongly on the liquid-solid interface models used. These interface models usually serve as wall boundary conditions in multi-dimensional numerical analyses. Most current models were derived based on 1-D fully developed analyses. Issues regarding the extension of the surface chemical equilibrium model to multi-dimensional nanofluidics simulations involving overlapping EDLs were investigated and discussed in this paper.
Measurements for the Moisture Permeations and Thermal Resistances of Cyclo Olefin Copolymer Substrates Deposited a Silicon Dioxide Film
Authors: Jou Rong-Yuan
Published: June 2009

Plastic substrates for organic light-emitting devices (OLED) are extremely sensitive to moisture and oxygen. A new amorphous engineering thermoplastic, nominated cyclic olefin copolymer (COC) has been used for this application, because of higher transparence, lower birefringence, lower dispersion and lower water absorption. However, COC plastic substrates can’t sustain plasma-based processing temperatures at 350°C. In this study, experiments of the moisture permeation rate testing and the thermal resistance experiments are conducted to explore the moisture diffusion barrier and thermal barrier characteristics of COC substrate deposited a SiO2 thin film on it. Silicon dioxide layer of thickness, 0.25μm, 0.5μm, and 1 μm, respectively, are fabricated by PECVD. For the permeation rate measurement, the Ca-test method is adopted. For the thermal resistance measurements, two methods of the thermocouple in vacuum environment and the IR thermography are adopted and measured results are compared. Different surface temperatures, 323.15K, 373.15K, 408.15K, and 473.15K, respectively, are applied upon the silicon dioxide film and temperature differences for varied thickness of silicon dioxide film are measured. Experimental results are presented to investigate the behaviors of moisture diffusion barrier and thermal barrier characteristics of the COC/SiO2 structure.
Developing Consistent Inlet Thermal Boundary Condition in Micro/Nano Scale Channels With Heat Transfer
Authors: Darbandi Masoud , Vakilipour Shidvash
Published: June 2009

In this work, we present a more realistic inlet boundary condition to simulate compressible and incompressible flows through micro and nano channels considering consistent momentum and heat transfer specifications there. At solid walls, a constant wall temperature with suitable jump is applied as the wall thermal boundary condition; however, two types of thermal inlet boundary conditions are investigated at the inlet. We firstly examine the classical inlet boundary condition, which specifies a uniform temperature distribution right at the real inlet. Alternatively, we apply the same boundary condition but at a fictitious place far upstream of the real channel inlet. To validate our results, the results obtained after employing the former boundary conditions are evaluated against other available numerical results and Lattice Boltzmann solutions. In this validation, the friction factor and Nusselt number are treated as the most important hydrodynamics and heat transfer factors to be appraised. Next, we present the results after applying the second type of inlet boundary conditions and compare them with those of applying the first type of boundary condition. This study suggests an innovation in micro/nano scale heat transfer treatment close to the channel inlets.
Experimental Observation of Jet Flow and Liquid Exploding Emission From Mini/Micro Tubes During Boiling
Authors: Wu D. , Peng X. F. , Wang B. X.
Published: June 2009

A series of experimental investigations were conducted to visually observe the fundamental features of boiling nucleation of water in micro capillary tubes covered with transparent metal film and ethanol in mini tubes winded with a heating wire as a heater. Normally, boiling nucleation and/or bubble generation were not observed even at very high heat fluxes compared with usual nucleate boiling situations. In mini tubes violent jet flows formed and played an important role of triggering the emission, while in micro tubes the liquid and/or vapor was instantaneously emitted as the applied heat flux reached a certain high value, rather than initialing nucleate boiling and jet flows which was much weaker than exploding emission. After the exploding emission, an ultra thin liquid film formed on the tube wall and evaporated intensely, causing a perceptible wall temperature drop.
Viscous Dissipation Effect of Liquid Flow in Microtubes
Authors: Guan Ning , Liu Zhigang , Zhang Chengwu
Published: June 2009

Viscous dissipation effects on de-ionized ultra pure water flow through smooth quartz glass microtubes with different inner diameters are investigated numerically and experimentally as the Reynolds number varies in the range from 0 to 700. In present study, a 2-D model adapted to microtube is presented to analyze the viscous dissipation characteristic in microtube considering EDL effect. According to the numerical simulation results, a new criterion Vc demonstrating the law of the viscous dissipation in microtube is summed up in this paper. Based on the micro-area thermal-imaging technology and a series of correction tests, the viscous heating temperature rise in microtube can be exactly measured by an IR camera with a special magnifying lens. Moreover, the temperature rise of the working fluid resulted from the heat generated by the pump is also considered in present experiments. The experimental results are compared with predictions of the numerical simulation and the theoretical Vc correlation. The comparisons indicate that the experimental data are in accordance with numerical and theoretical results.
Electroosmotic Pumping Using Porous Anodic Alumina Membranes
Authors: Chen Yu-Feng , Li Ming-Chia , Chang Wen-Jeng , Wang Chi-Chuan , Chen C. P.
Published: June 2009

