Effect of Heat and Mass Transfer and Electrochemistry on Performance in Solid Oxide Fuel Cell Stacks
Most fuel cell modelling at the stack scale to date has focused on either the flow distribution, or electrochemistry, neglecting any coupled effects, due to computational limitations. In this paper, the authors describe the development and application of a novel methodology, whereby diffusion terms in the transport equations are selectively replaced by rate terms. The method leads to improvements in calculation time of two orders of magnitude. The model is applied to solve for mass, momentum, energy, and species transport coupled with electrochemical reactions for solid oxide fuel cell stacks of practical size, employing both internal and external manifolds. Results for flow, species, temperature, voltage, and utilization distributions are analysed to determine the dominant heat and mass transfer effects and their impact on electrochemical performance for a 100-cell stack. After incorporating thermal radiation at external boundaries of a stack, results show reduced temperature and current density near the outer walls leading to an overall decrease in performance. In a further analysis, the transport properties and electrochemistry are selectively uncoupled from the flow distribution to determine the extent of coupling between transport and electrochemistry. It is demonstrated that it would be misleading to attempt to predict performance based on a model with uncoupled transport and electrochemistry.