Optimization of hydrogen recirculation ejector for proton-exchange membrane fuel cells (PEMFC) systems considering non-equilibrium condensation

Abstract

In proton exchange membrane fuel cell (PEMFC) systems, unconsumed hydrogen recirculation is enabled by utilizing an ejector, and the PEMFC system's efficiency is thereby enhanced. Apart from the structural parameters, an ejector's performance is also significantly affected by the non-equilibrium condensation phenomenon. Therefore, the ejector structural parameters' impact upon non-equilibrium condensation intensity and ejector efficiency is investigated under design conditions. Structural optimization of the ejector is performed within its operating range to uphold optimal efficiency in the presence of fluctuations in secondary flow pressure. The result shows that non-equilibrium condensation negatively affects the ejector's efficiency, but its impact diminishes with larger mixing chamber diameters and nozzle divergence angles. The optimized ejector performs best with a 2.40 mm diameter mixing chamber and an 11.0o nozzle divergence angle. On average, the optimized ejector's performance improves by 16.8%, reaching a maximum improvement of 22.8% within the effective operating range.