bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Micro Valve Using Micro Fluidic Device and Zero-Net-Flow-Rate Micro Jet
Authors: Koizumi Yasuo , Ohtake Hiroyasu
Published: June 2009

Characteristics of a mini/micro-size Y-type fluidic device were examined using water as test fluid. The cross-section of an inlet path and outlet branches was 1 mm × 1 mm square. That of signal ports was 1 mm × 0.5 mm. Although Reynolds number tested was low; less than 1000, the mini/micro-size fluidic device functioned as the fluidic device; flow provided for a signal port flowed out from an opposite outlet. It was also analytically proved by the commercial code of STAR-CD. A zero-net flow micro-jet which had been analytically predicted was experimentally confirmed. A piezoelectric element was used to produce the zero-net flow micro-jet. A new concept of the mini/micro-size fluidic device was proposed. In that design, the signal ports were replaced with the zero-net flow micro-jet which was formed by the piezoelectric element. It was confirmed that the new design would function as the fluidic device.
Effects of Obstacles on the Mixing Performance in Microchannels
Authors: Kim Tae-An , Kim Youn-Jea
Published: June 2009

The mixing of two or more fluid streams in microchannels needs quite long channel lengths. Therefore, in order to improve the mixing performance, obstacles have been placed in the channel to disrupt flow and to reduce the diffusion path. The disruption to flow velocity field alters the flow direction from one fluid to another. Properly designed geometric parameters, such as layout, angle with main flow direction and aspect ratio of obstacles, will be resulted in improving the mixing performance with only little increase of the pressure drop. In this study, T-type rectangular microchannel is used, which has two inlets with W×H×L = 100×100×100 μm3 and one outlet with W×H×L = 200×100×6950 μm3. Furthermore, the mixing channel has obstacles which are placed with an angle of inclination and with dimensions W×H×L = 10×100×h μm3 on the lower layer. In order to estimate the performance of the mixing, numerical analyses are carried out with water and ethanol. Especially, the diffusion coefficient, D, is set to 10−10 m2/s for simulating two-fluid diffusion-convection flow, the mixing efficiency and the pressure drop of microchannel are investigated with various values of the angle of inclination, aspect ratio (h = αH) of obstacle and Reynolds number. When the flow passes through on the obstacles, rotation flow is observed. This flow pattern is repeated at each cycle. Besides, in each case that obstacles are turned to the center of channel and to the side walls, rotational direction is changed reversely. In case of pressure drop, as the Reynolds number, the angle of obstacle (θ) and the aspect ratio (α) are increased, the pressure drop is also increased. Results show that the ratio between the maximum and minimum of pressure drop is the order-of-magnitude of 1 at Re = 1.667. Results also show that the angle of inclination of obstacles has more influence on the mixing performance than the height of obstacles and Reynolds number.
Measurement of Fluid Temperature Across Micro-Scale Gap Using 2-Color Ratiometric LIF Technique in Combination With Confocal Microscopy
Authors: Jeong Dong Woon , Lee Chi Young , Lee Sang Yong
Published: June 2009

In the present work, for non-invasive measurement of the liquid temperature in microchannels the 2-color ratiometric Laser-Induced Fluorescence (LIF) technique was improved by adopting the confocal microscopy. By using this technique, the fluorescent light from the tiny volume around a focusing spot can be selectively detected, and it enables us to measure the local liquid temperatures even at the close vicinity of the walls. To check the general performance of this method, as the preliminary stage, a test section consists of two horizontal plates in different temperatures, separated by a narrow gap filled with a mixture of Rhodamine B (a temperature-sensitive dye) and methanol was made, and the temperature distribution was examined. Based on the relationship between the fluorescence intensity and the temperature, a linear temperature distribution across the gap (by conduction heat transfer) could be confirmed. However, the measured results were subject to external disturbances such as excitation laser intensity fluctuation and irregular reflection of light from the glossy walls. Therefore, in the second stage, to eliminate those external disturbances, another fluorescent dye, Rhodamine 110 (a temperature-insensitive dye), having a different emission spectrum peak (525 nm) from the Rhodamine B (575 nm) was added. In principle, the external disturbance effects cancel out each other if the intensity ratio between Rhodamine B and Rhodamine 110 is used (instead of using Rhodamine B only). To compensate substantial reduction of fluorescence intensity by re-absorption of the fluorescence light emission from Rhodamine 110, which is inherent in the present 2-color thermometry, dependency of the intensity ratio on the depth of the measuring point also has been examined. In summary, the 2-color ratiometric confocal-LIF thermometry was found to be very useful tool to measure the local temperatures of the liquid flow field in micro-fluidic devices.
Numerical and Experimental Analysis of Monostable Mini- and Micro-Oscillators
Authors: Khelfaoui Rachid , Colin Ste´phane , Caen Robert , Orieux Ste´phane , Baldas Lucien
Published: June 2009

