Two-phase pressure drop response during load transients in a PEMFC

Transient behavior of PEM fuel cells can be categorized into electrochemical, thermal and two-phase flows. Overshoot/undershoot behavior has been observed in electrochemical cell voltage during transients, and are attributed to the transition time required for saturation conditions to reestablish. Similar behavior has been reported in two-phase flow pressure drop overshoot/undershoot in a previous work by the authors. In this work, three different temperatures, five ramp rates and four amplitudes of load change were used to investigate the transient two-phase pressure drop behavior. The overshoot/undershoot behavior is observed predominantly at the lower temperature of 40 °C, and is found to decrease at higher cell temperatures. There is a linear increase in the overshoot/undershoot behavior with increase in amplitude of load change. The overshoot/undershoot behavior was found to be independent of the ramp rates used to change the load current. The magnitude of overshoot in pressure drop was always larger than the magnitude of undershoot. The pressure drop required a longer time to return to steady state after an undershoot compared to the time required to return from an overshoot incident.