bluuebunny/crossref_metadata_2025 huggingface dataset:
The Visualization of Flow Boiling in a Uniformly Heated Micro Capillary Tube
Authors: Yan X. H. , Xu J. Z. , Tang D. W.
Published: September 2008

This work presents experiments on the visualization of flow boiling of water in a horizontally placed and uniformly heated micro capillary tube. Three micro capillary tubes of quartz glass with inner diameters of 520, 315 and 242 μm are prepared. Experiments are performed with deionized water over a mass flux range from 39.3 to 362.5kg/m2s, and the inlet temperatures of 30, 45, and 60 °C respectively. By a video system with microscope and high-speed camera, the vapor-water two-phase flow’s patterns are recorded and analyzed. It has been found that periodic change of two-phase flow patterns and dramatic fluctuations of pressure drop occur in the micro capillary tubes. A new arch flow pattern, liquid film evaporating, and liquid droplet have been observed firstly. Bubbly flow has not been observed during our visual experiments for the inner diameter of 242 μm, the flow patterns are only made up of single liquid phase flow and two-phase elongate slug flow. The main flow regimes in these micro-tubes are single-liquid flow, slug flow, and annular flow with liquid film surrounded in the micro-tube with inner diameter of 520 and 315μm. Trends of pressure drop and flow patterns’ transition are compared and the results show that the increasing process of pressure drop is approximately in the single-liquid flow and bubbly flow, while the decreasing process of pressure drop is in the state of annular flow.
Microphotometric Characterization of Fluid Segment Populations Generated in Different Simple Microfluidic Networks
Authors: Ko¨hler J. M. , Groß P. A.
Published: September 2008

The stability of fluid segments is limited by deformation stress and by coalescence events. Both factors are typical for the passage of fluid segments through micro fluidic networks. Therefore, the coalescence behaviour of micro fluid segments in simple net work structures in dependence of flow rate ratios was investigated and characterized by the composition of obtained segment populations. Series of segments of different size and distance were generated either in a double T- or in a triple T-arrangement. PTFE elements were used for the micro fluid network. Nearly pulsation-free fluid actuation was realized by syringe pumps. The flow conditions in the input streams of carrier liquid and injected solutions remained constant during the experiments. Segment sequences become divers by different injection, stacking and coalescence events. The resulting segment sequences were characterized by on-line micro photometry. The populations of obtained micro fluid segments during each experiment were characterized by the distribution of segment size and segment distance or segment periode, respectively. Simulations support the assumption, that the character of segment populations is mainly determined by the flow rate ratios and by the coalescence sensitivity beside the topology of the fluidic network.
Liquid Crystal Thermography of an On-Chip Polymerase Chain Reaction Micro-Thermocycler
Authors: Fung Tracy Helen , Chao Shih-Hui , Peach Joseph E. , Meldrum Deirdre R.
Published: September 2008

Microscale liquid crystal thermography is a technique to measure temperature distribution of microfabricated devices in real-time. This method utilizes a microscope to image the color map of a layer of temperature-sensitive encapsulated thermochromic liquid crystals (TLC) coated on a microfabricated device. This paper describes the TLC coating process on microscale devices, the characteristics of colorimetric hysteresis, and the calibration of temperature measurements. The calibrated measurements have been applied for characterization of an on-chip polymerase chain reaction (PCR) microscale thermocycler where precise and dynamic temperature control is essential for efficient DNA amplification. Tests on the micro-thermocycler were done around the ranges centered at 30 °C and 95 °C. The results illustrate the effects on the temperature distribution due to micro-thermocycler geometry, and provide important insight for micro-thermocycler design.
Real-Time Fluorescence Monitoring of the Polymerase Chain Reaction in a Novel Continuous Flow Reactor for Accurate DNA Quantification
Authors: Sayers Michael B. , Dalton Tara M. , Davies Mark R.
Published: September 2008

Real-time Polymerase Chain Reaction (PCR) is the preferred method for quantification of gene expression levels due to its extreme sensitivity. Fluorescence based real-time PCR is commonly used for the quantification of the initial amount of a specific sequence of DNA. Real-time quantification may be achieved using fluorescent dyes, by optically monitoring the product formation as the PCR cycles progress. Stationary well based real-time quantification is quite common, however continuous flow real-time PCR which is the aim of this work is still in its infancy. A compact, high throughput continuous flow thermal cycler has been developed which allows for real-time fluorescent measurements to be obtained. The principle of operation of this device is that the three thermal zones required for a polymerase chain reactor are maintained on both sides of an aluminium block and bio-compatible FEP Teflon capillary tubing is then wrapped around these constant temperature blocks. The capillary tubing is wrapped around the device fifteen times which provides thirty PCR thermal cycles. The device has been designed and optimised to accurately monitor the product expression level using the double stranded DNA binding dye SYBR green I. Initially the PCR mixture is segmented into small nanoreactors, separated by an immiscible carrier fluid to eliminate cross contamination and reduce the likelihood of sample degradation due to contact with the capillary wall. These PCR nanoreactors are then cycled through the tubing and the DNA amplified. Fluorescent optical monitoring of these nanoreactors takes place where a water glycerine mixture, which is refractive index matched to the tubing, allows for improved fluorescent measurements of the nano-volume reactors to be obtained. Plasmid DNA, 240 base pairs long, has been successfully amplified using this device and the temperatures for the denaturation, annealing and extension phases have been accurately measured. Real-time fluorecence images of the flowing nano-volumes were recorded every second cycle using a CCD camera and from these images amplification curves have been successfully generated. Samples with various initial concentrations of DNA have been thermally cycled on the continuous flow reactor. The measured increase in fluorescence intensity from the flowing nano-volume reactors as they progressed through the thermal cycler demonstrated the effect of initial DNA template concentration.
Micro-PIV Measurements of Flowfields Within Plugs in Two Phase Flows for µ-TAS Applications
Authors: King Colin , Walsh Edmond , Grimes Ronan
Published: September 2008

