Comparative numerical analysis of solid oxide fuel cell stacks using internal and external manifolds

A comprehensive numerical study evaluates the performance of a solid oxide fuel cell (SOFC) stack with various manifold configurations using a multi-scale model. The model solves coupled transport equations across different stack domains and is validated using experimental data from a 1 kW SOFC stack. The analysis examines reactant concentration, current density, and temperature distributions across three configurations: internal, external, and a newly proposed modified external manifold designed to improve inlet flow uniformity across individual cells within the stack. Results indicate the modified design significantly improves reactant distribution, reducing hydrogen and oxygen flow maldistribution by nearly 19% and 28%, respectively, compared to the internal design. Consequently, in the critical topmost cell, the active area operating above the nominal 70% fuel utilization decreases from 65% in the internal manifold case to less than 1% in the modified design. This contributes to a 52% reduction in current density variation, a 12% decrease in the solid temperature gradient, and a 14% reduction in cooling airflow requirements. These enhancements lead to more uniform electrochemical behavior and thermal operating conditions. In particular, the modified design improves efficiency by enabling higher voltage output at elevated load currents, while simultaneously enhancing durability through a more uniform current density distribution.