bluuebunny/crossref_metadata_2025 huggingface dataset:
Finding the Value of Immersive, Virtual Environments Using Competitive Usability Analysis
Authors: Satter Kurt M. , Butler Alley C.
Published: May 2012

Competitive usability studies are employed providing empirical results in a design evaluation and review context. Populations of novice and experienced users are tested against benchmarks. Benchmark 1 is used to evaluate error identification and correction. Benchmark 2 is employed to evaluate the user’s ability to understand spatial relationships. Both benchmarks 1 and 2 compare individual performance with performance of teams. Benchmarks 3 measures quantity of errors found in a 4 min time frame. For benchmark 1, there is a statistically significant difference, but for benchmark 2, there is no statistical difference. For benchmark 3, there is a statistically significant increase in errors found. This increase is evaluated for impact as cost avoidance. It is concluded that cost avoidance by using a cave automatic virtual environment (CAVE) immersive virtual environment easily justifies the CAVE system.
Rapid Mapping and Exploration of Configuration Space
Authors: Nelaturi Saigopal , Lysenko Mikola , Shapiro Vadim
Published: May 2012

We describe a graphics processing unit (GPU)-based computational platform for six-dimensional configuration mapping, which is the description of the configuration space of rigid motions in terms of collision and contact constraints. The platform supports a wide range of computations in design and manufacturing, including three- and six-dimensional configuration space obstacle computations, Minkowski sums and differences, packaging problems, and sweep computations. We demonstrate dramatic performance improvements in the special case of configuration space operations that determine interference-free or containment-preserving configurations between moving solids. Our approach treats such operations as convolutions in the six-dimensional configuration space that are efficiently computed using the fast Fourier transform (FFT). The inherent parallelism of FFT algorithms facilitates a straightforward implementation of convolution on GPUs with existing and freely available libraries, making all such configuration space computations practical, and often interactive.
Experimental and Numerical Analysis of Low Output Power Laser Bending of Thin Steel Sheets
Authors: Stevens Vicente , Celentano Diego , Ramos-Grez Jorge , Walczak Magdalena
Published: May 2012

This work presents an experimental and numerical analysis of a low output power single-pass laser forming process applied to thin stainless steel sheets. To this end, the proposed methodology consists in four stages respectively devoted to material characterization via tensile testing, estimation of thermal boundary conditions present in laser forming, realization of laser bending tests for two sets of operating variables, and finally, numerical simulation of this process carried out with a coupled thermomechanical finite element formulation accounting for large plastic strains, temperature-dependent material properties and convection–radiation phenomena. The numerical analysis, focused on the description of the evolution of the thermomechanical material response, is found to provide a satisfactory experimental validation of the final bending angle for two laser forming cases with different operating variables. In both cases, the predicted high temperature gradients occurring across the sample thickness show that the deformation process is mainly governed by the thermal gradient mechanism.
New Method of Productivity Equation for Multibranch Horizontal Well in Three-Dimensional Anisotropic Oil Reservoirs
Authors: Wu Junlai , Liu Yuetian , Yang Haining
Published: May 2012

As a highly efficient production method, multibranch horizontal well is widely used in the development of low permeability reservoirs, naturally fracture reservoirs, heavy oil reservoirs, shallow layer reservoirs, and multilayer reservoirs, because it can significantly improve the productivity of a single well, inhibit edge or bottom water coning, and enhance oil recovery. This paper presents a new productivity equation for multibranch horizontal well in 3D anisotropic reservoirs. By applying coordinate transformation, a 3D anisotropic reservoir is transformed into an equivalent isotropic reservoir with considering wellbore deformation and vertical radial flow. An analytical solution of multibranch horizontal well productivity in 3D anisotropic reservoirs is obtained by using pseudo-3D solving method and similar flow replaces theory. The results show that branch number n, branch length (l), and permeability anisotropy degree (β3) are the three main factors that have big effects on the production rate of multibranch horizontal well.
3-Omega-T-Type Method for Measuring the Thermophysical Properties of Micro/Nanowires
Authors: Zhang Xing , Wang Jianli
Published: May 2012

A novel 3ω-T type probe method is developed to investigate the thermal effusivity of micro/nanowires. In this method, a short hot wire subjected to an alternating current serves simultaneously as a heater and a thermometer, and a test wire is attached to the midpoint of the hot wire with an interstitial material. A measurement system based on a virtual lock-in is developed to measure the thermal impedance of the interposer and the thermal effusivity of the test wire. The same value of thermal effusivity is obtained with the presence of different interposers, and the interposer with small thermal impedance gives a decrease of the temperature oscillation of the hot wire. Using this method, the thermal resistances of bare metallic junctions are measured as a function of temperature. For the junction established by two crossed platinum wires with small diameters, the thermal contact resistance is found to decrease as temperature increases, which can possibly be explained the plastic deformation of the microscopic contacts.
Lattice Boltzmann Investigations on Drag Reduction in Microchannel Flow With Bionic Surfaces
Authors: Cui Jing , Li Weizhong , Liu Yang
Published: May 2012