The use of two phase flow in lab-on-chip devices, where chemical and biological reagents are enclosed within plugs separated from each other by an immiscible fluid, offers significant advantages for the development of devices with high throughput of individual heterogeneous samples. Lab-on-chip devices designed to perform the polymerase chain reaction (PCR) are a prime example of such developments. The internal circulation within the plugs used to transport the reagents affects the efficiency of the chemical reaction within the plug, due to the degree of mixing induced on the reagents by the flow regime. It has been hypothesised in the literature that all plug flows produce internal circulation. This work demonstrates experimentally that this is false, and seeks to elucidate the parameters influencing the internal circulation of plugs. The particle image velocimetry (PIV) technique offers a powerful non-intrusive tool to study such flow fields. This paper presents micro-PIV experiments carried out to study the internal circulation of aqueous plugs in two phase flow within 762μm internal diameter FEP Teflon tubing with FC-40 as the segmenting fluid. Experiments have been performed and the results are presented for plugs ranging in length from 1mm to 13mm with an average fluid velocity ranging from 0.3mm/s to 50mm/s. The results demonstrate that circulation within the plugs is not always present and requires design considerations to benefit from this phenomenon.
Laminar Mixing, Heat Transfer and Pressure Losses in a Chaotic Mini-Channel: Application to the Fuel Cell Cooling
Authors: Lasbet Yahia , Auvity Bruno , Castelain Cathy , Peerhossaini Hassan
Published: September 2008

Currently, the heat exchangers allowing the cooling of the low temperature fuel cells (PEMFC) are integrated in the bipolar plates and constituted of a network of straight channels. The flow regime is laminar, and thus, unfavorable to an intense convective heat transfer. In order to increase the power density of the fuel cells, the use of chaotic geometries in the cooling system is envisaged to intensify high convective heat transfer. In this numerical study, several chaotic three-dimensional mini-channels of rectangular section (2 millimeters × 1 millimeter) are evaluated in terms of heat transfer efficiency, mixing properties and pressure losses. Their performances are compared to those of a straight channel geometry currently used in the cooling systems of the PEMFC, and a serpentine 2-D channel. Hydrodynamic and thermal performances of these geometries are computed using the commercial CFD code Fluent©. At the inlet section, the velocity profile is hydrodynamically established. The thermophysical properties of the fluid are constant and equal to those of water at 300 K. The Nusselt number is evaluated for a Reynolds number equal to 200 and with a uniform density flux imposed on the walls and equal to 10,000 W/m2. For the calculation of the mixing rate, a condition of adiabatic wall is imposed. The inlet section is horizontally divided into two parts. Water in the higher part is at the temperature of 320K and in the lower part is at the temperature of 300K. The calculation of the mixing rate is made for Reynolds numbers equal to 100 and 200. The present study shows that a 3-D chaotic channel geometry significantly improves the convective heat transfer compared to regular straight or serpentine channels. Among all the studied geometries, one of them induces the higher heat transfer intensification (mean Nusselt number equal to 20) with a strong pressure loss. With an alternative geometry, we obtained a better compromise between high heat transfer and reduced pressure loss. However, all the chaotic geometries present similar mixing rate for the two studied Reynolds number. To confirm the performances of the selected geometries, an experimental study is currently undertaken. The final aim is to realize and test a prototype of chaotic heat exchanger in a bipolar plate of PEMFC.
Multiscale Design and Optimisation of a Radial Flow Heatsink
Authors: Hanly Kieran , Walsh Edmond , Grimes Ronan
Published: September 2008

Demands for increased functionality from mobile electronic products have led to an increase in the amount of heat that needs to be dissipated. The authors propose a novel mini-heatsink to meet the growing power density needs of the miniature electronics market. This paper looks at the optimisation of a miniature radial flow heatsink with laminar forced convection flow originating from the center. Two single length scale fins positioned at different angles were used to simulate a segment of the heatsink. A Labview PID program was used to monitor and maintain the temperature of these fins. The optimum angle at which maximum heat transfer occurred was determined as a function of pressure drop. The design was varied using the multiscale approach by inserting fins of a smaller length scale into regions of underutilised flow at the exit to achieve the highest heat transfer rate while simultaneously minimising the viscous drag. This method is in contrast to previous work where investigators inserted smaller length scales into the inlet of the original architecture in the regions of unused (isothermal) flow. Non-dimensional results are presented which show increased heat transfer with the addition of smaller length scales. This paper concludes that the multiscale design feature increased the heat transfer rate.
Estimation of the Heat Transfer Coefficient of a Microchannel Heat Sink Using an Optimal Control Technique
Authors: Simionescu Florentina , Harris Daniel K.
Published: September 2008

