Page 136 - Introduction to Transfer Phenomena in PEM Fuel Cells

4

Heat Transfer Phenomena

4.1. Introduction

Understanding heat transfer phenomena within a fuel cell is essential in
order to optimize its performance and contribute to its sustainability. The
heat released from a PEMFC is relative to the electrical energy delivered by
the battery itself. This generation of energy (heat) comes from the heat
released in the irreversible electrochemical reaction (~55%), entropic heat
(~35%) and the heat released by the Joule effect due to the ohmic resistance
of the membrane (~10%).

In a PEMFC, heat is removed through a cooling system or transferred by
conduction and convection at the cell interfaces.

Different modes of heat transfer are observed in the different components
of the PEMFC. Indeed, heat transfer through the membrane is ensured by
thermal conduction, while the conduction and convection are present at the
same time in the catalytic layers (CL) and the diffusion layers (GDL).
However, it should be noted that heat transfer and water transport in a
PEMFC are always coupled: (i) the evaporation and condensation
phenomena are respectively accompanied by the absorption and the latent
heat release; (ii) the transport of water and heat are simultaneous (the
temperature gradient induces the phase change and the transport of water);
(iii) the pressure of the saturating vapor is strongly dependent on temperature
[BOU 07, pp. 149–151].