In this paper, four types of micro-patterned surfaces, which are covered with ridge-shaped grooves, V-shaped grooves, shield-shaped grooves and straight slot grooves, are employed to investigate the drag reduction effect. Lattice Boltzmann method (LBM), a new numerical approach on mescoscopic level, is used to conduct the numerical simulations. The micro-grooved surfaces possess the drag reduction performance because the micro-structure affects the flow beahviours. The existence of the vortices formed within the grooves not only decrease the shear force between fluid and walls but also reduce the contact area between fluid and walls, which can lead to a reduction of pressure loss. The different grooved-surfaces have different degrees of drag reduction abilities: ridge-shaped grooves > V-shaped grooves > shield shaped grooves > straight slot grooves. Besides, the geometrical optimizations for the ridge-shaped grooves, which show the highest drag reduction performance, are performed as well. The results suggest that, for the purpose of drag reduction, the ridge-shaped grooves with smaller width-height ratio are recommended for the lower Reynolds number flow while the ridge-shape grooves with larger width-height ratio are more suitable for the larger Reynolds number flow.
DSMC Simulation of Pressure Driven Binary Rarefied Gas Flows Through Short Microtubes
Authors: Szalmas Lajos , Valougeorgis Dimitris , Colin Stephane
Published: May 2012

Binary gas flows driven by pressure gradient through short microtubes are studied by using an upgraded version of the Direct Simulation Monte Carlo (DSMC) method. Two types of mixtures, He/Xe and Ne/Ar, are examined. Several values of the channel length to radius ratio, the downstream to upstream pressure ratio and a wide range of the gas rarefaction are considered. Results are presented for the species and total flow rates and for the axial distributions of the macroscopic quantities. There is a pronounced difference of the flow behavior of the two mixtures due to the different molecular mass ratios. The flow rate of the He/Xe mixture for very short channels and large pressure drops is increased with increasing gas rarefaction, while the flow rate of the Ne/Ar mixture shows a different rarefaction dependence. The obtained results can be useful in optimal design of microfluidic or vacuum devices.
Continuous Particle Separation With AC Electro-Osmosis and Dielectrophoresis in a Microchannel
Authors: Liu Zhipeng , Speetjens Michel F. M. , Frijns Arjan J. H. , van Steenhoven Anton A.
Published: May 2012

This paper describes a particle-separation device combining AC electroosmosis and dielectrophoresis under pressure-driven flow. The whole device comprises an initial hydrodynamic-focusing compartment with Y junction and an electrohydrodynamic compartment with interdigitated coplanar ITO electrode arrays. In the electrohydrodynamic compartment, the electrode arrays on the bottom of the microchannel are inclined at a 10 degree angle with regard to the direction of channel. A lateral flow is generated by AC electro-osmosis flow triggered by a low-voltage AC electric field on the surface of the electrode. Superimposed upon the axial pressure-driven flow applied by the external syringe pump, AC electro-osmosis flow induces a depressed vortical flow above the electrodes. We find that when homogeneously suspended micro polystyrene particles with different sizes (0.86 μm and 5 μm) in the KCl solution (0.1 mM) are transported through the vortical flow region, the small particles, 0.86 μm, successfully become trapped in the lateral flow above the electrode arrays under the combination of AC electroosmosis and positive DEP, whereas the large particles, 5 μm, completely pass through the vortices. The effectiveness of this separation is investigated for different axial flow rates and amplitudes of the applied voltage. It is shown that with increasing flow rate, it becomes hard for the small particle to get trapped. The possibility of trapping, however, is enhanced by increasing the amplitude of the applied voltage. In addition, we found that the effectiveness of particle separation is frequency dependent, tending to zero at both low and high frequencies. The peak of the effectiveness happens at a so-called characteristic frequency which depends on the conductivity and geometry of the electrodes. We expect that this electrohydrodynamic method can be used to separate the particles with high effectivity for various applications in microsystems.
The Study of Rarefied Gas Flow Through Microfilters With Different Openings Using MONIR-DSMC
Authors: Darbandi Masoud , Karchani Abolfazl , Schneider Gerry
Published: May 2012

The main objective of this work is to evaluate the pressure loss at low subsonic rarefied flow through a microfilter having different opening shapes. As is known, a filter with a lower pressure drop is more suitable for different industrial and medical applications. We use our own developed DSMC solver, i.e., 3D MONIR-DSMC code to lunch our study. MONIR uses the NTC (no-time-counter) scheme to model the collision process. The VHS model is also chosen to simulate collision between particle pairs. The Opening factor which is known as one of the most important parameters affecting the microfilter design, is taken constant. The results show that the pressure drop for a rectangular holes is greater than the other hole shapes. Also, the hexagonal hole shapes provide efficient manners compare with circular, rectangular and cubic hole shapes, considering constant opening factor and hydraulic diameter magnitudes.
New MEMS-Based Micro-Coriolis Density Measurement Technology
Authors: Huber Christof , Touzin Mike R.
Published: May 2012