This study demonstrated electroosmotic pumping with high flow rate per unit area at a rather low applied voltage through an alumina nano-porous membrane driven by Platinum mesh electrodes. The electrode was placed perpendicular to, and had direct contact with nano-channel inlet to reduce the electric voltage drop in the reservoir. The complete set of the Poisson-Nernst-Planck equations for electrical potential and ionic concentration, coupled with the Navier-Stokes equation were solved for the purpose of a full understanding of the ionic transport and flow characteristics of EOF in nano-fluidics capillaries. The measured flowrate versus electrolyte (KCl) concentration reveals that the flowrate is usually high in low concentration (10−5 M∼10−7 M) regime in which a maximum value also occurs. In addition, a remarkable surge of flow rate is observed when the concentration surpasses below 10−4 M. The maximum flowrate achieved from this study is 0.09 mL min−2V−1 cm−2 and the energy transfer efficiency is 0.43% at an operation voltage of 20V. The flowrates investigated in this study are comparable to other existing results whereas the corresponding operation voltage used this study is about one to two order lower than most existing results. Numerical results exhibit correct trends for nano flows involving strong overlap of electrical double layers. Comparisons of numerical and experimental results were made and discussed.
Thermal Effects on Electro-Osmotic Flows in Triangle Microchannels
Authors: Liao Q. , Wen T. Y. , Zhu X.
Published: June 2009

Small triangle channels are frequently encountered in microelectromechanical systems (MEMS). In this paper, the electro-osmotic flows with a constant wall temperature in triangle microchannels are studied. We numerically solved the Poisson equation for electric potential, the Navier-Stokes equation, and the energy equation for the mixed electroosmotic/pressure driven flows with varying physical properties in triangle microchannels using the Galerkin method. The effects of the pressure gradient, the length ratio, κDh, and Joule heating on mass flux of electro-osmotic flow are discussed, respectively. The numerical results show the mass-flux increases with the increase of imposed positive pressure gradient. A larger Joule number leads to a larger mass flux of electrolytic solution under positive pressure gradient. It is also found that the mass flux increases with increasing the length ratio, κDh, at a given pressure gradient. The increase in Ju number induces a larger increase in the mass flux at a larger κDh.
Three Dimensional Shape Measurement of Micro Droplet Utilizing Micro LIF Technique
Authors: Sugii Yasuhiko
Published: June 2009

This paper describes a novel measurement technique for three dimensional shape of micro droplet utilizing micro LIF (Laser Induced Fluorescence) technique. A measurement system consisted of microscope equipped with 10x lens, high sensitive CCD camera, CW Nd:YAG laser, optical filters and so on. Calibration curve between thickness of micro droplet and emission of fluorescence dye solution was obtained by the use of the PDMS (polydimethylsiloxane) microchip, whose depth varied from 8 to 120 μm fabricated using photo lithography technique. The microchip based calibration method provides high measurement accuracy and eliminate photobreaching effect. Measurement accuracy of the present method in depth direction was about 2 μm assessed using laser displace meter and the spatial resolution in the x-y plane became 6.7 μm. The technique is useful to investigate a two phase flow in micro scale.
Enhancement of Mixing in a Microchannel by Using AC-Electroosmotic Effect
Authors: Wang Yangyang , Kang Sangmo , Suh Yongkweon
Published: June 2009

This study has focused on optimizing the AC-electroosmotic micro-mixer, which is composed of a microchannel with an array of rectangular electrodes attached on the bottom wall. The electrode array is spatial-periodically arranged in pairs symmetric with respect to the longitudinal central line. An AC electrode field is applied to the electrodes, which drives the secondary transverse flow in a circulating cell mode near the electrodes. The main flow along the channel longitudinal direction plus this secondary transverse flow contribute to the stretching and folding of the fluid flow, that is the chaotic behavior, and thus to the enhancement of the fluid mixing. To design the better micro-mixer, numerical simulations have been performed by using a commercial code (CFX 10). In the simulations, the concept of mixing index is employed to evaluate the mixing performance as well as to optimize the size and spacing of each electrode in one pair. It is found that the optimum design of one electrode pair, which leads to the best mixing performance, is not simply harmonic one. When the length ratio of the two electrodes in a pair closes to 2:1, the best mixing effect can be attained. The flow pattern was visualized. Furthermore, the velocity field will be measured with a PTV technique to validate the numerical simulations.
Effects of Polymer Morphology on the Rheological Behavior of Melt Within Micro-Channels
Authors: Chen Shia-Chung , Chien Rean-Der , Huang Song-Wei , Chen Chun-Sheng
Published: June 2009

