| Summary: | 碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 106 === The purpose of this study is to investigate the effect of bolt pre-loading variation (5-20MPa) on the efficiency of PEMFC (Proton Exchange Membrane Fuel Cell). In this work, the value of contact resistance and porosity of GDL (Gas Diffusion Layer) are the important factors to judge performance. A 3D FEM (Finite Element Method) model of a complete PEMFC stack was developed incorporated with the commercial software ANSYS 15.0. This stack consisted of one to four cells, and then explored the effect of bolt pre-loading variation on the efficiency of PEMFC with the electrochemical simulation Fluent 15.0.
The PEMFC module with an active area of 9cm^2 were composed of end plates, current collectors, bipolar plates, membrane, catalyst layer, and gas diffusion layer. And a PEMFC stack was assembled from a number of repeated units of membrane electrolyte assembly (MEAs) and bipolar plates. All elements were fixed by 8 pairs of bolts and nuts. The fixed nuts and bolts were pre-tensioned by the ANSYS built-in function. From the results of analysis, both contact resistance and porosity of GDL were decreased with the increasing of bolt pre-loading. In a 1-4cell PEMFC, the contact resistance was decreased 61.07%. The decreasing of contact resistance can lead to the ohmic losses and the increase of efficiency for PEMFC. However, the porosity was decreased 18.84%. The decrease of porosity of GDL will lead to the increase of resistance of permeability and result in the reduction of efficiency for PEMFC. The power density of the 1-4cell module was increased by 21.1% while the bolt pre-loading increasing. It is found that the bolt pre-loading of 10MPa is an optimal value for each fuel cell system. Then, we not only get the best conductivity, but also increase the gas transmission resistance. That provides the combination of low contact resistance and good porosity can obtain the maximum power density.
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