bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial Neural Network Approach Coupled with Genetic Algorithm for Predicting Dough Alveograph Characteristics
Authors: Abbasi Hajar , Emam‐Djomeh Zahra , Ardabili Seyyed Mahdi Seyedain
Published: December 2013

Alveograph is a useful device for rheological measurement of dough from biaxial extension. Our purpose in the current research was to apply soft computing tools for predicting the alveograph properties (maximum pressure for blowing the bubble [P], abscissa at bubble rupture [L], deformation energy [W]) using physicochemical properties of flour (protein, ash, wet gluten, gluten index, amylase activity, zeleny and particle size). Generalized feed‐forward artificial neural networks (ANN) with back‐propagation learning algorithms were employed to model the alveograph properties. A genetic algorithm (GA) was applied to optimize the parameters of the ANN's structure and inputs. Sensitivity analyses were conducted to explore the ability of the networks with using physicochemical properties of flour as inputs in predicting alveograph properties. The developed ANNs using GA were shown to have excellent potential in predicting the alveograph properties. Sensitivity analyses showed that zeleny (Sedimentation value) is the most sensitive input in predicting alveograph characteristics.

Practical Applications

The alveograph is a device to measure empirical rheological properties of dough during bubble inflation. Accurate prediction of dough rheology could provide many benefits to the baking industry, for example making inline process adjustments and modifying product formulation to satisfy consumer demands. In the current study, an ANN approach was applied to predict the alveograph properties of dough (P, L and W). The physicochemical properties of flour (protein, ash, wet gluten, gluten index, amylase activity, zeleny and particle size) and the parameters of alveography were set as inputs and outputs of the networks, respectively. A GA was applied as a suitable optimizer method to determine the best topology and inputs of the networks. The developed networks have excellent performance in prediction of outputs when compared with test data. Sensitivity analyses were also performed to investigate the suitability of inputs on estimating alveograph properties (outputs) of the dough.
“Medieval Belief and Modern Secularity: Teaching the Middle Ages to Contemporary College Students”
Authors: Harris Anne F.
Published: December 2013

This article presents pedagogical strategies to engage students of the modern, secular world with materials shaped by religious belief in the Middle Ages. Three specific challenges to the teaching of medieval culture are analyzed: resistance to the religious fervor surrounding miraculous objects such as relics, adherence to specific representations of the divine, and identification of the Middle Ages as a barbaric period marked by mistakes never to be repeated. Resonances between the Middle Ages and our contemporary world emerge, however, when questioning the structures, aesthetics, and audiences of both. By using medieval scenarios to formulate questions about modern problems, these pedagogical strategies seek to implicate students from both religious and secular backgrounds, and provoke interpretations of the Middle Ages that offer insight into the contemporary world.
Alterations in the predicted regulatory and coding regions of the sterol 14α‐demethylase gene (CYP51) confer decreased azole sensitivity in the oilseed rape pathogen Pyrenopeziza brassicae
Authors: Carter Helen E. , Fraaije Bart A. , West Jonathan S. , Kelly Steven L. , Mehl Andreas , Shaw Michael W. , Cools Hans J.
Published: December 2013

The incidence and severity of light leaf spot epidemics caused by the ascomycete fungus Pyrenopeziza brassicae on UK oilseed rape crops are increasing. The disease is currently controlled by a combination of host resistance, cultural practices and fungicide applications. We report decreases in sensitivity of modern UK P. brassicae isolates to the azole (imidazole and triazole) class of fungicides. By cloning and sequencing the P. brassicae CYP51 (PbCYP51) gene, encoding the azole target sterol 14α‐demethylase, we identified two non‐synonymous mutations encoding substitutions G460S and S508T associated with reduced azole sensitivity. We confirmed the impact of the encoded PbCYP51 changes on azole sensitivity and protein activity by heterologous expression in a Saccharomyces cerevisiae mutant YUG37:erg11 carrying a controllable promoter of native CYP51 expression. In addition, we identified insertions in the predicted regulatory regions of PbCYP51 in isolates with reduced azole sensitivity. The presence of these insertions was associated with enhanced transcription of PbCYP51 in response to subinhibitory concentrations of the azole fungicide tebuconazole. Genetic analysis of in vitro crosses of sensitive and resistant isolates confirmed the impact of PbCYP51 alterations in coding and regulatory sequences on a reduced sensitivity phenotype, as well as identifying a second major gene at another locus contributing to resistance in some isolates. The least sensitive field isolates carry combinations of upstream insertions and non‐synonymous mutations, suggesting that PbCYP51 evolution is ongoing and the progressive decline in azole sensitivity of UK P. brassicae populations will continue. The implications for the future control of light leaf spot are discussed.
Breastfeeding and wheeze prevalence in pre‐schoolers and pre‐adolescents: the Genesis and Healthy Growth studies
Authors: Guibas George V. , Xepapadaki Paraskevi , Moschonis George , Douladiris Nikolaos , Filippou Amalia , Tsirigoti Lydia , Manios Yannis , Papadopoulos Nikolaos G.
Published: December 2013

Background

To date, extensive research has been undertaken on a potential link of breastfeeding (BF) to wheezing illnesses. Nevertheless, an association remains to be established, partly due to age‐dependent discrepancies and different definitions of exposures/outcomes across studies. We thus investigated the relation of diverse infantile feeding patterns with wheeze/asthma prevalence in two cohorts of children of different ages (preschool and preadolescent).