An asymmetric micro-oscillator design based on a monostable fluidic amplifier is proposed. Experimental data with various feedback loop configurations point out that the main effect responsible for the oscillation is a capacitive and not a propagative effect. Actually, sound propagation in the feedback loop only generates a secondary oscillation which is not strong enough to provoke the jet switching. Data from a hybrid simulation using a commercial CFD code and a simple analytical model are in good agreement with the experimental data. A more compact plane design with reduced feedback loop volumes is also studied through a fully CFD simulation that confirms the previous conclusions.
Experimental Study of Flow Boiling in Microchannel
Authors: Singh S. G. , Duttagupta S. P. , Kulkarni A. M. , Puranik B. P. , Agrawal A.
Published: June 2009

With the reduction in size of electronic devices, the problem of efficient cooling is becoming more and more severe. Boiling heat transfer in microchannels is fast emerging as a promising solution to the problem. In the present work, microchannels were fabricated on a silicon wafer. A chrome-gold micro-heater was integrated and characterized on the other side of the wafer. The change in resistance of the micro-heater in the temperature range of 20 °C – 120 °C was found to be within 10%. Deionized water was used as working fluid in microchannel. The single-phase pressure drop across the microchannel was found to increase linearly with increasing flow rate in confirmation with conventional laminar flow theory. Also, the pressure drop decreases with an increase in heat input due to a reduction in viscosity. The study was extended to two phase flow with flow rate and heat flux as the control parameters. The onset of two phase flow, at a given heat flux, with a decrease in flow rate, can be identified by the departure of linear pressure drop to non-linearity; this point was also confirmed through visual observation. In two-phase region of flow, pressure drop was found to increase initially, passes through a maximum and then decreases, with a decrease in flow rate. The experiments are performed for several heat fluxes. Both the onset of two phase and maximum pressure drop in the two phase region shifts to higher flow rates with an increase in heat input. Such detailed experimental results seem to be missing from the literature and are expected to be useful for modeling of boiling heat transfer in microchannels. Another pertinent observation is presence of instability in two-phase flow. It was found that at higher flow rate and heat flux instability in two-phase flow was more. An attempt to record these instabilities was made and preliminary data on their frequency will be presented. This study may help to choose suitable operating conditions for a microchannel heat sink for use in electronics cooling.
Effect of Surface Catalytic Reaction on Homogeneous Premixed Combustion
Authors: Xu Kan , Liu M. H. , Cai X. D. , Chen Y. L.
Published: June 2009

Surface catalytic reaction is an important way to organize effective and stable combustion inside micro or mini-scale combustor. In this paper, the surface catalytic kinetics theory was used to study the effect of Pt-surface catalytic reaction on homogeneous lean fuel premixed combustion of CH4/Air in a 2-D mini-scale expanding channel. Using the CHEMKIN surface catalytic kinetics model, a numerical method was presented, which is based on the commercial code, FLUENT. The performance of our numerical procedure was validated by comparison of the results with those obtained from DETCHEM (Redenius, 2001) and the experimental data. Our studies found, compared with homogeneous combustion, the catalytic reaction produces a reduced extinction distance, a thicker flame, and a lower maximum temperature inside the flow field. Worthwhile, the temperature gradient on the unburned side of the flame is decreased. The effects of the surface catalytic reaction on the gas phase combustion are very sensitive to the equivalence ratio. The leaner the mixture is, the stronger the catalytic effects are.
Microflow Behavior of Liquid in the Presence of Laser-Induced Temperature Gradient
Authors: Motosuke Masahiro , Shimakawa Jun , Honami Shinji
Published: June 2009

A novel technique is presented for non-intrusive microflow control with laser-induced local temperature gradient. In microscale, fluid behavior is quite different from that in macroscale, especially an effect of fluid or interfacial properties on microflow becomes significant. The technique described in this paper utilizes the property change of fluids caused by a light-induced temperature change, i.e., photothermal effect. Absorption of a focused laser beam causes the local spot in temperature. Since the viscosity of general fluids has strong temperature dependence, a generation of local temperature gradient in microfluids results in the corresponding viscosity distribution, which is directly related to the flow behavior in microflow. In order to demonstrate the validity of this concept, we have developed an experimental system to irradiate focused laser beam on a flow in a microfluidic device and to measure velocity profile of the microflow simultaneously. As a heating source, a compact laser diode (LD) with the visible wavelength of 635nm is employed. Velocity measurement is performed by a micro particle image velocimetry (micro-PIV) technique. Optical separation between LD absorption and excitation/emission of fluorescent particle for micro-PIV measurement is confirmed. Change in the microflow behavior in a rectangular microchannel (500 μm × 50 μm) during the LD irradiation due to the photothermal effect is observed.
Numerical Analysis of the 3D Flow Induced by Propagation of Plane-Wave Deformations on Thin Membranes Inside Microchannels
Authors: Tabak Ahmet Fatih , Yes¸ilyurt Serhat
Published: June 2009

