Weight analysis on geometric parameters of ejector under high back pressure condition of SOFC recirculation system

Abstract

With advantages of no parasitic energy consumption, small size, and low noise, ejector is a promising choice for the solid oxide fuel cell (SOFC) anode gas recirculation system. However, it is difficult to design an ejector with good performance under the high back pressure condition of the SOFC system. In this paper, weight analysis on key geometric parameters of ejector is carried out based on the result of an experimentally validated ejector simulation model. Four main geometric parameters that have the most significant effect on ejector performance, namely the ejector diameter ratio (Dr), mixing chamber length (Lm), diffuser length (Ld), and nozzle outlet position (NXP), are analyzed in detail. The Dr has a decisive influence on the momentum exchange in the mixing phenomenon between the primary flow and secondary flow in the mixing chamber where the normal shock position changes accordingly. The Lm mainly affects the intensive mixing flow which leads the normal shock to appear prematurely. The Ld should be long enough for boosting back pressure and reducing the effect on the mixing process. The NXP has no effect on the normal shock position. The results show that the critical back pressure increases with the rise of normal shock position and the impact weight of Lm, Ld and NXP can be treated as 21∶10∶1 approximately and the Dr is thought to be a decisive factor. This weight analysis method will be helpful for designing ejectors used in the high back pressure condition of the SOFC anode recirculation system.