Methods

Wheeze ever/in the last 12 months (current) and doctor‐diagnosed asthma were retrospectively reported by parents of the participants of two cross‐sectional studies: the Genesis study (1871 children aged 1–5) and the Healthy Growth study (1884 children aged 9–13). Information on feeding practices (exclusive breastfeeding vs. mixed vs. formula feeding) and their duration (2 vs. 4 vs. 6 months) was recorded. Perinatal and anthorpometric data were also collected.

Results

In pre‐schoolers, regimes that did not entail exclusive BF were positively correlated to current/ever wheeze, both before and after adjustment for confounders. No differences between the associations of regimes with 2, 4 or 6 months of exclusive BF with current/ever wheeze were shown. Furthermore, there was no consistent correlation of feeding practices with physician‐diagnosed asthma. In pre‐adolescents, no association of infantile feeding patterns with the wheeze/asthma outcomes was observed.

Conclusions

Exclusive BF is associated with reduced prevalence of current/ever wheeze in pre‐schoolers; however, this appears to wane in older children. The association of a period of exclusive BF as low as 2 months with pre‐school wheeze prevalence, appeared to be comparable with that of 6 months of exclusivity.
Prisons and Religion in the Americas
Authors: Graber Jennifer
Published: December 2013

Since the 1970s and Michel Foucault's work discipline and power, scholars of religion in the Americas have looked to prisons to track changing ideas about human behavior, wrongdoing and reconciliation, social organization, and citizenship. This article provides a brief transatlantic history of the prison and scholarship on prisons and religion. It surveys work by historians, sociologists and anthropologists, and theologians and ethicists. It shows that religions have served as not only the material from which societies construct their disciplinary forms but also a resource upon which individuals draw when labeled criminal and communities invoke when seeking reform.
Chagas disease in Australia and New Zealand: risks and needs for public health interventions
Authors: Jackson Yves , Pinto Angie , Pett Sarah
Published: December 2013

Objective

International migration has changed the global distribution of Chagas disease, with the emerging importance of non‐endemic regions. We aimed at better documenting the Australia and New Zealand risk of Chagas disease and needs for interventions.

Methods

We reviewed Chagas disease‐related evidences, policies and practices in Australia and New Zealand and calculated the estimated prevalence.

Results

Australia hosts a rapidly growing population at risk and had 1928 infected residents in 2011; New Zealand had 98 in 2006. These figures underestimate the real situation, as they do not consider non‐permanent residents. The only existing policy in both countries is the identification of blood donors with a history of or a risk of infection via questionnaire. There is no programme of detection and care of patients. The lifetime economic burden of disease for society is potentially very high.

Conclusion

Chagas disease is an emerging health risk with potential high human and economic costs in Australia and New Zealand in the absence of public health attention. Implementing strategies to screen high‐risk groups and prevent transmission should be considered. Moreover, migration between the Western Pacific and Chagas endemic regions and the presence of vectors means this risk applies in the whole region.
Durable HIV RNA resuppression after virologic failure while remaining on a first‐line regimen: a cohort study
Authors: Hoffmann Christopher J. , Charalambous Salome , Grant Alison D. , Morris Lynn , Churchyard Gavin J. , Chaisson Richard E.
Published: December 2013

Adherence interventions are a recommended strategy to salvage failing antiretroviral therapy without regimen change. We assessed the durability of resuppression when using this approach. Of 300 patients who resuppressed on the same regimen (41% of all those with virologic failure), 148 (45%) remained suppressed during follow‐up for a median of 2.4 years (interquartile range [IQR]: 1.1, 4.0). Resuppression can be durable following viraemia without a switch in antiretroviral therapy regimen.
A new bead‐based human platelet antigen antibodies detection assay versus the monoclonal antibody immobilization of platelet antigens assay
Authors: Porcelijn Leendert , Huiskes Elly , Comijs‐van Osselen Ilona , Chhatta Aniska , Rathore Vipul , Meyers Matthew , de Haas Masja
Published: December 2013

Background

The performance of a newly developed Luminex bead‐based platelet (PLT) antibody detection method (PAKLx) was compared with the monoclonal antibody immobilization of PLT antigens (MAIPA) assay and the LifeScreen Deluxe Luminex bead‐based HLA Class I antibody detection method (LMX).

Study Design and Methods

Six sera containing anti‐human PLT antigen (HPA)‐1a (n = 2), HPA‐1b, HPA‐2b, HPA‐3a, or HPA‐5b were tested in titration. A total of 194 sera, including HPA‐1a, ‐1b, ‐2a, ‐2b, ‐3a, ‐5a, and ‐5b antibodies with or without HLA antibodies (n = 63); glycoprotein (GP) IV antibodies (n = 1); PLT autoantibodies (n = 3); HLA antibodies (n = 45); and samples with no PLT‐reactive antibodies (n = 82), were tested in both assays.

Results

Comparable levels of sensitivity were obtained for the MAIPA and PAKLx. The PAKLx showed four (6%) false‐negative results in 67 sera with HPA or GP‐reactive antibodies: anti‐HPA‐3a (n = 1) or anti‐HPA‐5b (n = 3). The PAKLx showed in 10 of the total 194 samples (5%) the presence of antibodies not detected by the MAIPA. This concerned broadly GP‐reactive antibodies (n = 7), anti‐GPIIb/IIIa combined with anti‐HPA‐3a (n = 1), anti‐HPA‐1a (borderline, n = 1), and anti‐GPIV (n = 1). Testing 175 sera for anti‐HLA Class I antibodies in the PAKLx and LMX showed four discrepant results: PAKLx negative and LMX positive, n = 3 and n = 1, respectively.

