| The flooded evaporator has a better heat transfer performance than dry-type evaporator leading to that it is widely used in large industrial refrigeration systems. Considering the large power consumption of circulating pump in the traditional refrigeration system with the flooded evaporator, the flooded evaporator-ejector refrigeration system is put forward. Due to that the gas-liquid two-phase ejector has a direct and significant effect on the immersion rate and the heat transfer performance of the flooded evaporator, it is of great significance to investigate and optimize the performance of gas-liquid two-phase ejector, especial the entrainment coefficient of the gas-liquid two phase ejectors. With the aim mentioned above the author studies the gas-liquid two-phase ejector with numerical simulation method and the main contents are as follows:(1) A brief research about the large power consumption of circulating pump in the traditional refrigeration system with the flooded evaporator is carried out. And it show that the flooded evaporator-ejector refrigeration system can produce a good energy efficiency and energy saving.(2) The Laval nozzle has a great impact on the performance of gas-liquid two-phase ejectors, so it will lead to a great deviation to design the Laval nozzle without considering the effect of the two-phase flow in the old way. Considering that the gas-liquid two-phase flow is much complicated than single-phase flow in the Laval nozzle, a hypothesis of complete balance about the gas-liquid two-phase flow is put forward to simplify the gas-liquid two-phase flow in the Laval nozzle and to simplify the design method of the Laval nozzle in this paper. And with some experience method, a basic design method for gas-liquid two-phase ejector is completed. Sound velocity value in Laval nozzle can be obtained through the simulation, and the deviation from14.94%-24.42%is obtained by comparing the simulation results with value used in designing the Laval nozzle. With the comparison of sound velocity designed as a single phase flow, the sound velocity designed with the method carried out in this paper is much close to the actual flow velocity for predicting the sound velocity in the Laval nozzle considering the gas-liquid two-phase flow. So the design method for Laval nozzle carried out in this paper can be used as the basic design method.(3) According to the design method, a basic physical model of gas-liquid two-phase ejector with R22as working medium is achieved. And the flow in the gas-liquid two-phase ejector is analyzed. By comparing the important parameter, the void fraction in two-phase flow, the simulation results and experienced value are within11.65%deviation and both of them have the same trend, which verified the accuracy of the two phase flow calculation model.(4) The flow field of the gas-liquid two-phase ejector with R22is analyzed, such as the field about pressure, temperature, density and speed. The processes about mass transfer and phase change between gas phase and liquid phase are analyzed, and the condensation shock caused by gas condensation and shock wave in the gas-liquid two-phase ejector is captured and analyzed, and its basic features are empirical validated.(5) Some simulation results about structures and the working condition of gas-liquid two-phase ejectors have been achieved, and the gotten results of entrainment efficiency of gas-liquid two-phase ejectors are from0.16to1.1, and the simulation results show that the entrainment coefficient has significant relationship with the condensation shock. Adjusting the mix ratio about the structure of mixing chamber can change the occurrence position of condensation shock. On the premise of existing of the condensation shock, the distance from the occurrence position of condensation shock to the export of mixing chamber influences the magnitude of the entrainment coefficient. Within a certain range, the value of entrainment coefficient gets bigger as the distance get smaller. But when the distance is smaller to some extent, the entrainment coefficient is weakly affected by occurrence position of condensation shock. When the back pressure is raised to some extent, the condensation shock will disappear and the entrainment coefficient decreases sharply. |
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