Numerical Investigation of Compact Flow-Field Designs in Proton Exchange Membrane Fuel Cell Bipolar Plates Using Integrated Flow Rectifiers

Abstract

Bipolar plates (BPs) are crucial components of proton exchange membrane fuel cells (PEMFCs), responsible for reactant distribution, current collection, and water/thermal management. In parallel-channel BP configurations, a header region is required to achieve uniform reactant delivery over the active area, especially at high current densities. However, the header can occupy approximately 30-40% of the BP area, increasing material cost and reducing volumetric power density. Therefore, compact headers with flow rectifiers are investigated in this dissertation to improve flow uniformity, control pressure drop and enhance electrochemical performance. At the flow-field design level, this thesis first investigates GuideVane (GV) structures as flow rectifiers in PEMFC bipolar plate headers. A three-dimensional steady-state CFD model is developed to examine how GV configurations affect Single-Phase reactant distribution in the header and parallel-channel regions. Key parameters, including GV number, gap aspect ratio, obstacle size, and GV arrangement, are evaluated in terms of flow uniformity and pressure-drop behavior. The results show that properly designed GV structures with multi-gap structure can form rectangular Pin-Type flow-rectifying elements, redistributing reactant flow more uniformly across the active area without excessive hydraulic loss. This observation motivates the next stage of the study, where compact headers with equidistant Pin-Type obstacles are investigated. The second part of this thesis extends the study to a three-dimensional computational investigation of compact header designs with integrated flow obstacles in a proton exchange membrane fuel cell bipolar plate. The analysis examined how header size, obstacle geometry, and porous-region characteristics affect reactant distribution, pressure drop, and overall cell performance. A combined performance metric was used to evaluate the trade-off between flow uniformity and hydraulic losses. The results showed that compact headers can improve the effective use of the bipolar plate area and increase apparent power density; however, they also create challenges related to flow maldistribution and pressure loss. The findings further indicated that performance is governed by the coupled interaction between header dimensions, obstacle size, and porosity, rather than by a single parameter. Therefore, compact header designs require strategically placed flow rectifiers to improve reactant distribution while preserving the benefits of reduced inactive plate area. Building on these rectifier studies, two compact header layouts with different flow rectifiers were developed: GuideVane and Pin-Type designs. Both configurations were refined through iterative design optimization to improve flow uniformity while maintaining acceptable pressure loss. The optimized designs were then evaluated using a three-dimensional multiphysics proton exchange membrane fuel cell model under Single-Phase electrochemical operating conditions. This analysis connected header geometry to cell-level performance by examining current-density distribution, species transport, and electrochemical response. Compared with the bare case (without flow rectifiers), both optimized compact headers improved reactant utilization, reduced localized transport limitations, and increased volumetric power density. Under Single-Phase conditions, the GuideVane design showed better overall performance for compact header applications. Finally, the optimized compact-header configurations are examined under Two-Phase operating conditions using coupled Volume of Fluid (VOF) and electrochemical modeling frameworks. This analysis investigates how GV- and Pin-Type rectifier geometries affect liquid-water transport, water accumulation, flooding tendency, pressure drop, and cell performance at high current density. The results show that compact-header geometry strongly influences both reactant delivery and water-removal pathways, offering advantages over larger header designs. The comparison further shows that Pin-Type rectifiers provide stronger water-removal capability by promoting pressure-driven droplet evacuation within the header and flow-field regions. By integrating compact-header design, optimized flow rectifiers, and Two-Phase performance analysis, this thesis lays the groundwork for developing PEMFC bipolar plates with improved flow distribution, enhanced water management, higher volumetric power density, and more reliable operation.