| With the aggravation of environmental and energy problems,China’s "dual carbon" strategy highlights the importance of energy conservation and emission reduction.At present,the electricity consumption of the refrigeration industry accounts for about 20% of the total electricity consumption in the world,improving the energy utilization rate of the refrigeration system and developing excellent natural working fluids have become the focus of the refrigeration industry.The optimization of refrigeration system mostly focuses on adding auxiliary equipment,developing new technology and optimizing component structure.The throttling expansion process of the traditional vapor compression refrigeration cycle has a large loss.As a fluid mechanical device,the ejector has the characteristics of simple structure,reliable operation,and adaptability to two-phase flow,using ejector instead of expansion device to reduce throttling loss is one of the research hotspots.Direct contact condensation heat transfer has the advantages of large heat exchange area,small thermal resistance,high efficiency and small temperature difference heat transfer.The preliminary research results of the research group show that direct contact condensation can improve the performance of the refrigeration cycle.In order to further optimize the direct contact condensation refrigeration cycle,a new type of refrigeration cycle is proposed,which uses natural working fluids R290 and R717 as circulating working fluids,and uses jet ejection combined with direct contact condensation heat transfer.In this paper,based on the assumed working conditions,the thermodynamic model of the system is established by MATLAB for performance analysis,and the effects of state parameters such as evaporation temperature,direct contact condensation temperature,main cycle subcooling and ejector mixing temperature on the performance of system 4E（energy,exergy,exergoeconomic and environment）are explored.At the same time,the performance is compared with the traditional vapor compression refrigeration cycle and direct contact condensation refrigeration cycle.Finally,according to the thermodynamic calculation parameters,the two-phase ejector with working medium R290 is designed and calculated,and the ejector is simulated and verified by CFD simulation software.The main conclusions are as follows:（1）Evaporation temperature,ejector mixing temperature and direct contact condensation temperature have significant effects on COP and exergy efficiency of the system.Among them,the evaporation temperature has a great influence on the COP of the system.When the evaporation temperature increases by 10 ℃,the COP increases by about15%,the exergy efficiency decreases with the increase of the evaporation temperature.The mixing temperature of the ejector has the same effect on the system COP and exergy efficiency,and both increase first and then decrease with the increase of temperature,there is an optimal mixing temperature near the evaporation temperature,which makes the system performance the best.The direct contact condensation temperature has the greatest influence on the exergy efficiency of the system.（2）Compared with the traditional vapor compression refrigeration cycle（cascade refrigeration cycle,vapor compression jet ejector refrigeration cycle）and direct contact condensation refrigeration cycle,the performance of the ejector direct contact condensation refrigeration cycle is significantly improved.Under typical working conditions,the COP is increased by 4.83% and 1.57% compared with the cascade refrigeration system and the vapor compression ejection refrigeration system,respectively,and the COP is increased by about 5.43% compared with the direct contact condensation refrigeration system.（3）The results of exergoeconomic analysis and environmental analysis both show that the auxiliary circulation accounts for most of the system loss and TEWI value,which has a great impact on the overall performance of the system.The application of the development of residual cooling resources such as LNG in the direct contact condensation and refrigeration cycle of ejector has positive significance for the improvement of system performance.（4）The two-dimensional numerical simulation results of the ejector are in good agreement with the theoretical analysis results of the ejector thermodynamics.Under the design condition,the relative average error between the injection coefficient obtained by numerical simulation and the theoretical analysis value is about 13.1%,and the model is reliable. |