Cooling of electronic devices requires the use of heat spreaders whose function is to allow the spreading of the heat flux lines in the 3-D space and to increase the exchange area with the coolant. The objective of this analysis is to estimate the convective heat transfer coefficient of a microchannel heat sink that corresponds to a maximum amount of heat removed from heat source placed on the top surface of the sink. This problem is solved using an optimal control technique in which we control the solution of the heat equation with the convective boundary condition, taking the heat transfer coefficient as the control. A conjugate gradient method is used to solve the optimal control problem. The results show that the temperature distributions corresponding to the controlled solution are lower than those corresponding to the uncontrolled solution. This study can provide guidance in designing micro heat pipe sinks, which have emerged as an effective technique for cooling electronic components.
Heat Transfer Behavior of Oxide Nanoparticles in Pool Boiling Experiment
Authors: Milanova Denitsa , Kumar Ranganathan , Kuchibhatla Satyanarayana , Seal Sudipta
Published: September 2008

The heat transfer characteristics of silica (SiO2), ceria (CeO2), and alumina (Al2O3) nanofluids at 0.5% concentration and particle size of 10nm and 20 nm in pool boiling have been analyzed. The influence of acidity on heat transfer has been studied. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles, their mutual interactions towards the wire. When there is no particle deposition on the wire, the nanofluid with any oxide suspension increases CHF by about 50% within uncertainty limits regardless of the type of the oxide particle and its size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. Amorphous oxides (SiO2) are generally more disordered and less closely packed compared to the crystalline oxides such as CeO2 and Al2O3. The arrangement of the atoms within the unit cell and the layer of water molecules at the surface possibly influence the natural convection as well as the CHF. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly 3-fold increase in CHF. This deposition occurs for the charged 10 nm silica particle, and was not seen for other oxide particles. The chemical composition, oxidation and packing of the particles within the deposition on the wire are shown to be the reasons for the extension of the boiling regime and the net enhancement of the Critical Heat Flux.
Non-Newtonian Flow Behavior in Microchannels for Emulsion Formation
Authors: Arora Ravi , Daymo Eric , Tonkovich Anna Lee , Silva Laura , Stevenson Rick , Lamont Mike , Lerou Jan
Published: September 2008

Emulsion formation within microchannels enables smaller mean droplet sizes for new commercial applications such as personal care, medical, and food products among others. When operated at a high flow rate per channel, the resulting emulsion mixture creates a high wall shear stress along the walls of the narrow microchannel. This high fluid-wall shear stress of continuous phase material past a dispersed phase, introduced through a permeable wall, enables the formation of small emulsion droplets — one drop at a time. A challenge to the scale-up of this technology has been to understand the behavior of non-Newtonian fluids under high wall shear stress. A further complication has been the change in fluid properties with composition along the length of the microchannel as the emulsion is formed. Many of the predictive models for non-Newtonian emulsion fluids were derived at low shear rates and have shown excellent agreement between predictions and experiments. The power law relationship for non-Newtonian emulsions obtained at low shear rates breaks down under the high shear environment created by high throughputs in small microchannels. The small dimensions create higher velocity gradients at the wall, resulting in larger apparent viscosity. Extrapolation of the power law obtained in low shear environment may lead to under-predictions of pressure drop in microchannels. This work describes the results of a shear-thinning fluid that generates larger pressure drop in a high-wall shear stress microchannel environment than predicted from traditional correlations.
Carbon Nanotubes as Nano-Pumps: A Molecular Dynamics Investigation
Authors: Banerjee Soumik , Murad Sohail , Puri Ishwar K.
Published: September 2008

This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from a solution containing both positive and negatively charged ions. Metal ion separation from drinking water or during material processing applications can be an important issue. We use molecular dynamics simulations to demonstrate that a pair of carbon nanotubes with patterned positive and negative charges can form the basis of an effective device for the separation or encapsulation of ions. We consider three different charge patterns: i) Electrodes, where all the atoms of a CNT are charged with a finite surface charge density; ii) Alternate axial bands of positive and negative charges on each electrode; and iii) Alternate circumferential rings of positive and negative charges on the electrodes. The charge pattern determines the preferential intake of water and/or ions by a nanotube. As conventional electrodes they adsorb ions, but with an alternate band or ring charge pattern they adsorb the water molecules. Our simulations show that a charged CNT can be used as a nano-pump that provides purified water or ions from an impure solution.
The Effects of Liquid Compressibility on the Nucleation and Growth of Bubbles in Forced Convective Flow Boiling Within Microchannels
Authors: Fogg David W. , Goodson Kenneth E.
Published: September 2008

