Modeling of Transport Phenomena in Polymer Electrolyte Fuel Cell Stacks: Thermal, Water, and Gas Management

Abstract

The design of a polymer electrolyte fuel cell (PEFC) stack requires careful consideration of the thermal, water, and gas management to ensure high stack performance. This research aims to develop a mathematical and numerical framework for PEFC stacks that serves two main objectives: the first involves the study of the fundamental aspects of the PEFC and the associated transport, electrochemical processes and multiphase flow for both a single cell and stack. The second objective concerns the development and integration of applied research for the PEFC single cell and stack, including new designs and management issues (thermal, gas, and water) to achieve an enhanced fuel cell performance.

A two-phase flow model comprising equations of conservation of mass, momentum, species, charge, phenomenological membrane model and agglomerate catalyst layer model is developed and validated against experimental single cell data in terms of global and local current densities. The model is then extended to account for the environment in a fuel cell stack. Four different thermal management strategies that are commonly used in fuel cell stacks, namely liquid-cooling, forced air-convection cooling, edge-air cooling, and natural convection cooling, are identified and simulated. The results suggest that careful balance has to be struck between stack application, performance, cooling methodology, complexity of the design, size, weight and cost. Furthermore, the model is also extended to account for transient characteristics of PEFC operating with a dead-end anode, where gas and water management are of interest. It is shown that performance deterioration due to hydrogen depletion, water accumulation and nitrogen crossover can be recovered by frequent anode purging. In addition, the model can be used to develop effective and efficient purging strategies.

Finally, it is noted that the thesis provides basic guidelines for fuel cell engineers to design and enhance fuel cell performance.