Density measurements have long been used within the scope of process and product quality control in a variety of applications and industries. In the petroleum industry, measuring the density or specific gravity of liquid fuels has been reported to be the preferred method for both accuracy and ease of use, for example in blending operations. In the drinking water, beverage and pharmaceutical industries, density measurement is an important quality related fluid parameter. To see wide spread use, a measurement technology must not only be capable of accurately monitoring a parameter, but it must do so in an economical way. This paper explores laboratory and field hazardous area applications of a newly developed MEMS (Micro Electro Mechanical System) technology for density measurement. This microfluidic sensor, based on the Coriolis principle, has on-chip density / specific gravity, temperature and viscosity measurement capabilities, as will be demonstrated in the experimental results. These very compact MEMS devices are immune to vehicular vibration and have an extremely fast response time, due their high resonant frequencies. The ability to differentiate between types of fuels such as gasoline, ethanol, methanol, diesel, biodiesel, butanol, and to detect water and air contamination using density measurement, will be demonstrated. Concentrations of fuel blends such as E85 and others can be accurately determined. The density of liquid ingredients, additives and pharmaceutical liquids can be measured with high reproducibility. Measuring fluids under high flow rates is accommodated with an internal by-pass design. An intrinsically safe Class 1 Div 1 (or Zone 0) circuit has been developed to enable use of this technology with flammable liquids or in explosion hazardous atmospheres.
Microresonator Concept for Mass Detection in Liquids
Authors: Allievi Alejandro
Published: May 2012

We evaluate enhanced mass detection possibilities with electrostatic actuation of a mechanical microoscillator positioned at a fluid-liquid interface. An analytical model is used to simulate the rotational motion of such configuration inside a microchannel either completely filled with two immiscible liquids, or partially filled forming an air-liquid interface. Simulation results show that improvements in sensitivity can be obtained through the use of fluid-liquid interfaces. For point mass detection, sensitivities of at least 9–15Hz/ng can be achieved using liquid-liquid interfaces. For air-liquid interfaces, it is conceivable to detect point masses in the order of tens of picograms.
Axial Heat Conduction in the Context of Developing Flows in Microchannels
Authors: Moharana Manoj K. , Singh Piyush K. , Khandekar Sameer
Published: May 2012

For practical microchannel applications involving convective heat transfer, the flows are usually, not only laminar, they are also simultaneously developing in nature. Moreover, flat plate substrates with microchannels engraved/ machined or etched on them are emerging as one of the most popular flow geometries. Not analyzing such situations as conjugate heat transfer problems with multi-dimensional effects, often leads to erroneous estimation of heat transfer coefficients. In this context, we report three dimensional numerical simulations of simultaneously developing internal convective flow through a square microchannel (side = 400 μm), treating the substrate thickness, flow Reynolds number and the thermal conductivity of the substrate and the fluid, in the conjugate formulation. Constant heat flux is applied at the bottom of the substrate, away from the fluid-solid interface, as in real-time situations. The parametric study reveals that depending on geometry considerations, flow parameters and thermo-physical properties of fluid-solid combination, conjugate heat transfer effects must be accounted for, to correctly estimate the local Nusselt number.
Second-Order Gaseous Flow Models in Long Circular and Noncircular Microchannels and Nanochannels
Authors: Duan Zhipeng
Published: May 2012

Gaseous flow in circular and noncircular microchannels has been examined and a simple analytical model with second-order slip boundary conditions for normalized Poiseuille number is proposed. The model is applicable to arbitrary length scale. It extends previous studies to the transition regime by employing the second-order slip boundary conditions. The effects of the second-order slip boundary conditions are analyzed. As in slip and transition regimes, no solutions or graphical and tabulated data exist for most geometries, the developed simple model can be used to predict friction factor, mass flow rate, tangential momentum accommodation coefficient, pressure distribution of gaseous flow in noncircular microchannels by the research community for the practical engineering design of microchannels such as rectangular, trapezoidal, double-trapezoidal, triangular, rhombic, hexagonal, octagonal, elliptical, semielliptical, parabolic, circular sector, circular segment, annular sector, rectangular duct with unilateral elliptical or circular end, annular, and even comparatively complex doubly-connected microducts. The developed second-order models are preferable since the difficulty and “investment” is negligible compared with the cost of alternative methods such as molecular simulations or solutions of Boltzmann equation. Navier-Stokes equations with second-order slip models can be used to predict quantities of engineering interest such as Poiseuille number, tangential momentum accommodation coefficient, mass flow rate, pressure distribution, and pressure drop beyond its typically acknowledged limit of application. The appropriate or effective second-order slip coefficients include the contribution of the Knudsen layers in order to capture the complete solution of the Boltzmann equation for the Poiseuille number, mass flow rate, and pressure distribution. It could be reasonable that various researchers proposed different second-order slip coefficients because the values are naturally different in different Knudsen number regimes. The transition regime is a varying mixture of different transport mechanisms and the mixed degree relies on the magnitude of the Knudsen number. It is analytically shown that the Knudsen’s minimum can be predicted with the second-order model and the Knudsen value of the occurrence of Knudsen’s minimum depends on inlet and outlet pressure ratio. The compressibility and rarefaction effects on mass flow rate and the curvature of the pressure distribution by employing first-order and second-order slip flow models are analyzed and compared. The condition of linear pressure distribution is given. This paper demonstrates that with some relatively simple ideas from knowledge, observation, and intuition, one can predict some fairly complex flows.
Large-Eddy Simulation of Physiological Pulsatile Flow Based on a Dynamic Nonlinear Subgrid-Scale Stress Model
Authors: Molla Md. Mamun , Wang Bing-Chen , Kuhn David C. S.
Published: May 2012

