bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevalence of methicillin‐resistant Staphylococcus spp. in the conjunctival sac of healthy dogs
Authors: Mouney Meredith C. , Stiles Jean , Townsend Wendy M. , Guptill Lynn , Weese J. Scott
Published: December 2013

Objectives

To determine the prevalence of selected coagulase‐positive methicillin‐resistant Staphylococcus aureus (MRS) in the conjunctival sac in a group of healthy dogs and to compare the prevalence of ocular MRS colonization with colonization of typically assessed body sites including the nasal cavity and rectum.

Animals studied

123 healthy dogs were used in the prevalence study: 40 dogs from a shelter and 83 privately owned dogs.

Procedures

The sampling procedure included culturing three separate sites per subject in the following order: the lower conjunctival fornices, the nares, and rectum.

Results

A low prevalence of 1.6% (2/123) of MRS was detected in healthy dogs. Methicillin‐resistant Staphylococcus pseudintermedius was isolated from two dogs, one from a conjunctival swab and the other from a rectal swab.

Conclusion

The survey data indicate the ocular surface is a potential site of MRS colonization, although the prevalence was low in healthy dogs.
Age‐related changes in afferent pathways and urothelial function in the male mouse bladder
Authors: Daly Donna M. , Nocchi Linda , Liaskos Marina , McKay Neil G. , Chapple Christopher , Grundy David
Published: December 2013

Key points

The prevalence of bladder conditions such as overactive bladder syndrome and urinary incontinence significantly increases with age, but how bladder function is altered by ageing is unclear.

Sensory nerves together with the epithelial lining of the bladder known as the urothelium play a key role in mediating bladder function.

In aged male mice we find a significant increase in natural bladder voiding, augmented afferent nerve firing during bladder filling and a significant increase in urothelial responses to purinergic receptor stimulation.

This suggests that with ageing there is increased purinergic transmission in the mouse bladder which may lead to increased sensation and result in bladder hypersensitivity.

These findings help us better understand how the function of the bladder may be affected by advancing age.

The prevalence of lower urinary tract storage disorders such as overactive bladder syndrome and urinary incontinence significantly increase with age. Previous studies have demonstrated age‐related changes in detrusor function and urothelial transmitter release but few studies have investigated how the urothelium and sensory pathways are affected. The aim of this study was to investigate the effect of ageing on urothelial‐afferent signalling in the mouse bladder. Three‐month‐old control and 24‐month‐old aged male mice were used. In vivo natural voiding behaviour, sensory nerve activity, urothelial cell function, muscle contractility, transmitter release and gene and protein expression were measured to identify how all three components of the bladder (neural, contractile and urothelial) are affected by ageing. In aged mice, increased voiding frequency and enhanced low threshold afferent nerve activity was observed, suggesting that ageing induces overactivity and hypersensitivity of the bladder. These changes were concurrent with altered ATP and acetylcholine bioavailability, measured as transmitter overflow into the lumen, increased purinergic receptor sensitivity and raised P2X3 receptor expression in the urothelium. Taken together, these data suggest that ageing results in aberrant urothelial function, increased afferent mechanosensitivity, increased smooth muscle contractility, and changes in gene and protein expression (including of P2X3). These data are consistent with the hypothesis that ageing evokes changes in purinergic signalling from the bladder, and further studies are now required to fully validate this idea.
The small GTPase Rac1 is required for smooth muscle contraction
Authors: Rahman Awahan , Davis Benjamin , Lövdahl Cecilia , Hanumaiah Veena T. , Feil Robert , Brakebusch Cord , Arner Anders
Published: December 2013

Key points

The role of the small G‐protein Rac1 was investigated in smooth muscle, using a smooth muscle‐specific knockout mouse and pharmacological blockers.

Inhibition of the interaction between Rac1 and upstream regulators inhibited the α‐receptor contractions and potentiated prostaglandin F2α contractions in vascular tissue.

The inhibition was mediated via an attenuation of the Ca2+ transient.

A global inhibition of Rac1 activity inhibited contractions in response to several agonists in a range of smooth muscle tissues.

The results demonstrate a novel Rac1‐associated signalling pathway for regulation of smooth muscle contraction.

The role of the small GTP‐binding protein Rac1 in smooth muscle contraction was examined using small molecule inhibitors (EHT1864, NSC23766) and a novel smooth muscle‐specific, conditional, Rac1 knockout mouse strain. EHT1864, which affects nucleotide binding and inhibits Rac1 activity, concentration‐dependently inhibited the contractile responses induced by several different modes of activation (high‐K+, phenylephrine, carbachol and protein kinase C activation by phorbol‐12,13‐dibutyrate) in several different visceral (urinary bladder, ileum) and vascular (mesenteric artery, saphenous artery, aorta) smooth muscle tissues. This contractile inhibition was associated with inhibition of the Ca2+ transient. Knockout of Rac1 (with a 50% loss of Rac1 protein) lowered active stress in the urinary bladder and the saphenous artery consistent with a role of Rac1 in facilitating smooth muscle contraction. NSC23766, which blocks interaction between Rac1 and some guanine nucleotide exchange factors, specifically inhibited the α1 receptor responses (phenylephrine) in vascular tissues and potentiated prostaglandin F2α and thromboxane (U46619) receptor responses. The latter potentiating effect occurred at lowered intracellular [Ca2+]. These results show that Rac1 activity is required for active contraction in smooth muscle, probably via enabling an adequate Ca2+ transient. At the same time, specific agonists recruit Rac1 signalling via upstream modulators, resulting in either a potentiation of contraction via Ca2+ mobilization (α1 receptor stimulation) or an attenuated contraction via inhibition of Ca2+ sensitization (prostaglandin and thromboxane receptors).
Synaptic noise is an information bottleneck in the inner retina during dynamic visual stimulation
Authors: Freed Michael A. , Liang Zhiyin
Published: December 2013