Micro molding has shown great commercial potential in recent years and determination of the rheological behavior of the polymer melt within micro structured geometry is vital for accurate simulation modeling of micro molding. The lack of commercial equipment is one of main hurdles in the investigation of micro melt rheology. In this study, a melt viscosity measurement system for low and high density polyethylene polymer melt flowing through micro-channels was established using a micro channel mold operated at a mold temperature as high as the melt temperature. For measured pressure drop and volumetric flow rate, capillary flow model was used for the calculation of viscosity utilizing Rabinowitsch correction. The calculated results of low crystallinity LDPE resin were also compared with those of high crystallinity HDPE resin to discuss the effect of degree of crystallinity on the viscosity characteristics of polymer within micro-channels. It was found that the measured LDPE and HDPE viscosity values in the test ranges are significantly lower (about 40∼56% and 22∼29% for LDPE and HDPE, respectively, flowing through a channel size of 150μm) than those obtained with a traditional capillary rheometer. Meanwhile, the percentage reduction in the viscosity value and the ratio of slip velocity relative to mean velocity all increase with decreasing micro-channel size. In the present study we emphasize that the rheological behavior of the high crystallinity HDPE and low crystallinity LDPE resins in microscopic scale are all different from that of macroscopic scale but HDPE displays a less significant lower. The reason can be attributed to for LDPE resin within the micro-channel can create the higher extra bonding force between the bulk chains than HDPE resin. Thus, it will have the lower adhesive force between the bulk chains with the micro-channel wall, resulting in higher degree of wall slip.
Water Morphologies and Distribution in Wet Soil and Sands
Authors: Yu Mingzhi , Peng Xiaofeng , Fang Zhaohong
Published: June 2009

Water morphologies and distribution were probed into by a CCD combined with a microscope. Observations and analysis showed that besides bound water, interstitial water, and free water, there is surface capillary water on the relative coarse matrix surfaces in soil and sands. At low moisture content, water morphologies in wet soil and sands are bound water, liquid bridges (or interstitial water), surface capillary water. When moisture content is high, water in soil and sands does not distribute homogeneously, however, some water masses (free water) and gas zones were found. Meanwhile, surface capillary water and bridges were still found on the solid surfaces and among the particles gaps enveloped in the gas zones.
Numerical Simulation on Pressure Drops for Air-Water Two-Phase Flow in Micro-Channels
Authors: Peng Hao , Ling Xiang
Published: June 2009

Rigorous two-phase flow modeling is one of the great challenges in the thermal sciences. A two-dimensional computational fluid dynamics (CFD) simulation of air-water two-phase pressure drop characteristics in micro-channels by using volume of fluid (VOF) method was carried out in this paper. The simulations were performed in a horizontal micro-channel with a diameter of 1.1 mm and a length of 200 mm. Firstly, a variety of air-water two-phase flow patterns (including bubbly, slug, slug-annular and annular flow) were simulated in order to validate the feasibility and reliability of the VOF method. Next to that, the two-phase pressure drops in micro-channel were analyzed numerically by using the same CFD method. Also the comparison of pressure drop among the numerical simulations, experimental data and the results calculated by homogeneous equilibrium model was presented. The agreement between numerical results and the existing experimental data was found to be satisfactory. Based on this good agreement, it is finally found that the numerical analysis procedure proposed in this paper can be used to achieve a better prediction for micro-channel air-water flow characteristics.
Thermal Behavior in a Multi-Layer Metal Thin-Film With Interfacial Contact Conductance by the Parabolic Two-Step Model
Authors: Tsai Tsung-Wen , Lee Yung-Ming
Published: June 2009

The effect of the contact conductance on micro-scale heat transport in a multi-layered metal thin-film subjected to ultra-fast pulse laser heating is investigated in this study. The interfacial contact conductance existing at the interface is included in the analysis. The parabolic two-step (PTS) model is applied to predict the electron and lattice temperature. The equations can be solved by Laplace transform and the Riemann-sum approximation. The results show that the contact conductance plays an important role in the micro-scale heat transport processes for a multi-layered metal thin-film. Hence, in order to eliminate the thermal failure of the surface layer, the thermal resistance existing at the interface should be as small as possible.
A Friction Factor Correlation for Gas Flow in Parallel Plate Microchannels by Considering Combined Effects of Compressibility and Rarefaction
Authors: Yan Xiaohong , Wang Qiuwang
Published: June 2009