Propulsion mechanisms of microorganisms are based on either beating or screw-like motion of thin elastic biopolymers. Arguably, this motion is optimal for propulsion at very low Reynolds numbers. Similar actuation mechanisms can be utilized in the design of an autonomous microswimmer or even a micropump. In principle, propagation of plane-wave deformations on a thin-membrane placed inside a channel can lead to a net flow in the direction of the wave propagation. In this study we present effects of the amplitude, frequency, and the width of the membrane on the time-averaged flow rate and the rate of work done on the fluid by the membrane by means of three-dimensional transient simulations of flows induced by plane-wave deformations on membranes. Navier-Stokes and continuity equations are used to model the flow on a time-varying domain, which is prescribed with respect to the motion of the membrane. Third party commercial software, COMSOL, is used in to solve the finite-element representation of the 3D time-dependent flow on moving mesh. Numerical simulations show that the flow inside the microchannel depends on the square of the amplitude and is proportional to the excitation frequency. Lastly, characteristic flow rate vs. pressure head curve and efficiency of a typical pump are obtained from 3D transient simulations, and presented here.
Entrance Length Characteristics in Microchannels Using Micro-Particle Image Velocimetry
Authors: Ahmad Tariq , Hassan Ibrahim , Muwanga Roland
Published: June 2009

An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of micro-Particle Image Velocimetry (micro-PIV), a non-intrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data is obtained for two different microchannel hydraulic diameters of 500 μm and 100 μm, both of which have cross-sectional aspect ratios of one. The working fluid is distilled water, and velocity profile data is acquired over a laminar Reynolds number range from 0 to 200. The test sections were designed as to provide a sharpedged microchannel inlet from an infinitely sized reservoir, at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100, to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier-Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts, and no influence of scaling was observed.
Microfabricated EHD Pumps With High Aspect Ratio Electrodes
Authors: Zangeneh Kazemi Pouya , Selvaganapathy Ponnambalam Ravi , Ching Chan Y.
Published: June 2009

This work presents the design, fabrication and testing of electrohydrodynamic (EHD) micropumps with three dimensional (3-D) electrodes. It is known that the body force on the fluid due to an electric field is increased by increased injection of charges. In this design, 3-D micro pillars are used electrodes to provide high electrode-fluid contact area and to improve charge injection. Three different electrode designs were used to investigate the effect of different parameters, such as electrode spacing and pillars size, on the pump performance. The electrodes were fabricated using nickel, and were integrated into a microchannel of dimensions 22mm × 5mm × 100μm. The micropumps were tested under a no-flow condition with ethanol as the working fluid. The preliminary results suggest that the new 3-D electrodes improve pump performance over pumps with 2-D planar electrodes. A maximum pressure head of 780 Pa was achieved at an applied voltage of 150 V with the 3-D electrodes.
Flow Boiling in Minichannels Under Normal, Hyper and Microgravity: Local Heat Transfer Analysis Using Inverse Methods
Authors: Luciani Se´bastian , Brutin David , Rahli Ouamar , Le Niliot Christophe , Tadrist Loune`s
Published: June 2009

The objective presented in this paper is here to provide basic knowledge on the systems of biphasic cooling in mini and microchannels during hyper and microgravity. The experimental activities are performed in the frame of the MAP Boiling project founded by ESA. The main aspect of this paper is to present the use of inverse methods to estimate local flow boiling heat transfers coefficient in minichannels. To observe the influence of gravity level on the fluid flow and to take data measurements, an experimental setup is designed with two identical channels; one for the visualization and the other one for the acquisition of data. These two devices enable us to study the influence of gravity on the temperatures and pressures measurements. The two minichannels are modeled as a rectangular rod made up of three materials; a layer of polycarbonate® (λ = 0,2 W.m−1.K−1) used as insulator, a cement rod (λ = 0,83 W.m−1.K−1) instrumented with 21 K-type thermocouples and in the middle a layer of incone® (λ = 10,8 W.m−1.K−1) in which the minichannel is engraved. Pressures and temperatures measurements are carried out simultaneously at various levels of the minichannel. Above the channel, we have a set of temperatures and pressures gauges and inside the cement rod, 5 heating wires providing a power of 11 W. The K-type thermocouples sensors enable us to acquire the temperature in various locations (x, y and z) of the device. With these temperatures and the knowledge of the boundary conditions, we are able to solve the problem using inverse methods and to obtain local heat flux and local surface temperatures on several locations. All the results on hydrodynamics and pressure drop will be provided in a second paper in the same congress.
Molecular-Level Modeling of Interfacial Phenomena: Use of Molecular Dynamics Simulations in Tandem With Statistical Thermodynamics Models
Authors: Carey Van P.
Published: June 2009

Nanoscale aspects of interfacial phenomena can be critically import in convective vaporization and condensation in nanochannels or microchannels. Molecular dynamics (MD) simulations have been extensively used to model and explore the physics of interfacial phenomena at the molecular level. Efforts to improve MD simulations have often focused on development of more physically realistic interaction potentials used to model intermolecular force interactions, or on development of more efficient computing strategies. An important, and often overlooked aspect of MD simulations is the role that theoretical models from statistical thermodynamics can play in MD simulations. This paper argues that use of alternate statistical thermodynamics models, and unconventional strategies for using them, can be effective ways of enhancing MD simulations. The advantages of these types of approaches are explored in the context of three recent MD simulation studies of interfacial region thermophysics that have made use of statistical thermodynamics theory in novel ways. Examples considered include studies of the interfacial region between bulk liquid and vapor phases, thin liquid films on solid surfaces, and stability free thin liquid films. These examples illustrate ways that MD simulations can be combined with other models to enhance computational efficiency or extract more information from the MD simulation results. Successful strategies for implementing these types of scheme are examined, and their general applicability is assessed.
Blood Flow Through Channels and Clearances in Implantable Pumps
Authors: Day Steven W.
Published: June 2009

