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Comprehensive analytical and numerical analyses were performed, focusing on anode water loss, cathode flooding, and water equilibrium for polymer electrolyte fuel cells. General features of water transport as a function of membrane thickness and current density were presented to illustrate the net effect of back-diffusion of water from the cathode to anode over a polymer electrolyte fuel cell domain. First, two-dimensional numerical simulation were performed, showing that the difference in molar concentration of water at the channel outlet is widened as the operating current density increases with a thin membrane ( Nafion ® 111), which was verified by Dong et al. [Distributed performance of polymer electrolyte fuel cells under low-humidity conditions. J Electrochem Soc 2005; 152: A2114–22]. Then, analytical solutions were compared with computational results in predicting those characteristics of water transport phenomena. It was theoretically estimated that the high pressure operation of fuel cells expedites water condensing and results in shorter anode water loss and cathode flooding locations. In this study, it was also found that a thin membrane ( Nafion ® 111) facilitates water transport in the through-membrane direction and therefore water concentration at the anode and cathode channel outlets reaches an equilibrium state particularly at low operating current densities. Moreover, the difference in the anode water concentration between Nafion ® 111 and Nafion ® 115 membranes becomes intensified in the in-plane direction under the same water production condition, while the cathode water concentration profiles remains almost same.

A numerical simulation of brushless DC motor is performed to elucidate thermo-flow characteristics in winding and bearing with heat generation. Rotation of rotor and blades drives influx of ambient air into the rotor inlet. Recirculation zone exists in the tiny interfaces between windings. The flow separation causes poor cooling performance in bearing part and therefore the redesign of the bearing groove is required. The design parameters such as the inlet location, geometry and bearing groove threshold angle have been selected in the present simulation. As the inlet location moves inward in the radial direction, total incoming flow rate and heat transfer rate are increased. Total incoming flow rate is increased with increasing the inlet inner length. The effect of the bearing groove threshold angle on the thermal performance is less than that of other design parameters.

This paper presents a numerical evaluation of the flow distribution and thermal performance of a multi-pass, multi-channel heat exchanger as functions of the number of passes and inlet diameter. To determine the optimal number of passes for a fixed size of heat exchanger, we investigated the JF factor by varying the number of passes and the inlet diameter. We determined the optimal number of passes for a given inlet diameter by studying the variation of the JF factor as a function of the ratio of the inlet diameter to header height ratio. For instance, the optimal number of passes was two for an inlet diameter of 50 mm, and the performance based on the JF factor was improved by about 89% compared to a reference heat exchanger. We further optimized other design parameters, such as the inlet location, separator location, and header width to improve the heat exchanger performance by an additional 20%.

This paper describes the development of a mathematical model and application of the numerical results to predict the adhesion forces between wheels and rails. The adhesion force is realized on a small area of a wheel–rail contact. Many factors have an influence on the adhesion process for these surfaces (e.g., environment, pollution, parameters and conditions of railway vehicle service, track, etc.). The paper focuses on different modelling aspects. Experimental investigation on the process of friction in the contact zone was performed. The data obtained were used to create a mathematical model. The adhesion, which is dependent on load from the wheel to the rail, temperature, friction conditions in the contact zone and wheel slip, was calculated. Finally, a quick method to determine the adhesion force between the wheels (wheel pair) of a railway vehicle and rails (rail track) is presented.

Local Nusselt numbers in the cooling flow passage of the automobile disc brake with helically fluted surfaces are presented. The flat surface in the flow passage is modified to the helically fluted surface for the purpose of enhancing the heat transfer rate, thereby reducing the thermal stress and deformation in the disc brake. Thermochromic liquid crystals and shroud-transient technique are used to measure spatially-resolved surface temperature distributions, which are used to deduce local Nusselt numbers. The Reynolds number Re ranges from 30,000 to 70,000, the helix angle θ is fixed at 45° and the dimensionless streamwise distance z/d ranges from 1.5 to 4.5. The results show that in general, local Nusselt numbers monotonically decrease with a distance away from both windward and leeward crests of the helical flute and reach a minimum value near its valley for all Re’s and z/d’s tested. The local Nusselt numbers on the helically fluted grooves are maximum 51.6 to 93.7% higher than values measured on the flat surface. The heat transfer enhancement magnitudes become more pronounced with smaller Re and z/d. The largest enhancement occurs at the windward side of the helical flute at z/d=1.5 and Re=30,000. It is also found that at Re=30,000 the average Nusselt numbers on the helically fluted surface are maximum 37% higher than those on the flat surface. The numerical results show that with 10 braking cycles, the temperatures with helically fluted surface are maximum 44.3%, 36.8%, and 36.6% lower than those with the flat surface in the inlet, the center, and the outlet, respectively.