Forced convective flow boiling in microchannels is characterized by the nucleation and rapid growth of vapor bubbles in confined geometries. Experimental studies of these flows have been limited to the measurement of wall temperature, inlet liquid velocity, inlet and outlet pressures, and high speed imaging forcing analysts to infer the conditions inside the channel from measured external values. The present study examines the evolution of the pressure field during bubble growth prior to bubble departure using a one-dimensional fully compressible Lagrangian-Eulerian model. Numerical results for a single bubble growing from a nucleation site for both constant pressure and constant volumetric flow rate conditions demonstrate the magnitude of the pressures generated and bound the magnitude of the reflected pulses from the channel ends. The reflected pulses can locally decrease the pressure in the channel below the levels predicted by incompressible models. Additional simulations predict nucleation and growth of bubbles at sites that would be inactive if liquid compressibility is neglected. The results indicate the acoustic characteristics of microchannels for flow boiling can not be neglected and will be important in the optimization of microchannel designs.
Forced Convection Boiling in Microchannels for Improved Heat Transfer
Authors: Baummer Thomas B. , Al-Hajri Ebrahim , Ohadi Michael M. , Dessiatoun Serguei V.
Published: September 2008

This paper presents experimental results from research investigating the heat transfer capabilities of microchannel surfaces using a novel force-fed boiling and evaporation technique. The evaporative surfaces being investigated consist of a series of parallel, high-aspect ratio, open topped microchannels. The different sample surfaces vary in channel density, channel aspect ratio, and channel width and have heat transfer surface areas up to ten times their nominal surface areas. Liquid enters the channels of the evaporative surface from above through a developed system of feed channels. This method organizes a liquid-vapor circulation at the boiling surface that results in dissipation of very high heat fluxes in the boiling/thin film evaporation mode. By using the force-fed boiling technique, nominal area heat transfer rates of 100,000 W/m2-K have been achieved with HFE-7100 as the working fluid [1]. In force-fed boiling, the many very short microchannels are working in parallel; therefore the feed pressure and pumping power are very low. This technique may prove valuable to a wide range of heat transfer applications, particularly for heat removal at high heat flux surfaces.
A Study on the Flow Characteristics of the Novel-Designed Nano Fountain-Pen
Authors: Lee J.-H. , Kim H.-M. , Kim Youn J.
Published: September 2008

Atomic force microscope (AFM) probe was developed for applications of the dip-pen nanolithography (DPN), which is capable of surface patterning. Nano fountain-pen is a novel device to make the constant patterning in micro process using new designed probe. The modeled nano fountain-pen is composed with reservoir, micro channels, tip and chamber. The reservoir is linked to micro channels embedded in a V-shaped cantilever. Working fluids are transported through micro channels from a reservoir to substrate, realizing continuous writing at the nano scale. This so-called fountain-pen nanolithography (FPN) device allows continuous fluid supply for different localized applications. Instead of traditional method only using capillary force, liquid can be definitely and exactly injected with membrane pumping by the repulse force of tip. Using a commercial code, FLUENT, the velocity, pressure and flow rate are obtained under laminar, unsteady and three-dimensional incompressible flow with no-slip condition, and results are graphically depicted.
Possible Mechanisms for Thermal Conductivity Enhancement in Nanofluids
Authors: Gupta Amit , Wu Xuan , Kumar Ranganathan
Published: September 2008

This study discusses the merits of various physical mechanisms that are responsible for enhancing the heat transfer in nanofluids. Experimental studies have cemented the claim that ‘seeding’ liquids with nanoparticles can increase the thermal conductivity of the nanofluid by up to 40% for metallic and oxide nanoparticles dispersed in a base liquid. Experiments have also shown that the rise in conductivity of the nanofluid is highly dependent on the size and concentration of the nanoparticles. On the theoretical side, traditional models like Maxwell or Hamilton-Crosser models cannot explain this unusually high heat transfer. Several mechanisms have been postulated in the literature such as Brownian motion, thermal diffusion in nanoparticles and thermal interaction of nanoparticles with the surrounding fluid, the formation of an ordered liquid layer on the surface of the nanoparticle and microconvection. This study concentrates on 3 possible mechanisms: Brownian dynamics, microconvection and lattice vibration of nanoparticles in the fluid. By considering two nanofluids, copper particles dispersed in ethylene glycol, and silica in water, it is determined that translational Brownian motion of the nanoparticles, presence of an interparticle potential and the microconvection heat transfer are mechanisms that play only a smaller role in the enhancement of thermal conductivity. On the other hand, the lattice vibrations, determined by molecular dynamics simulations show a great deal of promise in increasing the thermal conductivity by as much as 23%. In a simplistic sense, the lattice vibration can be regarded as a means to simulate the phononic transport from solid to liquid at the interface.
Gas Flow in a Grooved Channel Due to Pressure and Temperature Gradients
Authors: Naris S. , Valougeorgis D.
Published: September 2008

