Environmental Engineering Reference
In-Depth Information
Fig. 6.19 Acquisition versus
time of C
v
and hydrogen rel-
ative pressure at anode inlet
for the experiment of
Fig.
6.18
Fig. 6.20 Correlation dia-
gram between stack power
and temperature after 1 h
steady-state tests
maintained with the purge strategy described above (see
Sect. 6.3
), at least for
temperatures up to 325 K (800 s), while for higher temperatures a slow and
progressive increase of the coefficient of variation is observed from 2 to 4%. Over
800 s, the progressive increase of membrane electric resistance, due to its dehy-
dration, evidenced the necessity for the stack of external humidification already
from 325 K in steady-state conditions at 1.2 kW. After this temperature, the
humidification technique previously described is adopted, but this does not result
in C
v
diminution (Fig.
6.19
) while the more evident effect of purge confirmed the
lasting phenomenon of membrane dehydration.
The results of Figs.
6.11
,
6.12
,
6.13
,
6.14
,
6.15
,
6.16
,
6.17
,
6.18
, and
6.19
evidence that water management in a PEM fuel cell system has to be accurately
optimized with strategies depending on stack power and temperature, for prede-
fined values of stoichiometric ratio. The results of Fig.
6.20
and Table
6.5
, which
refer to 20 different steady-state experiments of about 1 h, can be used to analyze
