
245Heat and Mass Transfer in Fuel Cells
absence of any kind of reaction or fuel reforming. Considering the diffusion
ux given by Fick’s law of diffusion, the equation is expressed in terms of mole
concentration as
∂
∂
+
∂
∂
+
∂
∂
+
∂
∂
=
∂
∂
∂
∂
C
t
u
C
x
v
C
y
w
C
z
x
D
C
x
iiii
ij
i
+
∂
∂
∂
∂
+
∂
∂
∂
∂
x
D
C
xx
D
C
x
ij
i
ij
i
,
(6.69)
where the velocity components u, v, and w are computed based on the
Navier–Stokes equation given by Equation 6.15.
6.3.2.2 Mass Species Transport Equation in Electrodes
For the porous electrode–gas diffusion layer with bulk uid motion given by
Darcy or Brinkman’s equation, the governing species transport is given as
=⋅
′′
+
S
()ρ .