| Summary: | 碩士 === 國立成功大學 === 系統及船舶機電工程學系碩博士班 === 95 === This research is to build two-dimensional mathematical models and to conduct experiments, and to analyze the performance of transient condition of the proton exchange membrane fuel cell. In this model the finite element analytic method was used to solve the coupling multiple nonlinear partial differential equations. Equations of the fuel cell contain Brinkman equation describing fluid between the porosity thin film diffusion and the catalyst layers, and charge equation for the electric field response of the two-pole and the exchange membrane. Besides, the Stefan-Maxwell species equation resulted from the mixed diffusion coefficient that the process in the diffusion and catalyst layers needs is used to express specie concentration variations.
The research purpose of this article is to build a model where the flow field uses alternately the counter flow and parallel flow, and to discuss which one fits in this case and has better performance. Then predict the performance of the proton exchange membrane fuel cell in the start-up and the step-up process under different temperatures , pressures and inlet velocities. The concentration and velocity distributions as well as the instantaneous drop of voltage and the cathode and anode electric current and their variations between exchange membrane are also investigated in fuel cell start-up and step-up process. Before the start-up, the electric current is not changed due to the none of entering fuel; when started-up instantaneously, the concentration instantaneously joins. After the start-up, the system was already the stable state condition, and then electric current output is stable.
The main result is that parallel flow can get wetter so as to lengthen the life of the cell, but counter flow can get better performance. The fuel cell operating at the lower temperature(50℃) produces the highest electric current and drop of voltage. If it operated at over 80℃, the PEM of fuel cell might be hurt. The higher the pressure in the inlet and outlet is, the higher the electric current and drop of voltage become. And so is velocity, the higher the velocity in the fuel inlet is, the better performance can be gotten. Above all the result, increasing back pressure is the most obvious influence in start-up and step-up process of PEMFC. It can be an experience on the design a PEMFC in the future.
|
|---|
