Research On Performance Of Marine Ultra-low Temperature Cascade Refrigeration System

With the vigorous development of China's marine economy and the “Belt and Road” strategy,ocean-going fisheries,as an important part of the marine economy,carry the burden of China's marine economic development and blue granary construction,and carry out fisheries with coastal countries and regions,and have the responsibility for cooperation,economy,trade and people-to-people exchanges.China has the world's most advanced fishing boat production technology,but the refrigeration equipment for fishing boats is still not advanced enough.In ocean-going fisheries,the performance and efficiency of refrigeration equipment not only affects the quality of the catch,but also determines the operating radius of ocean-going fishing vessels,which affects the production of fishing vessels and determines the capacity of fishing vessels.In addition,refrigeration systems account for a relatively high proportion of all energy consumption in fishing vessels.Studying the performance of refrigeration systems is conducive to energy saving and emission reduction of fishing vessels,improving the economic benefits of fishing vessels,and systematically optimizing existing refrigeration systems for fishing vessels and advanced marine ultra-low temperature refrigeration systems.Research and development is of great significance for improving the fishery economy and building a strong fishery country.At present,there are few domestic researches on the application of cascade refrigeration systems of fishing vessels.Based on this,this paper combined cascade refrigeration systems with marine ultra-low temperature cold storage,relying on a self-built marine ultra-low temperature cascade refrigeration test benches,using theoretical analysis and experimentally verified method to analyze the factors that affect the performance of the cascade system,and aimed to provide the necessary theoretical guidance for the selection of marine ultra-low temperature refrigeration systems and the application of the cascade refrigeration system.The main research contents of this topic are as follows:(1)The method of controlling a single variable was used to experimentally study the condensing temperature of 32 ? with the evaporation temperature from-45 ? to-65 ?,the evaporation temperature of-55 ? with the condensation temperature of 28 ? to 36 ?.In the cascade refrigeration cycle,the compressor compression ratio,exhaust temperature,suction pressure,refrigerant flow rate and refrigeration coefficient changed as follows,1 ? decrease in the evaporation temperature had a greater impact on the system performance coefficient than 1 ? increase in the condensation temperature.When the evaporation temperature dropped from-50 ? to-55 ? or the condensation temperature rose from 28 ? to 30 ?,the refrigeration coefficient of the cascade system decreased the fastest.When the condensation temperature rose from 34 ? to 36 ?,the compressor suction pressure increased slowly,but the compressor exhaust temperature reached a maximum of 90 ?.(2)Using an electric heating module for thermal load simulation in the R404A/R23 cascade cold storage,the compression ratio of high and low temperature cycles,refrigerant flow rate and compressor exhaust temperature of the cascade refrigeration system under different loads were measured.With the increase of the system thermal load,the compression ratio of the compressors at both the high and low temperature cycles showed a downward trend,but the low temperature cycle decreased faster.The compression ratio of the high-temperature cycle of the system was not equal to that of the low-temperature cycles,which reduced the operating efficiency.When the system thermal load increased,the exhaust temperature of the low-temperature compressor decreased,and the refrigerant flow of the low-temperature compressor increased accordingly.To a certain extent,this make the system more secure and stable.(3)Using the method of thermodynamic model analysis,the R404A/R23 cascade refrigeration system and the R404 A two-stage compression refrigeration system were analyzed in different regenerators under the conditions of evaporation temperature of-65? and condensation temperature of 40?.A comparative analysis was performed under the effect of the regenerator efficiency on the unit cooling capacity,exhaust temperature,refrigerant flow rate,system performance,and input power of the two systems.At the same time,the operating costs of the two systems were also compared.The circulation is beneficial to the high-temperature circulation part of the R404 A two-stage compression system and the R404A/R23 cascade system,but it was not conducive to the low-temperature circulation part of the cascade system of R23 as a refrigerant.When the system regenerator efficiency was 0.9 and the cascade system high and low temperature end regenerator efficiency were 0.9 and 0.1,respectively,the performance coefficient of the two refrigeration systems and the input power of the compressor were the maximum and minimum values,respectively.(4)Using the EES model and experimental verification method,under the condition with the condensing temperature of 32?,the evaporation temperature and intermediate temperature of the cascade system and the two-stage compression system were changed.The influence of various refrigeration parameters and performance was proposed.When the condensation temperature was 40? and the evaporation temperature was-65 ?,-60 ?,-55 ? respectively,the COP of the cascade cycle was 21.33%,22.25% and 22.18% which were higher than those of the two-stage cycles,and at this time,the performance coefficient of the cascaded cycle was the highest when the intermediate temperature was-16.12 ?,-12.87 ?,-10.11 ? respectively,which indicated that the performance of the cascaded system was significantly better than that of the doubled system when the operating conditions were the same.