Environmental Engineering Reference
In-Depth Information
which allows the reaching during the stationary phase of the cycle R values similar
to those obtained with the management strategy N.4. During this test, the output
cathode temperature is maintained constant at 315 K, with 303 K and 100% of
relative humidity at the inlet. In Fig.
7.47
a, the voltage profile reaches the mini-
mum value of about 48 V at the end of the acceleration step, with a partial
recovery up to 51 V at the end of steady state phase. This behavior shows a stack
working irregularity, not evidenced by the R profile reported in Fig.
7.47
b, which
follows the values reported in Fig.
7.40
.
The utilization of the management strategy N.1 provides the results shown in
Fig.
7.48
(same thermal management of Figs.
7.43
,
7.44
, and
7.47
), in particular
stack voltage does not decrease under 53 V maintaining this value almost constant
during the stationary phase, while R follows the values expected by Fig.
7.40
and
reaches about 2.5 at 160 A. The difference in stack performance observed between
the management strategies N.1 and 2 is confirmed by the C
v
values reported in
Fig.
7.49
, which evidences that the statistical indicator of cell voltage regularity
does not reach the value 2.5 for the highest flow rate (33 Nm
3
/h) while it over-
comes the value 3.5 for 24 Nm
3
/h at the end of the acceleration phase. This
confirms that during the fastest dynamic phases the necessity to preserve stack
Fig. 7.48 a Stack voltage
and current acquisition versus
time during the dynamic
cycle characterized by the
maximum stack current vari-
ation of 50 A/s. Air manage-
ment strategy N.1.
b Stoichiometric ratio and air
flow rate acquisition versus
time for the experiment of (a)
a
80
250
Stack Current
Stack Voltage
75
200
70
150
65
100
60
50
55
50
0
0
10
20
30
40
50
60
Time [s]
b
40
5
38
4
36
3
34
2
32
Stoichiometric Ratio
Air Flow Rate
1
30
0
0
10
20
30
40
50
60
Time [s]