Models And Application Of Gas Distribution, Mass Transfer And Electrochemistry In PEM Fuel Cell

Fuel cell has many advantages such as energy transformation efficiency is high and without pollution, which has become the main stream of the fuel cell study. The scholars at home and abroad have done a great deal of investigation from every aspect in order to improve the performance of PEM fuel cell.This paper discusses the modeling and optimization of the distribution uniformity of fuel cell stack cathode gas and effects of the single cell cathode porosity distribution of gas diffusion layer on the cell performance, and states the problems about the energy transfer of the cell, the basic theory and efficiency of electrochemistry.At first, this paper simplifies a 30kW stack based on the model of the equivalent flow resistance and researched the distribution uniformity of fuel cell stack cathode gas and discusses the factors that influence the distribution uniformity of fuel cell stack, and puts forward several ways of optimization after the study of the further simplified model. The results show that the uneven distribution of the reaction gas in the single cell leads the great differences of the cell performance in different domains of the cell stack; the factors like mass flow rate of the inlet manifold, manifold section area, manifold hydraulic diameter and single cell flow resistance may lead the change of the gas distribution uniformity; through increasing the manifold section area, changing the manifold form and single cell flow resistance, the uniformity of the single cell gas distribution can be improved effectively.Then, this paper researches the effects of the single cell cathode porosity distribution of gas diffusion layer on the cell performance from analytical and statistical point of view. It constitutes the model of linear and nonlinear gradient diffusion layer, the calculated results show that larger the gradient of the linear gradient diffusion layer is, the better the cell performance is, as for the performance of the nonlinear gradient diffusion layer, the parabola is the best, step transition the next, the linear is the last. It establishes the uniform, singular and two kinds of normal distributions models of diffusion layer statistical distribution, the result shows that the more singular the statistical distribution of the cathode gas diffusion layer porosity is, the better the cell performance is, and the more uniform, the worse the cell performance is.Last, this paper analyzes the energy transformation forms of fuel cell process from the perspective of the thermodynamics, the enthalpy change of the response transforms into two forms of energy, the electrical energy and heat energy. It concludes some basic theories and models and simple deducing processes of the fuel cell electrochemistry; it describes some different definitions of fuel cell efficiency and analyses the ways of using the combined heat and power system to improve the fuel cell energy utilization efficiency.