The flow of a gas in a grooved nano or micro channel, due to the imposed pressure and temperature gradients in the longitudinal direction, is investigated via a kinetic approach. The solution is valid in the whole range of the Knudsen number, from the free molecular regime through the transition and slip regimes up to the hydrodynamic regime. The flow has common characteristics with the classical Poiseuille and thermal creep problems but the presence of the rectangular grooves that are placed periodically in one of the two stationary walls results to a two-dimensional flow pattern. The problem is modeled by the linearized S model kinetic equation, which is solved for the perturbed distribution function by the discrete velocity method. Maxwell diffuse type reflecting boundary conditions are used to model the gas-surface interaction, while periodic boundary conditions are imposed at the inlet and outlet of the channel. The reported results include overall velocity streamlines and flow rates, which are estimated, in the whole range of the Knudsen number for various values of the depth and the length of the groove and the periodicity length of the channel. Several interesting flow patterns and characteristics are examined in terms of the geometrical parameters of the flow configuration.
Using Protein-Functionalized Microchannels for Stem Cell Separation
Authors: Charles Nichola , Kanofsky Jared , Liesveld Jane L. , King Michael R.
Published: September 2008

Current hematopoietic stem cell (HSC) separation methods utilize immunomagnetic techniques where antibodies are conjugated to paramagnetic or iron-dextran particles so that the cells can be precipitated using a magnetic field. Antibodies are usually targeted against CD34 antigen, a known HSC marker that is lost as the cell matures into a terminally differentiated blood cell. While this method is able to produce stem cell purities greater than 80% in most cases, cell yield is usually low (<50%) and there is evidence to suggest that not all HSCs express CD34 and hence, cannot be selected using these methods. Our long-term aim is to move away from immunologic isolation methods and instead focus on general HSC behavior in the presence of specific proteins. Selectins are a group of adhesion molecules that have been shown to selectively retard HSC rolling in comparison to more mature blood cells so that, under the right conditions, HSC isolation from whole blood should be possible. Since this functional method is independent of specific HSC surface marker, it would enable isolation of all HSC sub-populations as well as improve the overall yield. We have used two geometries for HSC isolation using selectins. The first assembly was a commercially available parallel plate flow chamber with rectangular cross-section. This proved to be inefficient for cell separation due to the emergence of dead zones within the chamber and excessive cell accumulation along the tubing and fittings that comprised the inlets and outlets. We have evaluated this chamber and two redesigns using finite elements software. Ultimately we decided on a simpler approach — to replace the flow chamber with a capillary tube, which reduced unwanted cell accumulation due to gravity or dead zones while increasing the effective area for separation, and hence allowing for better HSC isolation.
Finite Element Modelling of Blood Flow in Artery Stenosis
Authors: Hanspal Navraj S. , Fujiwara Keigi , King Michael R.
Published: September 2008

Recent work by our laboratories suggest that the endothelial cells that line blood vessels respond dramatically to shear stress gradients over millimeter and micrometer length scales, contributing to the progression of the atherosclerosis disease state. In this paper, we present a CFD model for the prediction and quantitative analyses of the hemodynamic behavior of blood flow in stenosed arteries of a guinea pig, comprised of a nearly axisymmetric vessel constriction. The blood is considered to be incompressible and the flow model is described by the Navier-Stokes and the continuity equations. A standard Galerkin finite element technique has been applied for the solution of the flow equations within a 2-D axisymmetric framework. Elemental discretization is based on the use of C0- continuous Taylor-Hood type isoparametric finite elements that are used for the approximation of the unknown field variables. An implicit-theta time-stepping scheme has been chosen for the temporal discretization of the flow equations. The rheological behaviour of blood is incorporated within the main flow model through the use of different non-Newtonian constitutive equations. Relationships of the stenosis severity and flow data such as flow rate and flow pressure are obtained from the numerical simulations. The results are presented in the form of velocity vectors and pressure surface plots and are examined for stability, convergence and theoretical consistency.
An Efficient Method for Estimating Flow in the Serpentine Channels and Electrodes of PEM Fuel Cells
Authors: Pharoah J. G.
Published: September 2008

This paper presents the development of a simple resistance network model to represent the flow in the serpentine channels and electrodes of PEM fuel cells. The model results are compared to full 3D CFD predictions and reasonable agreement is demonstrated while computational times are reduced from 8 hours to seconds. The CFD results are also used to extract correlations for the pressure losses in the serpentine bends which can be used to alleviate the major shortcoming of the resistance model. As is, the resistance model is linear in velocity and as such is insensitive Re variations, but with the addition of non-linear losses in the bend this will no longer be the case.
A Novel and Miniaturised Thin Film Pellistor for Carbon Monoxide Detection in Hot Gas Flows
Authors: Kolb Gunther , Detemple Peter , Latta Daniel , Schmitt Stefan , Men Yong , Zapf Ralf
Published: September 2008

