Cody Rath

Abstract

Over the past few decades, polymer electrolyte membrane (PEM) fuel cells have been gaining increased attention as a possible replacement for the internal combustion engine. Fuel cell vehicles are an attractive alternative because of the fact that they can operate without the use of fossil fuels, are more efficient than internal combustion vehicles, and have no harmful emissions with the only byproducts being heat and pure water. Managing this water has been shown to be a key area of research. In order for fuel cells to operate properly, there must be a certain level of hydration present in the membrane; however, too much water can cause the cell to flood, which reduces access of reactants to the reaction sites and consequently the amount of electrochemical reactions. These effects cause a decrease in the overall efficiency and performance of the cell. One specific area of interest that has gained attention recently is the buildup of water in the reactant gas channels. Several works have focused on droplet channel interactions, however many only investigate the droplet growth process, or just the interaction between the droplet and the air cross flow. Few works have investigated the interaction between the growing droplet when it is exposed to a base and channel side which typically have differing surface energies. This issue is addressed in this work at a fundamental level by investigating droplet formation and accumulation in a corner. The work presented here utilizes an ex situ experimental approach that visualizes the dynamics of a water droplet as it emerges from a fibrous material and interacts with a solid side wall surface. A test section is designed and used to characterize the movement of the droplet interfaces as a function of geometry, surface energy, i.e. contact angle, and surface roughness. The governing principle behind the design of this setup is the Concus - Finn Condition and it is proposed here that this condition can be used as a tool for designing channels with improved water management. It has been determined that the local contact angle is a critical parameter when analyzing the behavior of a growing droplet on the surface of a fibrous material as it interacts with the channel side wall. Also, local contact angle values were found to exceed the previously measured contact angles for the surfaces due to the severely strained interface of the droplet over the porous structure. The Concus-Finn condition can be successfully used to determine the behavior of a droplet in a corner based on the local contact angle. A force balance analysis is used to support this finding and to determine the driving forces that cause the droplet behavior.

Library of Congress Subject Headings

Fuel cells--Mechanical properties; Fluid-structure interaction; Surface roughness

Publication Date

1-1-2011

Document Type

Thesis

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Kandlikar, Satish

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: TK2931 .R38 2011

Campus

RIT – Main Campus

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