Key points

At chemical synapses, vesicles fuse with the presynaptic membrane at random, generating noise in postsynaptic currents.

To determine how much noise synapses generate, we recorded excitatory postsynaptic currents from ganglion cells in an in vitro preparation of the mammalian retina during flickering visual stimulation.

Postsynaptic currents received noise from three sources: substantial noise from bipolar cell synapses, somewhat more from the presynaptic retinal circuitry, but little from sources intrinsic to the ganglion cell.

Presynaptic circuit elements but not bipolar cell synapses were significant sources of noise shared by pairs of ganglion cells.

Signal‐to‐noise ratio was substantially reduced from the presynaptic bipolar cell array to the postsynaptic ganglion cell, indicating that synaptic noise can reduce the amount of information transmitted to a neuron.

In daylight, noise generated by cones determines the fidelity with which visual signals are initially encoded. Subsequent stages of visual processing require synapses from bipolar cells to ganglion cells, but whether these synapses generate a significant amount of noise was unknown. To characterize noise generated by these synapses, we recorded excitatory postsynaptic currents from mammalian retinal ganglion cells and subjected them to a computational noise analysis. The release of transmitter quanta at bipolar cell synapses contributed substantially to the noise variance found in the ganglion cell, causing a significant loss of fidelity from bipolar cell array to postsynaptic ganglion cell. Virtually all the remaining noise variance originated in the presynaptic circuit. Circuit noise had a frequency content similar to noise shared by ganglion cells but a very different frequency content from noise from bipolar cell synapses, indicating that these synapses constitute a source of independent noise not shared by ganglion cells. These findings contribute a picture of daylight retinal circuits where noise from cones and noise generated by synaptic transmission of cone signals significantly limit visual fidelity.
Visualization Study of Dropwise Condensation on a Super-Hydrophobic Surface
Authors: Li Lanlan , Liang Shiqiang , Tang Dawei , Chen Liang
Published: December 2013

Compared with conventional filmwise condensation, dropwise condensation has the advantage of high heat transfer coefficient when properly enhanced. To better understand the inherent mechanism of this outstanding performance and optimize the structure of the condensation surface, this paper focuses on the visualization experiments of dropwise condensation on a superhydrophobic surface to study the dynamic behaviors of droplet nucleation and growth. The surface is fabricated by chemically growing an n-octadecanethiol self-assembled monolayer coating with microscopic roughness on a copper surface. Some characteristics of interest such as the droplet nucleation, the droplet diameter, the number and the path of the droplets are obtained using image processing software. The experimental results indicate that the nucleation sites of the droplets are fixed, which in turn verifies the droplet nucleation theory. In addition, the nucleation of the small droplets together with the coalescence of the existing droplets contributes significantly to the variation of the number of the droplets.
Transport of Magnetic Particles Under a Uniform Magnetic Field in Microchannels
Authors: Zhu Gui-Ping , Nguyen Nam-Trung
Published: December 2013

This paper reports the numerical and experimental investigation on magnetic particle concentration in a uniform magnetic field. The flow system consists of water-based ferrofluid and glycerol/DI water mixture streams. Two regimes were observed with spreading and mixing phenomena. With a low magnetic field strength, the spread of magnetic particles is caused by improved diffusion migration. With a relatively high field strength, instability at the interface would occur due to the mismatch in magnetization of the fluid streams. The transport of magnetic particles is induced by chaotic mixing of the fluids caused by a secondary flow. The mixing phenomena are characterized by magnetic flux density. For configuration with flow rate and viscosity ratio (between diamagnetic and magnetic streams) being set at 1 and 0.5, the mixing efficiency analyzed based on magnetic particles concentration increases approximately by 0.3 at around 3.5 mT. This value of magnetic flux density indicates the requirement on instability inception. The mixing efficiency increases with magnetic flux density increases further. Complete mixing can be achieved with a magnetic flux density at around 10 mT. The magnetic approach offers a wireless, heat-free and pH-independent solution for a lab-on-a-chip system.
Experimental Study of the Heat Transfer Characteristic in Vertical Rectangular Capillary Microgrooves Heat Sink Under an Electric Field
Authors: Fang Xiazhen , Hu Xuegong , Yu Dong , Guo Cong
Published: December 2013