Pulsatile laminar-turbulent transitional flow in a three-dimensional (3D) constricted channel represents a challenging topic and has many important applications in bio-medical engineering. In this research, we numerically investigate the physics of a physiological pulsatile flow confined within a 3D channel with an idealized stenosis formed eccentrically on the top wall using the method of large-eddy simulation (LES). The advanced dynamic nonlinear subgrid-scale stress (SGS) model of Wang and Bergstrom [1] was implemented in the current LES approach to properly resolve the unrealistic SGS dissipation effects and numerical instabilities that are intrinsic to the Smagorinsky type dynamic models (DM). The Reynolds numbers tested in the simulation are 1700 and 2000, which are characteristic of human blood flows in large arteries. An in-house 3-D LES code has been modified to conduct our unsteady numerical simulations, and the results obtained have been validated using two different grid arrangements and the experimental results of Ahmed and Giddens [2]. The numerical results have been examined in terms of the resolved mean velocity, turbulence kinetic energy, viscous wall shear stress, resolved and subgrid-scale Reynolds stresses, as well as the local kinetic energy fluxes between the filtered and subgrid scales.
Optimizing Energy Output of Piezoelectric Microcantilevers
Authors: Rezaeisaray Mehdi , Raboud Don , Moussa Walied
Published: May 2012

This work presents some new methods in optimizing electrical energy, harvested using a micro piezoelectric cantilever. Both mechanical and electrical aspects have been considered. Mechanically, two items have been considered to maximize the generated voltage: geometry of the cantilever and placement of the electrodes. It has been shown that for given sizes of length and width of the harvester and for a given natural frequency, the output voltage can be increased by adjusting the thickness of the beam and the proof mass and consequently increasing the amplitude of vibration. As well, the placement of the electrodes plays a very important role in optimizing output voltage. It has also been shown that piezoelectric cantilevers with shorter top electrodes induce higher voltage than cantilevers with longer top electrodes. Overall results agree with the analytical equations reported in literature so far. Moreover, distribution of top electrodes along the width of the cantilever has been taken into consideration. It has been shown how output voltage can be approximately doubled by using two narrower top electrodes along the width of the cantilever. All analysis in this work was carried out in ANSYS. In this research, to improve the electrical efficiency, diodes have been considered in the circuit to reduce electrical losses in comparison to rectifiers which have been used in conventional harvesters. Applying these methods to particular test cases, a 71% increase in output voltage was observed for the case of geometry optimization, a 116% increase was observed for the case of shortening the top electrode and losses in the electrical circuit were reduced by approximately 50% by using diodes comparing to using rectifiers. While these results focused on cantilever based harvesters, the ideas contained are equally applicable to other structures.
A Novel Passive Micromixer Based on Asymmetric Split-and-Recombine With Fan-Shaped Cavity
Authors: Xia Guodong , Li Jian , Wu Hongjie , Zhou Mingzheng , Wang Haiyan
Published: May 2012

A novel passive micromixer with fan-shaped cavity based on the principle of flow planar asymmetric split-and-recombine (P-ASAR) and focusing/diverging is designed. The micromixer consists of two split sub-channels with unequal widths and one fan-shaped cavity structure on the major sub-channel which are similar to a diamond ring structure. In order to yield optimum mixing effect, different parameters of geometry structure under a wide range of Reynolds numbers (1–80) have been investigated by numerical simulation with three-dimensional Navier-Stokes equations. The steady laminar flow was solved by using a finite-volume method and SIMPLE algorithm. Enhanced micromixing is achieved by utilizing a synergistic combination of unbalanced inertial collision, Dean vortices and expansion vortices. As a result of interplay between inertial, centrifugal and viscous effects, Dean vortices arise in the vertical plane of curved channel. Expansion vortices appear in the horizontal plane due to an abrupt increase of the cross-sectional area. The mixing index is used to evaluate the degree of mixing. Our studies show that vortices are observed in the channels at high Reynolds numbers. The geometry parameters of fan-shaped cavity structure affect the mixing index of micromixer. When the ratio of the widths of the major sub-channel and fan-shaped cavity channel is 1/3, the mixing index of this type micromixer could reach around 75% at Reynolds numbers larger than 60. The relation between mixing intensity and pump power consumption has been analyzed at a wide range of Reynolds numbers simultaneously.
Effects of Surfactant on the Motion of a Large Bubble in a Capillary Tube
Authors: Gursel Gokalp , Olgac Ufuk , Muradoglu Metin
Published: May 2012