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink for which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink properties (viscosity, surface tension), operating condition (roller rotating speed, initial immersed angle) on the film thickness. The result indicates that the film thickness has a strong dependency on the rotating speed, while the surface tension has negligible effect.

The micro-encapsulated thermochromic liquid crystal has been used for the surface temperature measurement using its color change with heat. There are exciting new opportunities to apply this liquid crystal to the investigation of important and interesting heat transfer/fluid flow problems. The various techniques of using liquid crystal for the measurement of the local Nusselt numbers in very complex geometries are presented in this paper.

The local heat transfer measurements in the cooling flow passage having both flat surface and semi-cylindrically grooved surface geometries inside the automobile disc brake were made. A uniform wall heat flux boundary condition on both surface geometries was created using gold film Intrex. Liquid crystal was used to measure the surface temperature. The experiments were made at Reynolds number (based on the hydraulic diameter of the rectangular duct) of Re=23,000, groove pitch-to-width (P/D) from 3 to 7, and groove depth-to-width (H/D) from 0.15 to 0.2. The results show that the magnitudes in the average Nusselt number on the grooved surface are maximum 92.8% higher than those on the flat surface without groove. A computer program utilizing the coupled FEM numerical technique that can predict the temperature distributions on the disc brake to analyze the thermal deformation has been developed.

A strategy for the synthesis of sol-gel hybrid materials that contain perfluorocyclobutyl groups is reported. Sol-gel films have been prepared from three types of siloxane monomers using a typical sol-gel method in an acidic atmosphere, followed by UV irradiation and dimerization. The materials show high thermal stability that exceeds 400 °C. At a wavelength of 1 550 nm, the refractive index, the bire-fringence, and the optical loss of the sol-gel materials are found to be in the ranges of 1.4368-1.4876, -0.0003-0.0029, and 0.34-0.45 dB · cm -1 , respectively.

Ethynyl-terminated fluorinated poly(arylene ether sulfide) (E-FPAESI) was synthesized via nucleophilic aromatic substitution from dihydroxy monomer and pentafluorophenyl sulfide, followed by the reaction with 3-ethynylphenol. Dihydroxy monomer was synthesized in four steps via bromination, Grignard, Suzuki cross-coupling, and demethylation techniques. The number-average molecular weights and polydispersities of the E-FPAESI were in the ranges of 7700−23 000 and 1.53−2.89, respectively. The glass transition temperatures of the polymers varied from 126 to 171 °C and upon curing in the range of 168−236 °C. E-FPAESI exhibited high thermal stability up to 451−483 °C. The refractive indices and birefringences of the spin-coated polymer films were in the ranges of 1.4943−1.5047 and 0.0004−0.0009 at 1550 nm wavelength, respectively. The optical loss for E-FPAESI was about 0.45 dB/cm at 1550 nm wavelength.

Optimal values of the design parameters for a fin-tube heat exchanger of a household refrigerator under frosting conditions are proposed to improve its thermal performance and extend its operating time. In the optimization procedure, fin spacings of the heat exchanger are selected as the design parameters, and the average heat transfer rate, frost mass, and operating time are considered to be objective functions. The response surface and Taguchi methods are employed to optimize the design parameters. As a result, the average heat transfer rate and operating time of the optimum models increases by up to 6.3% and 12.9% compared to that of the reference model, respectively.

