An investigation of the transient performance characteristics of proton exchange membrane fuel cells (PEMFC) undergoing load change and during above freezing low-temperature start-ups are presented. A transient, non-isothermal, three dimensional, single phase computational fluid dynamics based model is developed to describe the transient processes of a PEMFC with conventional channels in co-flow configuration. The model equations are solved using a multi-domain approach incorporating water transport through membrane and multi-component species transport through porous diffusion layer. The dynamic response of the characteristic parameters such as membrane hydration, species concentration, cell voltage and temperature are simulated undergoing step changes in operating current density and also during start up and the results are discussed in detail. Accumulation of water in the polymer electrolyte seems to control the response time for load response and also start-up times along with the temperature of the cell. Steady state and transient simulations are compared. Steady state predictions are compared with benchmark experimental data from literature and the species concentration distributions were found to be in good agreement.

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