Transient Analysis of Current Density and Water Distribution on PEM Fuel Cell
Date Issued
2004
Date
2004
Author(s)
Hsin, Ming-Jen
DOI
zh-TW
Abstract
It is well known that proper water management inside a proton exchange membrane fuel cell is essential for obtaining good performance. Insufficient water lowers the conductivity of the membrane and causes high internal resistance whereas excess water leads to flooding of the electrode and decreases reaction area. However, water management is quite difficult because it is not easy to be observed directly.
The experiment set up demonstrates a new method of measuring current distribution and water distribution in a specially designed single fuel cell, using a transparent flow field plate and segmented gold foil current collectors. Each segment was electronically insulated from the neighboring compartments. With current multiplex method, current distribution was measured by shunts connected to the corresponding segments. Furthermore, image of water formed inside the cathode and anode are presented to explain the phenomenon of water flooding in the gas channels. This approach provides a useful tool for investigating different flow field designs and for optimizing utilization of the active electrode area with the most appropriate reactant stoichiometries and humidification conditions.
The results reveal that the water distribution propagates from outlet to inlet at cathode side and dry effect propagates from inlet to outlet. Water condensed from small droplet to swelled droplet and then clogged channels. Water molecules were carried by electro-osmotic drag near inlet areas and back diffusion phenomenon is growing vigorously near outlet. High stoichiometry causes inlet area to dry out and less water holdup than operating in low stoichiometry. Performance loss occurs at elevated temperature near inlet and water condenses more easily than low temperature condition. Under less humidification conditions, segment performance increases as distance from the gas inlet increases, indicating external humidification of the hydrogen increases performance. Furthermore, back flow occurs at gas outlet of multi-channels and leads to more flooding areas that decrease the performance.
Single serpentine has a characteristic of draining out water fluid. The current density varies more steeply between neighboring area of tri-serpentine flow type. Parallel-serpentine gets better performance of these three flow type, but it’s easy to be clogged by water fluid in last two channels. The optimum operating conditions for the studied cell are around 55°C and 50 ml/min with hydrogen humidification.
Subjects
燃料電池
水管理
電流密度
水分佈
暫態分析
Water distribution
Fuel cell
water management
Current density
Transient analysis
Type
thesis
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