The effects of compressibility and rarefaction for gas flow in microchannels have been extensively studied separately. However, these two effects are always combined for gas flow in microchannels. In this paper, the two-dimensional compressible Navier-Stokes equations are solved for gas flow in parallel plate channels with a slip boundary condition to study the combined effects of compressibility and rarefaction on the friction factor. The numerical methodology is based on the control volume finite difference scheme. It is found that the effect of compressibility increases the velocity gradient near the wall which then increases the friction factor. On the other hand, increasing the velocity gradient near the wall leads to a much larger slip velocity and implies a stronger rarefaction effect and a corresponding decrease in the friction factor. These two opposite effects make the effect of compressibility on friction factor for slip flow weaker than that for no-slip compressible flow. A correlation among fRe, Kn and Ma is presented. The correlation is validated with available experimental and analytical results.
Numerical Simulation of Fluid Mixing in the Ribbed Microchannels
Authors: Esfahanian V. , Kowsary F. , Rezaei Barmi M. , Noroozi N.
Published: June 2009

Micromixers have received much interest as essential part of microfluidic devices. Therefore, enhancement of mixing quality has gained a lot of attention in recent years. In the present study, improvement of mixing quality for two different miscible liquids is considered in passive micromixers. Numerical approach is based on a second order finite volume Jameson scheme in order to solve two dimensional incompressible Navier-Stocks and mass transport equations by implementing artificial compressibility. Mixing quality is influenced by Reynolds and Schmitt numbers as well as size and location of the ribs. Diffusion mechanism has the main role for mixing in micro scale fluid flows; therefore, increasing Peclet number leads to extend mixing time. In order to enhance mixing quality, ribs are used in different locations through the microchannel which cause more instability in the fluid flow and leads to a better mixing. The Reynolds number is constant while the Schmitt number is in the range of 10 to 100. However, in order to laminar fluid flow, ribs just have an influence near itself and faraway, mixing mechanism return to earlier state. Therefore, in low Reynolds numbers they have no effective influence. When Reynolds number increase, flow instability that is created by different ribs leads to a better mixing.
Thermal Conductivity of Si/SiGe Superlattice Film
Authors: Liu Chun-Kai , Chien Heng-Chieh , Dai Ming-Ji , Yu Chih-Kuang , Hsu Chun-Yeh , Huang Mei-Jiau , Luo Guang-Li
Published: June 2009

It has been proposed that the use of superlattice structure is effective for reduction of lattice thermal conductivity in the direction perpendicular to superlattice interfaces which can lead to improvement of figure of merit. In this work, we have evaluated the thermal conductivity of Si/SiGe superlattice structure films by theoretical analysis and experimental studies. In experiments, the ultra-high vacuum chemical vapor deposition (UHVCVD) has been employed to formation the Si/Si0.71Ge0.29 superlattice film. The cross-plane thermal conductivity of a Si/Si0.71Ge0.29 superlattice is measured based on the 3 ω method. In theoretical analysis, we use the Boltzmann transport equation to analyze the phenon transport in superlattice film. We compared the thermal conductivities of several Si/Si0.71Ge0.29 superlattice structure films by changing the thickness of Si and Si0.71Ge0.29. The results indicate that increasing the period (one layer Si and one layer Si0.71Ge0.29) length will lead to increase acoustic mismatch between the adjacent layers, and hence increased interfacial thermal resistance. However, if the total thickness of the superlattice film is fixed, reducing the period length will lead to decreased effective thermal conductivity due to the increased number of interfaces.
Heterodyne Detection Signal Analysis in Apertureless Scanning Near-Field Optical Microscopy
Authors: Chuang C. H. , Lo Y. L.
Published: June 2009

Apertureless scattering near-field optical microscopy (A-SNOM) is generally performed using a heterodyne detection technique since it provides a higher signal-to-noise (S/N) ratio than homodyne detection. Accordingly, this study constructs a robust interference-based model of the detection signal which takes account of both the tip enhancement phenomena and the tip reflective background electric field to analyze the amplitude and phase of heterodyne detection signals at different harmonics of the tip vibration frequency. The analytical results indicate that the high-order harmonic tip scattering noise decays more rapidly with a high-order Bessel function for small phase modulation depths than the near-field interaction signal. It is also shown that the signal contrast improves as the wavelength of the illuminating light source is increased or the incident angle is reduced. As compared with homodyne technique, it can be found the signal contrast is much improved in visible region in heterodyne technique. The results presented in this study provide an improved understanding of the complex signal detected in the heterodyne A-SNOM technique and suggest potential means of improving its S/N ratio such that the signal contrast of heterodyne A-SNOM can be improved.
Measurements on the Thermal Conductivity of Epoxy/Carbon-Nanotube Composite
Authors: Kuo Cheng-Hsiung , Huang Hwei-Ming
Published: June 2009