Conclusion

For the vast majority of the specimens tested (93%) the results of the PAKLx were in concordance with the MAIPA. The PAKLx is a fast, easy to perform, and sensitive PLT antibody screening method.
Effects of type 1 diabetes, sprint training and sex on skeletal muscle sarcoplasmic reticulum Ca2+ uptake and Ca2+‐ATPase activity
Authors: Harmer A. R. , Ruell P. A. , Hunter S. K. , McKenna M. J. , Thom J. M. , Chisholm D. J. , Flack J. R.
Published: December 2013

Key points

Skeletal muscle calcium resequestration and performance is increased in male rats with induced diabetes; and whilst muscle calcium resequestration is important during exercise, it has not been investigated in human diabetes or compared between sexes.

We show that Ca2+‐ATPase activity and Ca2+ uptake are higher among people with type 1 diabetes (T1D) compared with matched non‐diabetic controls (CON), but that performance during intense exercise was similar; Ca2+‐ATPase activity and Ca2+ uptake are also higher among men than women.

We show that Ca2+‐ATPase activity is reduced during intense exercise in men but not women, and is reduced by high‐intensity exercise training (HIET) in T1D and CON.

Fatigue is commonly reported by people with diabetes, but our data show that muscle calcium resequestration and performance during intense exercise and after HIET is not impaired in T1D, and hence other physiological or psychological mechanisms for fatigue in diabetes must be sought.

Sex influences muscle calcium regulation.

Calcium cycling is integral to muscle performance during the rapid muscle contraction and relaxation of high‐intensity exercise. Ca2+ handling is altered by diabetes mellitus, but has not previously been investigated in human skeletal muscle. We investigated effects of high‐intensity exercise and sprint training on skeletal muscle Ca2+ regulation among men and women with type 1 diabetes (T1D, n = 8, 3F, 5M) and matched non‐diabetic controls (CON, n = 8, 3F, 5M). Secondarily, we examined sex differences in Ca2+ regulation. Subjects undertook 7 weeks of three times‐weekly cycle sprint training. Before and after training, performance was measured, and blood and muscle were sampled at rest and after high‐intensity exercise. In T1D, higher Ca2+‐ATPase activity (+28%) and Ca2+ uptake (+21%) than in CON were evident across both times and days (P < 0.05), but performance was similar. In T1D, resting Ca2+‐ATPase activity correlated with work performed until exhaustion (r = 0.7, P < 0.01). Ca2+‐ATPase activity, but not Ca2+ uptake, was lower (−24%, P < 0.05) among the women across both times and days. Intense exercise did not alter Ca2+‐ATPase activity in T1D or CON. However, sex differences were evident: Ca2+‐ATPase was reduced with exercise among men but increased among women across both days (time × sex interaction, P < 0.05). Sprint training reduced Ca2+‐ATPase (−8%, P < 0.05), but not Ca2+ uptake, in T1D and CON. In summary, skeletal muscle Ca2+ resequestration capacity was increased in T1D, but performance was not greater than CON. Sprint training reduced Ca2+‐ATPase in T1D and CON. Sex differences in Ca2+‐ATPase activity were evident and may be linked with fibre type proportion differences.
Performance Evaluation of the Flow in Micro Junctions: Head Change Versus Head Loss Coefficients
Authors: Schmandt Bastian , Herwig Heinz
Published: December 2013

Losses due to the flow through conduit components in a pipe system can be characterised by head loss coefficients. They basically account for the dissipation in the flow field or, in a more general sense, for the entropy generation due to the conduit component under consideration. When only one single mass flow rate is involved, an entropy based approach is straight forward and ṁ can be used as a general reference quantity. If, however, the mass flow rate is split or united like in junctions, some new aspects appear.

In our study the general approach for these kind of conduit components is discussed. Like for single mass flow rates losses are accounted for by determining the entropy generation rates. New aspects for the branched flows are an additional parameter, the splitting ratio, and the fact that there is an energy transfer between the single branches that has to be accounted for appropriately. It turns out that this energy transfer changes the total head in each flow brach in addition to a sole loss of total head. Therefore, the coefficients should be named head change coefficients when this effect occurs.

As an example the flow through a T-shaped junction is considered, for which head loss coefficients are determined for both branches and discussed with respect to their physical meaning.
Pool Boiling Heat Transfer With Binary Mixture on Open Microchannel Surface
Authors: Kalani Ankit , Kandlikar Satish G.
Published: December 2013

Two-phase cooling is considered an attractive option for electronics cooling due to its ability to dissipate large quantities of heat. In recent years, pool boiling has shown tremendous ability in high heat dissipation applications. Researchers have used various fluid medium for pool boiling including water, alcohol, refrigerants, nanofluids and binary mixture. In the current work, binary mixture of water with ethanol was chosen as the working fluid. Plain copper chip was used as the boiling surface. Effect of various concentrations of binary mixture was investigated. A maximum heat flux of 1720 kW/m2 at a wall superheat of 28°C was recorded for 15% ethanol in water. It showed a 1.5 fold increase in CHF over pure water.
Experimental Investigation on Shape of the Meniscus in Open Rectangular Microgrooves Heat Sinks With Micro-PIV
Authors: Yu Dong , Hu Xuegong , Guo Chaohong , Tang Dawei , Nie Xuelei , Hu Linghong , Gao Fei , Zhao Tao
Published: December 2013

