bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunable Morphology of Monodisperse Polymer Particles With Microfluidics
Authors: Wang Baoguo , Weitz David A. , Shum Ho Cheung
Published: May 2012

In this work, we propose a novel method to fabricate polymer particles with controlled morphology in microchannel by solidification of polymer solutions and study the transition in the shape of these particles from spheres, to cups, and to donuts. The non-spherical geometries are achieved through nonuniform diffusion of the solvent, leading to non-uniform solidification. By adjusting the flow rates of both continuous and dispersed phases, the spatial heterogeneity in the solvent diffusion rate and thus the morphology of the final polymer particles can be tuned. This approach offers a one-step continuous process for the fabrication of non-spherical polymer particles. The technique is applicable to different polymers under appropriate polymer-solvent combinations. The ability to tune the shapes of polymer particles easily will create new opportunities for applications that require anisotropic functional particles, such as in biomedical engineering.
The Onset of Nucleate Boiling in a Micro-Channel Subjected to a Pulsed Heat Flux
Authors: Lee Hee Joon , Browne Eric A. , Peles Yoav , Jensen Michael K.
Published: May 2012

A numerical study of subcooled onset of nucleate boiling (ONB) in a micro-channel under pulsed heating using the volume of fluids (VOF) model was conducted. The ONB time was determined when the void fraction at the microheater surface starts to exist. A smooth thin Pt heater was located between the water in the channel and the solid material. The theoretical superheat for homogeneous nucleation did not predict the transient ONB results of convective flow of water. Once heat load increases at the heater, transient flow boiling starts to occur. From a parametric study, it was found that the time constant increases with large substrate thermal diffusivity, low Reynolds number, and large channel diameter.
A Micro-Sized Generic Demonstrator for Studying Synthetic Biological Processes
Authors: Uth Marc-Florian , Herwig Heinz
Published: May 2012

In the field of synthetic biology, enzymatic pathways are used to enhance the efficiency of chemical production processes. These pathways consist of micro reactors that are filled with porous media and enzymes that catalyze the partial reactions. In the present study we summarize the requirements of the micro reactors used for these applications and give an overview of the different problems that have to be solved. Furthermore we present the idea of a generic demonstrator as a research tool. In the interdisciplinary field of synthetic biology it can enhance the interaction between different groups. It will serve as a common base for numerically as well as for experimentally working groups. We propose a definition of a generic demonstrator for a micro fluidic reactor as it is typically used in this field. Besides, present work of our group is presented, that analyzes the flow field in the micro channels of the reaction zone that is filled with porous media. We show how computational costs can be saved by studying the entry lengths of these channels.
Deviation of the Calculated of Density of Refrigerant Fluids in Both Super and Sub Critical Regions
Authors: Mobinipouya Neda
Published: May 2012

A numerical procedure has successfully predicted accurate values of thermodynamic properties in seven cubic equations of state (EOS) in predicting thermodynamic properties of nine ozone-safe refrigerants both in super and sub-critical regions. Refrigerants include R22, R32, R123, R124, R125, R134a, R141b, R143, and R152a and equations of state, considered here, are Ihm-Song-Mason (ISM), Peng-Robinson (PR) [2], Redlich-Kwong (RK), Soave-Redlikh-Kwong (SRK), Modified Redlickh-Kwong (MRK), Nasrifar-Moshfeghian (NM), and TCC were shown in this paper. In general, the results are in favor of the preference of TCC and PR EOS over other remaining EOS’s in predicting gas densities of all aforementioned refrigerants in both super and sub critical regions. Typically, PR and SRK are in good agreement with those obtained from recent correlations and speed of sound measurements. Therefore, these two EOS stand over other EOS both in sub and super critical regions. All EOS follow two-parameter principle of corresponding states at T/Tc higher than 8 and lower than 1 except NM EOS. In the temperature range 1<T/Tc<8, PR and SRK still follow above mentioned principle. The same trend has been observed for other refrigerants.
Heat Transfer in Spiral Channel Heat Sinks
Authors: Ghobadi M. , Muzychka Y. S.
Published: May 2012

Heat transfer in a spiral heat sink is examined experimentally and analytically. The spiral channel was fabricated on a base plate of copper. The cross section of the channel is square with 1 mm sides. A copper cap plate was bolted tight to seal the channel. Water and four low viscosity silicone oils (0.65 cSt, 1 cSt, 3 cSt and 10 cSt) were used as a medium; thus a Prandtl number from 5 to 100 was examined. Tests considered fluid entering from the side of the heat sink and exiting from the middle of heat sink and entering from the side and exiting from the middle. Heat transfer behavior over a wide range of flow rates from laminar to turbulent has been examined. Enhancement due to the spiral geometry was observed, and no significant difference was reported between the side and middle inlet condition. The dimensionless mean wall flux and the dimensionless thermal flow length were used to analyse the experimental data instead of Nusselt number and channel length. The spiral channel has been discretized, so that a single Dean number can be assumed in each cell, and two current models were applied to obtain the average Nusselt number. These are used to obtain the dimensionless mean wall flux and comparisons made with the experimental points.
Phase Change Material Particulate Flow Through a Rectangular Channel: Effect of Parachute-Shaped Particles on the Heat Transfer
Authors: Small Laura , Hassanipour Fatemeh
Published: May 2012

