Browsing by Author "Chu, Hsin-Sen"

Now showing 1 - 20 of 25

A transient model of PEM fuel cells based on a spherical thin film-agglomerate approach
(2007-10-25)
Chang, Shih-Ming
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
The objective of this study is to investigate the transient behavior of a PEM fuel cell by using a one-dimensional, two-phase mathematical model. This model treats the catalyst layer as a spherical thin film-agglomerate. Effects of various transport parameter as well as other factors such as catalyst loading, gas diffusion layer thickness and liquid water permeability on the transient evolution of major model properties and cell performance are investigated in detail. Numerical results show that the evolution of ionic potential drop and oxygen consumption experience several steps before they reach steady state. The same situation can also be seen for the evolution of water saturation and current density. A detail inspection of these phenomena shows a close relation between these transport variables and cell performance. Parametric studies of other design factors' effects reveal there optimum values which lead to a greater current output during its evolution period. (c) 2007 Elsevier B.V. All rights reserved.
A two-phase, transient model for the cathode of a pemfc using thin film-agglomerate approach
(2006)
Chu, Hsin-Sen
;
Chang, Shih-Ming
;
機械工程學系
;
Department of Mechanical Engineering
This study presents a transient, one-dimensional, and two phase model of the proton exchange membrane fuel cell cathode. A thin film-agglomerate approach is applied to the catalyst layer. The model includes the transport of gaseous species, liquid water, proton, and electrochemical kinetics. The effect of water flooding both in the gas diffusion layer and catalyst layer in the cathode are investigated. The effects of agglomerate radius and the catalyst layer thickness on the overall cell performance are also investigated. The results show that the time for fuel cells to reach the steady state is in the order of 10 sec due to the effect of water accumulated both in the porous layer and the membrane. However the time for proton transport is in the order of 0.1 sec. In addition, before the ionic potential reaches the steady state, it would get a critical value. The critical value would depend on the operating cell voltage. There seems to be an optimum in the catalyst layer thickness and agglomerate radius.
An analytical solution for transport of oxygen in cathode gas diffusion layer of PEMFC
(2006-09-29)
Tsai, C. R.
;
Chen, Falin
;
Ruo, A. C.
;
Chang, Min-Hsing
;
Chu, Hsin-Sen
A two-dimensional theoretical model is developed in this study to simulate the transport phenomena of oxygen in cathode gas diffusion layer (GDL) of proton exchange membrane fuel cell (PEMFC). An analytical solution is then obtained accordingly to characterize the effects of GDL on cell performance. It is found that the concentration flux of oxygen across the GDL is primarily dominated by the thickness and porosity of GDL. For a thicker GDL, the diffusion resistance increases and thus lowers the cell performance especially under high current density condition. On the other hand, an increase of porosity will enhance the transport of oxygen and result in significant improvement of cell performance. The influences of system parameters including the temperature, channel height, inlet velocity, and inlet pressure on the diffusion of oxygen in GDL are also examined systematically. Results provide insights into the characteristics of oxygen diffusion in GDL and benefit the optimal design of PEMFC. (c) 2006 Elsevier B.V. All rights reserved.
An experimental study of the heat transfer in PS foam insulation
(2009-02-01)
Tseng, Pen-Chang
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
Heat transfer mechanisms in 14 samples of vacuum insulation panels (VIPs) are examined to reveal the influence of porous foam structure on VIP performance. The samples were produced by in-house equipment that was able to vary the foam structure by modulating the process temperature and pressure. Two parameters are proposed to describe the foam structure, namely, the broken cell ratio and the average cell size. Under a specific solid volume fraction, the average cell size shows a linear dependence on the broken cell ratio. Furthermore, the radiation and conduction heat transport data correlate well with these parameters. Radiation heat transfer increases as the broken cell ratio (cell size) increases, but solid conduction decreases as the broken cell ratio (cell size) increases. Consequently, an optimum broken cell ratio (cell size) exists such that the total heat transport is minimum under a specific solid volume fraction. However, the majority of VIP heat transfer is solid conduction. Solid conduction accounts for more than 80% of the total heat transport and is largely affected by the solid volume fraction. A rule of thumb for improving VIP performance is to reduce the solid volume fraction as much as possible to eliminate solid conduction, and maintain the cell size at an optimum value that is dependent on the solid volume fraction.
