Ejector design for PEM fuel cells and assessment of its scalability

Recirculation of the unconsumed anodic gas present in the exhaust stream of Proton Exchange Membrane Fuel Cells (PEMFC) represents a solution frequently used for improving the utilization efficiency of hydrogen. The design of an anodic recirculation system (ARS) can include an ejector that carries the recuperated hydrogen stream directly into the fuel supply line. Compared to pumps, ejectors have no moving parts and do not require power to work, thus increasing the overall efficiency of the cell. On the other hand, they are sensitive to load changes and need an attentive design process. Nozzle diameter and position, convergent and divergent angle, the ratio between nozzle and mixing chamber diameters are several parameters that are usually optimized by trial and error. In this work the development and validation of a 3D CFD model for an ejector to be used on a 5000 W PEMFC was performed. In addition, three new geometries of ejectors to be coupled with 3000 W, 1000 W and 300 W fuel cells were designed. Finally, the scalability and convenience of an ejector for different static power requests were assessed.