Impact of Fuel Utilization on Flow and Reaction Uniformity in a 1 kWe SOFC Stack: A CFD-Based Study

This study presents a high-fidelity, full-scale 3D CFD model to investigate the effects of fuel utilization on flow and reaction uniformity in a 1 kWe planar SOFC stack consisting of 40 unit cells. Unlike conventional studies relying on simplified geometries, this model integrates detailed channel structures, porous media transport, electrochemical reaction kinetics, and radiative heat transfer. Model validation using experimental data shows less than 3.2% deviation, and grid independence is confirmed using the Richardson extrapolation method. A parametric study was conducted across five different fuel utilization (U_f) conditions ranging from 0.3 to 0.7. Results show that higher fuel utilization enhances the electrochemical reaction rate but may induce fuel depletion in downstream regions. At a utilization rate of 0.7 (U_f = 0.7), rapid hydrogen consumption near the inlet causes a shift in thermal hotspots upstream and increases the H₂O molar fraction, resulting in a lower peak temperature than at U_f = 0.6. Furthermore, models that include electrochemical reactions were found to provide a more accurate representation of flow within the stack channels compared to single-phase flow evaluation methods. The production and consumption of chemical species within the channels influence flow uniformity, with differences reaching up to 0.36% at the bottom of the stack and up to 0.72% at the top. These findings offer valuable insights for optimizing SOFC design and operation, contributing to the development of more efficient fuel cell systems.