In this study, the EHD (electrohydrodynamic) enhancement of heat transfer in open vertical rectangular capillary microgrooves heat sink was studied, and with the help of a high-speed digital camera with maximum speed of 100,000 frames per second, the nucleate boiling phenomena in microgrooves were also visually investigated. The tests results have shown: (1) the input heat flux has no influences on the threshold voltage basically, while the absolute temperature drop ΔT of the lower or higher input heat fluxes were smaller than that of the midrange ones. (2) the threshold voltage was getting small with the decreasing distance between the electrodes, meanwhile the absolute temperature drop ΔT was growing larger and larger. (3) the threshold voltages of NO. 1 microgrooves (the dimensions are listed in Table 1) were lower than that of NO. 2, and ΔT of NO. 1 microgrooves was larger than that of NO. 2. (4) the bubble growth process was becoming longer with the increasing applied voltage.
An Experimental Study of Heat Transfer Enhancement in Microchannels
Authors: Wang Yingying , Peles Yoav
Published: December 2013

Heat transfer downstream a single micro pillar, with and without a jet in a microchannel was experimentally studied. By comparing the thermal performances of a plain microchannel, a microchannel with a pillar, and a microchannel with a jet issued from a pillar, the effect of this scheme was evaluated. An enhancement of Nusselt number of up to 100% was observed.
Effect of Decreasing Heat Transfer Surface Size on Boiling Heat Transfer
Authors: Koizumi Yasuo , Morita Yoshiki
Published: December 2013

Pool boiling heat transfer experiments were performed for small heat transfer surfaces at 0.101 MPa by using ethanol as test fluid. The test heat transfer surfaces were made of copper. The diameters of the heat transfer surfaces were 1.0, 2.0, 3.0, 5.0, 7.0 10.0 and 20.0 mm. When the heat flux was low, small isolated bubbles left from the heat transfer surface irrespective of size of the heat transfer surface. As the heat flux was increased, coalescent large bubbles were formed on the heat transfer surface in the case that the surface diameter was larger than 5.0 mm. Large bubbles left from place to place of the coalescent large bubbles on the heat transfer surface. In the case that the surface diameter was smaller than 3.0 mm, a single bubble stayed on the heat transfer surface and a single bubble periodically left form the bubble when the heat flux was increased to the middle and high heat flux region. As the diameter of the boiling surface became smaller, the boiling heat transfer was enhanced and the critical heat flux increased. The dependency of the critical heat flux on the heat transfer surface size was well correlated with the Ded and Lienhard relation developed for spheres.
Experimental Investigation of Degree of Premixing on Isothermal Air-Water Two-Phase Flow Through Minichannel
Authors: Mehta Hemant B. , Banerjee Jyotirmay , Dodiya Jukesh A. , Solanki Sanket
Published: December 2013

The study on the effect of degree of premixing on isothermal gas-liquid two-phase flow pattern and flow pattern maps in microscale channels is inadequate. The present paper discusses the experimental investigation on air-water two-phase flow through 2.25 mm horizontal circular minichannel. Two type of inlet channel geometry, T-junction (TJ) and Y-junction (YJ), are considered. Six different flow patterns are observed and flow pattern maps are developed. The developed flow pattern maps for TJ and YJ channels are compared with the maps available in the literature. The surface tension dominated region is found to have major effect of inlet channel geometry. The results obtained for minichannel can be guidelines to analyze and design diverse two-phase microfluidic applications.
Effect of Tube Diameters on the Flow Phenomena of Gas-Liquid Two-Phase Flow in Microchannels
Authors: Ide Hideo , Kawaji Masahiro
Published: December 2013

The studies on microfluidics have advanced with the use of microchannels in micro bioreactors, applications in biomedical engineering, bioengineering and pharmaceuticals, fuel cells and compact heat exchangers for heating and cooling of micro electro mechanical systems. For a wide application of microchannels, it is very important to elucidate the effect of the tube diameters on the flow phenomena of gas liquid two-phase flow in microchannels. The flow phenomena and the frictional pressure drop of gas-liquid two-phase flow were investigated experimentally by using three kinds of circular microchannels made of fused silica tubes, with inner diameters of 0.1 mm, 0.15 mm and 0.25mm. In these channels, bubbly flow, slug-churn flow, and annular flow were observed. In annular flow, two characteristic flows of ring film flow and disturbed ring film flow were observed. For the 0.25 mm diameter microchannel, several conductance probe sensors were flush mounted to the channel wall in order to measure the very thin mean film thickness or liquid holdup in a microchannel. The flow patterns maps were also made by using the high speed video images and the holdup wave signals. The effects of tube diameter on the flow patterns were investigated.
An Investigation of the Pressure Drop Associated With Liquid-Liquid Slug Flows
Authors: Mac Giolla Eain Marc , Egan Vanessa , Punch Jeff , Walsh Patrick , Walsh Edmond
Published: December 2013