Implantable rotary blood pumps are very effective at supporting patients with heart failure. New designs demonstrate distinct advantages over their predecessor diaphragm type pumps and have generated vast interest in the medical devices community, as demonstrated by hundreds of technical publications and newer commercially available devices. In addition to mechanical design criteria, these pumps share the requirement of moving a relatively large amount of blood through a miniaturized pump without damaging the blood cells. The fluid channels within the impeller are typically 1–3 mm wide and the clearance between the blades, rotating at 2,000–10,000 rpm, and the stationary housing is approximately 100–300μm. This paper gives examples of experimental and numerical methods to characterize the flow field, and a summary of how the flow affects blood cells and design strategies to minimize blood damage.
Brownian Dynamics Simulations of Polymer Behavior in Nanofluidic and Microfluidic Systems
Authors: Kumar Satish
Published: June 2009

Brownian dynamics (BD) is a stochastic simulation method that can quantitatively describe the non-equilibrium behavior of long polymers (∼1 micron contour length) over long time scales (∼1 s). With the increasing use of nanofluidic and microfluidic devices for the handling of biopolymers such as DNA, BD has the potential to be a powerful design tool for the separation and transport processes carried out in these devices. As a coarse-grained simulation method, BD also serves as a natural bridge between atomistic and continuum modeling. In this talk, an introduction to the Brownian dynamics simulation method will be given along with simulation results for some applications of current interest. The introduction will review basic molecular models for polymers (bead-rod, bead-spring) and the stochastic differential equations used to describe their dynamics. The applications will focus on polyelectrolyte adsorption and electrophoresis.
Microfluidics and Their Biomedical Applications
Authors: Lee Gwo-Bin
Published: June 2009

Bio-micro-electro-mechanical-systems and microfluidic technologies combining knowledge from biology, analytical chemistry and miniaturization techniques have proven to be a promising approach to realize the concept of lab-on-a-chip, which perform a total analysis of a small amount of samples on a single chip. In this keynote paper, I am going to briefly introduce our previous works regarding several crucial microfluidic technologies including microfluidic focusing/switching and micro/nano-droplets formation. These technologies have been popular recently for microfluidic devices and systems. Several examples will be demonstrated, including micro flow cytometers for cell counting and sorting, and droplet formation chips for emulsion applications. The development of these technologies may be promising for biomedical applications.
A Fast Computational Method for Particle Dynamics in Dielectrophoretic Lab-on-Chip Systems
Authors: Chowdhury Indranil , Jandhyala Vikram , Rockway John D.
Published: June 2009

An accelerated boundary element method (BEM) is proposed for predicting the motion of bio-particles under combined electromagnetic and fluidic force fields. Many Lab-on-chip (LoC) designs are based on dielectrophoretic (DEP) manipulation of polarized species inside microfluidic channels. The BEM approach presented here relies entirely on modeling the surface of the computational domain, significantly reducing the number of unknowns when compared to volume-based methods. Additionally, the need for re-meshing the whole domain at each time-step of particle movement is prevented. A coupled circuit-EM formulation is presented for accurate prediction of dielectophoretic field distribution due to on-chip electrodes. This allows the circuit control of the resulting electromagnetic fields. Next, BEM formulations for predicting DEP and fluidic traction forces on arbitrarily shaped bio-particles are presented. EM fields produced by the electrodes induce the DEP forces, while the fluid flow is driven by a pressure gradient across the channel. The resultant motion of the subjected particles is studied using a simple time-stepping algorithm. The algorithm has a time complexity of O(N3), where N is the number of unknowns), which leads to a large bottleneck during simulation of each time step. This problem is addressed by implementing oct-tree based O(N) multilevel iterative solvers. The methodology is used to study the field distribution due to distributed electrode systems and particle motion in fluidic channels. Evidence of O(N) behavior of the fast solver is presented. The resulting simulator can be used to study complicated distributed structures and explore new LoC design ideas.
Numerical and Experimental Study of Gas Flows in 2D and 3D Microchannels
Authors: Guo Xiaohui , Huang Chihyung , Alexeenko Alina A. , Sullivan John P.
Published: June 2009

