Multiphysics Modeling and Heat Distribution Study in a Catalytic Microchannel Methanol Steam Reformer

A steady state multiphysics model of a microchannel methanol reformer for hydrogen production was developed and validated to study the effects of catalyst layer structural parameters and heat supply strategies on the reformer performance. The hydrogen generated by the studied reformer was designated for use in high-temperature proton exchange membrane (HT-PEM) fuel cells. The dimensions of the reformer and inlet flow rate of methanol were selected to produce enough hydrogen to feed fuel cells in the 100 to 500 W range. The study considered a 2-dimensional domain for the thin coating of the reforming catalyst to account for the internal diffusion limitations and the coating layer structural parameters. The multicomponent Maxwell-Stefan diffusion equation was implemented to account for diffusion fluxes inside the porous structure of the catalyst. The multiphysics model was validated using the reported experimental data by implementing four different reaction kinetics models of methanol steam reforming. The study considered the best fitted kinetics model to evaluate the performance of the microchannel methanol reformer. The results showed that the Catalyst effectiveness factor was only relatively low at the entrance of the reformer for a catalyst layer thickness greater than 50 mu m. In addition, the study revealed that for efficient use of the catalyst, the effective heat supply strategy should be improved. Additionally, the design feasibility of the segmented catalyst layer to achieve a certain amount of methanol conversion with less catalyst was demonstrated. It was determined, for the same inlet conditions, that the segmented catalyst layer design required 25% less reforming-catalyst to achieve 90% conversion compared to the conventional continuous coating design.