Experimental Study of Conical Rotary Compressor for High Pressure Ratio Applications

The Conical Rotary Compressor (CRC) is a positive displacement machine characterized by internal meshing, variable pitch, and variable rotor profile. Compared to twin screw machines, the CRC has a shorter leakage line length, no leakage triangle, no discharge port, and co-directional thermal expansion, providing advantages when operating at high pressure ratios (Pi). Over-compression or under-compression can be avoided by matching external Pi with internal Pi, which depends on the volumetric index (Vi) of the CRC. However, higher Vi values lead to increased manufacturing complexity and cost. For this study, a CRC with Vi 6.8 was selected, and Vi was modified by reducing the inner rotor length from the discharge side. Experiments were conducted at five different Vi values (6.8, 5.8, 4.6, 4, and 3) with Pi varying from 11 to 41. The results showed that 75% isentropic efficiency and 95% volumetric efficiency were achieved at a pressure ratio of 21. The isentropic efficiency and volumetric efficiency remained higher than 45% and 75%, respectively, even at a pressure ratio of 41. Performance began to decrease when Vi was lower than 4, resulting in significant under-compression. The efficiency contour and Vi contour obtained from this study can be used for performance prediction and optimization of CRC design.