In the experiments conducted at Purdue, the air flow in rectangular cross-section microchannels was investigated using the pressure sensitive paints. The high resolution pressure measurements were obtained for inlet-to-outlet pressure ratios from 1.76 to 20 with the outlet Knudsen numbers in the range from 0.002 to 0.06 based on hydraulic diameter of 157.9 micron and the length-to-height ratio of about 50. In the slip flow regime, air flow was simulated by the 2D and 3D Navier-Stokes equations with no-slip and slip boundary conditions. For various pressure ratios, the entrance flow development, compressibility and rarefaction effects were observed in both experiments and numerical simulations. It was found that accurate modeling of gas flows infinite-length channels requires that inlet and outlet reservoirs to be included in computations. Effects of entrance geometry on the friction factor were studied for 3D cases. In both experiments and numerical modelings, significant pressure drop was found starting at the inlet chamber. The numerical modeling also predicted an apparent temperature drop especially at the channel exit.
Selective Wettability Assisted Nanoliter Sample Generation via Electrowetting-Based Transportation
Authors: Chen Ting-Hsuan , Su Chun-Min , Chih Hsueh-Ching , Yang Cheng-Tsair
Published: June 2009

A novel method for nanoliter sample generation is demonstrated. In this method, an electrowetting-based platform (EWOD) was used to transport a water droplet which was sandwiched between two hydrophobic plates, and the transportation was carried out by the direct electrical control of planar electrodes on the bottom glass substrate. In contrast to the air environment in ordinary EWOD, silicone oil was employed to surround the water droplet to reduce the surface hysteresis; therefore, the fluidic operations including cutting and transportation became easier to manipulate. While the droplet was moving through the electrodes, a nanoliter sample was produced within the circular hydrophilic area which was patterned on the upper ITO coated plate. Hence, based on the definition of selective wettability areas, the sample volume is capable to be well generated and controlled. Besides, in order to optimize the dimensions of electrode, the dimensional criterion for complete sample generation was investigated. The result shows that larger electrode width permits more flexibility to determine the radius of hydrophilic circle. Upon this mechanism, the hydrophilic circle of 0.25 mm diameter is able to generate the tiny sample of 3.9 nanoliter. Since the dimensions of the hydrophilic circle could be easily patterned in tens microns, this method has the potential to achieve the picoliter sample via similar procedure. Consequently, according to the tiny sample generation and reduction of hysteresis, such method is well-suitable for the versatile applications.
Study of Ultrasonically-Induced Fluid Flows Using Micro-Particle Image Velocimetry
Authors: van der Linden Heiko , Lindken Ralph , Westerweel Jerry
Published: June 2009

This paper describes our recently started research into the flow phenomena that occur in microchannels and microcavities during ultrasonic agitation. With micro-particle image velocimetry we have seen rapidly changing flows together with the occurrence of cavitation events. Both these processes suggest that very high shear forces are present in the solution in combination with rapidly changing pressure fluctuations. The research presented here is of importance for the design of ultrasonic mixers and ultrasonic cell lysis devices.
Study of the Hot Spots in Integrated Circuits Cooled by Microfluidic Heatsinks
Authors: Motieifar Alireza , Shafai Cyrus , Soliman Hassan M.
Published: June 2009

The thermal input into high-power Integrated Circuits (IC) can have local peaks or hot spots with heat fluxes far exceeding 100 W/cm2. In this work, the temperature distribution on a microfluidic heatsink has been simulated using the FEM method. The effects of the fluid flow and thickness of the heatsink on the hot spot temperature have been studied. Simulations have been performed for a 1 cm × 1 cm heat sink loaded with 100 W/cm2 heating power, with a 1 mm hot spot of 1000 W/cm2 and a 3 mm hot spot of 500 W/cm2. Heat sinks fabricated from silicon, nickel, and copper are considered. These results show that the effect of increasing the thickness of the heatsink on the peak temperature of the hot spot depends on the solid material and the fluid flow. Simulations showed that the hot spot temperature rise can be about 40% higher if a nickel heat sink is used instead of a copper heat sink.
Flow Characteristics and Frictional Pressure Drops of Gas-Liquid Two-Phase Flow in Mini-Micro Pipes and at Vena Contract and Expansion
Authors: Ohtake Hiroyasu , Ohtaki Hideyasu , Koizumi Yasuo
Published: June 2009

The frictional pressure drops and two-phase flow patterns of gas-liquid two-phase flow in mini-micro pipes and at vena contract and expansion were investigated experimentally. Test liquid was water; test gas was argon. The diameter of the test mini-pipe was 0.5, 0.25 and 0.12 mm, respectively. The pressure drop data and the flow pattern were collected over 2.1 < Ug < 92.5 m/s for the superficial gas velocity and 0.03 < Ul < 10 m/s for the superficial liquid velocity. The experimental results show that the flow patterns were slug, churn, ring and annular flows; pure bubbly flow pattern was not observed in a range of the present experimental conditions. The two-phase friction multiplier data for D > 0.5 mm showed to be in good agreement with the conventional correlations. On the other hand, the two-phase friction multiplier data for D < 0.25 mm differed from the calculated values by the conventional correlations. Then, thickness of liquid film around a gas plug and size of gas core were estimated and the effect of frictional pressure drop on channel size was discussed through Knudsen Number of gas and instability on liquid-gas interface. The coefficients of sudden enlargement and sudden contraction in mini-pipes for the gas-water two-phase flow were modified from the present experimental results.
Fabrication of Lenses With High Light-Collecting Ability Using Water Molds
Authors: Chao Shih-Hui , Carlson Robert , Meldrum Deirdre R.
Published: June 2009

