Page 145 - Introduction to Transfer Phenomena in PEM Fuel Cells

134 Introduction to Transfer Phenomena in PEM Fuel Cells
Convective thermal resistance R is written as
1
R = hA s c [4.25]
c
⋅
4.4. Thermal management in a PEMFC
For constant operation, the PEMFC must be maintained at a desired
temperature. The continuous control of the PEMFC temperature is via the
good thermal management of the different flows that exist in the fuel cell.
The evacuation of these flows is essential, and a cooling system must
therefore be considered.

4.4.1. Cooling systems

There are several methods to cool a PEMFC stack. The method chosen
depends on the size and application of the stack. According to Shah
[SHA 03], stacks whose power is < 100 W can be cooled only by the air that
enters the cathode side (considered as a reactant); stacks whose power varies
between 200 W and 2 kW can be cooled by channels separate to those of the
reactants. Stacks whose power is > 10 kW require a cooling liquid. Faghri
[FAG 05] briefly described the problems of thermal transfer in a PEMFC.
Faghri [FAG 08] presented the possibility of integrating a heat pump into the
stack in order to improve its thermal management. In one of his designs, he
proposes to integrate a heat pump in the lower part of the bipolar plates.
Reichler [REI 09] presented a theoretical study on cooling performance
through innovative cooling systems for fuel cell electric vehicles.

4.4.2. Convection cooling of the airflow at the cathode

This is one of the simplest solutions; this method does not require a
complicated architecture or an industrial cooling fluid. This system (see
Figure 4.1) is desirable for small stacks delivering a low power (<100 W).
The heat dissipation is ensured by the flow of air, also considered as a
reactant, in the flow channels on the cathode side. Moreover, this method
does not control the stack temperature; it depends solely on the temperature
and humidity of the surrounding air, hence why the regulation of the stack