A liquid–liquid slug flow regime is generated when two immiscible liquids are pumped into a channel at varying flow rates. However, the addition of a second immiscible phase is accompanied by an increase in pressure drop relative to the single phase flow case. The focus of this work is to experimentally investigate the pressure drop associated with a liquid–liquid slug flow regime and in particular to examine the effects of slug length, slug numbers and continuous phase on the pressure drop in a hard walled FEP Teflon circular capillary of 1.59mm inner diameter. The flow was analysed over the dimensionless Reynolds and Capillary number ranges of 0.68–97.63 and 0.000045–0.06 respectively by employing four different carrier fluids; Pd5, Dodecane, FC40 and AR20 with water as the dispersed phase. Experiments involved varying the dimensionless water slug length between 1.05–11.01 and the dimensionless oil slug length between 0.71–14.14. Results show a large increase in pressure drop for such flows compared to single phase values. A comparison between the experimental data and correlations in the literature highlights the lack of flow physics in their composition. An alternative approach is presented that can be used for predictive purposes to estimate the interfacial contribution to the total pressure drop in a liquid–liquid slug flow regime.
Application of Nanofluids in a Shell-and-Tube Heat Exchanger
Authors: Cox Jonathan , Kanjirakat Anoop , Sadr Reza
Published: December 2013

Innovations in the field of nanotechnology have potential to improve industrial productivity and performance. One promising applications of this emerging technology is using nanofluids with enhanced thermal properties. Nanofluids, engineered colloidal suspensions consisting of nano-sized particles (less than 100nm) dispersed in a basefluid, have shown potential as industrial cooling fluids due to the enhanced heat transfer characteristics. Experiments are conducted to compare the overall heat transfer coefficient and pressure drop of water vs. nanofluids in a laboratory scale industrial type shell and tube heat exchanger. Three mass particle concentrations, 2%, 4% and 6%, of SiO2-water nanofluids are formulated by dispersing 20 nm diameter nano particles in desalinated water. Nanofluid and tap water are then circulated in the cold and hot loops, respectively, of the heat exchanger to avoid direct particle deposition on heater surfaces. Interestingly, experimental result show both augmentation and deterioration of heat transfer coefficient for nanofluids depending on the flow rate through the heat exchangers. This trend is consistent with an earlier reported observation for heat transfer in micro channels. This trend may be explained by the counter effect of the changes in thermo-physical properties of fluids together with the fouling on the heat exchanger surfaces. The measured pressure drop in the nanofluids flow shows an increase when compared to that of basefluid that could limit the use of nanofluids in heat exchangers for industrial application.
Diffusion and Mixing in Microchannel Analyzed by the Luminol Chemiluminescence
Authors: Matsuo Ruru , Matsumoto Ryosuke
Published: December 2013

This study focused on the diffusion and mixing phenomena investigated by using luminol chemiluminescence (CL) to estimate the local chemical reaction rate in the T-junction microchannel. Generally, the degree of mixing in microchannel is calculated by the deviation of the obtained concentration profiles from the uniform concentration profile by using fluorescence technique. Thus, the degree of mixing is a macroscopic estimate for the whole microchannel, which is inappropriate for understanding the diffusion and mixing phenomena in the mixing layer. In this study, the luminol CL reaction is applied to visualize the local chemical reaction and to estimate the local diffusion and mixing phenomena at an interface between two liquids in microchannel. Luminol emits blue chemiluminescence when it reacts with the hydrogen peroxide at the mixing layer. Experiments were carried out on the T-junction microchannel with 200 microns in width and 50 microns in depth casted in the PDMS chip. The chemiluminescence intensity profiles clearly show the mixing layer at an interface between two liquids. The experimental results are compared with the results of numerical simulation that involves solving the mass transport equations including the chemical reaction term. By calibrating CL intensity to the chemical reaction rate estimated by the numerical simulation, the local chemical reaction profile can be quantitatively estimated from the CL intensity profile.
The Cross Flow Mechanism in the Micro Channel of a Polymer Electrolyte Fuel Cell
Authors: Salahuddin K. M. , Oshima Nobuyuki , Saha Litan Kumar
Published: December 2013

In this article we presented the recent activities in the field of gas flow in the micro channel and porous media of a polymer electrolyte fuel cell (PEFC). The gas flow behavior in the micro-channel, especially in the case of serpentine channel is very complex due to the appearance of cross flow through the gas diffusion layer (GDL). The gas flow behavior in the separator channel and GDL of a PEFC has been studied by using a transient, isothermal and three dimensional numerical models. To predict gas flow phenomena accurately the precise calculation of mass conversation is necessary which is strictly maintained in our present simulation. The effects of physical characteristics and geometrical properties have been investigated to quantify the amount of cross flow and pressure loss. The cross flow has been investigated in terms of volume mass flux through the GDL under the rib. The ratio cross flow rate to the total flow rate increases when gas channel pitch length decreased. Moreover, with increasing of permeability this ratio also increases. The effect of cross flow and bend region characteristics on the pressure loss has been identified. In addition, to isolate the contribution of cross flow on the performance of fuel cell, the simulation was carried out with electrochemical reaction using parallel straight channel. We designed a parallel flow field to induce artificial cross flow through the GDL. The numerical results show that the flow cross-over through the GDL under the rib significantly facilitate the oxygen transport towards the catalyst layer. Therefore, it is possible to overcome the oxygen transport limitation. Consequently, the cross flow can increase the current density by reducing the oxygen transport limitation, although this also increases the non-uniformity in current density.
The Appropriate Blend Proportional Factor Value of Two Staggered Grids Used in the Free Energy Based LBM With Large Density Ratio
Authors: Gong Jia-ming , Oshima Nobuyuki , Tabe Yutaka
Published: December 2013

