PEM燃料電池薄膜電極組內水分子暫態運動行為研究
Study of Transient Behavior of Water Molecules in Membrane Electrode Assembly of PEM Fuel Cells
Date Issued
2005
Date
2005
Author(s)
Fang, Qi-Fu
DOI
zh-TW
Abstract
The behaviors of the water transport in the proton exchange membrane fuel cells are considered by numerical simulation in this study. The mathematical model includes the gas diffusion layers of the anode and cathode, the catalyst layers of the anode and cathode, and the membrane. The water content distribution in the membrane based on the diffusion of water and electro-osmotic water drag is taken into account. The water concentration distributions in the gas diffusion layers and catalyst layers are only considered the diffusion of water. The volume of membrane is assumed to be changing with the variation of hydration, and this hypothesis can make this model much approach the reality. By using different operational conditions, the water transport transient behaviors are investigated.
Results from the model show that when the water concentrations of relative humidification are insufficient, the water concentration in each layer reduces and the time needed to reach steady state is longer. By using the larger porosity of the gas diffusion layer, it can effectively prevent the anode side of the membrane from being dry, the cathode side of the membrane from flooding. When the thickness of the membrane is thinner, the water content in the membrane is more uniform and higher, and the time needed to reach stable is shorter. Furthermore, increasing the water concentrations of relative humidification, raising the porosity of the gas diffusion layer, and lessening the thickness of the membrane can make membrane resistance and membrane overvoltage lower. From aspect of swell of the membrane, the water content of the membrane has difference distribution at difference operational current densities in the same membrane expansion coefficient, and this phenomenon will not bring about expansion identically in the membrane. If membrane expansion coefficient is so large, that value of water content at the cathode side of the membrane is higher than 16.8, and this means that the situation of the flooding at the cathode side of the membrane will be occurred. The time needed to reach stable when the membrane is expansive is longer than it when the membrane is not expansive.
Subjects
薄膜膨脹
水傳輸
暫態
燃料電池
transient
fuel cell
water transport
membrane swell
Type
thesis
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