Reduction of outgassing in a high temperature superconducting (HTS) power cable cryostat is very important to achieve a long interval vacuum pumping and to drop the minimum vacuum condition in the cryostat. So, in order to reduce outgassing from the cryostat surface, cleaning and baking are needed processes in manufacturing the cryostat. The outgassing surface of the cable cryostat is larger than the vacuum space of the cable cryostat, therefore the vacuum condition of the cable cryostat degrades quickly at a small outgassing rate. In this paper, to analyze the thermal insulation performance of cable cryostat, we have measured the outgassing rate of the sample HTS power cable cryostat in various structures of thermal insulation (with or without multilayer insulation and filled with liquid nitrogen or without liquid nitrogen) and predicting the trend of the vacuum condition changes by the measured outgassing rate data. A long term outgassing test is performed for three months

A mathematical model is proposed to evaluate the frosting behavior of a fin–tube heat exchanger under frosting conditions. Empirical correlations of the heat transfer coefficients for the plate and tube surfaces and a diffusion equation for the frost layer are used to establish the model. The correlations for the heat transfer coefficients, derived from various experimental data, were obtained as functions of the Reynolds number and Prandtl number. The proposed model is validated by comparing the numerical results with experimental data for the frost thickness, frost accumulation, and heat transfer rate. The numerical results agree well with the experimental data. It is also found that this model can be applied to evaluate the thermal performance of a common fin–tube heat exchanger under frosting conditions.

To improve the electrochemical performance of Si–Zr thin films, we have investigated the effect of the replacement of Zr by Ag in the films. The Si–Zr–Ag thin films were prepared by co-sputtering from each pure target and then analyzed for structure, composition and electrochemical performance. The Ag-containing films show a plateau like region in the charge–discharge profiles, while the steep slopes are seen in the Si–Zr film. The Si–Zr–Ag films also show high capacity and good rate capability compared to the Si–Zr film, maintaining a comparable capacity retention with cycles. The improved electrochemical performance of Si–Zr–Ag films is attributed to the highly dispersed Si phase in the film, which was induced by formation of Zr–Ag bonds, and the lower impedance exerted by Ag alloying.

The effects of condensers installed in the stacked air-conditioning plant rooms of a high-rise apartment building were studied numerically. The performance of the condensers was evaluated using the coefficient of performance (COP) and condenser group performance indicator (CGPI) parameters. The effects of wind direction, wind velocity, and the arrangement and location of the condensers were investigated. The performance of condensers above the 30th floor was seriously degraded due to the stacking effects. The heat dissipation performance of the condensers in the higher floors dropped significantly when the frontal wind was greater than 4 m/s and the side wind was greater than 8 m/s. The condenser should be arranged in such a manner that the fan of the condenser faces the outside of the building to exhaust the hot air directly to the outside. To prevent the hot air from reentering the air-conditioning plant room and to allow fresh air to enter instead, the condenser considered in this study must be located at the lower left corner of the air-conditioning plant room.

The present experiment investigates the effects of the pore density of aluminum foam heat sinks, the jet velocity, the jet-to-jet spacing and the nozzle plate-to-heated surface separation distance in a 3/spl times/3 square multi-jet impinging array on the averaged Nusselt number. Thermal performances of 10, 20, and 40 PPI (pores per inch) aluminum foam heat sinks and a conventional plate-fin heat sink are evaluated in terms of the averaged Nusselt number. The jet Reynolds number is varied in the range of Re=1000-13650. The highly permeable 10 PPI aluminum foam heat sink shows higher Nusselt numbers than the 20 and 40PPI aluminum foam heat sinks both in the multi-jet and the single jet impingements. For the single jet impingement, the aluminum foam heat sinks display 8-33% higher thermal performance compared to a conventional plate-fin heat sink while the enhancement is 2-29% for the multi-jet impingement. The multi-jet impingement shows higher heat transfer enhancement than the single jet impingement for high jet Reynolds number and smaller jet-to-jet spacing in the present experiment.

