Research On Performance Of Mixed Refrigeration Working Fluid And Automatic Cascade Cryogenic Refrigeration Unit

The automatic cascade refrigeration cycle is an important direction for the development of cryogenic throttle refrigcrators,it has the advantages of single-stage compression and multi-stage condensation to produce low temperature environment,simple structure,safe operation and low cost.In the paper,a two-stage automatic cascade refrigeration system with condenser and separator is studied.The vapor-liquid equilibrium characteristics of ternary refrigerants are studied by using equation of state PT and PR,the vapor-liquid phase transition process of ternary refrigerants is analyzed.The R227/R23/R14 is selected as mixed refrigerant in the second-level automatic cascade refrigeration system,the physical properties of the refrigerant mixtures,such as temperature and pressure,were analyzed by the software NIST Refprop 9.1.Thermodynamic calculation of non-azeotropic refrigerant mixtures R227/R23/R14 was carried out,when the refrigeration temperature of-80 C can be obtained in the secondary cascade refrigeration cycle system.A segregator is proposed in refrigeration system and applied to test and engineering prototype.In the performance test of the two-stage auto-cascade refrigeration system,the cooling process of the refrigeration unit can be divided into four stages:delay stage,fast stage,slow stage and stable adjustment stage.After the system runs for 2 hours,the temperature of the refrigeration unit reaches-80?,and the temperature is stable at-80?.Environmental temperature has a great influence on the refrigeration capacity and system performance,when the environmental temperature decreases,the refrigeration capacity of the system increases and the system performance improves.At the same temperature temperature,the temperature of the refrigerator affects the refrigeration capacity and system performance.When the temperature of the refrigerator rises,the refrigeration capacity of the system increases and the performance of the system is better.Refrigeration units should choose high thermal conductivity medium.Because the thermal conductivity of R11 is higher than that of alcohol,the higher the thermal conductivity of heat conducting medium,the larger the refrigeration capacity of the system and the better the performance of the system.The molar concentration of refrigerants R23,R14 and R227 has an effect on the system performance and refrigeration capacity.In the test,the molar concentration ratio of R23/R14/R227 is 15/30/55 when the refrigeration capacity of the system is the largest and the system performance is the best.When the refrigeration temperature reaches-80?,the refrigeration capacity of the system is 480W and the COP of the system is 0.152.The test results provide guidance for engineering design of automatic cascade refrigeration system.