Performance Improvement of a Vaneless Diffuser of Centrifugal Compressor

Abstract

Performance tests were conducted for centrifugal compressors of CFC11 having vaneless diffusers whose flow passage widths decrease linearly from near the outlet to the outlet. The beginning point of reduction in diffuser width was selected appropriately and its reduction ratio was optimized experimentally. The optimum value of the width reduction ratio was 0.5. The surge margin was improved and the compressor adiabatic efficiency was improved over wide range of flow rates, as compared with a compressor without a width reduction region at the diffuser outlet. At surge inception, the static pressure difference between the hub and shroud walls of the diffuser inlet decreased as the width reduced at the diffuser outlet. The pressure difference between the hub and shroud walls of the diffuser inlet at surge inception was characteristic constant value independent of the conditions of inlet guide vane opening. Therefore, surge inception can be predicted by measuring the pressure difference between the two walls of the diffuser inlet. © 1992, The Japan Society of Mechanical Engineers. All rights reserved.