The design optimization of a 7 × 7 pin-fin heat sink is performed numerically. To achieve higher thermal performance of the heat sink, the thermal resistance at the junction of the chip and the heat sink and the overall pressure drop in the heat sink have to be minimized simultaneously. The fin height (h), fin width (w), and fan-to-heat sink distance (c) are chosen as the design variables, and the pressure drop (ΔP) and thermal resistance (θ ja ) are adopted as the objective functions. To obtain the optimum design values, we used the finite-volume method for calculating the objective functions, the Broydon-Fletcher-Goldfarb-Shanno method for solving the unconstrained nonlinear optimization problem, and the weighting method for predicting the multiobjective problem. The results show that the optimum design variables for the weighting coefficient of 0.5 are as follows: w = 4.653 mm, h = 59.215 mm, and c = 2.669 mm. The objective functions corresponding to the optimal design are calculated as ΔP = 6.82 Pa an...

This paper presents a semi-empirical model to predict the growth of frost formation on the cold cylinder surface. The model in this paper is composed of the correlations for frost properties including the various frosting parameters and local heat transfer coefficient. The effects of varying the correlations for local heat transfer coefficient on the frost growth are examined to establish the model. The numerical results are compared with the experimental data from the previous researchers. The results agree well with the experimental data within a maximum error of 13%. As the results, the frost thickness decreases with changing angular position from the front stagnation to separation point. Also the effects of air velocity on the frost growth are negligible, as compared to the other frosting parameters.

A mathematical model is presented to predict the frost properties and heat and mass transfer within the frost layer formed on a cold plate. The model consists of the laminar flow equations for air-side and the empirical correlation of local frost density. The correlation of local frost density used in this study is obtained from various experimental conditions by considering frosting parameters. The numerical results are compared with experimental data to validate the model, and agree well with experimental data within a maximum error of 9%.

The optimization of the plate heat exchanger with staggered pin arrays for a fixed volume is performed numerically. The flow and thermal fields are assumed to be periodic fully developed flow and heat transfer with constant wall temperature and they are solved using the finite-volume method. The optimization is carried out by using the sequential linear programming (SLP) method, and the weighting method is adopted for solving the multiobjective problem. The results show that the optimal design variables for the weighting coefficient of 0.5 are as follows: S = 6.497 mm, P = 5.496 mm, D 1 = 0.689 mm, and D 2 = 2.396 mm. The Pareto optimal solutions are presented also.

The heat and flow characteristics in a single-phase parallel-flow heat exchanger was examined numerically to obtain its optimal shape. A response surface method was introduced to approximately predict its performance with respect to the design parameters over the design domain. The inflow/outflow angle of the working fluid, the location of inlet/outlet, the protruding height of flat tube and the height of header were chosen as a design parameter The evaluation of the relative importance of the design parameters was performed based on a sensitivity analysis. An efficiency index was used as an evaluation characteristics value to simultaneously consider both the heat transfer and the pressure drop. The efficiency index of the optimum model, compared to that of the base model, was increased by 9.3%.

This study proposes dimensionless correlations for predicting the properties of frost formed on a cold plate. Frosting experiments are carried out to obtain the correlations with various environmental parameters including the air temperature, air velocity, absolute humidity, and cooling plate temperature. The thickness, density, surface temperature, effective thermal conductivity, average heat and mass transfer coefficients of the frost layer are correlated as functions of the Reynolds number, Fourier number, absolute humidity, and dimensionless temperature by using a dimensional analysis. The correlations proposed in this study agree well with the experimental data within a maximum error of 10%, and can be used to predict the average frost properties in the following ranges: the air temperature of 5–15 °C, air velocity of 1.0–2.5 m s−1, absolute humidity of 0.00322–0.00847 kg kga−1, and cooling plate temperature of −35–−15 °C.

A numerical simulation is performed to examine the heat and fluid flow characteristics of the branching system in a single-phase parallel-flow heat exchanger (PFHE) and to obtain its optimal shape. The relative importance of the design parameters [injection angle of the working fluid (Θ), inlet shape and location (Yc), and height of the protruding flat tube (Yb)] is determined to decide the optimization sequence. The optimal geometric parameters are obtained as follows: Θ=−21°, Type A, Yc=0 and Yb=0. The heat transfer rate of the optimum model compared to that of the reference model is increased by about 55%. The optimal values of the parameters can be applicable to the Reynolds number ranging from 5000 to 20,000.

