Influence of Oil Volume Upon Operation and Performance of Screw Machines With High Built-In Volume Ratio

Abstract A performance calculation of a screw compressors with increased built-in volume ratio was performed and presented in this paper to establish how increased built-in volume ratio influences compressor efficiency. It is known that screw compressors have limited built-in volume ratio which is determined by their standard discharge port size and position close to the bores cusp. However, if the discharge port size is reduced beyond its cusp position, the screw machine built-in volume may be increased. In such a case, influence of the oil volume in the air-oil mixture of oil-flooded compressors increases the machine built-in volume further. A performance improvement achieved if the built-in volume ratio is doubled in comparison with the standard port during the machine operation at high pressure ratio of more than 20, is up to 26% in the specific power and adiabatic efficiency. This confirms superiority of the reduced size high pressure port for compressors which operate at high pressure ratio.