This paper presents the experimental investigation on shape of the meniscus in cross sections along the axial direction of open rectangular microgrooves heat sinks with input heat flux under pure evaporation heat transfer condition. The images of the shape of the meniscus in rectangular open microgrooves heat sinks were recorded by a CCD camera with the speed of 10 frames per second. Microgrooves heat sinks were placed in four inclined angles, horizon, inclined 15 degrees, inclined 25 degrees and inclined 35 degrees, and heat flux is 0.09W/cm2, 0.14 W/cm2 and 0.25 W/cm2. The results show that the shape of the meniscus is parabolic not round. When the microgrooves heat sinks are placed horizontally, the shape of the meniscus and the curvature of the meniscus in cross sections changes little along the axial direction of the microgrooves. When the microgrooves heat sinks were placed inclined 35 degrees, the meniscus moves downward to the microgroove bottom. At the same distance to the reservoir and the same heat flux, the curvature of the meniscus in inclined 35 degrees is larger than that in inclined 25 degrees, and similarly, the curvature of the meniscus in inclined 25 degrees is larger than that in inclined 15 degrees. While at the same heat flux, the microgrooves heat sink is placed in inclined 35 degrees, the curvature of the meniscus increases with the increase of the distance to the reservoir.
Effect of the Surface Tension of Liquid-Solid Interface on Liquid Flow in Parallel-Plate Sub-Micron Channels Using Multi-Body Dissipative Particle Dynamics
Authors: Yamada Toru , Asako Yutaka , Faghri Mohammad , Sundén Bengt
Published: December 2013

The liquid flow in sub-micron channels is simulated using multi-body dissipative particle dynamics (MDPD) to study the effect of the surface tension between liquid and wall surface on the flow in sub-micon scale. The solution domain is considered to be two-dimensional, where DPD particles are randomly distributed. Periodic boundary condition is employed in the flow direction and the solid walls are created by distributing DPD particles in the additional layers on the top and bottom of the domain. The different surface tensions between liquid and wall surface are obtained by changing the interaction parameters between the liquid and wall DPD particles. The ratio of Capillary number (Ca) to Reynolds number (Re) is used to relate the DPD units to the physical units. The results are shown in the form of slip length and the effect of the surface tension on the liquid flow in sub-micron channels is discussed.
Theoretical Conclusions About the Claims of Anomalous Heat Transfer Enhancement Associated With Nanofluids
Authors: Li Wenhao , Yang Chen , Nakayama Akira
Published: December 2013

A theoretical answer to the controversial issue on the anomalous convective heat transfer in nanofluids has been provided, exploiting the Buongiorno model for convective heat transfer in nanofluids with modifications to fully account for the effects of nanoparticle volume fraction distributions on the continuity, momentum and energy equations. Firstly, a set of exact solutions have been obtained for hydrodynamically and thermally fully developed laminar nanofluid forced convection flows in channels and tubes, subject to constant heat flux. From the solutions, it has been concluded that the anomalous heat transfer rate, exceeding the rate expected from the increase in thermal conductivity, is possible in such cases as titania-water nanofluids in a channel, alumina-water nanofluids in a tube and also titania-water nanofluids in a tube. Moreover, the maximum Nusselt number based on the bulk mean nanofluid thermal conductivity is captured when the ratio of Brownian and thermophoretic diffusivities is around 0.5, which can be exploited for designing nanoparticles for high-energy carriers. Secondly, another set of exact solutions have been obtained for free convection in a vertical channel filled with a nanofluid, exploiting the Buongiorno model with nanoparticle volume fraction modifications. The effects of the bulk mean volume fraction of nanoparticles, the ratio of Brownian and thermophoretic diffusivities and the buoyancy ratio on both velocity and temperature profiles has been investigated in depth for the first time. The volume fraction of nanoparticles increases exponentially towards the cold wall, which makes the velocity and temperature gradients steeper near the hot wall than those near the cold wall. Unlike the case of forced convection, no anomalous heat transfer enhancement has been observed in this case of free convection, so that the Nussult number based on the thermal conductivity of nanofluid stays close to unity as in pure base fluid free convection.
Study on Nucleate Boiling Heat Transfer by Measuring Spatially Instantaneous Local Surface Temperature and Observing Instantaneous Bubble/Liquid Fluid Behavior
Authors: Koizumi Yasuo , Hayashi Kenta
Published: December 2013

