The performances of R717/R744-DCC refrigeration cycle

the R744 gas discharged from R744 compressor contacts directly with the R744 super-cooled liquid provided auxiliary super cooling by R717 refrigeration cycle

are analyzed. The following conclusions are obtained. The optimum condensing temperatures of R744 main cycle exist in the R717/R744-DCC refrigeration cycle

and at the optimum condensation temperatures

the maximum coefficient of performance and minimum R717 condenser heat load are obtained. With the increasing of super cooling degree of R744 main cycle supercooled liquid

the maximum coefficient of performance reduces

the minimum R717 condenser heat load increases

the condensation temperatures of R744 main cycle increases

and the refrigerant mass flow rate of R744 evaporator decreases. Meanwhile

compared with that of R717/R744 cascade refrigeration cycle

at the same operating conditions and the optimum R744 main cycle condensing temperatures

the maximum coefficient of performance of R717/R744-DCC cycle increases 5.2%

and the minimum R717 condenser heat load reduces 1.6%. Furthermore

in the range of -10-8℃ condensation temperatures of R744 main cycle

the mass flow rate of R744 evaporator of R717/R744-DCC refrigeration cycle reduces 1.75%-2.61%

and the mass flow rate of R717 condenser of R717/R744-DCC refrigeration cycle reduces about 0.51%-0.82%.