The effect of blend proportional factor α used in the free energy based two-phase flow LBM model with large density ratio on the shape description of a water droplet is investigated. The blend proportional factor α which combines the two kinds of staggered grids is adopted in the calculation process of the Poisson equation based fractional step method to satisfy the mass conservation in the LBM scheme, it is found to lead to varied degrees of shape deformation of a simulated liquid water droplet. The shape deformation degree of a liquid water droplet with certain dimensionless radius is measured by the radius lengths in 8 directions. The appropriate α which gives the better shape description accuracy of a water droplet with certain dimensionless radius is explored and its value change tendency with the dimensionless radius lengths is summarized. The α’s effect on the shape deformation is also presented.
Application Process Tomography to Measure Particle Migration in Microchannel
Authors: Othman Nur Tantiyani Ali , Takei Masahiro , Obara Hiromichi
Published: December 2013

Nowadays, fluid flow in a microchannel has emerged as an important area of research. This has been motivated by their various applications such as medical and biomedical use, computer chips, and chemical separations. Usually, electrical impedance tomography (EIT) is visualized, into a cross-sectional image representing the distribution of density. EIT is recently developed imaging technique, with which images of the conductivity or permittivity of the subject can be rapidly collected with channels of external electrodes. Therefore, we considered application of EIT to the microchannels. In this paper, we develop the EIT for microchannel nano particles concentration in microchannel with 60 multi-layer electrodes and measured using cross-sectional impedance measurement technique. Based on the reconstructed image using the EIT system and analytical calculation using Maxwell equation, we discuss the initial concentration condition effect and the stream transitional migration to estimate particle migration behaviors in the fluid flow. The measured results shows up to 24% particles moved from upstream to downstream cross-section, where the particles move away from center streamlines to near wall vicinity area and the number of the particles migration towards wall vicinity area is clearly increased near the outlet area. The stream transitional particle migration due to inertia lift forces is investigated with the effect of the initial particle concentration.
Study of Supersonic Micro-Channel for Cooling Electronic Devices
Authors: Takahashi Yuya , Okajima Junnosuke , Iga Yuka , Komiya Atsuki , Fu Wu-Shung , Maruyama Shigenao
Published: December 2013

In this study, we focus on a micro-scale cooling device using a supersonic single phase gas flow. The single phase gas cooling system has advantages for cooling electronics device in a micro-scale. Generally, the forced convective heat transfer by single phase gas flow has a lower heat transfer coefficient than other heat transfer mechanisms. However, the heat transfer rate can be largely improved with a low temperature flow that is generated by isentropic expansion in supersonic nozzle. The objective of this study is to conduct a numerical evaluation of the possibility of this cooling system with a supersonic air flow through a heated micro-fin array. In order to calculate the supersonic flow inside the nozzle and evaluate the effect of the nozzle shape on the heat transfer, two types of nozzles are designed. One nozzle is a typical supersonic nozzle called Laval nozzle. The other is named Bump nozzle which has a simple arc shape at the throat. The channel size of both nozzles are about 200 μm in width and 2743.1 μm in length. In order to estimate the cooling performance, the numerical simulations were conducted by using ANSYS FLUENT 12.1 with the density-based Roe-FDS method. The inlet pressure, outlet pressure, and total pressure were set to 290 kPa, 100 kPa, and 367.1 kPa, respectively. The stagnation temperature and wall temperature were assumed 300 K and 350 K, respectively. The values of bulk mean temperature and Nusselt number were estimated. In both nozzles, the calculated bulk mean temperature was about 230 K and the Nusselt number was 7.54, which is the theoretical value of laminar forced convection between the parallel plates. The results showed that the Bump nozzle had almost the same cooling performance as the Laval nozzle in spite of its simple geometry in the each single channel. In addition, the Bump nozzle can have 4 times the number of channels the Laval nozzle configuration can occupy the same area because of its shape. This indicates that cooling performance of a device that includes the Bump nozzle geometry is higher than that of the Laval nozzle.
Principles of Refrigerant Circuiting in Single Row Microchannel Evaporators
Authors: Mehendale Sunil
Published: December 2013

