Page 141 - Introduction to Transfer Phenomena in PEM Fuel Cells

130 Introduction to Transfer Phenomena in PEM Fuel Cells
4.2.2. Energy balance for compounds and gases
The generalized energy balance equation for membrane electrode
assembly (MEA) can be written in the form [FEL 86]:
Q = Q + h ⋅ A ⋅ ( e T f ,av ) h+ a ⋅ A ⋅ ( e T a,av ) [4.10]
T −
T −
f
a
f
s
c
where:
– Q is the heat transmitted by conduction in the solid structure;
c
– Q is the heat source generated by the electrochemical reaction;
s
– h , h are the convective heat transfer coefficient of fuel H 2 (f) and air
f
a
(a);
– A, A are the exchange surface with fuel H 2 (f) and air (a)
a
f
respectively;
– T , T f,av and T a,av are the temperature of the electrode, the fuel and
e
the air respectively.

4.2.3. Energy balance for the gas phase

Temperature gradients in the flow channels are generally assumed to
depend solely on convection due to mass and heat transfer from the channel
walls to the gas [SRI 06]:

1
 nc ⋅ ∂ T g +  c ⋅ n ∂ i ⋅ ( g T s ) h+ g ⋅ B ⋅ ⋅ ( g T s ) = [4.11]
⋅
T −
T −
0
i
p
g
p
i x ∂ i x ∂ a
where:
– B is the ratio between the gas-heat exchange surface and the cell
g
surface;
– T, T are the temperature of the gas and the solid;
s
g