Abstract

Minichannels in Polymer Electrolyte Membrane Fuel Cells

In this paper, we provide an overview of the application of minichannels, typically on the order of 1 mm hydraulic diameter, in the design of polymer electrolyte membrane (PEM) fuel cells. In these electrochemical devices, minichannels deliver reactant hydrogen and oxygen to the anode and cathode electrodes, respectively, while transporting product water out of the cell. The channels must be designed for low pressure drop, to avoid excessive parasitic power losses from gas handling equipment. However, the channels also need to operate in a flow regime in which the overall water balance in the fuel cell can be maintained. While it is critical that the polymer membrane be sufficiently hydrated to facilitate proton transfer, if liquid water accumulates, a condition of "flooding" occurs wherein excessive transport resistance precludes delivery of reactant gases to catalytic sites. An additional complication in the design of minichannels for fuel cells is that one wall of the channel is comprised of a porous gas diffusion medium, usually made from carbon fiber or cloth. Much of the gas- and liquid-phase mass transport into and out of the channel takes place through this material, and its bulk and surface properties can greatly influence how water is transported along the axis of the channel. The various aspects of minichannel design, including size and cross-sectional shape, surface properties and orientation are discussed, with particular emphasis on fuel cell water management. In addition to reviewing these fundamental aspects of minichannel design, details are also provided on new experimental tools currently under development which are applied to relate channel water transport and accumulation to fuel cell performance.

Brief Bio

Thomas A. Trabold is a Senior Research Engineer at the General Motors Fuel Cell Activities organization in Honeoye Falls, New York. Dr. Trabold completed his Ph.D. in chemical engineering at Clarkson University in 1989. He has conducted research in the areas of impingement heat transfer and evaporation, two-phase flow in ducts and tube bundles, and coating and drying processes. AT GM, Dr. Trabold is currently leading the research effort to understand the fundamentals of water management within polymer electrolyte membrane (PEM) fuel cells, including two-phase transport through minichannels and porous media.