A mathematical model is developed to predict the transport phenomena during evaporation in the extended meniscus region of a micro-capillary channel. In this model, the vapor pressure variation and the disjoining pressure effect are included and the friction force at the liquid–vapor interface is considered as well. The results show that the local heat transfer coefficient has an extremely large value in the thin film region. The heat transfer rate, however, is larger for the meniscus than for the thin film region. The maximum liquid velocity appears at approximately 40% of the extended meniscus region and the variation of the heat flux has a negligible effect on the maximum liquid velocity. It is also found that the length of the extended meniscus region is affected by the heat flux, the channel height and the dispersion constant.

A mathematical model is presented to predict the behavior of frost formation by simultaneously considering the air flow and the frost layer. The present model is validated by comparing with several other analytical models and our experiments. It is found that most of the previous models cause considerable errors depending on the working conditions or the correlations used in predicting the frost thickness growth, whereas the model in this work estimates the thickness, density, and surface temperature of the frost layer more accurately within an error of 10% except the early stage of frosting in comparison with the experimental data. Numerical results are presented for the variations of heat and mass transfer during the frost formation and for the behavior of frost layer growth along the direction of air flow. Also, a correlation between the convective heat and mass transfer is obtained as Le(1−n)=0.905±0.005 in this work.

A mathematical model considering the air side and the frost layer is presented to predict the frost layer growth. The standard k- model for the air flow and the diffusion and energy equations for the frost layer are employed. The numerical results are compared with experimental data to validate the present model, and agree well with experimental data within a maximum error of 10%. The present model predicts well the frost properties and heat and mass transfer with respect to the frosting time. The variation of total heat transfer strongly depends on the operating condition, and has a similar trend to that of the sensible heat transfer. The frost properties along the flow direction are also investigated.

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.

A mathematical model to predict the flow and heat transfer characteristics for a thin film region of a micro-channel is proposed. Gradient of the vapor pressure and the capillary force are considered. The effects of channel height, heat flux and slip boundary condition at the solid–liquid interface are investigated. The length of the thin film region is calculated by comparing the magnitude of the capillary and disjoining pressures. The length and the thickness of the thin film region decrease exponentially with increasing heat flux. The channel height has no effect on the shape of film thickness. In the case of slip condition, the decreased film thickness causes the capillary and disjoining pressures to increase.

The modeling for turbulent flow through a porous medium has not been confirmed because of an undetermined constant which appears in the governing equations. In the present study, turbulent porous modeling based on one energy equation has been extended to turbulent clear flow. An undetermined constant is also suggested by performing microscopic analysis in the flat tube geometry. The undetermined constant is found to be 0.99 by comparing the results of macroscopic and microscopic analysis. It is shown that the results of the macroscopic analysis using the constant agree well with those of the microscopic analysis, with a maximum error of 3.5%.

A mathematical model is presented to predict the two-phase flow and heat transfer phenomena of the evaporating extended meniscus region in a micro-channel. The pressure difference at the liquid-vapor interface can be obtained by the augmented Laplace-Young equation. The correlative equations for film thickness, pressure, and velocity in the meniscus region are derived by applying the mass, momentum, and energy equations into the control volume. The results show that increasing the heat flux and the liquid inlet velocity cause the length and liquid film thickness of the extended meniscus region to decrease. The variation, however, of the heat flux and liquid inlet velocity has no effect on the profile of film thickness. The majority of heat is transferred through the thin film region that is a very small region in the extended meniscus region. It is also found that the vapor velocity increases gradually in the meniscus region. However, it increases sharply at the junction of the meniscus and thin film regions.

This paper proposes dimensionless correlations predicting properties of the frost layer formed on a cold flat surface. Experiments are carried out to obtain the correlations with various environmental parameters such as air temperature, air velocity, absolute humidity, and cooling plate temperature. As a result, the frost properties (frost layer thickness, density, surface temperature, thermal conductivity) are correlated as a function of Reynolds number, Fourier number, absolute humidity and non-dimensional temperature by using a dimensional analysis. The correlations agree well with the previous and our experimental data within a maximum error of 10%, and are used to predict the frost properties in the following ranges: Reynolds number of 20216 to 53763, Fourier number of 0.1962 to 2.5128, absolute humidity of 3.22 to 8.47, and non-dimensional temperature of 0.125 to 0.5.