A small water droplet on a computer monitor screen enables us to see the detail of a single pixel. Such droplets are almost perfectly spherical, ideal as optical lenses. We developed a novel fabrication method that uses water droplets as molds to make small, highly spherical lenses. Poly(dimethylsiloxane) (PDMS) spherical lenses have been made for demonstration: When uncured PDMS encapsulates water droplets and then solidifies, the cavities occupied by water become concave lenses or as a mold to make convex lenses. The light-collecting ability of these lenses is 6.25 times better than those made using traditional methods, while the cost is much lower. These lenses can be easily integrated with lab-on-a-chip devices for optical manipulation and/or detection.
Performance Comparison of Rectangular and Air-Foil Shapes Offset Strip Flow Paths Micro Heat Exchangers
Authors: Yang Chien-Yuh , Yeh Chun-Ta , Lin Ting-Yu
Published: June 2009

Six micro heat exchangers with rectangle, airfoil and shuttle type strips was designed and fabricated in the present work. Two major parameters were considered for heat transfer performance comparison. One is the effect of strip type and the other is the strip arrangement. From the test results, we may notice that for both rectangle and airfoil strips heat exchangers, those with shorter strips performed lower thermal resistance than those with longer strips. Furthermore, the heat exchangers with more strips have better heat transfer performance. However, the space between strips is limited by the fabrication techniques.
Improved Serpentine Laminating Micromixer: Numerical Investigation and Experimental Verification
Authors: Park Jang Min , Kim Dong Sung , Kang Tae Gon , Kwon Tai Hun
Published: June 2009

It is a difficult task to achieve an efficient mixing inside a microchannel since the flow is characterized by low Reynolds number (Re). Recently, the serpentine laminating micromixer (SLM) was reported to achieve an efficient chaotic mixing by introducing ‘F’-shape mixing units successively in two layers such that two chaotic mixing mechanisms, namely splitting/recombination and chaotic advection, enhance the mixing performance in combination. The present study describes an improved serpentine laminating micromixer (ISLM) with a novel redesign of the ‘F’-shape mixing unit. Reduced cross-sectional area at the recombination region of ISLM locally enhances advection effect which helps better vertical lamination, resulting in improved mixing performance. Flow characteristics and mixing performances of SLM and ISLM are investigated numerically and verified experimentally. Numerical analysis system is developed based on a finite element method and a colored particle tracking method, while mixing entropy is adopted as a quantitative mixing measure. Numerical analysis result confirms enhanced vertical lamination performance and consequently improved mixing performance of ISLM. For experimental verification, SLM and ISLM were fabricated by polydimethylsiloxane (PDMS) casting against SU-8 patterned masters. Mixing performance is observed by normalized red color intensity change of phenolphthalein along the downchannel. Flow characteristics of SLM and ISLM are investigated by tracing the red interface of two streams via optical micrograph. The normalized mixing intensity behavior confirms improved mixing performance of ISLM, which is consistent with numerical analysis result.
Characterization of Micro Fluidic Devices by Optical Measurements
Authors: Schlu¨ter Michael , Hoffmann Marko , Ra¨biger Norbert
Published: June 2009

Micro fluidic devices are successfully in use for several applications in chemical engineering and biotechnology. Nevertheless, there is still no breakthrough for micro process engineering because of a lack in understanding the mechanisms for local hydrodynamics and mass transfer on micro scales. Micro Particle Image Velocimetry (μ-PIV) combined with Confocal Laser Scanning Microscopy (CLSM) enables the measurement of three-dimensional flow and concentration fields in micro devices for common stationary cases. By quantitative analysis of pressure drops, mixing qualities and residence time distributions an adjustment of micro reactor devices for the demands of chemical and biochemical reactions becomes possible.
Miniaturized Refrigeration System With Advanced PCM Micro Encapsulation Technology
Authors: Farid Mohammed , Smith Michael , Sabbah Rami , Al Hallaj Said
Published: June 2009

Technology advances in microchips and miniaturized refrigeration systems require heat to be removed at a high flux. Microchannel heat exchangers have been implemented for the efficient removal of heat in these applications. However, the maximum achievable heat flux is still limited even when two-phase flow (evaporation) is used, due to the formation of vapor film along the wall of the heat exchanger. In this presentation, the principle of using a suspension of microcapsules in liquid as a heat transfer fluid to improve the performance of microchannel heat exchangers will be discussed. The microcapsules contain phase change material, which melts and solidifies at a specified range of temperatures. These microcapsules improve the fluid effective specific heat capacity and thermal conductivity due to latent heat effect and micro mixing respectively.
Flow Boiling Heat Transfer Mechanism in Minichannels
Authors: Kuznetsov V. V. , Shamirzaev A. S.
Published: June 2009