This study presents numerical simulations of forced convection with parachute-shaped encapsulated phase-change material particles in water, flowing through a square cross-section duct with top and bottom iso-flux surfaces. The system is inspired by the gas exchange process in the alveolar capillaries between the red blood cells (RBC) and the lung tissue. The numerical model was developed for the motion of elongated encapsulated phase change particles along a channel in a particulate flow where particle diameters are comparable with the channel height. Results of the heat transfer enhancement for the parachute-shaped particles are compared with the circular particles. Results reveal that the key role in heat transfer enhancement is the snugness movement of the particles and the parachute-shaped geometry yields small changes in heat transfer coefficient when compared to the circular ones. The effects of various parameters including particle diameter and volume-fraction, as well as fluid speed, on the heat transfer coefficient is investigated and reported in this paper.
Analysis of Integral Transform Solutions for Thermally Developing Flow in Microchannels With Isothermal Wall
Authors: Chalhub D. J. N. M. , Sphaier L. A.
Published: May 2012

There is a growing interest for applications of heat and mass transfer in microchannels. Consequently, several numerical and experimental studies related to transport phenomena in microchannels have been carried-out. The flow problem in microchannels is different from the macro-scale problems due to rarefaction effects, surface roughness, viscous dissipation heating as well as other effects. As a result, a number of studies have been proposed for investigating the micro-flow problem and how each of these phenomena affect heat and mass transfer characteristics. Naturally, there is particular focus on how the observed micro-scale phenomena differ from the traditionally known macro-scale effects. In the realm of simulation studies for heat transfer in micro-sized channels, this paper proposes a comparison between hybrid solution strategies for solving steady heat transfer problems within microchannels. The Generalized Integral Transform Technique (GITT) is employed as the main solution methodology; however, different solution approaches are investigated in order to determine advantages and drawbacks of each alternative. The presented results can serve as guidance for choosing an optimum solution methodology for thermally developing heat transfer in microchannels using GITT implementations.
Influence of Rarefaction Effects on the Nusselt Number During Regenerative Heat Exchange
Authors: Sphaier L. A. , Quaresma J. N. N.
Published: May 2012

Heat regenerators can be found in a considerable number of engineering applications, and are either used as pair of fixed matrices or as single rotary matrix. These matrices are composed of numerous channels, traditionally of about a few millimeters in diameter. The thermal design of heat regenerators is usually done considering models that rely on well-established simplifying assumptions. Most of these assumptions are valid for mini- and larger scale channels; nevertheless, with the growing tendency towards miniaturization, mini- to micro-scale channels come into play. As a result some classical simplifying assumptions may no longer be applied to reduced-size channels. One such effect is that of rarefaction, in which the mean free path of the molecules can no longer be considered negligible. In this context, this paper proposes an investigation on how rarefaction and additional effects encountered in regenerative heat exchange (such as a transient regime and thermal wall storage) can influence the heat transfer coefficient. The obtained results can be of assistance in achieving better thermal designs for miniaturized heat exchangers.
Capacitance-Based Droplet Position Sensing Optimization Through Digital Microfluidic Parameters
Authors: Murran Miguel Angel , Milani Abbas S. , Najjaran Homayoun
Published: May 2012

Design of a closed-loop droplet position control is an essential step towards the development of fully automated digital microfluidic devices. However, the performance of any closed-loop controller is ultimately limited by the accuracy and precision of the feedback sensors. In this paper, an effective capacitance based droplet sensor was designed and optimized through simulation to reduce the droplet position error. A full factorial design was conducted on the droplet sensor simulation model to observe the behavior of the position error as a function of the parameters of a digital microfluidic device. An empirical model was then fitted to the data obtained from the designed simulations and optimized to reduce the position estimate error. Results suggest that the performance of the capacitance based droplet sensor studied in this work is most dependent on the dielectric thickness, droplet radius, electrode pitch, electrode separation, filler fluid permittivity, and plate gap. Isoperformance curves of the sensor performance were obtained using the empirical model to show the interaction between digital microfluidic parameters, as well as to aid in the design of digital microfluidic devices equipped with a similar capacitance based droplet sensor.
Experimental Analysis of Gas Flow Forced Convection in Microtubes
Authors: Morini Gian Luca , Yang Yahui , Chalabi Habib , Lorenzini Marco
Published: May 2012

This paper deals with the experimental analysis of forced micro-convection features of heated gas flows through commercial stainless steel microtubes having an inner diameter of 172 μm and 500 μm. The experimental results, in terms of Nusselt numbers, are compared to the classical correlations validated for conventional pipes and to the correlations proposed for gas flows through microtubes under laminar and transitional conditions (Re ∈ [400–3500]). The cross sections of the tested microtubes enabled the analysis of the effects of wall axial heat conduction on the Nusselt number which determines a dependence of the convective heat transfer coefficients on the Reynolds number even in the laminar regime, especially for low inner diameters. It is highlighted in the paper that the effects due to overall heat losses, to viscous dissipation and the problems in the right determination of the axial gas bulk temperature distribution cannot be ignored in the thermal analysis of gas flows through microtubes.
Fast Mixing in Microchannels by Input Modulation: A Numerical and Experimental Study
Authors: Iorio C. S. , Perfetti C. , Dubois F.
Published: May 2012

