Modeling On Water Removal From Polymer Electrolyte Membrane Fuel Cell During Gas Purging

It is imperative to remove residual water under cold environment for polymerelectrolyte membrane fuel cell (PEMFC) after shutdown in order to prevent waterfrom freezing which will bring negative effect on next start up. Gas purging is amethod to remove residual water. In this study, a three dimensional two-phasetransient model of gas purging during shutdown is developed to investigate thevariation of water distribution and water removal process of (PEMFC). The effects ofoperating condition including temperature and gas flow rate on the drying process areinvestigated. The influence of structure parameters including the depth of channel, thethickness of membrane, porosity and permeability of gas diffusion layer (GDL) on thedrying process of PEMFC are also studied.During gas purging, the water removal rate in cathode (GDL) is larger under ribthan that under channel within the first few seconds. When the water saturation incathode GDL is low enough, the water removal rate of cathode GDL under channelbecomes larger than that under rib. In the anode GDL, the drying process is the samewith the later process of cathode GDL. The initial cell temperature has significanteffect on the water removal during gas purging and high initial cell temperature isbeneficial for water removal. However, the purging gas temperature has littleinfluence on the variation of cell temperature and thus water content of PEMFC. Highgas flow rate is beneficial for drying process of PEMFC, leading to a relativelyuniform water distribution in membrane. But the benefit from accelerate gas flow isless as the gas flow rate further grows up. When the gas flow rate is different in twosides of fuel cell, the difference of drying process in fuel cell is negligible. Thethickness of membrane has a significant effect on the drying process of gas purging.The water removal rate is larger for fuel cell employed with a thinner membrane. Thepermeability of GDL also has a significant effect on the water removal in GDL exceptfor that in membrane. The porosity of GDL has little influence on the variation ofwater content of PEMFC. The results of this study provide valuable reference for fuelcell cold start and control strategy and thus have theoretical significance.