
220 Fuel Cells
The friction for laminar ow in a circular channel is given by
f
=
. The
friction factor for a rectangular channel depends on the aspect ratio, b/a. For
example, it varies from
for an aspect ratio of b/a = 1 to
for an aspect ratio of b/a = ∞. A correlation of
D
for laminar ow in
a rectangular channel is given as
fRe
b
a
b
a
D
H
=−
+
−24 113553 1 9467 1 7012
2
.. .
bb
a
b
a
b
a
+
−
345
0 9564 0 2537
(6.9)
As we have mentioned before, the pressure drop in the reactant gas ow
channels plays a critical role in the operation and performance of a fuel cell.
The higher the pressure ...