Numerical Investigations of the Effect of Unsteady Generator Pressure on Supersonic Ejector Performance

Ejector Refrigeration systems (ERS) is experiencing a renewed interest compared to the conventional refrigeration system, owing to the significant reduction in electricity demand and rise in awareness of ozone depletion. The preferred mode of operation which gives maximum entrainment ratio (ER) is choking of both primary and secondary streams at different locations, known as double-choking (critical mode). High values of ER show greater carrying capacity of the motive fluid and hence improved pumping performance. The substantial fluctuating behavior of driving energy for the ejector may force ejector operation away from the narrow range around design conditions and can severely affect the performance of ERS. The present work considers unsteady numerical modeling of a supersonic ejector with generator pressure variations while maintaining constant suction and discharge pressures. The investigation reveals that as the primary stagnation pressure builds, the ejector operation mode transits from single choked to double choked, and ER reaches its optimum at the point of transition. The evolution Fabri-choke, visualization of Fabri-choke, associated complex shock structures, and their relation to ER are discussed in detail.