Abstract: To explore the effect of dryness of different organic working fluids on the theoretical power of steam-liquid mixing phase power cycle with screw expander, typical wet working fluid R152a, typical dry working fluid R245fa and three typical zeotropic mixtures Ca, Cb and Cc, which are composed by different mass fractions of R152a/R245fa, are chosen as research objects. By changing the screw machine expansion ration RV, working fluid bubble point temperature T5 and other variables, it is easily obtained the relationship between the theoretical power Pt and the dryness of working fluid at the exit of the evaporator x. The results show that on the one hand, in the same condition, the theoretical power of wet working fluid Pt is significantly higher than that of dry working fluid and isentropic working fluid; one the other hand, with the increase of RV or T5, the system maximal theoretical power of all kinds of working fluids Pmax will shift from the area that x ranges from 0.9 to 1.0 to the area that x ranges from 0 to 0.2, the difference is that the impact of changes of RV or T5 on wet working fluid is greater than dry working fluid and isentropic working fluid. This shows that the optimum working fluid of steam-liquid mixing phase power cycle with screw expander is wet working fluid, so it can provide a reference when select organic working fluid for steam-liquid mixing phase power cycle with screw expander.

Key words: Dryness, Screw expander, Steam-liquid mixing phase, Theoretical power, Zeotropic