Numerical Study of Fabri-Choking Assisted Secondary-Flow Bypass to Enhance the Entrainment of a Supersonic Ejector

Ejector refrigeration system (ERS) finds extensive industrial applications since it can make use of waster energy. Entrainment ratio (ER), defined as the ratio of mass flow rate of secondary to primary fluid, is the key factor that determines the refrigeration effect of an ERS. The ERS gives maximum ER at double-choked operating condition. That is primary fluid gets choked at the throat of the primary nozzle, whereas the secondary fluid chokes inside the mixing duct at a hypothetical aerodynamic-throat formed by the under-expanded primary-jet. This condition is termed as “Fabri Choking”. The mass flow rate of secondary fluid is restricted by the Fabri-choking. This paper proposes a novel geometrical modification, called secondary-flow bypass, that overcomes the mass flow restriction imposed by Fabric choking. To this effect, a novel bypass configuration for the secondary-flow is utilized, which bypasses the location of Fabri-choke inside the mixing duct. Generally, the static pressure inside the mixing duct increases due to pseudo-shocks. However, it is shown that the formation of Fabri-choke is always associated with a sudden reduction in wall static pressure. Present study numerically investigates the flow through modified geometry. As the secondary-flow choked, the series of shocks occurred in the constant-area duct moved downstream from the flow entrainment region, thereby enhancing the mixing and entrainment. In addition, secondary-fluid injection into the primary-nozzle supersonic flow produces complex shock structures inside the mixing duct. Several bypass configurations were numerically analyzed and found the optimal configuration of the bypass for maximum entrainment.