Efficient mixing in micro-channels is one of the most debated topics in the design of microfluidic devices for the outmost importance it has in many industrial processes. Different mixing mechanisms could be easily found in literature but a usual accepted classification divides the different devices in three major categories: diffusion, distribution-based and convective devices. For all of them, the goal is to break the intrinsic laminar character of very small Reynolds number flows typical of microfluidic to enhance the mixing of the different interacting streams. In this study, we focused on the numerical modeling of the so-called injection mixer. In these devices, the mixing is driven by the dynamic of the injection streams. Attention is given to the inlet region where the different streams first mix together. Computations tackled with the case of a three inlet micro-channel — thickness: 400μm, width: 3mm, length: 30mm — where the injection rates are modulated according to prescribed wave form and normalized to have a constant flow rate at the outlet. Linear and sinusoidal waveforms have been tested. For each configuration, an assessment of the mixing efficiency based on standard deviation of the stream concentration is evaluated together with a typical mixing length and time. Results are then compared with the case where the injection rate is constant. Preliminary results shows that injection mixer with modulated injections can achieve mixing efficiency that are at least comparable with the diffusion based systems. The waveform that is more suitable depends on the characteristic injection period and on the phase shift between different injections. Pulse waveform determines high efficiencies, but requires higher injection rates and creates pressure fluctuations that could be disturbing in applications. Experiments have also been carried and results are compared with the numerical ones. The results obtained are useful to better understand the behavior of injection mixing devices and to provide some hint to reduce the mixing length by coupling a preliminary mixing due to modulation of the inlet streams with other mixing configurations.
Poiseuille Flow of Rarefied Gases Between Concentric Cylinders
Authors: Taheri Peyman , Struchtrup Henning
Published: May 2012

Miniaturized devices are used currently in many engineering applications. Nonetheless, despite much progress in their fabrication, the fundamental understanding of fluid flow and heat transfer on the microscale is still not satisfactory. In this study, rarefaction effects in pressure-driven gas flows in annular microchannels are investigated. The influence of Knudsen number, aspect ratio of the annulus, and surface accommodation coefficient on wall friction, mass flow rate, and thermal energy flow rate is discussed. For this, the linearized Navier–Stokes–Fourier (NSF) and regularized 13-moment (R13) equations are solved analytically. The results are compared to available solutions of the Boltzmann equation to highlight the advantages of the R13 over the NSF equations in describing rarefaction effects in the process. Moreover, in order to improve the accuracy of the NSF system a second-order slip boundary condition is proposed.
Heat and Mass Transfer With Chemical Reactions Producing Hydrogen in Microchannels
Authors: Kuznetsov Vladmir V. , Vitovsky Oleg V. , Kozlov Stanislav P.
Published: May 2012

The reduction of effective transfer length on microscale eliminates the external diffusion limitation on reaction rate and makes it possible to realize the non-equilibrium chemical reactions. The peculiarities of methane and carbon monoxide steam reforming in a minichannel reactor with activation of reactions on thin film catalyst prepared by nanotechnology are considered in this paper. Consistent accomplishment of these reactions can increase the hydrogen yield and reduce the concentration of carbon monoxide in the product. Steam reforming of methane was studied on Rh/Al2O3 nanocatalyst deposited on the inner wall of the annular minichannel. Steam reforming of carbon monoxide was studied at Pt/CeO2/Al2O3 nanocatalyst deposited on the walls of the minichannel plate. The procedure of catalyst preparation which makes the nanoparticles of two nanometers in size is developed. The catalyst has uniform fraction of nanoparticles and optimal oxygen mobility in the lattice of carrier. During tests the data on the composition of the reacting gas mixture in temperature range from 200 C to 940 C were obtained including data on conversion in controlled temperature field when hydrogen content in the product reaches 68% and carbon monoxide content reduces to 1%. Methane steam reforming and water gas shift reaction in the minichannel were modeled numerically. The detailed information on the temperature and species concentration fields has been obtained, and kinetics of multistage reactions was defined when the external heat is supplied to proceed the steam reforming. The temperature regimes of high conversion of methane and carbon monoxide were defined and discussed in connection with the experimental data.
Magnetic Nanoparticle Based Nanofluid Actuation With Dynamic Magnetic Fields
Authors: Bilgin Alp , Kurtoglu Evrim , Erk Hadi Cagdas , Sesen Muhsincan , Acar Havva Funda Yagci , Kosar Ali
Published: May 2012