Microchannel evaporators are being increasingly considered for application in residential and commercial cooling and heat pump applications. This work analyzes the principles of refrigerant circuiting design in refrigerant-to-air heat exchangers using an element-by-element model developed for a microchannel evaporator. Geometric parameters such as microchannel tube depth, tube height, and port size, louvered fin density, louver angle, louver height, louver pitch, and fin height, as well as the air side face velocity, the refrigerant pressure-drop and heat transfer as a function of refrigerant mass flux are considered in the analysis. The model was first validated using data available in the open literature, thus providing a high level of confidence in the predictive ability of the model. Starting with a given microchannel tube and louvered fin geometry and a fixed number of tubes (and fins), the thermal performance of the heat exchanger was simulated over a wide range of two pass circuit configurations and tube lengths. It was found that the heat transfer versus pressure-drop trade-off provides an optimum relationship between the fraction of tubes in the first pass and the heat exchanger length. The sensitivity of the evaporator cooling capacity to the percentage of tubes in the first pass was also explored.
Optimal Design and Operation of Microdevices for Chemical Production
Authors: Tonomura Osamu
Published: December 2013

Microreactors engage the attention of researchers and engineers in the pharmaceutical and chemical industries as well as universities. When the production capacity of micro chemical plants is increased by numbering-up approach, it is important to realize the uniform flow distribution among the parallelized microreactors. In addition, a blocked microreactor needs to be identified as early as possible to achieve the stable long-term operation of micro chemical plants. However, it is not practical to install the sensors in all the microreactors from the viewpoint of cost or space. In this research, a system that can detect and diagnose a blocked microreactor by using just two flow sensors is developed. The effectiveness of the developed system is demonstrated by numerical and experimental investigations, and it is clarified that the developed method has high robustness to changes in the fluid properties and the microreactor characteristics such as pressure drop. The developed system will be applicable to various types of micro chemical plants with parallelized microreactors.
Hydrogen Viscosity Measurements With Capillary Tube Under High Pressure
Authors: Uehara Temujin , Yoshimura Kosuke , Yusibani Elin , Shinzato Kan’ei , Kohno Masamichi , Takata Yasuyuki
Published: December 2013

Viscosity of hydrogen has been measured at high pressures and high temperatures by using capillary tube method. The measurement apparatus was designed specifically for high pressure gas up to 100MPa. The capillary used quartz glass tube 0.1mm in inner diameter and 400mm in length. The measurement range is 0.1MPa to 100MPa, and room temperature up to 723K. We have to generate laminar flow inside the capillary tube that is the range of Reynolds number from 250 to 900. Since we measured nitrogen gas viscosity at the same range and many nitrogen viscosity data have already been measured in these ranges, nitrogen data was used in this study to confirm the accuracy of our apparatus before measurements of hydrogen. The measurement results of hydrogen are evaluated compared with our existing correlation (Yusibani Correlation)[1]. The results of hydrogen viscosity agree well with the existing correlation within 2% except for the measurements at 723K. The relative uncertainty of the present measurement system is estimated to be as much as 2%.
A Device Concept for Demixing of Gas Species Based on Excitation of Internal Energy Modes
Authors: Gorji M. Hossein , Jenny Patrick
Published: December 2013

In this work a phenomenon arising from gas-wall interaction in rarefied regimes is presented and discussed. It is hypothesized that the effect of energy transfer between different modes of molecules scattered from walls can be used for demixing of different gas species. In order to study this effect, first a kinetic wall boundary model for diatomic gas molecules is devised. The model is derived by generalizing the Cercignani–Lampis gas-surface interaction kernel in order to embody the gas internal degrees of freedom (DoF). Here, opposed to the extensions of e.g. [5], energy exchange between different molecular modes are honored and thus different physical phenomena arising from inelastic gas–surface collisions can be observed.
Heat Transfer Enhancement With Iron Oxide Nanoparticle Based Ferrofluids
Authors: Kurtoglu Evrim , Kaya Alihan , Gözüaçık Devrim , Acar Havva Funda Yağcı , Kosar Ali
Published: December 2013

Nanofluids are colloidal compounds, where the solid phase material is composed of nano sized particles, and the liquid phase can potentially be any fluid but aqueous media are common. As a common nanofluid type, ferrofluids are formed by holding solid nanoparticles in suspension by weak intermolecular forces and may be produced from materials with different magnetic properties. Heat transfer performance of ferrofluids is one of the crucial properties among many others that should be analyzed and considered for their wide range of applications. For this purpose, experiments were conducted in order to characterize heat transfer properties of ironoxide based ferrofluids flowing through a microchannel. In this study, convective heat transfer experiments were conducted in order to characterize convective heat transfer enhancements with Lauric acid coated ironoxide (Fe3O4) nanoparticle based ferrofluids, which have volumetric fractions between 0%–∼5% and average particle diameter of 25 nm, in a 2.5 cm long hypodermic stainless steel microtube with an inner diameter of 514 μm and an outer diameter of 819 μm. Heat fluxes up to 184 W/cm2 were applied to the system at three different flow rates (1ml/s, 0.62ml/s and 0.36 ml/s). Promising results were obtained from this study, which are suggesting the use of ferrofluids for heat transfer applications can be advantageous.
Simulation of Magnetic Actuation of Ferrofluids in Microtubes
Authors: Özbey Arzu , Karimzadehkhouei Mehrdad , Kurtoğlu Evrim , Koşar Ali
Published: December 2013