Analysis of Pyramidal Surface Texturization of Silicon Solar Cells by Molecular Dynamics Simulations
(2008)
Chung, Hsiao-Yen
;
Chen, Chiun-Hsun
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
The purpose of this paper is to explore the relations between surface texturization and absorptance of multicrystalline silicon solar cells by a simple new model, based on the classic molecular (MD) dynamics simulation, alternative to complex electron-photon interactions to analyze the surface texturization of solar cells. In this study, the large tilted angle leads to the lower efficiency of solar cell. To consider the effect of incident angle, a range of high efficiency exists due to the increasing probability of second reflection. Furthermore, the azimuth angle of incident light also affects the efficiency of solar cells. Our results agree well with previous studies. This MD model can potentially be used to predict the efficiency promotion in any optical reflection-absorption cases. Copyright (C) 2008 Hsiao-Yen Chung et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Analysis of surface texturization of solar cells by molecular dynamics simulations
(2008)
Chung, Hsiao-Yen
;
Chen, Chiun-Hsun
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
The purpose of this paper is to develop a simple new model, based on the classic molecular dynamics simulation (MD), alternative to complex electron-photon interactions to analyze the surface texturization of solar cells. This methodology can easily propose the absorptance differences between texturing and nontexturing solar cells. To verify model feasibility, this study simulates square, pyramidal, and semicircular texturization surfaces. Simulations show that surface texturization effectively increases the absorptance of incident light for solar cells, and this paper presents optimal texturization shapes. The MD model can also be potentially used to predict the efficiency promotion in any optical reflection-absorption cases. Copyright (C) 2008 Hsiao-Yen Chung et al.
Current density analysis in a molten carbonate fuel cell unit with non-uniform inlet flow and high anode gas utilization
(2007-12-01)
Liu, Syu-Fang
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
This study investigates the electrical performance of a planar molten carbonate fuel cell unit with cross-flow configuration when both the anode gas utilization gets higher and anode gas inlet flows are non-uniform. A software package in this study solves two-dimensional, simultaneous, partial differential equations of mass, energy, and electro-chemistry' without considering stack direction variation. The results show that the anode gas utilization increases with a decrease in the molar flow rate, and the average current density decreases when the molar flow rate drops. Additionally, non-uniform inlet profile of the anode gas will induce a happening of non-reaction area. This non-reaction area deteriorates the average current density and then deteriorates the electrical performance to -4%.
Degradation of proton exchange membrane fuel cells due to CO and CO(2) poisoning
(2009-03-01)
Yan, Wei-Mon
;
Chu, Hsin-Sen
;
Lu, Meng-Xi
;
Weng, Fang-Bor
;
Jung, Guo-Bin
The Co and CO(2) poisoning effects on the degradation of cell performance or proton exchange membrane fuel cell (PEMFC) tinder transient stage were investigated. The mechanism of CO poisoning lies in the preferential adsorbing or CO to the platinum surface and the blocking or active sites of hydrogen. These phenomena were described with adsorption, desorption, and electro-oxidation processes of CO and hydrogen in the present work. In addition, it is well known that the reverse water gas shift reaction (RWGS) is the main effect of the CO(2) poisoning, through which a large part of the catalytic surface area becomes inactive due to the hydrogen dissociation. The predicted results showed that, by contaminating the fuel with 10 ppm CO at the condition of P(H) = 0.8 atm and P(co2) = 0.2 atm, the current density of the PEM fuel cell was lowered 28% with rate constant of RWGS k(rs) from zero to 0.02. With 50 ppm CO, the performance drop was only 18%. For the reformed gas, CO(2) poisoning became much more significantly when the CO content in the reactant gas was small. (C) 2008 Elsevier B.V. All rights reserved.
Effect of inlet flow maldistribution on the thermal and electrical performance of a molten carbonate fuel cell unit
(2006-10-27)
Liu, Syu-Fang
;
Chu, Hsin-Sen
;
Yuan, Ping
;
機械工程學系
;
Department of Mechanical Engineering
This study investigates the temperature and current density distributions in a molten carbonate fuel cell unit when the inlet flows of the anode gas and the cathode gas are mal-distributed in eight patterns. The two-dimensional simultaneous partial differential equations of mass, energy and electrochemistry are solved numerically. The results indicate that the maldistribution of anode and cathode gases dominates the current density field and the cell temperature field, respectively. Moreover, the non-uniform inlet flow slightly affects the mean temperature and mean current density, but worsens the distribution of temperature and current density for most maldistribution patterns. According to the results, the variations of the cell temperature in Pattern G and the current density in Pattern D are 12% and 37% greater than those in the uniform pattern when the deviation of the non-uniform profile is 0.25. Consequently, the effect of non-uniform inlet flow on the temperature and current density distribution on the cell plane is evident, and cannot be neglected. (c) 2006 Elsevier B.V. All rights reserved.
