Abstract: Different mass fractions of R245fa/R152a are chosen to compose three typical Zeotropic mixtures M1, M2 and M3. In the proposed temperature range, the Zeotropic mixtures are investigated as the working mediums of the double circulation low-temperature waste heat recovery system with screw expander. An internal recuperator is introduced to the system because of the obvious temperature glide during phase change for Zeotropic mixtures and low pressure drop, high export parameters with screw expander. The results show that utilizing Zeotropic mixtures can extend the range of choosing working mediums for double circulation low-temperature waste heat recovery system with screw expander and heat transfer process with variable temperature heat source can be a good match for Zeotropic mixtures and can reduce irreversible loss of temperature difference of heat transfer,meanwhile, can reduce mass flow rate of working medium; Among the proposed Zeotropic mixtures, the cycle efficiency of isentropic working medium is not the highest, but the expansion volume ratio is the lowest. For Zeotropic mixtures a significant increase of thermal efficiencies can be gained when an internal recuperator was introduced to the system.

Key words: Double circulation, Low-temperature, Screw expander, Waste heat recovery, Zeotropic mixtures