| Nowadays,the rapid economic development inevitably produces increasingly sharp contradictions between energy storage and utilization and environmental protection.Therefore,the refrigeration technology driven by low-grade heat has gradually attracted the attention and research of domestic and foreign scholars.Among them,ejector refrigeration technology has many advantages,such as high efficiency and the simple structure.The core component of the ejector refrigeration system is the ejector.However,the entrainment ratio of the ejector is too low,resulting in the efficiency of the entire system cannot be improved,so the ejector refrigeration is less used in the market.At present,the optimization of the ejector structure mainly includes the optimization of the geometric dimensions of the four parts of the Laval nozzle,the suction chamber,the mixing chamber and the diffuser.In this paper,the maximum entrainment ratio and the key geometry size of the ejector under the given operating parameters is calculated by using the gas dynamic function method.Besides,the shifted Witozinsky curve is used as the flow profile in the contraction section of suction chamber,and the profile designed by the characteristics line method is used as the flow profile in the expansion section to develop the structure of the new ejector.By numerical simulation,the entrainment ratio of the traditional ejector,the ejector that only changes the suction chamber profile,the ejector that only changes the nozzle profile,and the ejector that changes both the suction chamber and the nozzle are compared under different operating parameters.The results of numerical simulation show that the improved suction chamber profile improves the flow velocity of the secondary fluid at the entrance of the mixing section,and the improved nozzle expansion profile makes use of the isentrophic expansion principle to make the flow field of the primary fluid and the secondary fluid more uniform and stable at the entrance of the mixing section and reduces the mixing loss.In order to verify the accuracy of numerical simulation,an ejector with the shifted Witozinsky curve is designed in this paper,and the performance of the ejector under different operating parameters is studied by using the ejector performance experimental equipment.The experimental results show that: the entrainment ratio increases with the increase of the secondary fluid and the primary fluid pressure,and decreases with the increase of mixing fluid pressure.The results of numerical simulation is quite qualified to predict the actual conditions of the ejector.The performance of the ejector with the shifted Witozinsky curve is better under off-design conditions. |