Effects of cathode humidification on the gas-liquid interface location in a PEM fuel cell
(2006-10-27)
Lee, Chun-I
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
This study investigates the location of the gas-liquid interface under various humidity conditions in the cathode gas diffusion layer and the conventional flow field of a polymer electrolyte membrane fuel cell (PEMFC), using commercial computational fluid dynamics (CFDRC) analysis, based on a three-dimensional steady state isothermal model. The effects of the formation of liquid water on the transport of reactant gas are considered in the model. The simulation results indicate that the gas-liquid interface approaches the gas flow channel inlet and the cell performance declines gradually as liquid water obstructs the pores in the porous media as the relative humidity of the cathode is increased. Additionally, the oxygen fraction, the water fraction and the liquid water saturation field along the flow channel are presented. (c) 2006 Elsevier B.V. All rights reserved.
Effects of chlorides on the performance of proton exchange membrane fuel cells
(2011-05-01)
Yan, Wei-Mon
;
Chu, Hsin-Sen
;
Liu, You-Lun
;
Chen, Falin
;
Jang, Jer-Huan
This paper investigates the effects of cathode gases containing chloride ions on the proton exchange membrane fuel cell (PEMFC) performance. Chloride solutions are vaporized using an ultrasonic oscillator and mixed with oxygen/air. The salt concentration of the mixed gas in the cathode is set by varying the concentration of the chloride solution. Five-hour tests show that an increase in the concentration of sodium chloride did not significantly affect the cell performance of the PEMFC. It is found that variations in the concentration of chloride do not show significant influence on the cell performance at low current density operating condition. However, for high current density operating conditions and high calcium chloride concentrations, the chloride ion appears to have a considerable effect on cell performance. Experimental results of 108-h tests indicate that the fuel cell operating with air containing calcium chloride has a performance decay rate of 3.446 mV h(-1) under the operating condition of current density at 1 A/cm(2). From the measurements of the I-V polarization curves, it appears that the presence of calcium chloride in the cathode fuel gas affects the cell performance more than sodium chloride does. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Effects of non-uniform inlet flow on the performance of a molten carbonate fuel cell stack
(2007-06-01)
Liu, Syu-Fang
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
This study develops a quasi-three dimensional numerical method for analyzing three-dimensional temperature and cell voltage distribution in a ten-layer molten carbonate fuel cell. The authors consider the non-uniform profile as progressively increasing along the stacking direction, and assign it to the anode gas inlet or cathode gas inlet to form four kinds of patterns. Results indicate that the non-uniform molar flow rate of cathode gas obviously changes the temperature field of a molten carbonate fuel cell stack, and highest cell temperature occurs at the cathode gas exit in the layer with the lowest molar flow rate. Moreover, non-uniform anode gas in the stacking direction strongly affects cell voltage distribution in the molten carbonate fuel cell stack. Variation rate of average cell temperature and cell voltage among different layers along the stacking direction are 2% and 40%, apparently larger than the variation rate due to non-uniformity in the transverse direction in our previous research.
Effects of temperature on the location of the gas-liquid interface in a PEM fuel cell
(2007-09-27)
Lee, Chun-I
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
The objective of this study is to investigate the location of the gas-liquid interface at various temperatures in a polymer electrolyte membrane fuel cell under non-isothermal conditions. A mathematical model, coupled with the electrochemical process, two-phase flows, species transfer, and heat transfer is employed. A finite volume-based CFD approach is applied to investigate the species transport behavior in a fuel cell. The effects of two model parameters, namely cell temperature (T-cell) and humidification temperature (T-h), on the gas-liquid interface and cell performance are presented. Simulation results indicate that variations of these two parameters influence the location of the gas-liquid interface, the cell performance, and the distribution of liquid water saturation. At lower cell temperatures, the gas-liquid interface moves toward the inlet port of the channel when the humidification temperature is greater than the cell temperature. Therefore, the cell performance decreases as the liquid water clogs the passage for the transport of oxygen. Furthermore, these two factors are closely related to the membrane temperature distribution. Obvious variations in magnitude are seen at a cell temperature of 323 K and a humidification temperature of 343 K. (C) 2007 Elsevier B.V. All rights reserved.
