watts and was producing 1300 watts. Voltage (V), current (amps), power (watts), air
flow (SLPM), air temperature (C), and stack temperature (C) were all logged every 10
seconds at each of the nine load steps. The voltage and current data collected from each
of the six test runs was used to construct a confidence interval. This confidence interval
was used to ensure any changes in voltages due to contamination were significant.
Constant Load Testing
Contamination effects are easier seen under a constant load. At constant load the
voltage is also constant, and any change in voltage can be attributed to the contamination
effects. It is then necessary to also get baseline performance data on how the fuel cell
performs under constant load over time. Three loads were selected to cover the full range
of the Nexa fuel cell stack. The loads selected were 20, 30 and 40 amps. These currents
best reflect the linear portion of the polarization curve, the part of the curve that is likely
to be affected by the contamination. Six runs, each 45 minutes, for each of the three
loads were completed to again form a confidence interval by which we can compare the
constant load contamination testing.
Contamination Testing
Selected concentrations of contaminants are introduced into the air inlet stream of
the fuel cell by using a mixing manifold constructed from a pitot tube, pressure
transducer, pvc pipe, mass flow controller and a LabView program written to control the
process. The flow rate of the air in the pvc pipe leading to the fuel cell is calculated from
the differential pressure reading from the pitot tube using the formula given below:
FlowRatear (SLPM) = 0.1789 Cf D2 A 4-1
W,