Design And Research On The Cycle Performance Of R507/CO₂Cascade Refrigeration System

In recent years, due to extensively use of refrigerant CFCs and HCFCS, which leads to many environmental problems such as global warming and ozone depletion, etc. Using green, efficient natural refrigerants becomes an inevitable choice for the refrigeration industry future. The natural refrigerant CO2has a high latent heat value and CO2cascade refrigeration system can achieve a very low evaporation temperature, it is suitable for low temperature refrigeration industry, so CO2cascade refrigeration technology has become a research hotspot in current refrigeration industry. This paper combines with a CO2cold storage project in Chongqing, researches and designs a R507/CO2cascade refrigeration system. Taking R507as the high temperature level refrigerant, and CO2as the low temperature level refrigerant.The paper studies and analyzes the cycle characteristics of R507/CO? cascade refrigeration system though theoretical calculation. Through establishing the steady lumped parameter thermodynamic calculation model of R507/CO2cascade refrigeration system analyzes the effect of evaporation temperature of low temperature level CO2. condensation temperature of high temperature level R507and low temperature level CCK condensation heat transfer temperature difference and other thermodynamic parameters for cascade system performance coefficient and high and low level mass flow ratio, identifies the key factors affecting the performance efficiency of the cascade refrigeration system, proposes system optimization recommendations:(1) Meeting the conditions of CO2compressor discharge pressure within the design pressure range of the unit, increases CO2evaporation temperature or reduces R507condensing temperature can increase the COP of R507/CO2cascade refrigeration system;(2) Appropriately reduces condensate evaporator heat transfer temperature difference can also increase R507/CO2cascade refrigeration system COP. In addition, the paper also analyzes and comprises performance coefficient of NH3/CO2, R404a/CO2, R507/CO2cascade refrigeration systems under the same conditions. NH3/CO2cascade refrigeration system COP is maximum, and R404a/CO2cascade refrigeration system COP is minimized. The paper combines with a CO2cold storage project in Chongqing, under a given design operating conditions, designs R507/CO2cascade refrigeration system, selects the CO2compressor, R507compressor, condensate evaporator, R507system condensers, other major equipment and other auxiliary equipment with reference sample equipment selection. And carries on commissioning tests for R507/CO2cascade refrigeration system after the installation is complete, analyzes and makes treatment program for refrigerant R507or CO2leak emergency of the cascade system that may occur during the installation and operation.This paper makes theoretical research and system design for R507/CO2cascade refrigeration system cycle characteristics; it has a certain guiding significance for performance optimization and promotion of the cascade system application.