A thin film pellistor is under development at IMM for the selective detection of carbon monoxide in hot gas flows. The selective methanation reaction of carbon monoxide to methane is applied to generate chemical heat of reaction, which is then detected by direct measurement of thermal conductivity. The chemical reaction is performed over a nickel/calcium oxide/alumina catalyst, which is directly deposited onto a silicon nitride membrane being part of the sensor.
The Influence of Evaporation in Shear-Driven Liquid Film on Heat Removal From Local Heater
Authors: Gatapova Elizaveta , Kabov Oleg
Published: September 2008

The present work focuses upon shear-driven liquid film evaporative cooling of high heat flux local heater. Thin evaporating liquid films may provide very high heat transfer rates and can be used for cooling of high power microelectronic systems. Thermocapillary convection in a liquid film falling down a locally heated substrate has recently been extensively studied. However, non-uniform heating effects remain only partially understood for shear-driven liquid films. The combined effects of evaporation, thermocapillarity and gas dynamics as well as formation of microscopic adsorbed film have not been studied. The effect of evaporation on heat and mass transfer for 2D joint flow of a liquid film and gas is theoretically and numerically investigated. The convective terms in the energy equations are taken into account. The calculations reveal that evaporation from film surface essential influences on heat removal from local heater. It is shown that the thermal boundary layer plays significant role for cooling local heater by evaporating thin liquid film. Measured by an infrared scanner temperature distribution at the film surface is compared with numerical data. Calculations satisfactorily describe the maximal surface temperature value.
Thermohydraulic Performance Analysis of Offset Strip Fin Microchannel Heat Exchangers
Authors: Bapat Akhilesh V. , Kandlikar Satish G.
Published: September 2008

Recent experimental work on enhanced Silicon microchannels (Colgan et al., 2005, Steinke, 2005) indicates significant improvement in the heat transfer coefficient during single-phase liquid flow. The enhanced microchannel consists of multi-pass arrangements with offset strip fins of short lengths. An analytical treatment employing thermal boundary layer development in the entrance region of each offset fin geometry passage is performed. The analytical results are compared with the experiments and the reasons for the differences are discussed.
Simulation of a Layered Resonator for a Microfluidic Ultrasonic Separator
Authors: Shen Yijun , Atherton Mark A.
Published: September 2008

This paper focuses on the simulation of a layered resonator for a microfluidic ultrasonic separator with a special emphasis on analysing the stored energy-frequency product in the microfluid chamber. Since the acoustic force acting on a small spherical particle in a standing wave in the cavity of an ultrasonic separator is proportional to the product of the energy density in the standing wave and the driving frequency, the energy-frequency product can be used as a prediction of the separation performance in an ultrasonic separator. The electro-acoustic characteristics of the resonator under different conditions are also investigated. In particular, the influence of the reflector thickness on the stored energy-frequency product of the layered resonator is examined. Furthermore, the acoustic pressure distribution in the fluid chamber of the ultrasonic separator is investigated in detail. Predicted results from simulations compare well with experimental measurements and show that the model can be used to predict the electro-acoustic characteristics and the separation performance.
On the Application of Macro-Pipe Two-Phase Heat Transfer Correlations and Flow Regime Maps to Mini-Channels
Authors: Bar-Cohen Avram , Sher Ilai , Rahim Emil
Published: September 2008

The present study is aimed at evaluating the ability of conventional “macro-pipe” correlations and regime transitions to predict the two-phase thermofluid characteristics of mini-channel cold plates. Use is made of the Taitel-Dukler flow regime maps, seven classical heat transfer coefficient correlations and two dryout predictions. The vast majority of the mini-channel two-phase heat-transfer data, taken from the literature, is predicted to fall in the annular regime, in agreement with the reported observations. A characteristic heat transfer coefficient locus has been identified, with a positive slope following the transition from Intermittent to Annular flow and a negative slope following the onset of partial dryout at higher qualities. While the classical two-phase heat transfer correlations are generally capable of providing good agreement with the low-quality annular flow data the quality at which partial dryout occurs and the ensuing heat transfer rates are not predictable by the available macro-pipe correlations.
Period-speed analysis of a pendulum
Authors: Kostov Yavor , Morshed Ragib , Höling Barbara , Chen Ray , Siegel P. B.
Published: September 2008

We analyze a simple pendulum by measuring the period and the maximum speed of the bob. Both quantities are measured to high precision using a laser diode and an infrared photodetector located at the bottom of the pendulum. Expressing the period in terms of the maximum speed enables students to examine the large angle dependence of the period, and provides a method to calibrate the speed and do a detailed analysis of the effect of air friction on a sphere. We find that the force due to air friction is well described by a linear and quadratic term in the speed. We investigate the dependence of each term on the sphere’s diameter for Reynolds numbers from 250 to 104.
The trajectory of an electron in a plasma
Authors: Beck Arnaud , Meyer-Vernet Nicole
Published: September 2008

Collisions in gaseous plasmas are fundamentally different from collisions in neutral gases because a charged particle interacts simultaneously with many others via the Coulomb potential. This difference is not as intuitive for students as the billiard ball like collisions of neutral particles. We present trajectories of electrons in a weakly coupled plasma obtained from particle simulations. The trajectories illustrate the concept of distant collisions and the variation of the free path with energy, which has major consequences in plasma physics.
Robots in the introductory physics laboratory
Authors: Lowe Mary , Moore Howard , Langrall Edwin , Gehrman Chuck
Published: September 2008