Magnetic actuation of ferrofluids with dynamic magnetic fields is one of the most promising research areas with its wide and different potential application areas such as biomedical and micropumping applications. Ferrofluid has the potential of opening up new possibilities. To have more understanding about various fields of engineering, more research should be conducted by considering both the experimental and modeling aspects. The most important parameters determining the flow property, flow rates and overall system efficiency are the quality and the topology of magnetic fields used in these systems. Therefore, the methods of dynamic magnetic field generation constitute a central problem to obtain desired performance. This study includes modeling and simulation of ferrofluid actuation with dynamic magnetic fields by using the COMSOL software and reports that ferrofluid actuation can be successfully used and the simulation results agree well with the experimental results.
Absorption Characteristics of Thin Lithium Bromide (LiBr) Solution Film Constrained by a Porous Hydrophobic Membrane
Authors: Nasr Isfahani Rasool , Moghaddam Saeed
Published: December 2013

An experimental study on absorption characteristics of water vapor into a thin lithium-bromide (LiBr) solution flow is presented. The LiBr solution flow is constrained between a superhydrophobic vapor-permeable wall and a solid surface that removes the heat of absorption. As opposed to conventional falling film absorbers, in this configuration, the solution film thickness and velocity can be controlled independently to enhance the absorption rate. The effects of water vapor pressure and cooling surface temperature on the absorption rate are studied. An absorption rate of approximately 0.005 kg/m2s was measured at a LiBr solution channel thickness and flow velocity of 160 μm and 4 mm/s, respectively. The absorption rate increased linearly with the water vapor driving potential at the tested solution channel thickness. The high absorption rate and the inherently compact form of the proposed absorber promise compact small-scale waste heat or solar-thermal driven cooling systems.
Traction Force Measurement During Collective Cell Migration Measured by Multichannel Micropillar Device
Authors: Ohashi Toshiro , Sugawara Akito
Published: December 2013

Cell migration is essential for a variety of biological and pathological processes such as wound healing, inflammation and tumor metastasis. However, the mechanical environment within a group of cells during collective migration has not been well characterized. In this study, a polydimethylsiloxane (PDMS) multichannel device was fabricated using standard photolithography and soft lithography techniques and was used to monitor cellular traction forces during migration. A migration rate of 5.7 μm/h was measured in microchannels and leading cells in the moving front of the migration generated traction forces with a maximum magnitude of 14 nN at their front side. Traction forces generated by cells behind the leading cells directed forces backward at both the front and rear sides. However, traction forces generated by cells behind the second row had forces in random directions and with smaller magnitudes compared to those on the front and the second row. It is assumed that cells on the front line generated large traction forces and migrated actively as single cells, pulling adjacent cells forward, whereas the cell movement after the third row was restricted by mechanical linkages between their neighboring cells.
Estimation of Heat Generation From Power Si MOSFET Using Electro-Thermal Analysis
Authors: Kibushi Risako , Hatakeyama Tomoyuki , Ishizuka Masaru
Published: December 2013

This paper describes thermal and electrical properties of power Si MOSFET. The problem of hot spot in sub-micron scale Si MOSFET has been widely known. Recently, power Si MOSFET is key device in a lot of area, for example car electronics. In power Si MOSFET, high voltage is applied and high current is generated. Therefore, heat generation becomes higher and thermal management is important. In this paper, thermal and electrical properties of power Si MOSFET is evaluated with Electro-Thermal Analysis and fundamental heat generation phenomenon of power Si MOSFET is discussed. Under high electric field, electron thermal energy becomes much higher than thermal energy of crystal lattice. Therefore, in this paper, non-equiriblium energy state between electron and lattice is considered. Calculated results showed that hotspot appears in power Si MOSFET. Further, drain voltage dependence of hotspot temperature and temperature dependence of drain current are discussed.
Heat Transfer Enhancement Effect of Nanostructured Surface Made of Carbon Nanotube on SiC Ceramics
Authors: Noguchi Hiroki
Published: December 2013

The Japan Atomic Energy Agency (JAEA) has been conducting research and development on the thermo-chemical iodine–sulfur (IS) process, which is one of the most attractive water-splitting hydrogen production methods using the nuclear heat of a high-temperature gas-cooled reactor (HTGR). In researching this IS process, a silicon carbide (SiC) heat exchanger with good corrosion resistance was used in a corrosive situation in boiling sulfuric acid. With the aim of enhancing heat transfer in the SiC heat exchanger, a nanostructured surface made of carbon nanotubes (CNTs) was produced on a SiC substrate by surface decomposition. Two types of SiC, one produced by pressureless sintering (PLS-SiC) and one by chemical vapor deposition (CVD-SiC), were used as substrates. CNTs formed by the surface decomposition of SiC can vary depending on the crystal structure of the substrates. Additionally, in order to investigate surface wettability, nanostructured surfaces on the CVD-SiC with hydrophilicity and hydrophobicity were produced. The effects of heat transfer enhancement by the nanostructured surfaces were evaluated by a convective heat transfer test using de-ionized water. The nanostructured surface on the CVD-SiC with hydrophilicity was the only surface that showed any heat transfer enhancement. However, this enhancement was much smaller than those previously reported. The experiment showed that the small size of the nanopores influenced the heat transfer enhancement and that the wettability of the nanostructured surface was related to heat transfer enhancement.
Condensation and Collapse of Vapor Bubble Injected to Subcooled Pool
Authors: Ueno Ichiro , Saiki Takahito , Osawa Tomohiro , Hong Chungpyo
Published: December 2013