The finite-difference/front-tracking method is used to study the motion and deformation of a large bubble moving through a capillary tube in the presence of both insoluble and soluble surfactants. Emphasis is placed on the effects of surfactant on the liquid film thickness between the bubble and the tube wall. The numerical method is designed to solve the evolution equations of the interfacial and bulk surfactant concentrations coupled with the incompressible Navier-Stokes equations. A non-linear equation of state is used to relate interfacial surface tension to surfactant concentration at the interface. The film thickness is first computed for the clean bubble case and the results are compared with the lubrication theory in the limit of small capillary numbers, i.e., Ca ≪ 1, and found to be in good agreement with the predictions of Bretherton [1]. Thereafter, the method is used to investigate the effects of insoluble and soluble surfactants on the film thickness for a wide range of governing non-dimensional numbers. It is found that both the insoluble and soluble surfactants have a thickening effect on the liquid film, which compares well with both the experimental results of Krechetnikov and Homsy [2] and analytical predictions of Daripa and Pasa [3].
Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry Flows Under a Constant Heat Flux Boundary
Authors: Howard James A. , Walsh Patrick A.
Published: May 2012

This paper investigates laminar heat transfer characteristic of two-phase microencapsulated phase change material (MPCM) suspension flows within mini-channels under a constant wall heat flux boundary. Capsules containing paraffin wax with phase change temperature between 35.1°C and 44°C are examined and found to be well suited for electronics cooling applications using liquid cold plate technologies. In particular, it is shown that the large thermal capacity of MPCM slurries around the phase change temperature can lead towards greater isothermality of isoflux systems, a characteristic of significant interest to telecommunication, laser and biomedical applications. The principal focus of the study is to examine heat transfer characteristics within standard tube flow geometries, quantify the heat transfer augmentation/degradation observed and finally, elucidate the mechanisms from which these result. Through the study volume concentrations of the MPCM slurry were varied between 30.2% and 5.03%. High resolution local heat transfer measurements were obtained using infrared thermography and results presented in terms of local Nusselt number versus inverse Graetz parameter. These spanned both the thermal entrance and the fully developed flow regions with inverse Graetz number ranging from 10−3 to 100. Results show that significant heat transfer enhancements are attainable via the use of MPCM slurries over conventional single phase coolants. Overall, the study highlights mechanisms that lead to significant heat transfer enhancements in heat exchange devices employing micro-encapsulated phase change material slurries.
Fabrication of Microchannels by Stereolithography for Optical Use
Authors: Li Yongli , Brandner Juergen J. , Hansjosten Edgar , Anurjew Eugen , Newport David
Published: May 2012

In this paper the feasibility of obtaining optical access for micro devices made by stereolithography is investigated, to meet demands set by microfluidic research efforts. A commercially available resin SL5530 was selected for the UV polymerisation process. By optimising the design of the CAD models and the fabrication process, the suitability of the final product was improved for optical metrology. Transparent T-shaped microchannels were manufactured for future application in gas mixing study on interferometric system. Fringes patterns were first obtained from interferometric experiments and then the signals were extracted from the fringes pattern to analyse its suitability.
Flow Characteristics of Adiabatic Gas-Liquid Two-Phase Flow in a Horizontal Flat Rectangular Microchannel
Authors: Ide Hideo , Satonaka Kentaro , Fukano Tohru
Published: May 2012

Experiments were performed to obtain, analyze and clarify the mean void fraction, the mean liquid holdup, and the liquid slug velocity and the air-water two-phase flow patterns in horizontal rectangular microchannels, with the dimensions equal to 1.0 mm width × 0.1 mm depth, and 1.0 mm width × 0.2 mm depth, respectively. The flow patterns such as bubble flow, slug flow and annular flow were observed. The microchannel data showed similar data patterns compared to those in minichannels with the width of 1∼10mm and the depth of 1mm which we had previously reported on. However, in a 1.0 × 0.1 mm microchannel, the mean holdup and the base film thickness in annular flow showed larger values because the effects of liquid viscosity and surface tension on the holdup and void fraction dominate. The remarkable flow characteristics of rivulet flow and the flow with a partial dry out of the channel inner wall were observed in slug flow and annular flow patterns in the microchannel of 0.1 mm depth.
Electrohydrodynamic and Shear-Stress Interfacial Instability of Two Streaming Viscous Liquid Inside a Microchannel for Normal Electric Fields
Authors: Li Haiwang , Wong Teck Neng , Nguyen Nam-Trung
Published: May 2012

The electrohydrodynamic and shear-stress instability of the interface between two viscous fluids with different electrical properties under constant flowrates in microchannel is analytically and experimentally investigated. In analytical model, the two-layer system is subjected to an electric field normal to the interface between the two fluids; the electric field, surface charge and fluid dynamic are coupled only at the interface. In the experiments, two immiscible fluids, aqueous NaHCO3 (high electrical mobility fluid) and Poly (dimethylsiloxane) (low electrical mobility fluid) are pushed into the PMMA microchannel using syringes and syringe pump. The normal electric field is added to the aqueous NaHCO3 using high voltage power supply; the perturbation electric field are added using a function generator and a power amplifier. The results showed that the electric fields can induce the instability of fluids in microchannel; the increasing of viscosity and flowrates has a stabilizing effect to the flow; but increasing of thickness has a destabilizing effect to the flow. The results also show that the analytical solution has a good agreement with the experimental results.
Theoretical Study on the Wetting Length in Triangle Wetting Region of Rectangular Microgrooves
Authors: Wang Tao , Hu Xuegong , Guo Chaohong , Nie Xuelei , Xie Ningning
Published: May 2012