The present study is aimed at consideration of forced boiling heat transfer in a channel whose width is comparable and less than the capillary constant. When boiling occurs inside very small and non-circular passages the constrain phenomena become important in determining the aspects of flow phenomena such as the flow pattern and microscale heat transfer. We consider the experimental data on flow patterns and boiling heat transfer for two refrigerants (R318C and R21), which were obtained for rectangular and annular channels in a range of flow rates from 50 kg/m2s up to 900 kg/m2s and heat fluxes density of up to 90 kW/m2. The temperature variation over the channel perimeter and in time was measured for the rectangular channel also. Different heat transfer mechanisms were revealed depending of flow patterns. We observed dominant nucleation boiling and the joint mode of nucleation boiling and convective evaporation. We have also found the mode when evaporation of thin liquid films makes the main contribution to heat transfer. The modified model of Liu and Winterton and Kandlikar model describe well the experimental data for the flow patterns when nucleation boiling and convective heat transfer make the most contribution to heat transfer. The approach to predict the suppression of flow boiling in the annular flow is proposed based on comparison of the turbulent boundary layer thickness and cavity radius based on the tangency criterion for boiling incipience.
Bislug Flow in Circular and Square Cross-Sectional Microchannels
Authors: Hernandez Joseph E. , Scholfield B. Justin , Allen Jeffrey S.
Published: June 2009

Liquid-liquid slug or bislug flow can occur in any cross sectional capillary tube that is wetting and has a low Bond number. When two immiscible fluids are in contact in a capillary tube forming three fluid-fluid interfaces, spontaneous flow may occur due to a pressure imbalance across the menisci. Flow traverses the tube towards the liquid with the higher surface tension. Bislug flow in both prewet and non-prewet channels has been investigated. The bislug velocity in the prewet channels is faster than those in the dry. The velocity increase can be attributed to the decrease in the energy loss associated with the moving contact line. There is a dramatic increase in flow velocity in prewet square channels where the fluid is wicked into the corners. This wicking action decreases the perimeter length of the advancing contact line thereby minimizing energy dissipation.
Microfluidic Control Using Vapor Based Valves
Authors: Xu Wei , Xue Hong , Bachman Mark , Li G. P.
Published: June 2009

Microflow valving and regulating are two important functions for microfluidic systems for applications such as Lab-on-Chip. Although silicon based counterparts have been studied extensively, few good technologies exist for polymer based microvalves and regulators. In this paper, we present designs and methods for microvalve and microflow regulators that are readily integrated into polymer microfluidic devices. The technologies utilize “air-pocket” structures built into the sidewalls of the microchannels. When liquid is filled in such a channel, air is trapped in “air pocket” structures due to the hydrophobicity of the polymer. By creating a small thermal gradient between the fluid in the channel and the air in the pockets, one can controllably evaporate fluid into the air pocket where it condenses. This displaces air out of the pocket into the flow channel, increasing the resistance to flow. The air valve retreats to its original pocket when the temperature gradient is removed, thus allowing one to increase or decrease fluid flow at will. If the temperature gradient is maintained long enough, the air will completely block the channel, forming an irreversible valving of the flow. Therefore, the same device can be used as either a valve or flow-regulating device. Microfluidic prototypes were built and tested using this technology. The results show successful constant flow delivery as well as valve function. This novel vapor based microflow valve and regulator has advantages of low cost, simple design, and both ease of fabrication and integration.
New Method for Horizontal and Vertical Curve Negotiation Angle Calculation
Authors: Hua Lin , Hixon Larry
Published: June 2009

A new method for the “horizontal and vertical curve negotiation angle calculation” is developed and presented in this paper. The new method greatly reduces the complexity of the current procedure while maintaining the accuracy of the final result. An example is given to illustrate the difference between the current and the alternate method. The accuracy of the new method is shown as well. Discussion and conclusions are given in the final part of this paper.
Comparison of the Cyclic Variability of an Exhaust Gas Temperature Sensor and In-Cylinder Pressure Measurements
Authors: Morey F. , Seers P. , Gardiner D.
Published: June 2009

This paper presents a concept of an exhaust temperature sensor as a method to monitor cyclic variability of combustion. The goal is to determine if the cycle-to-cycle fluctuations of the sensor can be related to the cyclic variability of combustion as measured by a pressure transducer. Experiments were conducted with a port fuel spark ignition engine at different engine speeds and loads. For each operating point, different spark timing and different excess ratios were used to evaluate the sensitivity of the temperature-based sensor to quantify the cyclic variability of combustion as measured by the Coefficient of Variation (COV). The results demonstrated the sensitivity of the concept to relatively low levels of cyclic variability (circa 1–3% COV of IMEP). At a given speed and load, changes in cyclic variability indicated by in-cylinder pressure measurement were, in general, reproduced by the sensor. The relationship between the cyclic variability indications provided by the two sensors varied as the speed and load were changed.
Regulatory Risk Evaluation of Positive Train Control Systems
Authors: Hartong Mark W. , Cataldi Olga K.
Published: June 2009

