THE INVESTIGATION OF INLET CONDITION EFFECT ON THE SURGE RECOVERY PROCESS OF A S-CO2 RADIAL COMPRESSOR

The supercritical carbon dioxide (S-CO2) Brayton cycle is a power conversion cycle that utilizes supercritical carbon dioxide as the working fluid. One of the main characteristics is that the compressor operates with inlet conditions close to the critical point. However, approximating the S-CO2 compressor as an ideal gas turbomachinery model is limited by the rapid change in fluid properties near the critical point. Additionally, unlike most air Brayton cycles, the S-CO2 Brayton cycle is designed as a closed loop. To study the surge recovery process of the S-CO2 compressor, this study utilized an integral test loop with a turbo-alternator-compressor equipped with active magnetic bearings. Surge recovery performance tests were conducted at various speeds to investigate the effects near the critical point. Surge recovery performance was observed by reducing the compressor mass flow rate to induce a surge and then restoring the flow rate. The compressor instability was classified into surge and stall on the basis of speed, and the change of compressor inlet conditions affected the surge recovery performance of the S-CO2 compressor. The experimental results propose modifying the Greitzer B parameter as a means of estimating surge and stall in S-CO2 compressors.