Electrochemical reaction and performance of proton exchange membrane fuel cells with a novel cathode flow channel shape
(2007-04-15)
Chiang, Mu-Sheng
;
Chu, Hsin-Sen
;
Chen, Cha'o-Kuang
;
Jian, Sheng-Rui
;
機械工程學系
This study focuses on the investigation of the electrochemical reaction along a novel cathode flow channel of PEM fuel cells with various shoulder/channel (S/C) ratios at the outlet port. A three-dimensional mathematical model, considering conservation principles of mass, momentum, species and electric current is employed. Local variations of important model variables such as reactant concentration and local current density are presented by contour plots to elucidate the effects of channel geometry on transport process, catalyst reaction and cell performance. The potential fields of solid and membrane phases are also resolved in the cell domain and the driving force of the electrochemical reactions - the catalyst activation overpotential - is harnessed in modeling. Numerical calculations reveal the influence of the cathode channel configuration on the local distributions of various model variables. The results also show the dependence between optimal channel configuration and cell operating condition. At a medium reaction rate, the reaction sites underneath the shoulder region generate more current than the channel region. Therefore, a convergent channel configuration with a larger S/C ratio at the outlet port develops more current because such a design facilitates the electron transport and enhances local activation overpotential. However, as the cell voltage decreases and the reaction rate increases, such configuration loses its merit gradually as the requirement for a higher reactant concentration is more important and the reaction sites underneath the channel region have a higher reaction rate. Consequently, the divergent channel configuration with a lower S/C ratio of 0.67 perfonns better at a cell voltage of 0.22 V (c) 2007 Elsevier B.V. All rights reserved.
Numerical investigation of transport component design effect on a proton exchange membrane fuel cell
(2006-09-29)
Chiang, Mu-Sheng
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
A numerical investigation of the transport phenomena and performance of a proton exchange membrane fuel cell (PEMFC) with various design parameters of the transport component is presented. A three-dimensional fuel cell model, incorporating conservations of species, momentum, as well as current transport, is used. The Bulter-Volmer equation that describes the electrochemical reaction in the catalyst layer is introduced; the activation overpotential connects the solid phase potential field to that of the electrolyte phase. Through cell performance simulation with various channel aspect ratios and gas diffusion layer (GDL) thicknesses, a slender channel is found suitable for cells operating at moderate reaction rate, and a flat channel produces more current at low cell voltage. Plots of transverse oxygen concentration and phase potential variation indicate that these oppositely affect the local current density pattern. The relative strengths of these two factors depend on the transport component position and geometry, as well as on the cell operating conditions. Consequently, the curves of cell output current density demonstrate that the optimal GDL thickness increases as the cell voltage decreases. However, at the lowest considered cell voltage of 0.14 V optimal thickness decreases as that of a thick GDL. The oxygen deficiency caused by long traveling length and clogging effect of liquid water reverses this relationship. (c) 2006 Elsevier B.V. All rights reserved.
Numerical study of heat and mass transfer in a plate methanol steam micro reformer with methanol catalytic combustor
(2010-06-01)
Hsueh, Ching-Yi
;
Chu, Hsin-Sen
;
Yan, Wei-Mon
;
Chen, Chiun-Hsun
;
機械工程學系
A numerical study is performed to examine the characteristics of heat and mass transfer and the performance of a plate methanol steam micro reformer with a methanol catalytic combustor. The effects of the flow configurations for co- and counter-current flows are explored in the present study. The influences of the Reynolds number (Re) and various geometric parameters on heat and mass transfer phenomena in the channels are also investigated numerically. It is expected that the Reynolds number (Re) and various geometric parameters can be improved by thermal management to enhance the chemical reaction and thus augment the micro reformer performance. Comparing the co- and counter-current flows via numerical simulation, the results show that the methanol conversion for counter-current flow could be improved by 10%. This is due to the fact that counter-current flow leads to a better thermal management, which in turn improves fuel conversion efficiency. With a higher Reynolds number on the combustor side, the wall temperature is increased and the methanol conversion can thus be enhanced. Meanwhile, a reduced Reynolds number on the micro reformer side would increase the methanol conversion. The results also reveal that appropriate geometric parameters exist for a micro reformer with a combustor to obtain better thermal management and methanol conversion. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Numerical study of heat and mass transfer in the plate methanol steam micro-reformer channels
(2010-08-01)
Hsueh, Ching-Yi
;
Chu, Hsin-Sen
;
Yan, Wei-Mon
;
Chen, Chiun-Hsun
;
Chang, Min-Hsing
Effects of geometric and thermo-fluid parameters on performance and heat and mass transfer phenomena in micro-reformer channels were investigated by mathematical modeling. The geometric parameters considered were the channel length, channel height, catalyst thickness and catalyst porosity, while the thermo-fluid parameters included wall temperature, inlet fuel temperature, fuel ratio and Reynolds number. The results of the modeling suggest that the methanol conversion could be improved by 49%-points by increasing the wall temperature from 200 degrees C to 260 degrees C. The results also show that the CO concentration would be reduced from 1.72% to 0.95% with the H(2)O/CH(3)OH molar ratio values ranging from 1.0 to 1.6. The values of parameters that enhance the performance of micro-reformer were identified, such as longer channel length, smaller channel height, thicker catalyst layer, larger catalyst porosity, lower Reynolds number and higher wall temperature. (C) 2010 Elsevier Ltd. All rights reserved.