Magnetic nanoparticle suspensions and their manipulation are becoming an alternative research line and have very important applications in the field of microfluidics such as microscale flow control in microfluidic circuits, actuation of fluids in microscale, and drug delivery mechanisms. In microscale, it is possible and beneficial to use magnetic fields as actuators of such nanofluids, where these fluids could move along a gradient of magnetic field so that a micropump without any moving parts could be generated with this technique. Thus, magnetically actuated nanofluids could have the potential to be used as an alternative micro pumping system. Actuation of ferrofluid plugs with a changing magnetic field has been extensively studied in the literature. However; the flow properties of ferrofluids are sparsely investigated when the ferrofluid itself is forced to continuously flow inside a channel. As an extension of previous studies, this study aims to investigate flows of magnetic nanoparticle based nanofluids by a generated magnetic field and to compare the efficiency of the resulting system. Lauric Acid coated Super Paramagnetic Iron Oxide (SPIO-LA) was used as the ferrofluid sample in the experiments to realise actuation. Significant flow rates up to 61.8μL/s at nominal maximum magnetic field strengths of 300mT were achieved in the experiments. Results suggest that nanofluids with magnetic nanoparticles merit more research efforts in micro pumping. Thus, magnetic actuation could be a significant alternative for more common techniques such as electromechanical, electrokinetic, and piezoelectric actuation.
Simulations of Flow and Mass Transfer in a Passive Micromixer
Authors: Zadeh Hamid Farangis , Marahel Arash
Published: May 2012

We present three-dimensional simulation results regarding performance of a novel planar passive micromixer functioning at low Reynolds numbers. A combination of folding and contracting of microchannels is the main idea for designing of an effective, easy-to-produce, and non-expensive micromixer. The simulation results show that, depend on Reynolds number, centrifugal forces can generate different secondary flows and Dean vortices after each bend. Consequently, the thickness and the form of the contact layer between fluids become strongly affected. The simulation process is repeated for different Reynolds numbers from 10 to 100, and we observe that the maximum and minimum mixing efficiencies at the output channel are related to Reynolds number 60 and 80, respectively.
Vibration Analysis of Drug Delivery CNTs Using Transfer Matrix Method
Authors: Farshidianfar Anooshiravan , Ghassabi Ali A. , Farshidianfar Mohammad H. , Hoseinzadeh Mohammad
Published: May 2012

The free vibration and instability of fluid-conveying multi-wall carbon nanotubes (MWCNTs) are studied based on an Euler-Bernoulli beam model. A theory based on the transfer matrix method (TMM) is presented. The validity of the theory was confirmed for MWCNTs with different boundary conditions. The effects of the fluid flow velocity were studied on MWCNTs with simply-supported and clamped boundary conditions. Furthermore, the effects of the CNTs’ thickness, radius and length were investigated on resonance frequencies. The CNT was found to posses certain frequency behaviors at different geometries. The effect of the damping corriolis term was studied in the equation of motion. Finally, a useful simplification is introduced in the equation of motion.
Simulation of Microchannel Flows Using Higher Order Lattice Boltzmann With an Effective Mean Free Path
Authors: Nourmohammadzadeh Mohammad , Rahnama Mohammad , Jafari Saeed , Akhgar Alirez
Published: May 2012

Microscale flow simulation is considered in this paper for a microchannel flow geometry. Higher order Lattice Boltzmann Model was used as the numerical method for flow simulation, in which an effective mean free path was used in relaxation time appeared in LBM. To accurately describe rarefied gas dynamics beyond the Navier-Stokes level, high-order LB models have been used. One reason the standard lattice BGK model fails to capture the nonlinear constitutive behavior is that it only retains velocity terms up to second order in the Hermite expansion of the equilibrium distribution function. This is not sufficient to accurately describe stresses in isothermal flows. To capture nonequilibrium effects, we should retain up to fourth-order terms in the Hermite expansion. The effective mean free path makes it possible to investigate flow characteristics in slip flow regime, for which Knudsen number varies from 0.1 to 10 while does not change the computational efficiency of standard LBM. Results are obtained for pressure-driven and a shear flow configurations in microchannels. The nonlinear flow characteristics of the Knudsen layer were captured in shear flow regime.
Two-Phase Heat Sinks With Microporous Coating
Authors: Semenic Tadej , You Seung M.
Published: May 2012

To minimize flow boiling instabilities in two-phase heat sinks, two different types of microporous coatings were developed and applied on mini- and small-channel heat sinks and tested using degassed R245fa refrigerant. The first coating was epoxy-based and was sprayed on heat sink channels while the second coating was formed by sintering copper particles on heat sink channels. Mini-channel heat sinks had overall dimensions 25.4 mm × 25.4 mm × 6.4 mm and twelve rectangular channels with a hydraulic diameter 1.7 mm and a channel aspect ratio of 2.7. Small-channel heat sinks had the same overall dimensions, but only three rectangular channels with hydraulic diameter 4.1 mm and channel aspect ratio 0.6. The microporous coatings were found to minimize parallel channel instabilities for mini-channel heat sinks and to reduce the amplitude of heat sink base temperature oscillations from 6 °C to slightly more than 1 °C. No increase in pressure drop or pumping power due to the microporous coating was measured. The mini-channel heat sinks with porous coating had in average 1.5-times higher heat transfer coefficient than uncoated heat sinks. Also, the small-channel heat sinks with the “best” porous coating had in average 2.5-times higher heat transfer coefficient and the critical heat flux was 1.5 to 2-times higher compared with the uncoated heat sinks.
Hydrodynamic Focused Passive Separation Under Continuous Flow
Authors: Kanbar Jad , Clague David
Published: May 2012

