Modeling Of Two-phase Ejectors And The Working Characteristics

Increasing attentions are paid to various energy-saving and environmental protection technologies because of the increasing energy demand and higher environmental protection requirements.As a fluid device,the ejectors are free of consuming high-grade mechanical energy to increase the pressure of fluid.They are widely applied to refrigeration systems and heat recovery systems.Liquid-vapor ejectors and vapor-liquid ejectors are known as two-phase ejectors.The liquid-vapor ejector is greatly beneficial to recover expansion work,especially in the transcritical CO₂ refrigeration cycle which is well known as the transcritical CO₂ejectorrefrigeration system.The vapor-liquid ejector is also applied to the small organic Rankine cycle（ORC）to reduce pump power and improve system power generation efficiency.The ejectors are key component in the systems and directly determine the system performance.In this paper,the following aspects of the liquid-vapor ejector and vapor-liquid ejector are studied:Firstly,a liquid-vapor ejector model was established.Based on this model,the efficiencies of each component of liquid-vapor ejector were quantified.The empirical correlations of liquid-vapor efficiencies with respect to operating conditions,entrainment ratio,and pressure ratios are formulated.Moreover,the exergy analysis was used to analyze the liquid-vapor ejector to obtain the optimization potential and order of each component of the liquid-vapor ejector.The advanced exergy analysis indicated that the priority of the component of the liquid-vapor ejector is mixing chamber,the diffuser,and the nozzle.Furthermore,the exergy destructions of each component were studied when changing of working conditions to reveal their sensitivity of influence.The result showed that the liquid-vapor ejector exergy destruction is more sensitive to the isentropic efficiency of the nozzle,comparing to the efficiency of the mixing chamber and the diffuser.Secondly,the vapor-liquid ejector model was also established,and the exergy analysis of vapor-liquid ejector was performed as well.It indicated that the optimization priority of components of the vapor-liquid ejector obtained from the conventional exergy analysis is the same as that obtained from the advanced exergy analysis,which is the mixing chamber,the nozzle,and the diffuser.In addition,exogenous exergy destruction of the nozzle is zero,which means the exogenous destruction exergy is not influenced by the mixing chamber and the efficiency of diffuser.What’s more,the change of the vapor-liquid ejector exergy destruction with the temperature of the primary flow was analyzed.The result suggested that the vapor-liquid ejector has the largest exergy destruction,so the state of the primary fluid should be adjusted during the design and operation of vapor-liquid ejector.Finally,a vapor-liquid ejector test bench was designed,and a vapor-liquid ejector model was designed and manufactured.According to the designed test conditions of test bench,theoretical calculation was carried out and the devices were selected,and the vapor-liquid ejector experimental test bench has been built.Based on the characteristics,the data acquisition was compiled using MATLAB,which was able to read and display the real-time measured temperature,pressure and mass flow rate.It also could monitor the states of the working fluid by Refprop.The stable observation of the experimental working conditions and system adjustment were completed.Up to now,testing of the test bench,pressure holding,charging of the working medium and trial operation were carried out.