Operation and performance of screw machines with high built-in volume ratio

Abstract A performance calculation of a screw compressor with increased built-in volume ratio was performed in this paper to establish how increased built-in volume ratio influences its efficiency. It is known that screw compressors have limited built-in ratio which is determined by their standard discharge port size and position. However, if the discharge port is reduced beyond its cusp position, the screw machine built-in volume is 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. The 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% for the specific power and adiabatic efficiency. This confirms superiority of the reduced size high pressure port for compressors which operate at high pressure ratio.