A continuous flow symmetric passive separation device was designed using an equivalent circuit to create variable flow rates to drain channels and collection outlets. The inlet reservoir was placed in the axis of symmetry and in line to downstream buffer inlets for hydrodynamic focusing. This inlet reservoir was sufficiently larger than the different inlet connections that were punched into it. By varying the diameter of the inlet connection into the reservoir, the distribution and therefore separation of particles could be influenced to significance. Not only was the ratio of sample inlet diameter to reservoir important, but so was the relative position along the y-axis of the reservoir. We found that a 2:1 ratio and placement at the top and middle of the reservoir yielded the best separation results. Further analysis of the velocity profile in the reservoir was explored using COMSOL Multyphysics®. The observed paths of particle trajectory corroborated with the models. Lastly this device aimed to provide an aspect of separation simple enough to be included in conjunction with other passive separation geometries to further enhance results and throughput.
Effect of Channel Geometry on Two-Phase Flow Structure in Fuel Cell Gas Channels
Authors: Rath Cody D. , Kandlikar Satish G.
Published: May 2012

Water management issues continue to be a major concern for the performance of polymer electrolyte membrane (PEM) fuel cells. Maintaining the optimal amount of hydration can ensure that the cell is operating properly and with high efficiency. There are several components that can affect water management, however one area that has received increased attention is the interface between the gas diffusion layer (GDL) and the gas reactant channels where excess water has a tendency to build up and block reactant gasses. One key parameter that can affect this build up is the geometry of the microchannels. The work presented here proposes an optimal trapezoidal geometry which will aid in the removal of excess water in the gas channels. The Concus-Finn condition is applied to the channel surfaces and GDL to ensure the water will be drawn away from GDL surface and wicked to the top corner of the channel. An ex situ setup is designed to establish the validity of the Concus-Finn application. Once validated, this condition is then used to design optimal channel geometries for water removal in a PEM fuel cell gas channel.
Numerical Study on Bubble Formation in a Microchannel Flow-Focusing Device Using the VOF Method
Authors: Zadeh Shobeir Aliasghar , Radespiel Rolf
Published: May 2012

The liquid-gas two-phase flow in a flow-focusing device are numerically investigated and the results are compared with experimental data. The geometries and the structured meshes were generated using the Gridgen software, while the computations were conducted with Fluent. N2 (disperse phase) and Water-Glycerol solution (continuous phase) at standard atmospheric conditions are considered as fluids. Based on dimensional analysis, the effects of various parameters such as the flow rates of both phases (effect of CQ = Qd/Qc), the viscosities of both phases (effect of the respective Reynolds number Re), the surface tension (effect of the capillary number) and the geometrical properties of the channel (channel width W and injection angle β) on the bubble formation and its length are compared to available experimental results. The break-up mechanism of the bubbles in various capillary regimes is explained. The computed length of the generated bubbles as a function of the capillary number (varying the flow rate of the continuous phase) are in good agreement with the experiments. Further studies indicate that at a constant flow rate of the continuous phase, the bubble length rises strongly as the flow rate of the disperse phase increases. In contrast, the relative effects of the viscosity and the surface tension on the length of the bubbles are moderate. The numerical results using various injection angles show that the bubble length increases, as the injection angle is raised from β = 45° to β = 90°.
Co-Current Air-Water Two Phase Flow Patterns in Horizontal and Vertical Circular Tube Under Various Inlet Conditions
Authors: Zeguai S. , Chikh S. , Rahli O. , Tadrist L.
Published: May 2012

An experimental apparatus is setup to analyze a co-current air-water two phase flow in a 3 mm inner diameter tube with horizontal and vertical orientations. Air is axially injected through a nozzle of 260 μm of inner diameter. Air and water flow rates are accurately controlled at the inlet, covering a range of apparent velocities JL = 0.00118 to 0.0786 m/s, JG = 0.002 to 3.538 m/s for the horizontal tube and JL = 0.00078 to 0.0589 m/s, JG = 0.003 to 3.538 m/s for the upward flow. A fast camera with 250 fps is utilized to visualize the flow patterns. The experiments showed that the flow structures are very sensitive to inlet conditions. Within the covered range of velocities, several flow patterns were observed, namely bubbly flow, bubbly-slug transition flow, slug flow, slug-annular transition flow, annular flow, wavy annular flow and annular flow with dry zones. In the bubbly flow regime, a particular bubbly helical flow is observed before the dispersed bubbly flow.
Towards High Concentration Enhancement of Microfluidic Temperature Gradient Focusing of Sample Solutes
Authors: Ge Zhengwei , Yang Chun
Published: May 2012

