Performance improvement of twin screw refrigeration compressors for chillers by modifying the suction arrangement

Abstract

To improve the efficiency of the twin-screw refrigeration compressor at a high speed of about 3000 rpm, the suction arrangement was investigated in this paper. Several simplified CFD models of a twin-screw refrigeration compressor for chillers were established to parametrically analyze the influence of the suction delay, rotor wrap angle, and suction bearing distance. The parametric studies showed that the volumetric efficiency could be improved by 3 % by a suction delay of 18°, and more volumetric efficiency could be improved by shortening the length of it. The optimal delay angle was found to be linear with the rotational speed. Increasing the wrap angle from 300° to 330°, the volumetric efficiency decreased by 2–3 %, and the adiabatic efficiency increased by about 0.2 %. By increasing the distance between the suction bearings and the rotor end face from 5 mm to 80 mm, the isentropic efficiency increases by about 1.4 %. Based on the parametric studies, two modified machines were built and tested by experiments. Experimental results showed that the volumetric efficiency of machines #1 and #2 increased by 1.5 % at 3000 rpm. The isentropic efficiency of machine #2 increased by 0.78 % at 3000 rpm and 1.27 % at 3300 rpm.