Shape optimization and flow irreversibility mechanism analysis of normal temperature, high temperature and wet stream ejectors

Fuel recirculation ejector performance greatly impacts the safety and stability of fuel cell stack. In this study, we developed two shape optimization methods (parametric and non -parametric) for ejectors based on a quasi -twodimensional ejector model and surrogate optimization algorithm. This approach allows for high -efficiency coupled optimization of all structural parameters of an ejector. Furthermore, non -parametric optimization, without the limitation of structural parameters, can directly optimize the ejector shape. The performances of the basic, parametrically optimized, and non -parametrically optimized ejectors were experimentally tested under room temperature, high -temperature, and wet secondary flow conditions, and compared with the those of ejectors in previous studies. The distributions of flow parameters inside each ejector were obtained and the mechanisms by which the performance of the optimized ejector was enhanced were analyzed from the perspective of flow irreversibility. The results showed that optimized ejectors outperformed the basic ejector under most operating conditions and that the non -parametrically optimized ejector had the best performance. Compared with the basic ejector, the pressure lifting capacities of the optimized ejectors doubled under both room and high -temperature conditions at entrainment ratio of six, which is the best result reported so far. We also found that irreversible losses, such as losses in fluid friction and shock wave, as well as viscous dissipation inside ejectors were the main factors affecting their performance. The optimization methods proposed here can be utilized for the optimal design of ejectors and even other equipment in other fields.