This paper reports an improved technique to enhance microfluidic temperature gradient focusing (TGF) of sample solutes using Joule heating effects induced by a combined AC and DC electric field. By introducing the AC field component, additional Joule heating effects are obtained to generate temperature gradient for concentrating sample solutes, while the electroosmotic flow is suppressed under the high frequency AC electric field. Therefore, the required DC voltages for achieving certain sample concentration by Joule heating induced TGF technique are remarkably reduced. Moreover, the lower DC voltages lead to smaller electroosmotic flow (EOF), thereby reducing the backpressure effects due to the finite reservoir size. Concentration enhancements of sample solutes are improved by using a combined AC and DC electric field.
Recent Developments in Vapor Compression Technologies for Small Scale Refrigeration Applications
Authors: Barbosa Jader R.
Published: May 2012

This paper reviews the current trends and research efforts associated with the development of miniaturized mechanical vapor compression refrigeration systems. Over the past decade, there has been a significant number of studies devoted to the miniaturization of its components, the most critical being the compressor. The paper will focus on the thermodynamic and thermal aspects of the development of small compressors and other components of small-scale cooling cycles. Whenever appropriate, issues and challenges associated with different cycle and component designs will be addressed.
A Study of Discrepancies in Flow Boiling Results in Small to Micro Diameter Metallic Tubes
Authors: Karayiannis Tassos G. , Mahmoud Mohamed M. , Kenning David B. R.
Published: May 2012

There is a disagreement in the reports on flow boiling heat transfer on the dependence of the local heat transfer coefficient on local vapour quality, mass and heat flux and system pressure. As a result, various conclusions were reported about the dominant heat transfer mechanism(s) in small to micro diameter tubes. Yet, the reasons behind this large disagreement are not clear. The current study investigated experimentally two important parameters that may contribute in explaining the scatter in the published heat transfer results. The first parameter is the tube inner surface characteristics whereas the second is the length of the heated section. The surface effect was experimentally investigated through examining two stainless steel tubes manufactured by two different methods. The first tube is a seamless cold drawn tube whilst the second is a welded tube. The two tubes have similar design and dimensions and were investigated at 8 bar system pressure and 300 kg/m2 s mass flux. The inner surface of the two tubes was examined using a scanning electron microscope (SEM) and was found to be completely different. The heat transfer results demonstrated that the trend of the local heat transfer coefficient versus local vapour quality in the seamless cold drawn tube is completely different from that in the welded tube. Three heated lengths were investigated for a seamless cold drawn tube with an inner diameter of 1.1 mm over a wide range of experimental conditions; mass flux range of 200–500 kg/m2 s, system pressure of 6–10 bar, inlet sub-cooling value of about 5K and exit quality up to about 0.95. The results indicated that the heated length strongly influences the magnitude as well as the local behaviour of the heat transfer coefficient. There is a progression from nucleate boiling to convective boiling as the heated length increases. The variation in the heat transfer coefficient due to differences in the heated length may also influence the performance of the existing micro scale heat transfer correlations. The flow patterns observed at the exit of each test section are also presented.
Flow Boiling in Microscale at High Flowrates
Authors: Kos¸ar Ali
Published: May 2012

Boiling heat transfer is an important heat removal mechanism for cooling applications in micro scale and finds many applications. Many studies were conducted to shed light on boiling heat transfer in microchannels. They were concentrated on saturation boiling at low mass fluxes (G<1000 kg/m2s). With the enhancement in micro pumping capabilities, flow boiling could be performed at higher mass velocities so that high cooling rates (>1000 W/cm2) could be possibly attained. Due to the increasing trend in critical heat flux and suppression of boiling instabilities with increasing mass velocity flow boiling is becoming more and more attractive at higher mass velocities, where subcooled boiling conditions are expected at high mass velocities. With the shift from low to high flow rates, a transition in both boiling heat transfer (saturated boiling heat transfer to subcooling boiling heat transfer) and critical heat flux (dryout type critical heat flux to departure from nucleate boiling critical heat flux) from one mechanism to another is likely to occur. Few experimental studies are present in the literature related to this subject. In this paper, it is aimed at addressing to the lack of information about boiling heat transfer at high flow rates and presenting experimental data and results related to boiling heat transfer and Critical Heat Flux (CHF) at high flowrates. New emerging technologies resulting in local heating such as nano-scale plasmonic applications and near field radiative energy exchange between objects could greatly benefit from boiling heat transfer at high flow rates in micro scale.
Studying Interfacial Transport With Evanescent Wave-Based Particle Velocimetry and Thermometry
Authors: Yoda Minami
Published: May 2012

Interfacial phenomena due to surface forces are important in microfluidic devices with their relatively large surface areas and small volumes. Most experimental studies of interfacial transport estimate flow velocities from the motion of tracer particles less than 1 μm in diameter, and assume that the particle displacements over a known interval are due to the fluid velocity field. This talk discusses some of our research on measuring fluid velocities in Poiseuille and electrokinetically driven flows over the first ∼0.5 μm next to the solid wall from the motion of an ensemble of O(105) fluorescent spheres as small as 100 nm illuminated by evanescent waves. Because the evanescent-wave intensity decays exponentially with wall-normal distance, the particle-wall separation can be determined from the brightness of each particle image, and used to estimate the steady-state distribution of the tracers near the fluid-solid interface. Recently, evanescent-wave illumination has been combined with fluorescence thermometry, where water temperature fields are estimated from changes in the intensity of the emissions from aqueous solutions of temperature-sensitive fluorophores. The Poiseuille flow of a fluorescein solution through a heated channel at a Reynolds number of 8.3 was illuminated with evanescent waves to obtain the solution temperature at an average distance of 74 nm from the wall. The temperature results obtained over three different regions were in good agreement with numerical predictions of the wall surface temperature, even in the presence of temperature differences exceeding 15 °C over the 1 mm width of the channel.
Models for Pressure Drop for Poiseuille Flow in Trapezoidal and Triangular Microchannels in Silicon
Authors: Yovanovich M. Michael
Published: May 2012

