Page 151 - Introduction to Transfer Phenomena in PEM Fuel Cells

140 Introduction to Transfer Phenomena in PEM Fuel Cells
Yu et al. [YU 09] assessed the design of four Multi-Pass Serpentine
Flow-Fields (MPSFF) with two configurations: coil or conventional spiral
for the cooling plates of PEM fuel cells. They used the IUT criterion to
compare configurations, as previously defined by Chen et al. [CHE 03].
They compared the configurations with the maximum surface temperature
and with the difference in surface temperature (maximum and minimum).
With regard to the geometry, they preferred symmetrical geometries to
reduce the number of nodes in their simulations, thereby limiting the use of
the same heat flow values on both sides of the cooling plate.

Three different uniform heat flux values are used in the simulation to
cover the normal operating range of the PEM fuel cell. The velocity is
introduced as a boundary condition at the entrance of the channel. Their
results suggest that the IUT decreases and the pressure loss increases as the
Reynolds number increases in the six configurations.
The MPSFF design is motivated by the study of Xu et al. [XU 07] for
flow field structures of PEM fuel cell reactants, which is based on the
reforming of a single serpentine flow field, such that the pressure difference
between the adjacent flow channels improves the flow through the porous
electrode, as an interdigital flow field.

First, it is necessary to know the spatial distribution and the intensity of
the heat sources. There are three types of heat produced in a PEMFC in
operation: the heat due to the electrochemical reaction, the heat due to the
passage of the current (Joule effect) and the heat due to water phase changes
[COL 08].

4.5.1. In the polymer membrane

At the membrane level, the Joule effect is caused by proton transfer
resistance. It should be noted that the calculated resistance is that of the
membrane as a whole. The variations in conductivity in the thickness of the
membrane are neglected, and the heat source associated with the Joule effect
is uniformly distributed in its thickness. This volume density of heat flow
–3
( q  ), expressed in [W.m ] [RAM 09], is written as:
J
R ⋅ j²
q = m [4.26]

J
e m