A study of mass transfer characteristics of secondary flows in a tubular solid oxide fuel cell for power density improvement

The low power density has impeded wider adoption of solid oxide fuel cell stacks in powering vehicles and airplanes. The stack power density could be improved by the secondary flow in the radial direction induced by inserts in fuel channels. In this study, we constructed a numerical model to examine the effect of secondary flows on the electrochemical performance of a counter-flow type micro-tubular SOFC with an insert consisting of several humps. We show the secondary flow could enhance the fuel convective mass transfer in the diffusion layer of the porous anode, enabling more fuel to enter the porous anode and more produced steam to leave the reaction layer. This significantly improves the methane reforming and electrochemical reaction rates. We also examined the influence of the geometric parameters of the inserts on the electrochemical performance of the SOFC. We demonstrate that by increasing the insert radius and number of humps, the output power density increases at the expense of higher pumping power requirements. However, the enhanced electrochemical reactions outweigh the demand for pumping power. Our work demonstrates the effectiveness of secondary flows on the SOFC electrochemical performance improvement and helps build a foundation for SOFC channel designs and optimizations. Highlights: The effects of secondary flows on the electrochemical reactions are discussed. The secondary flow in radial direction could improve the SOFC power density. The influence of the insert geometric parameters is analyzed.