Numerical Investigation of Flow Uniformity and Local Reactant Utilization in a Vertically Stacked 4 × 1 kW SOFC with U- and Z-Type Pipeline Connections

Solid oxide fuel cell (SOFC) multi-stack systems require well-balanced reactant distribution to ensure stable operation, high efficiency, and long-term reliability. In this work, a 3D CFD framework was constructed for a vertically arranged 4 × 1 kW SOFC multi-stack system to examine the influence of U-type and Z-type manifold configurations on the distribution of mass flow, overall flow uniformity, and local utilization of the reacting gases. The system consists of four 1 kWe-rated planar solid oxide fuel cell stacks, individually rated at 1 kWe and comprising 40-unit cells. Results show that the preferred connection type differs between the cathode and anode sides. At 30% air utilization, the U-type connection provides better cathode-side air distribution, with mass flow uniformities of 0.9485 among the four stacks and 0.91842 among the 160-unit cells, while its local reaction gas utilization rates remain close to the prescribed value of 0.30. In contrast, the Z-type connection shows superior anode-side fuel distribution under all tested fuel utilization rates, with its mass flow uniformity increasing from 0.9740 to 0.9865 as the fuel utilization rate increases from 30% to 80%. At the representative 50% fuel utilization condition, the local reaction gas utilization rates of the Z-type connection are closer to the target value of 0.50 than those of the U-type connection. These findings highlight the greater suitability of the U-type connection for cathode-side reactant supply, whereas the Z-type connection is more effective for anode-side fuel distribution, providing useful guidance for pipeline connection design and flow-field optimization in vertically stacked multi-stack SOFC systems.