Page 140 - Introduction to Transfer Phenomena in PEM Fuel Cells

We can also write an equation based on the enthalpies, those entering will
be the enthalpies of hydrogen, oxygen and water vapor present in these
reactive gases. Heat Transfer Phenomena 129
The enthalpies of the outgoing flows are those of the electrical energy
produced, the unconsumed reactive flows and the heat lost by radiation,
convection or the cooling system. This new equation is written as:
el 
 ( ) = W + ( ) + Q [4.5]
h
h
i in
i out
–1
The enthalpy of a dry gas, or a mixture of dry gas expressed in [J. s ], is
written as:
m c ⋅
h =  ⋅ p T [4.6]

where:
–1
– m  is the mass flow rate of the gas or gas mixture, in [g. s ];
–1
–1
– c is the specific heat, in [J. g .K ].
p
If we take the higher calorific value (HCV) of a gas, we write:
m c ⋅ +
h =  ⋅ ( p T h 0 PCS ) [4.7]

where h 0 PCS is the enthalpy of the gas which corresponds to its HCV at 0°C,
–1
expressed in [J. g ] ; calorific values are usually reported at 25°C, which
means that the HCV needs to be calculated at the desired temperature
[BAR 05, FEL 86]. The enthalpy of liquid water is written as:

=
hm  HO () l c ⋅ p,HO ( ) l T ⋅ [4.8]
2
2
The enthalpy of the water vapor is written as:

=
hm  HO () g c ⋅ p,HO ( ) g ⋅ T h 0 fg [4.9]
+
2
2