Internal mixing mechanism and mixed layer development characteristics of hydrogen recirculation ejector

Abstract

Clarifying the internal flow characteristics and mixing mechanism of ejectors is highly important for improving ejector efficiency and further promoting the wide application of hydrogen fuel cells in various areas, such as ships, distributed power generation and energy storage. The employing of an ejector to recycle excess unreacted hydrogen in PEMFC can significantly improve its efficiency, but the mixed mechanism between the fluids in the ejector is unclear. In this study, a CFD numerical model of an ejector was established, the transport properties between the fluids were investigated, and the mixed mechanism of different fluids was revealed. The growth characteristics and mixed properties of the restricted compressible mixed layer were also elucidated. The results show that the mixing between fluids in the ejector satisfies the mixed mechanism of energy exchange with vortices as carriers. In addition, an adverse pressure gradient can effectively enhance mixing while accelerating vortex dissipation. For the restricted compressible mixed layer, the development can be divided into three stages by the influence of the velocity ratio and Mc. The mixing between the mainstream and the entrainment stream occurs in phases, with local development dominating at first and overall development dominating later.