A mathematical model of the hydrodynamic and heat transfer performances of two-phase flow (gas-liquid) in thin film region of micro channel is proposed. For the formulation of modeling, the flow of the vapor phase and the shear stress at the liquid-vapor interface are considered. In this work, disjoining pressure and capillary force which drive the liquid flow at the liquid-vapor interface in thin film region are adopted also. Using the model, the effects of the variations of channel height and heat flux on the flow and heat transfer characteristics are investigated. Results show that the influence of variation of vapor pressure on the liquid film flow is not negligible. The heat flux in thin-film region is the most important operation factor of micro cooler system.

The effects of the heat exchanger surface treatment on the frosting/defrosting behavior in a fin-tube heat exchanger are investigated experimentally. It is found that the hydrophilic surface mainly influences the frosting behavior, while the hydrophobic surface has some influence on the defrosting behavior. In view of the frosting, a surface-treated heat exchanger with either hydrophilic or hydrophobic characteristic shows little improvement in the thermal performance rather than the bare aluminum heat exchanger. The results reveal that the heat exchanger with a hydrophobic surface treatment is more effective in view of the defrosting efficiency and time. The amount of residual water on the surface-treated heat exchangers is shown to be smaller than that of the bare heat exchanger. Therefore further improvements on the performance of re-operations are expected.

The heat and flow analyses of a parallel-flow heat exchanger are performed. Two models with and without considering the effects of the geometric characteristic of flat tube are used. Comparing the two models, the modeling using the heat transfer correlations of flat tubes shows the better accuracy and stability of numerical solutions. The effect of flow distribution on the thermal performance is examined with varying the design factors (i.e., the locations of separators and inlet/outlet, and the aspect ratios of microchannels of the heat exchanger). The flow uniformities along the paths of the heat exchanger are proposed, and are observed to evaluate the thermal performance of the heat exchanger. The optimization using the ALM method has been accomplished by maximizing the flow uniformity. It is found that the heat transfer rate of the optimized model is increased by 6.0% compared to that of the base type and the pressure drop by 0.4%.

The characteristics of moisture ventilation in a dry room are studied numerically. The effects of three important parameters: the positions of outlets, the aspect ratio (β) of horizontal section and the air exchange rate (N), are analyzed in terms of the scales of ventilation efficiency. Ventilation performance is evaluated by varying the aspect ratio and the air exchange rate for the four different outlet arrangements. It is found that the ventilation performance is improved when the aspect ratio in the transverse arrangement of outlets is decreased. Ventilation efficiency reaches its highest value when β is set to be 4 in the longitudinal arrangement of outlets. Regardless of the aspect ratio, the upper arrangement of the outlets shows a better ventilation performance than the lower arrangement. For all geometrical models and aspect ratios investigated in this study, the increase of the air exchange rate for improving the ventilation performance is only valid up to 60 h−1.

A numerical analysis has been carried out on forced convection heat transfer in the developing region of a porous channel. The channel is filled with an isotropic porous medium. At the channel walls, a uniform heat flux is given. Comprehensive numerical solutions are acquired to the Brinkman-Forchheimer extended Darcy equation and the LTNE model which does not employ the assumption of local thermal equilibrium between solid and fluid phases. Details of thermal fields in the developing region are examined over wide ranges of the thermal parameters. The numerical solutions at the fully developed region are compared with the previous analytical solutions. The correlation for predicting local Nusselt number in a porous channel is proposed.

A numerical study has been carried out to investigate the flow and heat transfer from an aluminum foam heat sink in a confined channel. A uniform heat flux is given at the bottom of the aluminum foam heat sink, which is horizontally placed on the heated surface. The channel walls are assumed to be adiabatic. Cold air is supplied from the top opening of the channel and exhausted to the channel outlet. Comprehensive numerical solutions are acquired to the governing Wavier-Stokes and energy equations, using the Brinkman-Forchheimer extended Darcy model and the local thermal non-equilibrium model f3r the region of porous media. Details of flow and thermal fields are examined over wide ranges of the principal parameters; i.e., the Reynolds number Re, the height of heat sink h/H, porosity and pore diameter ratio .

