The Research On Performance Of Ultra-low Temperature Two-stage Compression Refrigeration Platform

With the development of global technology and the progress of science and technology,people are increasingly demanding high quality frozen food at low temperature especially in the development of frozen chain of tuna.Due to myoglobin in tuna is easily oxidized and then browning,which affects its edible value and economic value.After fishing,should be processing timely and sent to-55? ultra-low temperature cold storage for frozen storage.However,despite of our country ranked first in the world in term of the fishery professional staff size and the number of fishing boats,there is still a big gap compared with the developed countries.And the energy consumption of refrigeration system,which is indispensable for fishing vessels,has been restricting the development of ocean-going fishery in China.Further analysis and Research on refrigeration units,reducing energy consumption and improving energy utilization of the system have great significance for energy conservation and emission reduction and sustainable development.for this reason,ultra-low temperature two-stage compression refrigeration system is taken as the research object.The experimental bench of single-machine two-stage compression refrigeration system is studied by EES simulation and experimental.The main contents and conclusions of this study were listed as follows:(1)Thermodynamic models of two-stage compression refrigeration system was established.The R404 A single machine two-stage compression refrigeration system for marine ultra-low temperature was simulated by EES when the evaporation temperature or the condensation temperature changes.Experimental verification of simulation results was carried out on the basis of the ultra-low temperature experimental platform consisting of R404 A single machine two-stage compression refrigeration system with different conditions.The results of simulation and experiment indicated that with the decrease of evaporation temperature or increase of condensing temperature,the exhaust temperature of the compressor increased,The simulation results were in good agreement with the experimental results.When the evaporating temperature rises or the condensation temperature drops by 5?,the effect of evaporating temperature on COP was up to 7.8%than that of condensing temperature.(2)Under the condition of constant evaporation temperature and condensing temperature,the effects of different intermediate temperatures on the performance of single-machine two-stage compression refrigeration system are studied by EES and then verification by experiment.The results show that With the increase of intermediatetemperature,the COP value of refrigeration increases first and then decreases,and its value varies in the range of 5% when the optimum intermediate temperature increased 4? or decrease 4?.From the actual operation of the system show that in the case of a condensation temperature of 23? and the evaporation temperature of-55?,when the middle temperature is-18?,the refrigeration COP reaches the maximum.(3)The operating stability and performance of the refrigeration system under di fferent loads were studiedon the basis of super low temperature R404 A single stage two-stage compression refrigeration test bed.The expreiment results that with the i ncerase of heat load,the exhaust temperature of the compressor and compressor rati o decreased and the compression ratio of high pressure stage was reduced by about30%.however the refrigerant mass flow shows the opposite trend,which increased the reliability and stability of the refrigeration system.(4)The thermal properties data of refrigerant were provided by NIST REFPROP 8.0,The effects of different intermediate temperatures on the compressor power and the energy coefficient of refrigeration system in two kinds of refrigeration systems were analyzed and the operating costs of two kinds of refrigeration systems were compared at condensing temperature 40? and evaporation temperature-65?.The results show that compared to cascade compression system,the compressor power and R404 A refrigerant flow rate of two-stage compression system were lower and COP were higher.Two-stage compression refrigeration system energy would save 2836.8kW·h~4255.2kW·h throughout the year at condensing temperature of 40?,evaporation temperature of-65? and intermediate temperature of-14?.