Dissertation Defenses

Doctoral Dissertation Announcement

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Candidate: Sean Tamarun Goudy

Degree of: Doctor of Philosophy

Department: Mechanical and Aeronautical Engineering

Title: Modeling the Momentum and Mass Transfer within a Micro-Scale Polymer Electrolyte Membrane (PEM) Fuel Cell for Flows within the Slip Flow Regime

Committee:
Dr. Bade Shrestha, Chair
Dr. Iskender Sahin
Dr. Chris Cho
Dr. John Cameron

Date: Tuesday, March 9, 2010 2:00 p.m. - 4:00 p.m.
College of Engineering and Applied Sciences, D-115

Abstract:
Polymer Electrolyte Membrane (PEM) fuel cell systems are heterogeneous catalytic systems. Although there are many computational models that describe the behavior of PEM fuel cells, few simulate the catalyst surface concentration of reactant gases at the catalyst layer-membrane layer interface. In fact, most PEM fuel cell models make no distinction between the bulk concentration of reactants and the catalyst surface concentration of reactants. It is the surface concentration that is key when studying PEM fuel cell systems: the reactions occur at the surface of the catalyst.
Few researchers model the dynamics within the non-continuum flow region near the solid surfaces of the fuel cell. Micro-scale and nanoscale fuel cells are not completely described by continuum mechanics. At the micro-scale and nanoscale, more specialized tools, which account for the increased surface forces and micro length scales, are needed to understand the dynamics of these micro-devices. To address the need of understanding the behavior of micro-scale PEM fuel cells, this model simulates the micro-scale dynamics of a PEM fuel cell within the slip flow regime. This enhanced model simulates the fuel cell performance and improves the fuel cell design by modelling the micro-scale dynamics within a micro-scale PEM fuel cell. Special attention is given to simulating the behavior of each reactant and product near each solid surface. To correct for non-equilibrium behavior near the solid surfaces, slip boundary conditions are used to account for velocity slip.
This analysis models a PEM fuel cell to determine both the bulk reactant concentrations and the catalyst surface concentrations at the catalyst layer-membrane layer interface. The model shows that size has an impact on overall fuel cell performance. The model shows a reduction of the Ohmic losses. The reduction in the Ohmic losses is balanced by an increase in the parasitic losses within the fuel cell. Finally, the model clearly shows that the bulk concentration at the membrane-catalyst layer interface is not zero.