Analysis for the ejector used as expansion valve in vapor compression refrigeration cycle

• The mixing pressure was determined by using the optimization method.
• Whether the entrained flow would be choked at outlet of suction nozzle was studied.
• Whether a condensation shock would happen at the end of mixing chamber was studied.
• System performance at off-design condition is close to that with optimum ejector.
• No condensation shock happens before the mixed flow flows into the diffuser.

An ejector was used in a compression refrigeration cycle for improving its efficiency. A constant-pressure mixing model was adopted to simulate the ejector. Whether or not the entrained flow would be choked at the outlet of the suction nozzle and whether or not a condensation shock would happen at the end of the mixing chamber were both considered. The effect of the mixing pressure on the performances of the ejector and the hybrid system was evaluated. The mixing pressure was finally determined by using the optimization method. The performances of the ejector and the hybrid system at different operating conditions were studied. Lastly, the performances of the ejector with fixed geometry and the corresponding hybrid system at off-design operating conditions were also theoretically studied. The results indicate that the optimum ejector mixing pressure is a little lower than the entrained fluid's pressure, but far larger than its critical pressure. No condensation shock happens before it flows into the diffuser. The theoretical performances of the hybrid compression refrigeration system with fixed geometry ejector at off-design conditions are very close to that with the optimum geometry ejector.