Pool nucleate boiling heat transfer experiments were performed for water at 0.101 MPa to examine the elementary process of the nucleate boiling. Heat transfer surface was made from a copper printed circuit board. Direct current was supplied to heat it up. The Bakelite plate of the backside of a copper layer was taken off at the center portion of the heat transfer surface. The instantaneous variation of the backside temperature of the heat transfer surface was measured with an infrared radiation camera. Bubble behavior was recorded with a high speed video camera. In the isolated bubble region, surface temperature was uniform during waiting time. When boiling bubble generation started, a large dip in the surface temperature was formed under the bubble. After the bubble left from the heat transfer surface, the surface temperature returned to former uniform temperature distribution. Surface temperature was not affected by the bubble generation beyond 1.6 mm from the center of the bubble. In the isolated bubble region, a convection term was approximately 80 % in total heat transfer rate. The importance of the three-phase interface line in the heat transfer should be checked carefully. In the intermediate and high heat flux region, the variation of surface temperature and heat flux were small. Rather those were close to their average values even at critical heat flux condition. It seemed that the large part of the heat transfer surface was covered with water even at the critical heat flux condition. The heat flux at the area that appeared to be the three-phase contact line was not so high and close to the average heat flux.
Novel Electrical Control in Droplet Microfluidics Using an AC Electric Field
Authors: Tan Say Hwa , Semin Benoit , Baret Jean-Christophe
Published: December 2013

We report a novel electrical control in droplet microfluidics using an ac electric field. The method can be used to actively control and tune the size of water-in-oil droplets formed in a microfluidic flow focusing device. Electrodes fabricated using microsolidics technique are not in contact with the fluids and hence prevent undesirable electrochemical reactions. The proposed electrical control is able to change the size of the droplets in the order of millisecond and also to manipulate the size of the droplets formed at single droplet level through the change in applied voltages and signal. An electro-mediated droplet formation regime transition from dripping to jetting is also observed due to the changes in the Maxwell stress arising from the application of the ac electric field. At applied frequency of between 50 to 5 kHz, the change in droplet sizes follow similar trend for the case of pure DI water but is different for the case of NaCl solution.
Emissivity of Wavelength-Selective Radiator With Periodic Microcavities
Authors: Totani Tsuyoshi , Iwata Minoru , Wakita Masashi , Nagata Harunori
Published: December 2013

A periodic microstructure of the cubic cavity 6.0 μm wide, 6.0 μm deep, and 6.0 μm high is built on an ultraviolet curable resin via UV nanoimprinting. The 200 nm thick gold film is sputtered on the periodic micro structure. The hemispherical spectroscopic transmittance and reflectance of the periodic microstructure with the gold film are measured using a Fourier transform infrared spectrometer with an integrating sphere. The hemispherical spectroscopic transmittance is 0.0 from 2 to 15 μm wavelength. The hemispherical spectroscopic reflectance is 1.0 from 2 to 8 μm wavelength and from 12 to 15 μm wavelength. The bottom of the hemispherical spectroscopic reflectance is 0.4 near 10 μm. Assuming Kirchhoff’s law, the maximum normal emissivity of the periodic microstructure is 0.6 near 10 μm. It is clarified that the periodic microcavities with a gold film built via UV nanoimprinting and sputtering can enhance maximum spectral emissive power of radiation.
An Experimental Investigation of Gas-Liquid Heat Transfer in Rectangular Micro-Channels
Authors: Saisorn Sira , Wongwises Somchai , Kuaseng Piyawat , Nuibutr Chompunut , Chanphan Wattana
Published: December 2013

The investigations of heat transfer and fluid flow characteristics of non-boiling air-water flow in micro-channels are experimentally studied. The gas-liquid mixture from y-shape mixer is forced to flow in the 21 parallel rectangular microchannels with 40 mm long in the flow direction. Each channel has a width and a depth of 0.45 and 0.41 mm, respectively. Flow visualization is feasible by incorporating the stereozoom microscope into the camera system and different flow patterns are recorded. The experiments are performed under low superficial velocities. Two-phase heat transfer gives better results when compared with the single-phase flow. It is found from the experiment that heat transfer enhancement up to 53% is obtained over the single-phase flow. Also, the change in the configuration of the inlet plenum can result in the different two-phase flow mechanisms.
An Experimental Study of Two Phase Flow in Impinging Micro Channels
Authors: Chien Liang-Han , Liu Han-Yang , Liao Wun-Rong
Published: December 2013

A heat sink integrating micro-channels with multiple jets was designed to achieve better heat transfer performance for chip cooling. Dielectric fluid FC-72 was the working fluid. The heat sink contained 11 micro-channels, and each channel was 0.8 mm high, 0.6 mm wide, and 12 mm in length. There were 3 or 5 pores on each micro-channel. The pore diameters were either 0.24 or 0.4 mm, and the pore spacing ranged from 1.5 to 3 mm. In the tests, the saturation temperature of cooling device was set at 30 and 50°C, and the volume flow rate ranged from 9.1 to 73.6 ml/min per channel (total flow rate = 100∼810 ml/min). The experimental result showed that heat transfer performance increased with increasing flow rate for single phase heat transfer. For heat flux between 20 and 100 kW/m2, the wall superheat decreases with increasing flow rate at a fixed heat flux. However, the influence of the flow rate diminished when the channels are in two phase heat transfer regime. Except for the lowest flow rate (9.1 ml/min), the heat transfer performance increased with increasing jet diameter/spacing ratios. The best surface had three nozzles of 0.4 mm diameter in 3.0 mm jet spacing. It had the lowest thermal resistance of 0.0611 K / W in the range of 200 ∼ 240 W heat input.
Drag Reduction for Nanobubble Mixture Flows Through Micro-Apertures
Authors: Ushida Akiomi , Hasegawa Tomiichi , Narumi Takatsune , Nakajima Toshiyuki
Published: December 2013

