Numerical and experimental studies on transport phenomena of proton exchange membrane fuel cells

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 and examine the fluid flow, heat and mass transfer, species transport, electrochemical reaction, and current density distribution as well as to numerically visualize a real-time operation of a PEMFC. Several topics regarding to single fuel cell and fuel cell stack modeling, numerical and experimental visualization of liquid transport in the PEMFC, and model validation are explored in this study:;Secondly, application of the general model concretized in three 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. Those will severely affect the cell performance, especially when the flooding is significant. In addition, in the serpentine PEMFC case, 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 a real-time operation. In the fuel cell 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 and how performance of each single cell impacts on the stack performance.;Finally, an experimental visualization on liquid droplet motion in a PEMFC channel is described. By employing direct optical visualization method into a transparent serpentine-channel fuel cell, 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.;Firstly, 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 computational fluid dynamics (CFD) software package FLUENT R v6.3, with its user-defined functions (UDFs) written in C language in our own.