Additional volumetric sources in the thermal energy equation are present because not all chemical energy released in the electrochemical reactions can be converted to electrical work due to phase changes and irreversibilities of the processes. Volumetric heat source terms in various zones are listed in Table 20.1: Volumetric Heat Source Terms ([586]).

In this table, and are the magnitude of the solid phase and membrane phase current density, respectively, and = -2.263e6 J/kg is the latent heat due to water condensation.