In February of 2005, the Federal Railroad Administration of the U.S. Department of Transportation issued a set of new performance-based regulations governing the development and use of microprocessor-based signal and train control systems. The new standard, effective March 2005, requires that replacement systems be at least as safe as the existing condition. Among the key elements used in evaluating the compliance of products to the new performance standard are quantitative and qualitative risk assessments. This paper explains the performance standard that must be followed, the regulatory background behind it, various quantitative and qualitative risk modeling techniques that can be used to support claims of compliance, and issues associated with their implementation.
Modeling the Effect of Injector Nozzle-Hole Layout on Diesel Engine Fuel Consumption and Emissions
Authors: Park Sung Wook , Reitz Rolf D.
Published: June 2009

Numerical simulations were used to study the effect of reduced nozzle hole size and nozzle tip hole configuration on the combustion characteristics of a high speed direct injection diesel engine. The KIVA code coupled with the Chemkin chemistry solver was used for the calculations. The calculations were performed over wide ranges of equivalence ratio, injection timing and injection pressure. Three nozzle hole layouts were considered; the baseline conventional nozzle, and multi- and group-hole configurations. In the multi-hole case, the number of holes was doubled and the hole size was reduced, while keeping the same hole area as for the baseline nozzle. The group-hole configuration used the same hole number and hole size as the multi-hole case, but pairs of holes were grouped with a close (0.2mm) spacing between the holes. The results of the mixture distributions showed that the group hole configuration provides similar penetration and lower inhomogeneity to those of the baseline large hole nozzle with the same nozzle flow area. Consequently, the fuel consumption and pollutant emissions, such as CO and soot, are improved by using the group-hole nozzle instead of the conventional hole nozzle over wide operating ranges. On the other hand, the multi-hole nozzle has advantages in its fuel consumption and CO emissions over the conventional hole layout at intermediate equivalence ratios (equivalence ratios from 0.46–0.84) and conventional injection timings (SOI: 15° BTDC).
A Simulation Tool for Sizing Electrical Railway Lines
Authors: Sanz Bobi Juan de Dios , Jorreto Marcos Federico , Garzo´n Nu´n˜ez Jorge
Published: June 2009

Railway transport market necessities demand a speed increase of medium and long distance circulations. The commitment with environment and the saturation of the European airspace explain the present success of the European high speed railway lines and specially the Spanish High Speed Lines thanks to the courageous plan of investments that foretells a promising future for this sector. In order to reach greater speed in a more rational, economic and systematic way, the use of mathematical model based simulation tools that allow simulating the behaviour of the system in a trustworthy and economic form are a must. Railway lines’ requirements until now were based in proven veteran designs. Nevertheless the current demands are enormous and the use of computer tools to study the electrical behavior to reach the objective is unavoidable. Thus, simulation tools permits the calculation of the technical characteristics of the electrification system by obtaining the necessary physical magnitudes to evaluate correct operation and correctly sizing of the elements that are part of the electrification system.
Electronically Controlled Pneumatic Brake Systems for North American Freight Railroads
Authors: Cataldi Olga K. , Lauby Robert C.
Published: June 2009

A new braking technology for the Nation’s railroads is the subject of extensive attention in the Federal Government and the railroad industry. Electronically Controlled Pneumatic (ECP) brakes are a tested and validated technology superior to conventional pneumatic brakes and can bring significant improvements to the safety and efficiency of railroad operations. Advanced braking concepts like ECP brakes were first investigated by the Association of American Railroads (AAR) in 1990. Over the past 15 years, ECP brake technology has progressed rapidly. ECP brake systems have been field tested on various railroads since 1995. The Federal Railroad Administration (FRA) has been an active and consistent advocate of ECP brake system implementation. In 1997, FRA participated in an AAR initiative to develop ECP brake standards. In 1999, FRA funded a Failure Modes, Effects, and Criticality Analysis (FMECA) for the ECP brake systems specified in the AAR standards. FRA also took part in programs to develop and enhance advanced components for the application of ECP brake systems. During the early years of development, however, FRA did not initiate regulatory actions impacting ECP brake technology. The development and application of ECP brakes remained the sole responsibility of the brake manufacturers and the railroads. Progress towards implementation of ECP brake technology slowed and stalled due to difficulties in identifying an optimal implementation strategy to support the required investment. In 2005, FRA felt that it was time to reenergize ECP brake system interest. FRA took steps to assess industry readiness and the effectiveness of the ECP brake technology. FRA contracted with Booz Allen Hamilton, a major consulting firm, to assess current ECP brake technology and to identify cost, business and safety benefits, and implementation strategies. After a thorough analysis of ECP brake technology and a review of the results of numerous studies and initiatives, FRA concluded that the technology is mature and the time is right for implementation of ECP brake technology in the North American railroad industry. Therefore, FRA is currently proceeding with new rulemaking to support industry conversion to ECP brakes. FRA’s rulemaking activity is responsive to the railroad industry’s needs and should facilitate the introduction and widespread application of ECP brake technology. This paper discusses the safety and efficiency advantages of an industry conversion to ECP brakes as the primary method of train braking. The paper also describes the challenges associated with conversion to ECP brakes and FRA’s actions to support their implementation.