Models, numerical and experimental results for developed laminar flow of liquids in long isosceles trapezoidal and triangular microchannels KOH-etched in < 100 > silicon substrates are reviewed and compared. The equivalent rectangle model (ERM) based on a novel model for the effective aspect ratio was developed for non-circular microchannels; it will be compared with the numerical results of Morini (2004) and McHale and Garimella (2010) as well as the extensive experimental data of Wu and Cheng (2003) for several trapezoidal and triangular microchannels. In addition, a simple correlation equation for all numerical and experimental data (62 points) is presented. The equivalent rectangle model is accurate with rms difference of 3.1%. A maximum difference of −7% occurs for data obtained for flow through four very narrow trapezoidal microchannels.
A Tinier Target for B Cell Therapy in Multiple Sclerosis
Authors: Obhrai Jagdeep S.
Published: May 2012

Anti–IL-6 therapy may be an improved option for treatment of multiple sclerosis.
The Microbial Contamination of Mobile Communication Devices
Authors: Verran Joanna
Published: May 2012

This tip describes a simple laboratory exercise to assess the microbial contamination of mobile phones, and suggests extension work that enables additional exploration of the topic. At its most basic, it is suitable for the school classroom; more advanced development of the suggested activities are suitable for undergraduate project work.
Ethical and Practical Similarities Between Pedagogical and Clinical Research
Authors: Robson Rachel L. , Huckfeldt Vaughn E.
Published: May 2012

Clinical research and educational research face similar practical and ethical constraints that impact the rigor of both kinds of studies. Practical constraints facing undergraduate science education research include small sample sizes (largely a result of disproportionate incentives to conduct educational research at small colleges versus large universities), and the impossibility of randomizing individual students to separate arms of a study. Ethical constraints include gaining the informed consent and assuring the confidentiality of study participants, and the requirement of equipoise (i.e., that it is unethical to subject some study participants to an experimental treatment that researchers have good reason to believe to be inferior to another treatment). While these constraints have long been recognized for clinical research, their implications for educational research have not been fully recognized. Criticism that educational research lacks rigor should be tempered by the recognition that educational research is not parallel to laboratory research, but is parallel to clinical research. These parallels suggest solutions to some of the practical and ethical difficulties faced by educational researchers, as well.
Development of a Myxomycete Photoguide as a Teaching Tool for Microbial Taxonomy
Authors: Macabago Sittie Aisha B. , dela Cruz Thomas Edison E.
Published: May 2012

Recently, web-based identification guides have been developed to aid modern taxonomists in identifying organisms. Unfortunately, these guides can only be used wherever Internet access is available. Thus, these cannot often be brought directly to the field for quick and easy identification of any collected specimens. Since we believe that field experience is necessary for any students of biology or microbiology, we developed a photoguide on the myxomycetes we collected from Lubang Island, Occidental Mindoro, Philippines. This photoguide is intended to aid both classroom and laboratory learning of a specific group of eukaryotic microoganisms, the plasmodial slime molds or myxomycetes. It provides a quick visual aid in the identification of myxomycetes found in Lubang Island, but may also be present in any other terrestrial forest areas of the country and of the world.
Use of Microthemes to Increase Writing Content for Introductory Science Laboratory
Authors: Lewis Michelle L. , Bucheli Sibyl R. , Lynne Aaron M.
Published: May 2012

Writing is a learning activity, as well as a communication skill. Many instructors recognize the value of writing as a learning tool but struggle to develop effective writing assignments. Instructors are generally pressed for time during lecture due to the necessity to deliver content and, therefore, cannot dedicate time necessary to teach science writing skills effectively. Traditional term papers assigned to a class with varying writing skills may not accomplish the desired goal of teaching both technical writing skills and critical thinking skills. Students that are already struggling with content may be at a disadvantage in terms of conveying complex ideas. An answer to this problem is the microtheme paper which we employ in an Introductory Botany laboratory setting.
A New Edition of an Old FavoriteReview of:
Molecular Biotechnology—Principles and Applications of Recombinant DNA
, 4th ed.; Bernard R. Glick, Jack J. Pasternak, Cheryl L. Patten; (2010). ASM Press, Washington, DC. 1000 pages.
Authors: Sundari S. Krishna
Published: May 2012

Review of:
Molecular Biotechnology—Principles and Applications of Recombinant DNA , 4th ed.;
Bernard R. Glick, Jack J. Pasternak, Cheryl L. Patten; (2010) . ASM Press, Washington, DC. 1000 pages.
Development of a Community-Oriented Parasitological Survey as a Teaching Strategy for Medical Students
Authors: Ascencio Tatiana
Published: May 2012

