Feasibility study on high backswept angle impeller for high performance $S-CO_2$ centrifugal compressor design

Abstract

This study focuses on the feasibility of an impeller design with higher backswept for an $S-CO_2$ centrifugal compressor to improve its efficiency. As first step, an $S-CO_2$ centrifugal compressor performance is examined with in-house code while changing the backward sweep angle at the impeller exit. As a result, an $S-CO_2$ compressor can achieve the highest efficiency at −70° backswept angle, which is greater than the conventional design value -50°. As the next step, the results of a compressor performance test are covered to prove this theoretical possibility. Impellers having -50° and -70° backswept angle were designed and tested, and the results experimentally prove that impeller with -70° backswept angle has higher efficiency. To predict the surge line of the newly proposed compressor, the diffusion ratio at stall was introduced because the new impeller surge line cannot be predicted from pressure ratios. Finally, by integrating these results, a new compressor for KAIST MMR is designed, and as a result, the new system has improved cycle efficiency.