Numerical and Experimental Studies on Transport Phenomena of Proton Exchange Membrance Fuel Cells.

摘要

This dissertation presents a novel numerical approach to investigate the water management that is a critical issue in high-performance PEM fuel cell design and optimization. By incorporating the phase change and VOF method to investigate the liquid water transport, a general, three-dimensional, unsteady, multi-phase numerical model has been developed to simulate the fluid flow, heat and mass transfer, species transport, electrochemical reaction, and current density distribution and numerically visualize a real-time operation of a PEMFC. Several topics regarding to the single fuel cell and stack modeling, and experimental visualization are explored: First, the development of a general model of proton exchange membrane fuel cell (PEMFC) is presented. The incorporation of VOF method and fuel cell mathematical model is to investigate liquid water transport in PEMFCs by performing the formation and motion of liquid water in terms of volume-of-fluid. The general model was implemented into the commercial CFD software FLUENT v6.3, with its user-defined functions (UDFs) written in C language in our own. Second, application of the general model concretized in specific cases including a single PEMFC with interdigitated channel, a single PEMFC with serpentine channel and a PEMFC stack is discussed. In the interdigitated PEMFC case, the numerical results show several effects of flooding on the fuel cell performance: the presence of liquid water blocks the gas transport in the fuel cell, resulting in a degradation of local current density. In addition, the possibility of this numerical model approach demonstrates that the formation, motion and removal of liquid water in the channels and porous media can be numerically visualized. In the stack case, by adding liquid water droplets in different single cells in the stack to simulate the flooding phenomenon, the numerical results explain how liquid drops influence physical and transport characteristics of each single cell in the stack. Finally, an experimental visualization on liquid droplet motion in a PEMFC channel is described. The experimental data quantitatively and qualitatively show a good agreement with the numerical results obtained from the VOF model. Again, the success in the model comparison proves the confidence and applicability of the numerical model proposed in this dissertation.