The purpose of this study is to analyze the characteristics of the linear compressor for Stirling cryocooler. To ensure high performance and long life of the free piston, free displacer Stirling cryocooler, the operating parameters of the linear compressor should be optimized. The experimental results show the operating frequency of the linear compressor has significant effect to the input power characteristics, and the compressor with higher charging pressure of working fluid has high pressure ratio. For the high performance of the linear compressor, compressor has uniform magnetic force with different stroke, and the optimal operating frequency with respect to the charging pressure.

The modeling for turbulent flow through a porous media has not been confirmed because of a undetermined constant which appears in the governing equations. In present study, the turbulent porous modeling based on the local thermal equilibrium has been extended to the turbulent clear flow. A undetermined constant is also suggested by microscopic analysis. The microscopic analysis is performed in the flat tube with micro-channels, and it confirms that the undetermined constant is 0.99. It is shown that the results of the macroscopic analysis using confirmed constant agree well with those of the microscopic analysis with a maximum error of 3.5%.

Low temperature proton exchange membrane (PEM) fuel cells that use perfluorinated sulfonic acid are at present being commercialized in fuel cell vehicles, but these cells can operate only at relatively low temperatures, ca. < 100°C, and high hydration levels. High temperature PEM fuel cells that use phosphoric acid-doped polybenzimidazole can operate effectively up to 180°C; however, these are difficult to operate below 140°C without suffering loss of phosphoric acid when exposed to water.1 In this presentation, we discuss a new class of fuel cells based on ion pair-coordinated proton exchange membranes.2 In the ion pair-coordinated proton exchange membranes, quaternary ammonium functionalized membranes, also known as anion exchange membranes, are doped with phosphoric acid. Due to the high basicity of the quaternary ammonium hydroxide, the acidic proton of phosphoric acid is completely deprotonated to form a strong ionic interaction between quaternary ammonium and biphosphate. Our density functional theory calculation indicated that the ion-pair interaction is 8.5 times greater than the conventional acid base interaction in the phosphoric acid doped polybenzimidazole. The strong interaction between the ion pair enables fuel cell operation at lower temperatures with substantially higher water partial pressure than are possible for high-temperature phosphoric acid doped polybenimidazole fuel cells. In this presentation, the chemical structural difference between this new system and the conventional phosphoric acid-doped polybenzimidazole system will be compared. The benefits and challenges of the new system in fuel cell operations will be further discussed. Acknowledgment This work was supported by the US Department of energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager: Dimitrios Papageorgopoulos). References G. Bendlamudi Systematic Characterization of HT PEMFCs Containing PBI/H3PO4 Systems: Thermodynamic analysis and Experimental Investigations 104 (Logos Verlag Berlin GmbH, 2011). Kwan-Soo Lee, Jacob S. Spendelow, Yoong-Kee Choe, Cy Fujimoto, and Yu Seung Kim Nature Energy, 1, 16120 (2016).

Anion exchange membrane fuel cells (AEMFCs) have been a topic of extensive research from academia and industry as an alternative to proton exchange membrane fuel cells (PEMFCs). The AEMFCs offer benefits over PEMFCs such as facile fuel oxidation and enhanced oxygen reduction reaction catalysis1. However, the chemical stability of anion exchange membrane needs to be improved as most commonly used benzyltrimethyl ammonium cationic group undergoes direct nucleophilic substitution reaction, which results in loss of conductivity and fuel cell performance. One of the approaches to enhance the chemical stability is introducing electron conjugation into cationic functional group. Previous study demonstrated that the conjugated guanidinium possess better stability than non-conjugated guanidinium2. Herein, we report the progress on resonance stabilization of the guanidinium functional group. The extended-resonance stabilized guanidinium functionalized poly(phenylene) (PP-TMG) AEM was synthesized from the Diels-Alder poly(phenylene) by acylation reaction followed by activated fluorophenyl-guanidine reaction3. The alkaline stability of PP-TMG was compared with benzyltrimethyl ammonium-poly(phenylene) (PP-BTMA) and hexamethylenetrimethyl ammonium-poly(phenylene) (PP-HTMA). Spectroscopic analysis with small molecules and cationic group tethered polymers will be also provided to discuss the resonance stabilization effect. Acknowledgement This work is supported by the US Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager Dr. David Peterson). References: (1) Varcoe, J. R.; Atanassov, P.; Dekel, D. R.; Herring, A. M.; Hickner, M. A.; Kohl, P. A.; Kucernak, A. R.; Mustain, W. E.; Nijmeijer, K.; Scott, K.; Xu, T.; Zhuang, L. Energy Environ. Sci. 2014, 7 (10), 3135–3191. (2) Kim, D. S.; Fujimoto, C. H.; Hibbs, M. R.; Labouriau, A.; Choe, Y.-K.; Kim, Y. S. Macromolecules 2013, 46 (19), 7826–7833. (3) Kim, D. S.; Labouriau, A.; Guiver, M. D.; Kim, Y. S. Chem. Mater. 2011, 23 (17), 3795–3797.