Drag reduction effect for microbubble mixtures flows has been investigated and reported. However, few studies have focused on nanobubble mixtures, which have sub-micron meter size fine bubbles. In the present study, nanobubble mixtures for water and glycerol solution were passed through several sizes of micro-apertures, and the resultant pressure drops, as compared with water and glycerol solution alone, were evaluated. For small apertures, the experimentally measured pressure drop was less than that for water and glycerol alone. This phenomenon is considered in terms of interface behavior and attributed to the electric interaction between an electric double layer and fine bubbles. The results of the present study suggest that the addition of nanobubbles to a liquid results in excellent drag reduction.
Flow Boiling of R134a and R245fa in a 1.1 mm Diameter Tube
Authors: Pike-Wilson Emily A. , Mahmoud Mohamed M. , Karayiannis Tassos G.
Published: December 2013

New refrigerants are required for cooling systems due to the fact that refrigerants like R134a are about to be phased out. This paper presents a comparison between the flow boiling heat transfer and pressure drop results of refrigerants R245fa and R134a. The experiments with R245fa were conducted in a vertical cold drawn stainless steel tube with an inner diameter of 1.1 mm and heated length of 150 mm. Experimental conditions include: mass flux range 100–400 kg/m2s, heat flux range 10–60 kW/m2, pressures of 8 and 10 bar and 1.9 and 2.5 bar for R134a and R245fa corresponding to saturated temperatures 31 °C and 39 °C and exit vapour quality range 0–0.95. The data for R134a were obtained earlier using the same experimental facility at the same experimental conditions and with the same test tube. The results demonstrated that refrigerant properties have a significant effect on heat transfer and pressure drop. The pressure drop of R245fa is higher by up to 300% compared to that of R134a at similar conditions. In addition, the effect of mass flux and heat flux on the local flow boiling heat transfer coefficient was different. Heat transfer coefficients of R245fa showed a greater dependence on vapour quality. The agreement with past heat transfer correlations is better with R134a than with R245fa.
Effects of Temperature Dependent Properties on the Laminar Forced Convection in Straight Microchannels With Uniform Wall Temperature
Authors: Del Giudice Stefano , Savino Stefano , Nonino Carlo
Published: December 2013

The paper reports the results of a parametric investigation on the effects of temperature dependent viscosity and thermal conductivity on forced convection in simultaneously developing laminar flows of liquids in straight microchannels of constant cross-sections. Uniform temperature boundary conditions are specified at the microchannel walls. Viscosity is assumed to vary with temperature according to an exponential relation, while a linear dependence of thermal conductivity on temperature is assumed. The other fluid properties are held constant. Two different cross-sectional geometries, namely circular and flat microchannels, are considered. A finite element procedure is employed for the solution of the parabolized momentum and energy equations. The parabolic approximation of the Navier-Stokes and energy equations can be considered adequate for values of the Reynolds and Péclet numbers larger than 50. Computed axial distributions of the local Nusselt number are presented for different values of the Brinkman number and of the viscosity and thermal conductivity Pearson numbers. Moreover, a superposition method is proved to be applicable in order to obtain an approximate value of the Nusselt number by separately considering the effects of temperature dependent viscosity and those of temperature dependent thermal conductivity. Finally, it is found that the influence of the temperature dependence of thermal conductivity on the value of the Nusselt number is almost independent of the value of the Brinkman number, i.e., it is approximately the same no matter whether viscous dissipation is negligible or not.
Microchannel Device for Droplet Generation, Mixing, and Phase Separation for Continuous Counter-Current Flow Extraction
Authors: Kockmann Norbert , Holbach Alexander
Published: December 2013

Process intensification is a major goal in chemical engineering, which is often obtained by miniaturized devices with enhanced heat and mass transfer characteristics. This work shows a microchannel device for liquid-liquid extraction and reactions with integrated droplet generation, enhanced mixing and phase separation. Monodisperse droplets with diameters in the range from 0.3 to 0.7 mm are generated by co-current jet flow with different operating modes of aqueous and organic phase. Flow regime maps indicate operation conditions for small and monodisperse droplets of the organic phase. A glass plate with a single microstructured channel serves for sufficient residence time and intensive mixing between the two phases. At the outlet, a wider channel leads to droplet coalescence and agglomeration at a hydrophobic wall and outlet tube for the organic phase. A complete phase separation was possible over a wide range of flow rates. The closed channel setup of droplet generation, mixing and phase equilibrium, and finally phase separation allows for countercurrent switching of the plates. This arrangement needs additional pumps to overcome the pressure drop over the plates, at least one pump more than the number of plates.
Numerical Simulation of Condensed Water Behavior in Gas Diffusion Layers of PEFC Using the Lattice Boltzmann Method
Authors: Tabe Yutaka , Kamijo Ryuji , Honjo Yuji , Suzuki Kengo , Chikahisa Takemi
Published: December 2013

Numerical simulations using the lattice Boltzmann method (LBM) has been developed to elucidate the dynamic behavior of condensed water in a gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEFC). Here, a LBM model of two-phase flow with equal densities was applied, because the condensed water behavior is less affected by the gas flow. The simulation results showed that the LBM applied here can simulate dynamic capillary fingering at low migration speeds of liquid water in a GDL, which is similar to the results of the LBM simulation with large density differences. Using the equal density LBM, we conducted efficient large-scale analyses to elucidate the effect of the GDL structure and wettability on the liquid water behavior inside of the GDL.
Large Eddy Simulation of Two-Dimensional Jet Impingement Heat Transfer Enhanced by Submilli-Scale Ribs
Authors: Oda Yutaka , Takeishi Kenichiro
Published: December 2013