Parasitic diseases remain a serious public health problem in developing countries, especially in such tropical countries with weak environmental sanitation as El Salvador (located in Central America), and cause health problems like anemia, cognitive disorders, and malnutrition. Antiparasitic drugs are available for treatment, but community education is also necessary to prevent these diseases. By introducing a community-oriented parasitological survey into our Medical Parasitology and Mycology course (MPM), we hypothesized that exposing students to a real-life situation would help them acquire knowledge and skills required in their professional practice. This survey is also suitable for use by clinical laboratory students, nursing students (for educational purposes on the prevention of parasitic diseases), and general biology students (because they need to know the suitable process of obtaining a stool sample and the proper diagnosis of the parasites).
Teaching with the Macaulay Library: An Online Archive of Animal Behavior Recordings
Authors: Betancourt Ileana , McLinn Colleen M.
Published: May 2012

Using video and audio recordings of animal behavior, students in a variety of courses can pose questions and gather data from diverse species and locations to test their hypotheses. Such recordings are freely available online in the Macaulay Library, the world’s largest scientifically curated archive of natural history media. Managed by the Cornell Lab of Ornithology, the Macaulay Library currently houses about 50,000 video clips and 123,300 audio recordings (including the sounds of 75 percent of the world’s bird species, and recordings dating back to 1929). This article, aimed at faculty teaching biology and environmental science courses, summarizes how to search the online archive and visualize streaming sound files with Raven Viewer. It also describes how instructors have used these tools in introductory and upper-level laboratory and lecture classes as part of the NSF-funded Online Research in Biology project.
Using a Team Structure for Student-Assisted Facilitation of Laboratories in an Introductory Allied Health Microbiology Course
Authors: Sanchez David Jesse , Miranda Daniel
Published: May 2012

As many instructors have noted, it is challenging to lead a successful microbiology laboratory, especially for students without sufficient prerequisite training such as in pre-allied health/nursing classes. In the community college setting, this is compounded by the lack of adequate resources, especially teaching assistants or others, to help individual students during a laboratory experience. In addition, there is much transition in the student population of the college so asking students who have completed a class to help in this setting is often impractical.

To modify our system to allow students to more easily ask questions and get feedback, we designed a student facilitator system. This system allowed each student to be a leader of the team for a particular laboratory experience. Each student was individually trained to be supportive of the team as a whole. This program is useful in that it can be applied to any class-based laboratory setting to provide better student team interactions than if there were no facilitator.
A Simple, Research-Based Guide to Better TeachingReview of:
How Learning Works: Seven Research-Based Principles for Smart Teaching
; 1st ed.; Susan Ambrose, Michael Bridges, Michele DiPietro, Marsha Lovett, and Marie Norman. (2010). Jossey-Bass, John Wiley and Sons, Inc., San Francisco, CA. 301 pages.
Authors: Mixter Phil
Published: May 2012

Review of:
How Learning Works: Seven Research-Based Principles for Smart Teaching ;
1st ed.; Susan Ambrose, Michael Bridges, Michele DiPietro, Marsha Lovett, and Marie Norman. (2010) . Jossey-Bass, John Wiley and Sons, Inc., San Francisco, CA. 301 pages.
Journal Watch
Authors: Herzog Jennifer A.
Published: May 2012

The Journal Watch section highlights published journal articles which discuss recent developments and new technology used in microbiology and related fields.
You May be Relaxing ... But the Microbes Are Not!Review of:
Infections of Leisure
, 4th edition; David Schlossberg, editor; (2009). ASM Press, Washington, D.C. 431 pages.
Authors: Barbaro Susan E.
Published: May 2012

Review of:
Infections of Leisure , 4th edition;
David Schlossberg, editor; (2009) . ASM Press, Washington, D.C. 431 pages.
Playing the Game of Sequence AlignmentReview of:
Phylo
website from the McGill University Centre for Bioinformatics, http://phylo.cs.mcgill.ca/
Authors: Leonardo Michael R.
Published: May 2012

Review of:
Phylo
website from the McGill University Centre for Bioinformatics,
http://phylo.cs.mcgill.ca/
A Useful Roadmap Through the World of Algae, Protozoa, and FungiReview of:
Eukaryotic Microbes;
Moselio Schaechter; (2012). Academic Press, San Diego, CA. 479 pages.
Authors: Kavouras Jerry H.
Published: May 2012

Review of:
Eukaryotic Microbes; Moselio Schaechter;
(2012) . Academic Press, San Diego, CA. 479 pages.
Mushrooms for the MillionsReview of:
Mycophilia—Revelations from the Weird World of Mushrooms
; Eugenia Bone; (2011). Rodale Press, Emmaus, PA. 348 pages.
Authors: Eveleigh Douglas
Published: May 2012

Review of:
Mycophilia—Revelations from the Weird World of Mushrooms ;
Eugenia Bone; (2011) . Rodale Press, Emmaus, PA. 348 pages.