Study On The Gas-liquid Ejector And Bi-ejector Refrigeration System

With the improvement of people's living standard, air-conditioner has been more and more popularized. However, mechanical compression refrigerators consume a big quantity of electric power and indirectly make the problem severe, which brings forward a great challenge to the human's sustainable development. Among the various solutions, the utilization of solar energy and other regenerative energy for refrigeration is one of the promising choices. Because of its ability to utilize the low-temperature thermal energy resources, and its simple structure and reliable operation, the ejector refrigeration system has gained much attention.Based on single ejector refrigeration system, a bi-ejector refrigeration system was presented, in which the mechanical pump is replaced by a gas-liquid ejector to bring part of the condensate back to generator. During ideal operation state, the system will not consume electricity absolutely, which is the reason why to study this new-style refrigeration system.(1) In this paper, the study of the performance and characteristics of the gas-liquid ejector, which is a new-added part, is carried out. Physical model and mathematical model for gas-liquid ejector are established, and a soft ware is exploited to analyze the performance and design the structure of gas-liquid ejector using various refrigerants including R11 R12 R13 R14 R134a R22, R114, R500, R502 R717 R123 and R718 etc. The effect of different refrigerant and operating condition is discussed considering entrained ratio and structure design. When water is used as refrigerant, with numerical computation, the numerical result of pressure distribution along axle direction is given. The result shows that entrained ratio is decreased with the increasing of working temperature when gas-liquid ejector is used to lift the pressui'e of liquid.(2) Mathematical expression is induced to explain the utmost working state of gas-liquid ejector. When induced liquid's pressure is known, in order to reach the utmost entrained ratio, the higher the discharged pressure is, the higher the working pressure is needed. As the working pressure is up to some numerical value, lifting working pressure further makes less contribution to the discharged pressure. Thus the utmost entrained ratio decreases with the increasing of the discharged pressure while working pressure and induced liquid's pressure remains unchanged.(3) A design of bi-ejector refrigeration system is presented and analysis model for bi-ejector refrigeration system is established. Based on the study of gas -liquid ejector, a package of software for the performance predicting and structure designing is made. The performances of ejectors and system depend a great deal on the refrigerants as well as operation conditions, which presents reference to choose appropriate refrigerant and working condition for the system. The results show that the COP rises with the increasing generator and evaporator temperature and decreasing of condensate temperature. For R134a, the better operating condition is a condenser temperature lower than 32 and a evaporator temperature higher than 8. The utility effect of solar energy and waste heat by different systems is also discussed, which indicates that bi-ejector refrigeration system is worth to recommend and improve further in utilizing low-staged energy.