New Method Of Ejectors Optimization Design And Two-Stage Ejector Cooling Systems Performance Analysis

The ejector is a device that can improve pressure of low pressure fluid through high pressure fluid mix with it, which has many advantages such as no moving parts, simple structure and can use low grade waste heat and so on. It has been widely applied in chemical production, vacuum system, ejector refriegation and power system of steamship and rocket. There are many different ejector theories at present, but there is no theories is applicable to all working conditions and the ejector structure design is more rely on empirical formula. In addition, the natural working fluids receive more attention use in ejector refrigeration system at the aspect of the low-grade waste heat recovery as increasing requirements of energy saving and environmental protection. On the basis of these, the main ejecotor theories are comparative analyzed and a new more aoolicable theory is put forward in this paper. Finally, the two-stage ejector cooling systems performance natural working fluids are analyzed in the last chapter.Several main ejector theories in domestic and foreign are pick out to comparative analysis the commons and differents at the aspects of basic assumptions, conservation equations, derivate of mixing process, correct of irreversible process, suitable working fluids and working conditions. The design criteria and develop direction of ejector design theory are pointed. And a 2-D velocity field that can suitable for real gas is put forward and its entrainment ratio in critical and sub-critical are calculated. Compared with the Published experimental data, the 2-D velocity field model agree well in most conditions.The ejector internal will happen irreversible process such as shock wave in the mixing process due to the supersonic flow. The Reasons for the formation of shock wave and influence factors are analyzed. The effect laws of shock wave on ejector performance is get by simulate the ejector fluid field using computational fluid dynamics software Fluent. The relationship between shock wave length and nozzle distance is derived through shock fluid model in non-free space, which provide a theoretical basis for ejector structure design.The two-stage natural working fluid ejector refrigeration systems with rated cooling capacity of lOkW as the research object. The relationship between intermediate pressure allocation ratios and entrainment ratios, total compression ratio, expansion ratio for the two-stage ejectors cascade is studied. The adiabatic exponent is a key factor to affect the optimal allocation ratio. The method to select the ejector structure of two-stage cascade is put forward according to the applicability of ejector with cylindrical and conical mixing chamber. The systems performance using 2-D velocity field model are analyzed when the condensation temperature and evaporation temperature are vary. The relationship between natural working fluids systems performance and condensation temperature and evaporation temperature are summarized.