Browsing by Author "Chang, Shih-Ming"

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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.
Transient behavior of a PEMFC
(2006-10-27)
Chang, Shih-Ming
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
The transient behavior of a proton exchange membrane fuel cell (PEMFC) with porosity is investigated in this study using a two-phase, half-cell model. The thin film agglomerate approach is used to model the catalyst layer. Both vapor transport and liquid water transport in the PEMFC are examined in this study. Proton transport is much faster than the gaseous and liquid water transport. The ionic potential reaches a steady state level in similar to 10(-1) s but liquid water transport takes similar to 10 s. The variation of the ionic potential loss reaches a critical value, decreasing to a steady state, and is not monotonic. The gas diffusion layer (GDL) and the catalyst layer (CL) porosity, which can affect cell performance, have been carefully investigated. The current density rises rapidly within 10(-2) S, then remaining constant. After I s, this is affected by the cell voltage, GDL porosity, and CL porosity, and if the GDL porosity is below 0.4, the current density drops. For the gas diffusion layer porosity, the current density increases between epsilon(GDL) = 0.2 and epsilon(GDL) = 0.5, with increased GDL porosity. For the catalyst layer porosity, the optimum value appears between epsilon(CL) = 0.06 and epsilon(CL) = 0.1 (c) 2006 Elsevier B.V. All rights reserved.