We have incorporated robots into the introductory undergraduate physics laboratory to introduce a creative component and to show some applications of physics principles in a way that strongly engages student interest. We have developed low-cost mobile platforms and navigation methods suitable for large numbers of introductory level students. Radio remote control was the dominant navigation method implemented in the classroom, but autonomous navigation was also achieved. We discuss robot construction, the organization of the lab, student reactions, and our experiences in sustaining the program.
Isolation and Characterization ofAlicycliphilus denitrificansStrain BC, Which Grows on Benzene with Chlorate as the Electron Acceptor
Authors: Weelink Sander A. B. , Tan Nico C. G. , ten Broeke Harm , van den Kieboom Corné , van Doesburg Wim , Langenhoff Alette A. M. , Gerritse Jan , Junca Howard , Stams Alfons J. M.
Published: September 2008

A bacterium, strain BC, was isolated from a benzene-degrading chlorate-reducing enrichment culture. Strain BC degrades benzene in conjunction with chlorate reduction. Cells of strain BC are short rods that are 0.6 μm wide and 1 to 2 μm long, are motile, and stain gram negative. Strain BC grows on benzene and some other aromatic compounds with oxygen or in the absence of oxygen with chlorate as the electron acceptor. Strain BC is a denitrifying bacterium, but it is not able to grow on benzene with nitrate. The closest cultured relative isAlicycliphilus denitrificanstype strain K601, a cyclohexanol-degrading nitrate-reducing betaproteobacterium. Chlorate reductase (0.4 U/mg protein) and chlorite dismutase (5.7 U/mg protein) activities in cell extracts of strain BC were determined. Gene sequences encoding a known chlorite dismutase (cld) were not detected in strain BC by using the PCR primers described in previous studies. As physiological and biochemical data indicated that there was oxygenation of benzene during growth with chlorate, a strategy was developed to detect genes encoding monooxygenase and dioxygenase enzymes potentially involved in benzene degradation in strain BC. Using primer sets designed to amplify members of distinct evolutionary branches in the catabolic families involved in benzene biodegradation, two oxygenase genes putatively encoding the enzymes performing the initial successive monooxygenations (BC-BMOa) and the cleavage of catechol (BC-C23O) were detected. Our findings suggest that oxygen formed by dismutation of chlorite can be used to attack organic molecules by means of oxygenases, as exemplified with benzene. Thus, aerobic pathways can be employed under conditions in which no external oxygen is supplied.
Identification, Cloning, and Characterization of a Novel Ketoreductase from the Cyanobacterium
Synechococcus
sp. Strain PCC 7942
Authors: Hölsch Kathrin , Havel Jan , Haslbeck Martin , Weuster-Botz Dirk
Published: September 2008

A new ketoreductase useful for asymmetric synthesis of chiral alcohols was identified in the cyanobacterium
Synechococcus
sp. strain PCC 7942. Mass spectrometry of trypsin-digested peptides identified the protein as 3-ketoacyl-[acyl-carrier-protein] reductase (KR) (EC 1.1.1.100). The gene, referred to as
fabG
, was cloned, functionally expressed in
Escherichia coli
, and subsequently purified to homogeneity. The enzyme displayed a temperature optimum at 44°C and a broad pH optimum between pH 7 and pH 9. The NADPH-dependent KR was able to asymmetrically reduce a variety of prochiral ketones with good to excellent enantioselectivities (>99.8%). The KR showed particular high specific activity for asymmetric reduction of ethyl 4-chloroacetoacetate (38.29 ± 2.15 U mg
−1
) and 2′,3′,4′,5′,6′-pentafluoroacetophenone (8.57 ± 0.49 U mg
−1
) to the corresponding (
S
)-alcohols. In comparison with an established industrial enzyme like the alcohol dehydrogenase from
Lactobacillus brevis
, the KR showed seven-times-higher activity toward 2′,3′,4′,5′,6′-pentafluoroacetophenone, with a remarkably higher enantiomeric excess (>99.8% [
S
] versus 43.3% [
S
]).
Brominated Furanones Inhibit Biofilm Formation by
Salmonella enterica
Serovar Typhimurium
Authors: Janssens Joost C. A. , Steenackers Hans , Robijns Stijn , Gellens Edith , Levin Jeremy , Zhao Hui , Hermans Kim , De Coster David , Verhoeven Tine L. , Marchal Kathleen , Vanderleyden Jos , De Vos Dirk E. , De Keersmaecker Sigrid C. J.
Published: September 2008