We pay a special attention to the collapsing processes of vapor bubble injected into a subcooled pool; we try to extract the vapor-liquid interaction by employing a vapor generator that supplies vapor at designated flow rate to the subcooled pool instead of using a immersed heated surface to realize a vapor bubble by boiling phenomenon. This system enables ones to detect a spatio-temporal behavior of a single bubble of superheated vapor exposed to a subcooled liquid. We indicate the condensation rates as functions of the injection velocity of the vapor and the degree of subcooling of the pool. We indicate that an abrupt condensation of the injected vapor results in a fine disturbance over the vapor bubble surface before the collapse stage of the bubble. The wave number is sharply dependent on the degree of subcooling of the pool. The threshold of such a fine disturbance formation over the bubble corresponds with that the occurring condition of the maximum volume reduction rate of the vapor bubble.
Developments of MEMS-Based Thermocouple Array for Sensing Effects of a Flow Channel on PEMFC Local Temperature Distribution
Authors: Sugimoto Toshiki , Horiuchi Yuhei , Araki Takuto
Published: December 2013

Measuring temperature inside PEMFCs is necessary for proper water management, because water vapor pressure is a strong function of temperature. In this paper, we have developed thin film thermocouple (TFTC) array to measure temperature distributions near the Cathode Catalyst layer (CCL) with a resolution smaller than the rib-channel scale.

The sensor array was placed between CL and gas diffusion layer (GDL) at the cathode. No performance decrement was observed with the insertion of TFTC array. The measurements of temperature distributions showed that the temperature rises at the cathode CL is about 9 °C at 1.2 A/cm2 with supplying 98.5 % RH Hydrogen / Air.
Multiscale Simulation of Internal Rarefied Gas Flows
Authors: Lockerby Duncan A. , Patronis Alexander , Borg Matthew K. , Reese Jason M.
Published: December 2013

This paper describes the development and application of a multiscale method for the efficient simulation of a large class of low-speed internal rarefied gas flows. The method is an extension of the hybrid atomistic-continuum approach recently proposed by Borg et al (2013) [J. Comp. Phys., 233, pp 400–413] for the simulation of micro/nano flows of high-aspect ratio. The extension is twofold: 1) a modification to accommodate fluid compressibility; and 2) implementation using a direct simulation Monte Carlo (DSMC) method for the treatment of dilute rarefied gas flows. The method is applied to a pair of internal-flow configurations: flow through a converging-diverging channel and eccentric cylindrical Couette flow. For validation/verification purposes, the multiscale simulation results are compared to those obtained from a full-scale DSMC simulation: very close agreement is obtained in all cases. The multiscale simulation is an order of magnitude more computationally efficient than the full-scale DSMC for the first test case, and two orders of magnitude more efficient for the second case.
3D Focusing of Micro-Particles by Sheath Flow Warping
Authors: Perfetti C. , Iorio C. S. , Dubois F.
Published: December 2013

Observation of biological samples is a common issue in many applications relative to marine environment and in the field of water treatments. In particular, the ability to detect the presence of bacteria such as Criptosporidium and Giardia Lamblia in freshwater contributes to prevent people from critical diseases even in developed countries. The main challenge in this field is to analyze a large enough volume of biological sample to make it representative of the selected environment, while characterizing the species of interest whose size is often many order of magnitude smaller.

In order to obtain detailed information of the observed species, the magnification of the visualization systems — often optical microscopes — should fit the size of the objects, involving a restrained field of view. As a result; the rate of analysis is lowered and the characterization of the samples time-consuming. To tackle this issue, an increase of the flow rate is possible by focusing of particles in the observation field of view. Such technique allows for increasing the overall flow rate, inversely related to the sampling time.

In this article a new 3D hydrofocusing device is presented. A square section glass capillary (400×400μm2) used as the nozzle is inserted into a square section glass channel (2×2mm2). The inlets are fixed on a custom device that enables the sheath flow to completely wrap the sample flow after the injection. The 3D position of the particles used as representative substitutes of the biological species has been measured thanks to digital holographic microscopy and their distribution in cross-sections 2mm and 30mm downstream the injection nozzle compared to numerical simulations. A successful match of the location has been observed.

The carrier fluid used in the experiments was water seeded with 27–45μm diameter neutrally buoyant particles. Several flow rates have been tested for both samples and sheath flow to investigate the shape of the focused stream line and to validate the prototype design. A maximum constriction — ratio between the part of the cross-sections where particles are present with and without focusing sheath flow — of 47% has been observed confirming the potentiality of the technique.