The mathematical model is established in this article to describe the relationship between the wetting length of working liquid in the triangular wetting region of rectangular capillary microgrooves and the geometric dimension, tilt angle, type of working liquid and heat flux when heating the back of microgrooves heat sink. The model supposes that the vapour-liquid interface of meniscus is quadratic parabola but not arc. The predictions from the theoretical analysis are successfully compared with the experimental results.
Osmosis and Solute Size: A Molecular Dynamics Study
Authors: Cannon James , Kim Daejoong , Maruyama Shigeo , Shiomi Junichiro
Published: May 2012

Osmosis plays an essential role in a wide range of phenomena, and therefore it is useful to understand how to manipulate the rate at which osmosis occurs. In the present study we conduct molecular dynamics simulations to consider the influence of solute size on the osmotic pressure gradient which drives the flow. Our results show how selective choice of the size of the solute can enhance, or hinder, the establishment of a strong osmotic gradient.
Thermally Induced Oscillatory Two-Phase Flow in a Mini-Channel: Towards Understanding Pulsating Heat Pipes
Authors: Das Shyama Prasad , Lefe`vre Fre´de´ric , Khandekar Sameer , Bonjour Jocelyn
Published: May 2012

Research on Pulsating Heat Pipes (PHP) has received substantial attention in the recent past, due to its unique operating characteristics and potential applications in many passive heat transport situations. Reliable design tools can only be formulated if the nuances of its operating principles are well understood; at present, this is rather insufficient for framing comprehensive models. In this context, this paper reports experimental data on self-sustained thermally driven oscillations in a 2.0 mm ID capillary tube sub-system, consisting of only one vapor slug and one liquid plug (‘unit-cell’). Understanding such a sub-system/‘unit-cell’ is vital, as it represents a primary unit of a multi-turn PHP. Experiments have been performed with two fluids, i.e. Pentane (BP = 36.1°C) and Methanol (BP = 64.7°C) at different evaporator (40°C to 65°C) and condenser temperatures (−5°C to 15°C) respectively. High speed videography and spectrum analysis reveals that self-sustained thermally driven flow oscillations are observed for both fluids, albeit the dominant periodicity is different. Oscillation frequencies vary from 1.5 Hz to 4.2 Hz approximately, depending on the fluid, operating pressure and temperature. Increasing the difference of temperature between the evaporator and condenser sections leads to enhanced driving force for creating flow oscillations. The resulting phase velocities cause interfacial instabilities, resulting in the formation of secondary bubbles which break-off from the main meniscus. Results of this study can be compared to numerical models and will be useful to understand the physics of multi-turn PHPs.
Natural Convection With Porous Medium in a Narrow Horizontal Cylindrical Annulus With Linear Heat Generation
Authors: Mansour Kamyar
Published: May 2012

We consider the two-dimensional problem of steady natural convection in a narrow (micro) horizontal cylindrical annulus filled with porous medium due with linear volumetric heat generation. The solution is expanded in powers of a single combined similarity parameter, which is the product of the gap ratio to the power of two, and Rayleigh number. The series is extended by means of symbolic calculation up to 28 terms. Analysis of these expansions allows the exact computation for arbitrarily accuracy up to 50000 figures. Although the range of the radius of convergence is small, but pade approximation leads our results to be good even for much higher value of the similarity parameter.
Numerical Study of Micromixers for Stopped Flow
Authors: Du¨chs Dominik , Brunklaus Sabine , Spang Peter , Ritzi-Lehnert Marion , Drese Klaus
Published: May 2012

Computational fluid dynamics (CFD) simulations are conducted to compare the efficiency of different types of micromixers with respect to their potential application in chip-based stopped-flow designs. The evaluation of a mixing parameter for different geometries and at various flow velocities enables a comparison between the Berger ball mixer and other designs that are in principle suitable for applications in microfluidic chips.
Evaluating Seven Cubic Equations of State in Predicting Gas and Liquid Phase Thermodynamic Properties of Refrigerant Mixtures
Authors: Mobinipouya Omid
Published: May 2012