Two-dimensional jet impingement heat transfer enhanced by submilli-scale ribs has been studied by mass transfer experiments and large eddy simulations. Installation of ribs induces flow separation and reattachment, and realize high heat transfer coefficient in the wall jet region. Higher rib-height was found to be effective to make the enhanced heat transfer region larger. Large eddy simulation was found to predict reattachment length correctly, which then resulted in good agreement of local heat transfer coefficients between experiment and simulations except the stagnation and reattachment regions, where over- and under-estimation occurs.
Effect of Electric Field Distribution Generated in a Micro Space on Pool Boiling Heat Transfer
Authors: Kano Ichiro , Sato Kyohei
Published: December 2013

This paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling. A dielectric liquid of AE-3000 (AGC Co. Ltd) was used as working fluid. A heating surface was polished with the surface roughness (Ra) of 0.05 μm. A micro sized electrode, in which the slits were provided, was designed in order to generate non uniform electric field and to produce electrohydrodynamic (EHD) effects with the application of high dc voltages. The obtained results confirmed the enhancement of CHF since the EHD effects increased the CHF to 82 W/cm2 at the voltage of −3000 V, which was four times greater than CHF for the pool boiling. The usual traveling wave on the bubble interface induced by the Kelvin-Helmholtz instability was modified by adding the EHD effects.
Computational Analysis of Conjugate Heat Transfer in Gaseous Micro Channels
Authors: Croce Giulio , Rovenskaya Olga , D’Agaro Paola
Published: December 2013

A fully conjugate heat transfer analysis of gaseous flow, within slip flow regime, in short microchannel is presented. A Navier Stokes code, coupled with Maxwell and Smoluchowski slip and temperature jump model, is adopted.

Due to the link between temperature and velocity field in highly compressible flows, results are presented for Nusselt number, heat sink thermal resistance and resulting wall temperature as well as Mach number profiles for different conditions, commenting on the relative importance of wall conduction, rarefaction and compressibility. Compressibility plays a major role, and the reduction in heat transfer rate due to axial conduction is quite remarkable.
Analysis of Water Transport in the Vicinity of Micro-Porous Layer in PEFC With Freezing Method
Authors: Aoyama Yusuke , Suzuki Kengo , Tabe Yutaka , Chikahisa Takemi
Published: December 2013

This paper examines the role of micro porous layers (MPLs) in Polymer Electrode Fuel Cells (PEFCs) by observing the cross-sectional distribution of condensed water inside a cathode side MPL In addition, the forms of water condensation in the vicinity of a MPL are also compared between two places, under flow channels and under lands, by observing both inside the MPL and an interface between the MPL and a catalyst layer (CL). The freezing method and a cryo-scanning electronic microscope (cryo-SEM) are used for the observation. The result under the non-flooded condition shows that condensed water does not accumulate inside the MPL. This result indicates that the water produced by PEFC power generation passes through the MPL as vapor state under non-flooded conditions.
Simulation of Conjugate Convective-Conductive Heat Transfer in a Microchannel Within the Slip Regime Using GPU Accelerated Lattice Boltzmann Method
Authors: Widyaparaga Adhika , Pranowo
Published: December 2013

This study aims to investigate the significance of conjugate heat transfer in the microscale within the slip regime. As within the slip regime the continuum assumption is invalid due to presence of rarefaction effects, the Lattice Boltzmann method (LBM) is employed to overcome the limitations of Navier Stokes based solutions in this regime. We have constructed and compared two case models in which a fluid of higher temperature enters a microchannel. The conditions are set to obtain Knudsen numbers which result in the slip regime being dominant. To investigate the effect of conjugate heat transfer, the two models differed in the aspect that one model did not incorporate conjugate heat transfer and while the other did. The numerical calculation was validated by comparing the velocity profile results to exact theoretical approximations and was found to agree well. The results of comparison of models Case I and Case 2 have shown that temperature profile is affected significantly by conjugate heat transfer. The conjugate heat transfer at the microchannel wall (Case 1) was shown to maintain the initial temperature of fluid longer than compared to a purely isothermal wall (Case 2), thus signifying the importance of the consideration of conjugate heat transfer effects in microfluid models. We have implemented GPU based parallel processing to reduce computation time. The result of the incorporation of GPU processing was found to increase processing speed up to 15 times.
Integrated Microfluidic Pumping for Cooling Applications
Authors: Frijns Arjan J. H. , Liu Zhipeng , Derks Roy J. S. , Speetjens Michel F. M. , van Steenhoven Anton A.
Published: December 2013

Temperature management in microsystems is a technical problem with an increasing importance: although the power consumption of integrated circuits is not increasing, due to further miniaturization the local power density is still increasing. Moreover, in the near future more and more micro components will be integrated in flexible system-in-foil (SIF) packages. These packages can contain ultra-thin (8–50 micron) flexible embedded silicon chips combined with polymer electronics, optical systems and microfluidic channels e.g. for point-of-care diagnostics. However, the low thermal conductivity of the polymeric package is aggravating the heat management problem. The life span of micro components, but also the performance of some micro components, like (O)LEDs, can be strongly temperature dependent. Therefore an adequate temperature control is required.

