Investigation On Performance Optimization Of Pump-Free Double Heat Source Ejector Refrigeration System With R1234yf For Ship

With the increasing prosperity of the marine transportation industry,the ocean fishing industry and the number of marine products are developing rapidly.At the same time,the problems of global warming and energy shortage are becoming more and more serious,and the preservation of seafood in the process of ocean fishing has gradually received widespread attention.Therefore,it is of great practical significance to design a marine refrigeration system that can achieve food preservation while reducing energy consumption.Based on this,in order to break through the bottleneck of high energy consumption of marine refrigeration systems and promote the development of ocean fishing industry,this paper proposes a pump-free double heat source ejector refrigeration system based on ship waste heat and optimizes its performance.Firstly,this paper presents a detailed introduction on the traditional ejector refrigeration system and the pump-free double heat source ejector refrigeration system,and the operating fluid of the system is determined.At the same time,the components of the two systems are thermodynamically modeled and then the models are performed verification.The results show that:The main difference between the two systems is that there is a gas-liquid ejector driven by a specific heat source in the new system to replace the mechanical pump of the traditional ejector refrigeration system,which can realize the pump-free operation of the ejector refrigeration system and the application of heat sources in different temperature ranges.Compared the physical properties with some several commonly used refrigerants,the new refrigerant R1234yf is determined as the operating fluid of the system.It has been verified that the errors between the results acquired by the thermodynamic model and the experimental method are within the allowable range,as a result,the thermodynamic model established in this paper can be used for system performance prediction.Then,the operating conditions of the system are determined.At the same time,the effects of operating conditions on the ejector and system performance are studied,and then the performance of the two systems is compared.Through orthogonal optimization experiments,the optimal level of each factor and the degree of influence of each factor on system performance are analyzed.According to the ship’s waste heat temperature range and refrigeration requirements,the operating conditions of the system are determined as follows:evaporation temperature:-3℃～5℃;condensation temperature:24℃～32℃;first generator temperature:100℃～120℃;second generator temperature;125℃～145℃.The entrainment ratio of gas-gas ejector increases as the first generator temperature increases,but the system COP decreases;the entrainment ratio of the gas-gas injector,the entrainment ratio of the gas-liquid injector and the system COP all decrease with the increase of the condenser temperature;As the pressure drop of the primary flow increases,the entrainment ratio of the gas-liquid injector decreases but the system COP increases;When the temperature of the second generator increases,the entrainment ratio of the gas-liquid injector increases,but it has little impacts on the system performance.Under any operating conditions,the COP of the pump-free double heat source ejector refrigeration system is higher than that of the traditional ejector refrigeration system,with a maximum growth rate of 7.412%.Through orthogonal optimization experiments,it can be concluded that the optimal temperature of the first generator,evaporation,condenser is 110℃,5℃,26℃ and the optimal pressure drop is 2.26MPa;at the same time,the degree of influence of each factor on the system performance is as follows:condensation temperature>Evaporation temperature>First generator temperature>Pressure drop.After preliminary optimization,the system COP is 0.35.Finally,based on the optimal operating conditions of the system,the structure parameters of the gas-gas ejector are designed and optimized.The relationships between the ejector performance and structure parameters including ejector area ratio(AR)and nozzle exit position(NXP)are investigated.Based on this,the optimal area ratio and nozzle exit position are obtained,and the flow field characteristics inside the ejector under the optimal structural parameters are also analyzed.The results indicate that:As the area ratio increases,the entrainment ratio of the gas-gas ejector first increases and then decreases,and the optimal area ratio of the ejector is 5.28.The entrainment ratio of the gas-gas ejector first increases and then decreases with the increase of NXP,and the optimal NXP is 33.83mm.There is no backflow inside the ejector under the optimal operation conditions,which proves that the ejector is well designed.After the secondary optimization,the system performance increased by 17.34%.The pump-free double heat source ejector refrigeration system proposed in this paper can use low-grade heat source at different temperatures without high-grade energy input.It has high economy and energy efficiency ratio,and provides a choice for refrigeration of ships and some places with high heat energy but lack of electricity.