Aerodynamics of Rotatable Inlet Guide Vanes for Centrifugal Compressors

摘要

Fixed speed motors are the most common drivers for centrifugal compressors encountered in large air-conditioning and refrigeration units. Capacity is altered by changing the swirl entering the impeller. This is accomplished by rotatable inlet guide vanes. However, part-load operation of constant-speed centrifugal compressors with rotatable inlet guide vanes suffers from a substantial drop in compressor efficiency. When variable speed is used as a part-load control mechanism, centrifugal compressors suffer a much smaller efficiency reduction during part-load operation. The inlet guide vanes are therefore often blamed for the drop in efficiency of fixed speed compressors under part-load conditions. In order to verify this hypothesis the aerodynamic efficiency of rotatable inlet guide vanes at various setting angles was investigated. The measured mass-average total pressure loss over the inlet guide vanes was very moderate under all but the most extreme guide vane setting angles. This small pressure loss was not enough to explain the compressor efficiency drop encountered under part-load operating conditions. Modifying inlet guide vane geometry will therefore not help in improving part-load compressor efficiency.