The thermal management problems can potentially be addressed by embedding micro-channels containing a flowing cooling medium in close proximity and preferably directly underneath the electronic circuit. However, many applications do not allow for external pumps and therefore pumping needs to be integrated in these channels as well.

In this paper some promising integrated micro pumping techniques, like AC-electro osmosis and ferrofluidic pumping, will be described and discussed. The multi-physics modeling approach will be presented and the numerical results will be analyzed and compared with flow fields that are measured by 3D astigmatism micro particle tracking velocimetry (3D micro-PTV).
Reduced Order Models of Low Mach Number Isothermal Flows in Microchannels
Authors: Issa Leila , Lakkis Issam
Published: December 2013

We present reduced order models of unsteady low Mach number isothermal ideal gas flows in two-dimensional rectangular microchannels subject to first order slip boundary conditions. The Navier-Stokes equations are simplified using Low Mach Number expansions of the pressure and velocity fields. This approximation allows decoupling the density from spatial pressure variations, thus simplifying the momentum equation. The resulting diffusion equation and the subsequent pressure-flow-rate relationship enables modeling the flow using analog circuit components. The accuracy of the proposed models is investigated for steady and unsteady flows in a two-dimensional channel for different values of Reynolds and Knudsen numbers.
A Molecular Dynamics Analysis of Quantum Effect on the Thermodynamic Properties of Liquid Hydrogen
Authors: Nagashima Hiroki , Tsuda Shin-ichi , Tsuboi Nobuyuki , Koshi Mitsuo , Hayashi A. Koichi , Tokumasu Takashi
Published: December 2013

Liquid Hydrogen plays an important role in hydrogen energy society. Therefore it is important to understand its thermal and transport properties accurately. However cryogenic hydrogen has unusual thermodynamic properties because of its quantum nature. The thermal de Broglie wavelength of cryogenic hydrogen molecule becomes the same order as molecular diameter. Therefore, each molecular position and its momentum cannot be defined classically. Because of this nature, hydrogen molecules show higher diffusivity than classical counterpart. Until now, the effects of quantum nature of hydrogen and its mechanism on the thermodynamic properties have not been clarified in detail. Especially, how the quantum nature would effect on the energy transfer in molecular scale has not been clarified. An accurate understanding of the effect and mechanism of quantum nature is important for hydrogen storage method and energy devices which use hydrogen as a fuel. In this study, therefore, we investigated the effect of this quantum nature and its mechanism on the thermodynamic and transport properties of cryogenic hydrogen using classical Molecular Dynamics (MD) method and quantum molecular dynamics method. We applied path integral Centroid Molecular Dynamics (CMD) method for the analysis. First, we have conducted thermodynamic estimation of cryogenic hydrogen using the MD methods. This simulation was performed across a wide density-temperature range. Using these results, equations of state (EOS) were obtained by Kataoka’s method, and these were compared with experimental data according to the principle of corresponding states. As a result, it was confirmed that both quantitative and qualitative effect of the quantum nature on the thermodynamic properties of hydrogen are large. It was also found that taking account the quantum nature makes larger virial pressure and weaker intermolecular interaction energy. Second, we have calculated the diffusion coefficient of liquid hydrogen to clarify the effect of the quantum nature on the transport properties. We used Green-Kubo form for the calculation using velocity autocorrelation function. The simulation was performed across a wide temperature range. CMD simulation results were compared with classical simulation results and experimental data. We clarified the effect of quantum nature on the transport properties of liquid hydrogen.
A Microfluidic Culturing System for Observation of Free-Floating Microorganisms
Authors: Mogi Katsuo , Sugii Yasuhiko , Fujii Teruo , Matsumoto Yoichiro
Published: December 2013

We observed the effect of the ethanol toxicity on individual cells of Botryococcus braunii (B. braunii) in microchannel environment. For continuous observation of B. braunii in microchannel environment, a microfluidic device which has a specific channel structure was developed. By using the channel structure, microorganisms were sorted by their size and captured on the corresponding area in the channel. In the experiment, suspension of B. braunii with DAPI was injected into the device for the cell capturing in the experiment. Following the cell capturing, ethanol with DAPI 0.5% was injected into the channel for 60 minutes. Damaged cells were confirmed by their deformation and the fluorescence of DAPI. The strong fluorescence of DAPI was confirmed after 20 minutes. On the other hand, the fluorescence of the chloroplast became weak in contrast to the fluorescence of DAPI. We successfully confirmed the time condition of exposing B. braunii to ethanol in the micro channel.
Semi-Analytical Solutions to the Extended Graetz Problem in Rectangular Microchannel Flow Driven by Electroosmosis
Authors: Sphaier L. A. , Moreira D. C.
Published: December 2013

This paper presents semi-analytical solutions to the Extended Graetz Problem in micro-channels. The flow driving mechanism is electroosmosis combined with a pressure gradient. The hypothesis of a thin electrical double layer (EDL) is not considered, leading to a more realistic model. The considered problem is that of laminar flow in a rectangular channel. The solution methodology is based on the Generalized Integral Transform Technique. The presented solution yields a closed-form expression for calculating the Nusselt number. The only numerical step required by the solution involves the numerical computation of eigenvalues and eigenvectors, necessary for a matrix exponential evaluation. With the results, the effects of the channel geometry and flow driving mechanisms on the Nusselt number are analyzed.