燃料電池性能及水傳輸之模擬分析

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/2749

Title:	燃料電池性能及水傳輸之模擬分析
Authors:	江炫毅;Hsuan-Yi Chiang
Contributors:	機械工程研究所
Keywords:	孔隙率;接觸角;滲透率;微孔層;燃料電池;兩相流;二維;porosity;permeability;contact angle;fuel cell;two phase flow;micro porous layer
Date:	2006-06-29
Issue Date:	2009-09-21 11:54:42 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	摘要本文主要藉由兩相流理論，建立PEMFC燃料電池二維，穩態及等溫的單電池模型，討論陰極支撐層(Backing layer: 包含氣體擴散層(GDL)與微孔層(MPL))及催化層(CL)兩部分建立其數學模型及邊界條件，探討不同區域所產生的源項和改變操作條件及性能特性對電池性能的影響。陰極支撐層是以多成分模式考慮、主要成分有氮氣、氧氣、水汽與生成之液態水，討論氧氣、水汽與液態水在多孔介質中的分布。支撐層中的微孔層是一有細緻孔洞的多孔介質薄層，藉由微孔層的細緻孔洞，可防止催化層中觸媒掉落與減少催化層與氣體擴散層之間的接觸阻抗，另外可以將催化層所產生的液態水細化成小水珠以利於排除。本文中，藉由兩相流模型與理論，考慮氣體擴散層與微孔層之孔隙率、滲透率與接觸角以及氣體擴散層因擠壓而產生不同厚度的條件下，對液態水生成情況與電池性能的影響。催化層則是討論電化學反應中氧氣的傳遞以及產生之電流密度與液態水的分布情況，電化學反應是用Bulter-Volmer方程式來描述。研究結果顯示水汽與液態水之蒸發與凝結效應對燃料電池性能與液態水生成皆有顯著的影響。氣體與液體之間拖曳力則會使液態水的移動速度降低，造成液態水在催化層與氣體擴散層中堆積使電池性能下降。然而在考慮不同接觸角時，在氣體擴散層擁有較大與較小接觸角，其對於液態水皆有較佳的排除能力，因此可獲得較佳的電池性能。本研究最後探討氣體擴散層受擠壓的區域中孔隙率與滲透率變化的影響。當孔隙率與滲透率因受擠壓而變小會迫使部分原本經由受擠壓的氣體擴散層至出口的氧氣改經由催化層到達出口，而使得燃料電池有較佳的氧氣利用效率及較好的性能。 Abstract In this study, a two-dimensional, steady, and isothermal single cell model for a PEM fuel cell is established using a two phase flow theory. Backing layer, including gas diffusion layer (GDL) and micro porous layer (MPL), and catalyst layer (CL) are discussed to build the mathematical model with boundary conditions. Effects of various source terms, operating conditions, and properties on the performance of fuel cells are discussed. The fluid in the backing layer is composed of nitrogen, oxygen, steam, and liquid water. Their distributions are presented and discussed. The MPL can prevent the catalysts from falling into the GDL and con reduce the interface resistance between the MPL and GDL due to their fine pores. The liquid water can be more easily drawn out of the CL due to the enhanced capillary force at the interface. The effects of the porosity, the permeability, and the contact angle of the gas diffusion layer and the micro porous layer are studied. Effects of compressed thickness of the GDL and the above three factors on the production of water and the performance of the fuel cell are studied, The transport of oxygen in the electrochemical reaction, the current density, and the distribution of liquid water in catalysis layer are also investigated. The electrochemical reaction is described by the Bulter-Volmer equation. The results of this study indicate that the evaporation and condensation of water has significant effects on the performance of fuel cells and the production of liquid water. The drag force between the gas and the liquid slows down the speed of liquid water. The accumulated liquid water in the catalyst layer and the gas diffusion layer degrades the performance of the fuel cells. As far the effects of the contact angle, very lag or very small contact angles in the GDL facilitate the removal of liquid water and results in better cell performance. Finally, the effects of the porosity and the permeability of the compressed regions in the GDL are analyses. The influx of oxygen to the CL would change because of the smaller porosity and permeability due to compression. More oxygen is directed to the CL, and the cell performance is there fore enhanced.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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