Salmonella enterica
serovar Typhimurium is a main cause of bacterial food-borne diseases. As
Salmonella
can form biofilms in which it is better protected against antimicrobial agents on a wide diversity of surfaces, it is of interest to explore ways to inhibit biofilm formation. Brominated furanones, originally extracted from the marine alga
Delisea pulchra
, are known to interfere with biofilm formation in several pathogens. In this study, we have synthesized a small focused library of brominated furanones and tested their activity against
S. enterica
serovar Typhimurium biofilm formation. We show that several furanones inhibit
Salmonella
biofilm formation at non-growth-inhibiting concentrations. The most interesting compounds are (
Z
)-4-bromo-5-(bromomethylene)-3-alkyl-2(
5H
)-furanones with chain lengths of two to six carbon atoms. A microarray study was performed to analyze the gene expression profiles of
Salmonella
in the presence of (
Z
)-4-bromo-5-(bromomethylene)-3-ethyl-2(
5H
)-furanone. The induced genes include genes that are involved in metabolism, stress response, and drug sensitivity. Most of the repressed genes are involved in metabolism, the type III secretion system, and flagellar biosynthesis. Follow-up experiments confirmed that this furanone interferes with the synthesis of flagella by
Salmonella
. No evidence was found that furanones act on the currently known quorum-sensing systems in
Salmonella
. Interestingly, pretreatment with furanones rendered
Salmonella
biofilms more susceptible to antibiotic treatment. Conclusively, this work demonstrates that particular brominated furanones have potential in the prevention of biofilm formation by
Salmonella
serovar Typhimurium.
Comparative Mycotoxin Profiles of
Gibberella zeae
Populations from Barley, Wheat, Potatoes, and Sugar Beets
Authors: Burlakoti Rishi R. , Ali Shaukat , Secor Gary A. , Neate Stephen M. , McMullen Marcia P. , Adhikari Tika B.
Published: September 2008

Gibberella zeae
is one of the most devastating pathogens of barley and wheat in the United States. The fungus also infects noncereal crops, such as potatoes and sugar beets, and the genetic relationships among barley, wheat, potato, and sugar beet isolates indicate high levels of similarity. However, little is known about the toxigenic potential of
G. zeae
isolates from potatoes and sugar beets. A total of 336 isolates of
G. zeae
from barley, wheat, potatoes, and sugar beets were collected and analyzed by
TRI
(trichothecene biosynthesis gene)-based PCR assays. To verify the
TRI
-based PCR detection of genetic markers by chemical analysis, 45 representative isolates were grown in rice cultures for 28 days and 15 trichothecenes and 2 zearalenone (ZEA) analogs were quantified using gas chromatography-mass spectrometry.
TRI
-based PCR assays revealed that all isolates had the deoxynivalenol (DON) marker. The frequencies of isolates with the 15-acetyl-deoxynivalenol (15-ADON) marker were higher than those of isolates with the 3-acetyl-deoxynivalenol (3-ADON) marker among isolates from all four crops.
Fusarium
head blight (FHB)-resistant wheat cultivars had little or no influence on the diversity of isolates associated with the 3-ADON and 15-ADON markers. However, the frequency of isolates with the 3-ADON marker among isolates from the Langdon, ND, sampling site was higher than those among isolates from the Carrington and Minot, ND, sites. In chemical analyses, DON, 3-ADON, 15-ADON, b-ZEA, and ZEA were detected. All isolates produced DON (1 to 782 μg/g) and ZEA (1 to 623 μg/g). These findings may be useful for monitoring mycotoxin contamination and for formulating FHB management strategies for these crops.
PecS Is a Global Regulator of the Symptomatic Phase in the Phytopathogenic BacteriumErwinia chrysanthemi3937
Authors: Hommais Florence , Oger-Desfeux Christine , Van Gijsegem Frédérique , Castang Sandra , Ligori Sandrine , Expert Dominique , Nasser William , Reverchon Sylvie
Published: September 2008

Pathogenicity of the enterobacteriumErwinia chrysanthemi(Dickeya dadantii), the causative agent of soft-rot disease in many plants, is a complex process involving several factors whose production is subject to temporal regulation during infection. PecS is a transcriptional regulator that controls production of various virulence factors. Here, we used microarray analysis to define the PecS regulon and demonstrated that PecS notably regulates a wide range of genes that could be linked to pathogenicity and to a group of genes concerned with evading host defenses. Among the targets are the genes encoding plant cell wall-degrading enzymes and secretion systems and the genes involved in flagellar biosynthesis, biosurfactant production, and the oxidative stress response, as well as genes encoding toxin-like factors such as NipE and hemolysin-coregulated proteins. In vitro experiments demonstrated that PecS interacts with the regulatory regions of five new targets: an oxidative stress response gene (ahpC), a biosurfactant synthesis gene (rhlA), and genes encoding exported proteins related to other plant-associated bacterial proteins (nipE,virK, andavrL). ThepecSmutant provokes symptoms more rapidly and with more efficiency than the wild-type strain, indicating that PecS plays a critical role in the switch from the asymptomatic phase to the symptomatic phase. Based on this, we propose that the temporal regulation of the different groups of genes required for the asymptomatic phase and the symptomatic phase is, in part, the result of a gradual modulation of PecS activity triggered during infection in response to changes in environmental conditions emerging from the interaction between both partners.