Separate Reactant and Cooling Air

The need to separate the reactant air and the cooling air for anything but the smallest of PEM fuel cells can be shown by working through a specific example where the reactant gas and the cooling gas are combined. 

In Appendix 2, Section A2.6, it is shown that the heat generated by a fuel cell, if the water exits as a vapour, is 

Just 40% of this heat is removed by air, of specific heat capacity Cp flowing at a rate of m kg s and subject to a temperature change AT. So we can say that 

Substituting known values, that is, Cp = 1004 J kg K, AT = 30 K, and Vc = 0.6 V, and rearranging, we obtain the following equation for the cooling air flow rate  

If the reactant air and the cooling air are one and the same, then these two quantities are equal, and so the two equations can be equated. Cancelling Pe, substituting = 0.6 V, and solving for k we obtain 

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Figure 4.16 Three cells from a stack, with the bipolar plate modified for air cooling using separate reactant and cooling air.

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