Title

Investigations on proton exchange membrane fuel cells with different configurations and flow fields

Date of Award

1999

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Hongtan Liu, Committee Chair

Abstract

In this study, two mathematical models are developed. The first one is a simple mathematical approach that computes all transport and electrochemical parameters inside the different layers of a fuel cell regardless of its configuration. Through heat and mass transfer analogy, convective mass transfer coefficients at different Reynolds number are determined for both concentric cylindrical and conventional proton exchange membrane (PEM) fuel cells. Concentrations of oxygen and hydrogen are then determined at each layer of the fuel cell using steady-state diffusion analysis. The concentration equations are solved together with the electrochemical equations inside the fuel cell, to obtain the fuel cell voltage and power density. The results from this simple approach compared well with the existing numerical and experimental results. The second mathematical model is to study PEM fuel cell with conventional and non-conventional namely interdigitated flow fields. Through proper handling of the boundary conditions at the gas diffusion/catalyst layer interface, the numerical solution of the model resulted in the profiles of transport and electrochemical parameters in the cathode. Parameters such as pressure distribution, velocity profile, oxygen concentration, molar flux, current density, polarization and overall power density at different cell over-potentials in both flow fields were determined. The results demonstrates the superiority of interdigitated flow field over the conventional type in terms of overall performance and illustrated the importance of the convective term of the species equation in enhancing the reaction rates, leading to a significant improvement in the fuel cell performance. The effects of different parameters, such as cathode porosity, inlet oxygen mole fraction, and operating pressure on fuel cell performance have been studied using this 2-D mathematical model. Finally, a simple efficiency and economical analysis was formulated and implemented on PEM fuel cell with both conventional and interdigitated flow fields. The fuel cell efficiency analysis of both flow fields was determined in terms of first law efficiency. While, the fuel cell economics focused on annual fuel cost, annual capital cost and electricity cost as a function of a fuel cost at selected cell potentials. In addition, a minimum fuel cost to operate the fuel cell is determined in both conventional and interdigitated flow fields based on a nominal electricity cost of 0.08$/kW hr. Finally, a minimum cell cost is calculated in both flow fields based on the fuel cost of 10$/GJ and electricity cost of 0.08$/kW-hr.

Keywords

Engineering, Electronics and Electrical; Engineering, Mechanical; Energy

Link to Full Text

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