Optimum operating pressure ratios for scroll compressors

Abstract

A scroll compressor has a built-in volume ratio, and ideally it should be operated under a built-in pressure ratio condition that is a function of the built-in volume ratio. But in actual operation, the compressor shows its maximum efficiency at a pressure ratio that differs from the built-in pressure ratio. In this paper, theoretical performances are presented by analyses accounting of flow resistance at the openings of scroll wraps and leakage through wrap clearances. The flow resistance at the discharge opening causes an over compression loss in a built-in pressure operation but reduces a undercompression loss in a high-pressure operation, which indicates that the optimum operating pressure ratio shifts to a pressure ratio higher than the built-in pressure ratio. Leakage accelerates the pressure rise during a compression process so that the optimum pressure ratio becomes lower than it would be in the absence of leakage. Increase in the compressor speed moderates the under compression loss and leads to a higher optimum operating pressure ratio. © 1989, The Japan Society of Mechanical Engineers. All rights reserved.