Abstract: It is increased gradually in scientific research and daily life of two-stage auto-cascade low temperature refrigerator. Study and improve the refrigeration system performance plays an important role; characteristics of energy saving and environmental protection research also has important significance. Single-stage compression two-stage auto-cascade refrigeration system using non-azeotropic mixture refrigerant, the low temperature environment could be realized according to the pressure and temperature changes of refrigerant in the low temperature refrigerator and the relationship of vapor-liquid equilibrium. Three dimensional pressure-enthalpy diagram and enthalpy-composition diagram of two-stage auto-cascade cycle are analyzed using refrigerant properties analysis software NIST Refprop 8.0. The mixed refrigerant R600a and R23 is discussed and selected suitable for –60 ℃ low temperature refrigerator, and the operation temperature and pressure of system are analyzed. The temperature and pressure and the refrigerant substances at the conjunction changes with time of two-stage auto-cascade low temperature refrigerator are studied through experimental methods. A relatively complete concept of two-stage auto-cascade refrigeration system for low temperature refrigerator is established; a rational realization of the temperature and pressure changes and vapor-liquid equilibrium is recognized. It is important to improve the performance of this kind of refrigerator and the products popularization.

Key words: low temperature refrigerator;auto-cascade refrigeration;mixed refrigerant;single-stage compression