Theoretical And Experimental Study On A Two-stage Ejection Refrigeration System Driven By Two Heat Sources

Refrigeration technologies play an indispensable role nowadays. With the advent of the energy crisis, more and more attention has been paid on refrigeration methods driven by heat. Ejection refrigeration has its unique advantageous among heat driven refrigeration methods for its simplicity, low cost, and reliability. By the means of ejection refrigeration, a two-stage ejection refrigeration system driven by two heat sources is proposed in this paper. The proposed system can utilize heat sources at different temperatures simultaneously through ejection refrigeration. A circulating pump and a throat valve are used to feed liquid to two generators at different pressures in the proposed system. Through that means, the investment of the device is reduced, higher reliability can be achieved.For the working condition of engine exhaust gas and jacket water waste heat recovery, a theoretical study on the performance of the proposed system was carried out in this paper. The performances of the proposed system as a function of the working conditions have been obtained. The result shows, with an additional low grade heat source applied to drive the high-pressure stage ejector, the proposed system can provide 30% more cooling capacity than the traditional one stage ejection refrigeration system.An ejector with a converging mixing chamber is applied as the low-pressure ejector at design point. We have not seen reports on the determination of the optimum nozzle exit position of ejectors with a converging mixing chamber. In that context, in order to determine the optimum nozzle exit position of the ejectors with converging mixing chamber, a 1-D ejector model has been proposed in this paper.A theoretical study has been carried out, on the performance of ejectors with a converging mixing chamber, as a function of the nozzle exit position. The result shows, at first, the critical entrainment ratio increases with the nozzle exit position; over a certain range, the critical entrainment ratio remains constant. The critical pressure decreases with the increase of the nozzle exit position. Based on the simulation results, the working mechanism inside the ejector as a function of nozzle exit position has been analyzed, and a method has been proposed to determine the optimum nozzle exit position.An ejection refrigeration test rig has been designed and built. Different experimental processes can be realized by switching valves. An ejector with a movable primary nozzle has been designed to validate the proposed 1-D ejector model and optimize the parameters applied in the model. A method to determine the efficiencies has been proposed in this thesis. The simulation results coincide well with the simulation results with an average relative derivation of 3.33%. The optimum nozzle exit position of the low-pressure ejector has been determined through optimized parameters. Experimental studies have been carried out on the performance of the proposed system and the traditional system for comparison. The experimental result shows that the proposed system can effectively utilize heat sources at different temperatures simultaneously. And once again verified the proposed system can provide more cooling capacity than the traditional system by the means of utilizing an extra low grade heat.