Development of a twin screw expressor as a throttle valve replacement for water cooled chillers

An introductory report is given on a novel means of replacing the throttling process in vapour compression systems. Power is recovered from the two-phase expansion process and used directly to recompress a portion of the vapour formed during the expansion. Both the expansion and recompression processes are carried out in a twin screw machine with only one pair of rotors. These rotate, without the need for timing gear, in a process-lubricated, totally sealed unit which the authors have called an “expressor”. First test results indicate that the overall expansion-compression efficiency of the expressor is of the order of 55%. This corresponds roughly to 70 % expansion efficiency and 80 % compression efficiency. The simplicity of the expressor design, together with its promising performance give clear indications that it should be a highly cost effective component in large commercial chiller systems