Designing a hydrogen gas ejector for 5 kW stationary PEMFC system – CFD-modeling and experimental validation

Abstract

Ejectors are durable and inexpensive equipment for realizing hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems. In the present work, a hydrogen recirculation ejector targeted for high turndown ratio operation in a 5 kWe PEMFC system was designed, manufactured with 3D-printing, and characterized experimentally with both air and humid hydrogen.The ejector was modeled at the experimental conditions with computational fluid dynamics (CFD) assuming 2D axisymmetric flow and with three turbulence models. A systematic comparison of experimental and simulation results was conducted with humid hydrogen at conditions covering the entire operating map up to 6 bar gauge primary pressure. The simulation results deviate on average 60%–70% from the experimental results, the deviation being less pronounced at conditions relevant in PEMFC applications.The SST k-ω turbulence model was identified to agree best overall with the experimental data while the RNG and Realizable k-ε turbulence models were observed to accurately predict the position of maximum ejector efficiency. Hence, the SST k-ω model is more useful for predicting ejector performance while one of the two k-ε models should be adopted when optimizing ejector design.