The effect of flow distribution on thermal and flow performance of a parallel How heat exchanger has been numerically investigated. The flow distribution has been altered by varying the geometrical parameters that included the locations of the separators, and the inlet/outlet of the heat exchanger. Flow nonuniformities along paths of the heat exchanger, which were believed to be dominantly influential to the thermal performance, have been observed to eventually optimize the design of the heat exchanger. The optimization has been accomplished by minimizing the flow nonuniformity that served as an object function when the Newton’s searching method was applied. It was found that the heat transfer of the optimized model increased approximately 7.6%, and the pressure drop decreased 4.7%, compared to those of the base model of the heat exchanger.

The optimum shape and arrangement of staggered pins in the channel of a plate heat exchanger are studied in this paper. The following four dimensionless geometric parameters of the pins are selected as the important design variables: the distance (L), the volume (V), the angle ( β ) and the pitch (G). The pressure drop and heat transfer characteristics are examined, and an optimization is carried out to minimize a global objective function consisting of the correlation between the Nusselt number and the friction factor. The optimal geometric parameters are as follows: L =0.272 , V =0.106 , β =0.44 and G =0.195 . The optimal geometric parameters obtained from this study can be applied for a Reynolds number ranging from 500 to 1500.

Experiments were conducted to obtain the correlation on the airside heat transfer coefficient of wire-on-tube type heat exchangers using single layer samples. Correction factors to the Zhukauskas correlation were determined from the experimental results. Numerical analysis and experiments were performed to validate the applicability of these correction factors using three wire-on-tube type condensers. The results show that the average discrepancy between the performance experiments and present numerical results using the correction factors obtained from this study and Zhukauskas correlation shows 3.7%, while it was 24.7% when the existing correlation was used.

In this paper, a unified model for simultaneous filling and solidification is applied to the two-dimensional filling and solidification of a square cavity. The effects of wall temperature and gate position on solidification are examined. The mixed natural-convection flow and residual flow resulting from the completion of filling are included in this study to investigate the coupled effects of filling and natural convection on solidification. Two different filling configurations (assisting flow and opposite flow due to the gate position) are analyzed to study the effects of residual flow on solidification. The results clearly show the necessity to carry out a coupled filling and solidification analysis, including the effect of natural convection. A numerical algorithm that uses the implicit volume of fluid (VOF) method for filling and a general, implicit, source-based method for solidification are presented.

In this paper, the characteristics of moisture ventilation in a lithium ion battery manufacturing dry room are studied numerically using the standard k–ϵ turbulence model. Both the steady-state and the unsteady behavior of moisture ventilation are analyzed by considering two different cases; i.e., local moisture generation and uniformly distributed moisture generation in the room. In order to evaluate the characteristics of moisture ventilation, three scales of ventilation efficiency and characteristic ventilation time are presented from the numerical results. It is shown that moisture distribution is dependent strongly on the flow field. The characteristics of moisture ventilation are improved by 20% and 40% in terms of the 1st scale of ventilation efficiency (SVE1) and the 2nd scale of ventilation efficiency (SVE2), respectively, through the modifications of design variables such as the addition of inlets, outlets and partition. A significant improvement in the characteristic ventilation time and the mo...