From practical point of view, Refrigerants and refrigerant mixtures are widely used as working fluids in many industrial applications, such as refrigerators, heat pumps, and power plants the present work is devoted to evaluating seven cubic equations of state (EOS) in predicting gas and liquid phase volumetric properties of nine ozone-safe refrigerants both in super and sub-critical regions. The evaluations, in sub-critical region, show that TWU and PR EOS are capable of predicting PVT properties of refrigerants R32 within 2%, R22, R134a, R152a and R143a within 1% and R123, R124, R125, and TWU and PR EOS’s, from literature data are 0.5% for R22, R32, R152a, R143a, and R125, 1% for R123, R134a, and R141b, and 2% for R124. Moreover, SRK EOS predicts PVT properties of R22, R125, and R123 to within aforementioned errors. The remaining EOS’s predicts volumetric properties of this class of fluids with higher errors than those above mentioned which are at most 8%.In general, the results are in favor of the preference of TWU and PR EOS over other remaining EOS’s in predicting densities of all mentioned refrigerants in both super and sub critical regions. Typically, this refrigerant is known to offer advantages such as ozone depleting potential equal to zero, Global warming potential equal to 140, and no toxic.
Fluid Mechanics of Flow Through Rectangular Hydrophobic Microchannels
Authors: Kashaninejad Navid , Chan Weng Kong , Nguyen Nam-Trung
Published: May 2012

In this study, the effect of two important parameters have been evaluated for pressure driven liquid flows in microchannel in laminar regime by analytical modeling, followed by experimental measurement. These parameters are wettability conditions of microchannel surfaces and aspect ratio of rectangular microchannels. For small values of aspect ratio, the channel was considered to have a rectangular cross-section, instead of being two parallel plates. Novel expressions for these kinds of channels were derived using eigenfunction expansion method. The obtained two-dimensional solutions based on dual finite series were then extended to the case of a constant slip velocity at the bottom wall. In addition, for large values of aspect ratio, a general equation was obtained which is capable of accounting for different values of slip lengths for both upper and lower channel walls. Firstly, it was found out that for low aspect ratio microchannels, the results obtained by analytical rectangular 2-D model agree well with the experimental measurements as compared to one dimensional solution. For high aspect ratio microchannels, both models predict the same trend. This finding indicates that using the conventional 1-D solution may not be accurate for the channels where the width is of the same order as the height. Secondly, experimental results showed that up to 2.5% and 16% drag reduction can be achieved for 1000 and 250 micron channel height, respectively. It can be concluded that increasing the surface wettability can reduce the pressure drop in laminar regime and the effect is more pronounced by decreasing the channel height.
Contraction/Expansion Effects in 90° Miter Bends in Rectangular Xurographic Microchannels
Authors: Nguyen Lam , Elsnab John , Ameel Tim
Published: May 2012

Xurography is an inexpensive rapid prototyping technology for the development of microfluidic systems. Imprecision in the xurographic tape cutting process can result in undesired changes in channel dimensions near features that require a change in cutting direction, such as 90° miter bends. An experimental study of water flow in rectangular xurographic microchannels incorporating 90° miter bends with different channel widths in each leg is reported. A set of twelve microchannels, with channel depth approximately 105 micrometers and aspect ratio ranging from 0.071 to 0.435, were fabricated from double-sided adhesive Kapton® polyimide tape and two rectangular glass plates. The channels were reinforced with a mechanical clamping system, enabling high Reynolds number, Re, flows (up to Re = 3200) where Re was based upon hydraulic diameter and average velocity. Reported data include friction factor and critical Reynolds number for straight microchannels and loss coefficients for flow through 90° miter bends that contain either a contraction or expansion with cross-sectional area ratios of 0.5, 0.333 and 0.2. The critical Reynolds number, Recr, ranged from 1750 to 2300 and was found to be dependent on channel defects such as sidewall roughness, adhesive droplets, and corner imperfections. Loss coefficients through 90° miter bends with expansion decrease rapidly for Re < Recr. At the transition, the loss coefficient suddenly drops and approaches an asymptotic value for Re > Recr. For 90° miter bends with contractions, loss coefficients gradually decrease with increasing Re for 150 < Re < 1400. In addition, the loss coefficient decreases with decreasing area ratio through the contraction or expansion. The minor loss coefficient data were found to be dependent on Reynolds numbers and area ratio of contraction/expansion at the bend. The results suggest that the effect of the contraction/expansion was the dominant mechanism for minor losses in the 90° miter bend.
Liquid-Liquid Test Reactions to Characterize 2-Phase-Mixing in Microchannels
Authors: Kockmann Norbert , Roberge Dominique M.
Published: May 2012

Multiphase flow is often found in chemical engineering, food processing, or analytics. First contacting and droplet generation as well as coalescence and re-dispersion have high importance for the flow characteristics. In all processes, the channel geometry, fluid properties, and flow velocity determine the flow regime, droplet size, and interfacial area. The hydrolysis of alkyl acetates in organic phase with sodium hydroxide NaOH in the aqueous phase is investigated as flexible test reaction for mass transfer and interfacial area. For right design of the characteristic time for mass transfer, the alkyl group is chosen from ethyl, isopropyl or n-butyl, which differ in water solubility, diffusivity and rate constant. The consumption of NaOH is used for calculation of specific area and related mass transfer coefficient. Different channel geometries are characterized and design considerations are conducted.
Study of the Effect of Electrophoresis on Transport of Biomolecules in Microreactors
Authors: Jomeh Sina , Hoorfar Mina
Published: May 2012

