WORKING FLUID

PURPOSE:To provide a working fluid applicable to a high-temp. range and lowering the compression ratio and discharging temp. of the compressor, having excellent heat stability, heating capabilities and coefficient of performance and useful for use in a heat pump, which comprises pentafluorobenzene as an essential component. CONSTITUTION:A working fluid comprising pentafluorobenzene having a normal boiling point of 85 deg.C and a freezing point of -40 deg.C or below as well as an excellent heat stability as an essential component. The working fluid is compressed with a compressor 1 and fed into a condenser 2, where it is cooled and condensed with a high-temp. source fluid fed from a piping 3, while a load fluid is heated in a condenser 2 and applied to load heating through a piping 3'. The condensed working fluid is decompressed with a vacuum device 4, heated and evaporated with a heat source fluid which is fed through a piping 6 with an evaporator 5 and discharged through a piping 6', again sucked into the compressor 1 and repeating the above cycle.