Performance Analysis And Co MParison Of Transcritical CO₂ Ejector Refrigeration System For Shipborne Cold Cabin

Freon refrigerant has good performance in refrigeration system,but due to its environmental protection defects,the application of some Freon refrigerants in ozone layer cavity and greenhouse effect still poses a great threat.It is true that the outstanding performance and safety of Freon refrigerants in refrigeration systems make them irreplaceable.However,in the face of the earth’s environmental problems,the search for safe and efficient alternatives to refrigerants is in front of us.As a natural refrigerant,CO₂ has attracted wide attention and research from scholars in the field of refrigeration due to its outstanding environmental protection and excellent thermodynamic characteristics.CO₂ critical condition is 31.1℃and 7.38 MPa.In refrigeration system,it usually works in a cross-critical manner.Low pressure under low temperature condition results in large differential pressure between high and low pressure of the system and serious throttling loss.In order to solve the inefficiency of CO₂ refrigeration system,ejector is added to the system to recover throttle losses and improve the refrigeration performance of the system.In order to study the refrigeration performance of the trans-critical CO₂ two-stage compression refrigeration cycle with ejector and the traditional two-stage compression refrigeration cycle,the energy and conventional exergy model of the two systems are established,and the advanced exergy model is established on the basis of the conventional exergy model.The theoretical performance of the system is analyzed,and the optimization potential of the system components is analyzed through the commonality of the two methods.According to the established energy and two kinds of energy analysis models,the results of conventional energy analysis show that the main optimization objects of the system are the ejector,expansion valve 1 and evaporator,accounting for 22.13%,16.12%and 14.41%of the total exergy destruction respectively.At this time,the efficiency of the system is 23.94%,and the COP of the system is 1.252.According to the results of the advanced exergy analysis,the improvement of the system components should focus on the ejector and the high and low pressure compressor.Ejectors and high-pressure compressors account for the main part of avoidable damages（65.72%）.The main optimization objects of the system should be ejectors and high and low pressure compressors.By changing the main parameters in the system cycle within a certain range,it is observed that the gas cooler pressure and intermediate pressure have a great i MPact on the system.They all have an optimal value,which can maximize the performance of the system.In the actual experiment process,based on the simulation results,the performance of the two refrigeration systems under multiple operating conditions is studied on the existing experimental platform,and the trans-critical CO₂ refrigeration system with ejector is analyzed.According to the experimental results,the performance of the transcritical CO₂ refrigeration system with an injector has improved by 28.8%-84.2%co MPared to traditional transcritical CO₂ refrigeration systems.In order to maintain the best performance and maximum COP of the injection refrigeration system,the outlet temperature of the gas cooler should be maintained at 31℃to 33℃.At this temperature,the COP peak appears.At this time,the pressure of the gas cooler is 85 bar,the temperature of the evaporator is-35℃,and the opening of the low-pressure expansion valve is 100%.When the pressure of the gas cooler is changed and the other conditions are stable（the outlet temperature of the gas cooler is 35℃,the temperature of the evaporator is-35℃,and the opening of the low-pressure expansion valve is 70%）,there is a peak value in the COP change trend of the trans-critical CO₂ injection expansion two-stage compression refrigeration system.This position makes the overall performance of the system reach the best.After reaching the peak value,the overall performance of the system maintains a downward trend,in addition,a similar situation occurred in the simulation results,and the pressure range of the air cooler was 85bar-87bar.The COP of the low-pressure stage compressor has a peak at 46 Hz,which needs to be explored.The surge phenomenon of the compressor is more obvious when the compressor operates at low frequency,especially when the system flow is more serious at 30 Hz,and the system operation has problems.In the co MParative part of experiment and simulation calculation,it is found that there is an optimal value for the pressure of the gas cooler and the intermediate pressure to make the system performance optimal.The increase of the outlet temperature of the gas cooler has a negative i MPact on the trans-critical CO₂ two-stage compression refrigeration system with ejector.