A quasi-2D dynamic multiphase model of cold start process in proton exchange membrane fuel cell 2019-01-0390
It’s well acknowledged that startup of proton exchange membrane fuel cells (PEMFCs) at subzero temperatures is attracting numerous attention since it is of vital importance to successful commercialization. More efficient numerical or analytical model needs to be developed to forecast water and temperature distribution in real time. Among various models, the quasi-2D transient multiphase model of cold start stands out for its further consideration of mass transport along flow channel compared with one-dimensional models and less amount of calculation in contrast to three-dimensional models. In the study, conservation equations of energy, membrane water, ice, liquid water, species and electrochemical reactions are all solved. The distribution of physical parameters such as local current density (LCD) and temperature can be predicted during cold start process within minutes of simulation. More specifically, two different hydrogen supply modes are studied in detail: the flow-through-anode (FTA) mode and the off-gas-recirculation (OGR) mode. It is found that LCD decreases in the flow direction during the cold start process below freezing point in both modes, but the distribution of LCD is reverse when cell’s temperature rises above freezing point. Meanwhile, the LCDs are more concentrated in OGR mode than those in FTA mode owing to self-humidification effect, and this also leads to less ohmic loss and higher output voltage. But it should be noted that more water is remained in the OGR mode which results in more slowly temperature rising during the cold start. Compared with the FTA mode, characteristics of the OGR mode can be summarized as better current density distribution uniformity, higher energy usage ratio and longer startup time.