Numerical study of phonon radiative transfer in porous nanostructures
(2008-07-15)
Li, Sheng-Yen
;
Chu, Hsin-Sen
;
Yan, Wei-Mon
;
機械工程學系
;
Department of Mechanical Engineering
This study analyzes the phonon radiative transfer in two-dimensional porous silicon nanostructures with a phonon transport model based on the Boltzmann transportation equation. We focus on the inter-scattering between pores. The numerical results show that when the aspect ratio is less than 1.22, the scale factor dominates the thermal conductivity, and the thermal conductivity of nanostructures with in-line arrangement pores is determined by the dependent phonon scattering effect. In nanostructures with staggered arrangement pores, the phonons are prevented from transporting through the material. In general, the results show that the larger the pore size, the lower the thermal conductivity of the nanostructure. The results presented in this study provide a useful reference for the development of high-efficiency thermoelectric structures. (C) 2008 Elsevier Ltd. All rights reserved.
Numerical study on micro-reformer performance and local transport phenomena of the plate methanol steam micro-reformer
(2009-02-15)
Hsueh, Ching-Yi
;
Chu, Hsin-Sen
;
Yan, Wei-Mon
;
機械工程學系
;
Department of Mechanical Engineering
The objective of this work is to investigate the transport phenomena and performance of a plate steam methanol micro-reformer. Micro channels of various height and width ratios are numerically analyzed to understand their effects on the reactant gas transport characteristics and micro-reformer performance. In addition, influences of Reynolds number and geometric size of micro channel on methanol conversion of micro-reformer and gas transport phenomena are also explored. The predicted results demonstrated that better performance is noted for a micro channel reformer with lower aspect-ratio micro channel. This is due to the larger the chemical reaction surface area for a lower aspect-ratio channel reformer. It is also found that the methanol conversion decreases with increasing Reynolds number Re. The results also indicate that the smaller micro channel size experiences a better methanol conversion. This is due to the fact that a smaller micro channel has a much more uniform temperature distribution, which in turn, fuel utilization efficiency is improved for a smaller micro channel reformer. (C) 2008 Elsevier B.V. All rights reserved.
Transient analysis of water transport in PEM fuel cells
(2006-11-22)
Yan, Wei-Mon
;
Chu, Hsin-Sen
;
Chen, Jian-Yao
;
Soong, Chyi-Yeou
;
Chen, Falin
This paper theoretically studies the water transport phenomena in PEM fuel cells, mainly investigating the transient behavior in the gas diffusion layer (GDL), catalyst layer (CL) and proton exchange membrane (PEM). In the PEM, both diffusion and electro-osmosis processes are considered, while in the GDL and CL, only diffusion process is taken into account. The process of water uptake is employed to account for the water transport at the interface between the PEM and CL. The results indicate that the water content in the PEM and the time for reaching the steady state in the start-up process are influenced by the humidification constant, k, the humidification, and the thickness of PEM. The rise of the k increases the water content in the membrane and shortens the time for reaching the steady state. Insufficient humidification causes relatively small water content and long steady time. When the PEM is thinner, the water is more uniformly distributed, the water content gets higher, and the time for reaching the steady state is distinctly shorter. (c) 2006 Elsevier B.V. All rights reserved.