The effect of electrophoresis (i.e., applying uniform electric field to use the natural charge of particles) on the transport of a sample (like biomolecules) in active microreactors is numerically investigated. Navier-Stokes equations are solved along with the equations of electrostatics, species mass transport in the buffer and chemical reaction kinetics at reactive surfaces. Unlike previous studies, in which the effect of the charge of the sample bulk on the electric field has been neglected (i.e., the assumption of electroneutrality), here space charge density is assumed to be nonzero. As a result, the governing equations become fully coupled. The efficiency of the microreactor device is analyzed for two different geometries commonly used in biomolecule separation (i.e., open channel and microcylinders). It is shown that the electroneutrality assumption can drastically influence the final adsorbed concentration depending on the device configuration. Average adsorbed surface concentration is compared for each case as a measure of the performance of the device. The plots depicting the influence of the electric field and nonzero space charge density on the bulk concentration profile and the velocity field are also presented and discussed.
Experimental Study on the Effect of Synthetic Jet on Flow Boiling Instability in a Microchannel
Authors: Fang Ruixian , Jiang Wei , Khan Jamil
Published: May 2012

Two-phase flow instability in microchannel flow boiling exhibits pressure fluctuations with different frequencies and amplitudes. One possible way to suppress the dynamic instability is to introduce synthetic jet near the inlet of the channel. An important feature of synthetic jet is that it allows momentum transfer into the microchannel flow without net mass injection into it. The strength and frequency of the jet can be controlled by changing the driving voltage and frequency of the piezoelectric driven jet actuator. The effects of the synthetic jet together with upstream throttling are evaluated as a means of stabilizing the flow boiling instability. The results are compared with the case without synthetic jet. The pressure dynamics of the microchannel flow caused by the synthetic jet are also analyzed.
Effect of the Hydrophilic Compact Aluminum-Foam Filled Flow Channel on Water Removal From the Cathode Catalyst Layer
Authors: Friess Brooks R. , Yew Samuel C. , Hoorfar Mina
Published: May 2012

The polymer electrolyte membrane (PEM) fuel cell is a zero emission power generation system that has long been considered as a replacement for conventional fossil fuel combustion systems. However, before constituting a viable market for commercial use, the fuel cell’s efficiency and reliability need to be improved significantly. It has been shown that water management has a significant effect on the power and reliability of the cell as the electrolyte membrane must be well hydrated to allow for ion transfer while excess water blocks the activation sites on the cathode side. The latter effect is known as flooding which occurs at large current densities and compromises the normal operation of the fuel cell. To enhance water management, a prodigious amount of studies have been conducted to optimize the properties and structures of different layers. One of the key results of these studies has been the design of a flow field pattern on the relatively hydrophobic surface of a graphite plate which is believed to provide a better mechanism for removing water droplets from the cathode flow channel. However, the wettability gradient between the catalyst layer (i.e., hydrophilic) and the flow channel (which is currently more hydrophobic) introduces problems as the water droplets formed at the catalyst layer will not likely detach, and hence create a film of liquid that will block the activation sites. If the flow channel is made out of a material that is more hydrophilic than the catalyst layer, water removal and transport will be enhanced as water naturally moves from low surface energy to high surface energy sites. However, recent numerical studies conducted on simulation of water transport in the channels show that removing the water film formed on the hydrophilic channels is limited due to the pressure of the gas flow in the channels. To resolve this problem, the use of compact aluminum foams in the flow channels is studied in this paper. It is shown that the hydrophilicity of the foam-filled flow channel helps the transport of the water droplets at the catalyst layer to the channel in which a liquid film is formed. This film is then removed due to the increased pressure developed in the porous media of the foam (as opposed to the regular open flow channel). The paper includes the experimental results obtained for the fuel cell performance using the new geometry with and without the gas diffusion layers (GDLs). These results will be compared to a similar flow channel that does not include the compressed aluminum porous structure. This work will result in finding the optimum geometry for achieving maximum performance in the flooding regime.
Wirelessly Powered Electrowetting-on-Dielctric (EWOD)
Authors: Byun Sang Hyun , Cho Sung Kwon
Published: May 2012

Recently, EWOD (Electrowetting on dielectric) has attracted a great deal of interest with applications of digital lab-on-a-chip in which microfluids are manipulated in a discrete form of droplets using electrical inputs. In most EWOD applications, the commonly used powering method is wired transmission, which may not be suitable for implantable lab-on-a-chip applications. In this paper, we will investigate wireless power transmission for EWOD utilizing the inductive coupling. Unlike the conventional inductive coupling, wireless EWOD requires a high voltage (> 50 V) at the receiver side which is connected to the EWOD chip since EWOD naturally operates under high input voltages. To satisfy this condition, the resonant inductive coupling method at a high resonant frequency is introduced and investigated. To optimize the transmission efficiency, we study the effects of many parameters such as the frequency, the inductance and the capacitance at the transmitter as well as receiver, the gap between the transmitter coil and receiver coil, and so on, by measuring the voltage at the receiver and the contact angle of droplets placed on wirelessly operated EWOD chip. In addition, by introducing amplitude modulation (AM) to the resonant inductive coupling, wireless AC electrowetting which generates droplet oscillations and is one of the commonly used operational modes is also achieved.