This study measures the thermal conductivity of the MWNT/epoxy bulk composite material to enhance the heat transfer rates of the high power LED device. In this study, three different weight percentages (0.0 wt%, 0.3 wt% and 0.5 wt%) of MWNT/Epoxy composite and five different heat generating rates were employed for the investigation. The case of pure epoxy resins (0.0 wt%) was used as a reference. The responding time and the thermal conductivity of the composites were evaluated. The results show that the response is the fastest for composite with 0.5 wt% MWNT among three composites studied herein. The responses of the 0.3%wt and 0.5%wt composite are increased by 14.3%∼26.7% relative to that of the pure epoxy. Compare with that of the pure epoxy, the thermal conductivities for the cases with 0.3 wt% and 0.5 wt% MWNT/epoxy composite are increased by 15.9%∼44.9%. Further, the thermal conductivity does not vary with temperature for the temperature range studied herein. In the present study, the thermal conductivity of the composite material is found to increase mildly with the increasing heat generation rate.
Characteristics of Heat Transfer and Flow on a Surface With Small-Scale Concave Spherical Pits
Authors: Wang J. S. , Qiu Y. , Li L. Y.
Published: June 2009

Small-scale concave spherical pits, which have a special effect on heat transfer enhancement and turbulent drag reduction, are investigated by numerical simulation in detail. Two kinds of small-scale concave pits structures are designed on surface of a plate, which are located in the bottom of a rectangle channel. The characteristics of heat transfer and flow in channel are investigated and compared with a same channel with plate bottom by means of LES. Flow structure and temperature distribution near the pits are analyzed. The numerical simulation results indicate that the concave spherical pits disturb the flow field and vortex is induced by the pits. The turbulent coherent structure is affected by the induced vortex. The numerical simulation indicates that small scale pit can generate the vortex in couple. The range of vortex is accord with the array of small scale pit. The small scale pit can enhance the intensity of vortex. As a result, the temperature field near the pit is changed with generation of the vortex. The heat transfer mechanism on plate with small scale concave spherical pit is summarized.
Chaotic Mixing in Three-Dimensional Micro Channel
Authors: Van-Le Thuy Hong , Kang Sangmo , Suh Yong Kweon , Wang Yangyang
Published: June 2009

The quality of chaotic mixing in three-dimensional micro channel flow has been numerically studied using Fractional-step method (FSM) and particle tracking techniques such as Poincare´ section and Lyapunov exponents. The flow was driven by pressure distribution and the chaotic mixing was generated by applying alternating current to electrodes embedded on the bottom wall at a first half period and on the top wall at a second half period. The equations governing the velocity and concentration distributions were solved using FSM based on Finite Volume approach. Results showed that the mixing quality depended significantly on the modulation period. The modulation period for the best mixing performance was determined based on the mixing index for various initial conditions of concentration distribution. The optimal values of modulation period obtained by the particle tracking techniques were compared with those from the solution of concentration distribution equation using FSM and CFX software and the comparison showed their good match.
Nucleate and Transition Boiling in Inclined Narrow Spaces
Authors: Stutz Benoiˆt , Tormen Ve´ronique
Published: June 2009

The purpose of this work is to describe nucleate and transition boiling occurring in an inclined narrow space (0° ≤ φ ≤ 35°) between a heated upward-facing copper disk and an unheated surface for saturated n-pentane. The distance between the heated surface and the confinement plate is enclosed between 200 μm ≤ s ≤ 90 mm. The heat flux and the wall temperature are determined by mean of an inverse heat conduction method. The instantaneous volume fraction of the vapour phase within the confined space is measured using capacitive sensors. The influence of the confinement and the inclination angle on the boiling curves and the flow patterns are analysed. The evolution of void fraction with the heat flux increase, the reduction of the gap size and the inclination of the heated surface are determined. Boiling becomes unsteady for given heat flux and inclination angle ranges. The boiling cycles are characterized by periodic liquid feeding and two-phase structure expulsion from the confined space. The cycle’s frequency increase with the heat flux and the inclination angle increase is analyzed. The conditions of unsteady boiling apparition are summarized in unsteady boiling pattern maps.