Research On Performance Of Two-stage Ejection Refrigeration System With Internal Heat Exchanger

In recent years,with environmental pollution and energy shortages in our country,energy efficiency and environmental protection have been a concern.The conventional compression refrigeration not only consumes a large amount of high-grade energy,but also has the problem of environmental pollution.Therefore,low-grade heat-driven refrigeration cycle systems have received increasing attention.The ejection refrigeration technology is a type of low-grade heat source driven refrigeration,ejection refrigeration technology can use solar energy,waste heat,industrial waste heat,etc.This unique advantage makes it one of the research hotspots of refrigeration technology today.However,the disadvantage of such systems is the low coefficient of performance.In order to improve the performance of injection refrigeration and maintain system stability,this project has improved and perfected the system based on the existing two-stage ejection refrigeration system driven by two heat sources,focusing on the influence of the presence or absence of internal heat exchanger on the performance of the ejection refrigeration system.The main contents of this paper’s research are as follows:(1)The two-stage ejection refrigeration system with single-fluid heat recovery is described,a corresponding thermodynamic calculation model is established,and EES calculation software is used to analyze the effect of internal heat exchanger on a two-stage ejection refrigeration system,and compared with the traditional single-stage non-internal heat ejector refrigeration system,the calculation results show that the internal heat exchanger is added to the system.Compared with the traditional single-stage ejector refrigeration system,the performance of the system can be improved obviously.The change law of the two-stage ejection refrigeration system with internal heat exchanger and the traditional single-stage injection refrigeration system is the same.(2)In order to understand more about the energy use of the two-stage injection refrigeration system with internal heat exchanger,the energy of this system is analyzed.Detailed energy loss calculations are performed on the components of the system using the R236 fa and compared with the conventional single-stage ejection refrigeration system.The calculation results show that the generators and ejectors have the highest total energy losses,accounting for 81.27% of the system energy losses.Followed by the condenser.By determining the weakest link in the system,the available energy of thesystem can be increased,laying the foundation for future energy-saving transformation.(3)Using CFD software,the single-fluid R236 fa is used as the working fluid,and the length of the internal heat exchanger,the inner diameter of the tube,and the gas-liquid distribution method are taken as the research objects,and the casing-type regenerator used in the system is numerically simulated.The whole hexahedron structured mesh is used in mesh generation to improve the quality and accuracy of the calculation.The simulation results show that the length,pipe diameter and gas-liquid distribution of the internal heat exchanger have different effects on the heat transfer effect,which lays a theoretical foundation for the design and selection of the internal heat exchanger.(4)According to the working principle of two-stage ejection refrigeration system with internal heat exchanger,based on the existing two-stage injection refrigeration system,the construction of experimental stage with two-stage ejection refrigeration system is completed by system local transformation and valve change-over,adjustment of installation position of each part and diameter of pipe,etc.The influence of generation temperature,condensing temperature and evaporation temperature on the system performance is analyzed by changing the frequency of the pump and the power of the electric heating and the size of the throttle valve.It is shown that that the COP and the ejection coefficient of the system increase with the increase of the flow and temperature of the generator and evaporator,decreasing with the increase of the condensation temperature,which has good compliance with the theoretical result.