Aerodynamic Characteristics of a Centrifugal Compressor Working in Supercritical Carbon Dioxide

Abstract

Development of a closed cycle gas turbine with supercritical carbon dioxide as a working fluid is underway to generate power from low-range or intermediate-range waste heat sources. A demonstration test using a reduced scale turbomachine was conducted and the aerodynamic characteristics of a compressor were examined. A compressor was selected as centrifugal with 30mm outer diameter and rated rotational speed of 1.7kHz and mass flow rate of 1.2kg/s. To reduce compression work, the operating condition at the inlet to compressor was chosen in a supercritical state close to the critical point of 7.38MPa, 304K where the compressibility coefficient z becomes markedly small and real gas effect dominant. The experimental range in terms of z is 0.16<z<0.6. The measured pressure ratio and adiabatic efficiency of the compressor are compared with calculations conducted using the Meanline method. The compressor performance in the supercritical liquid-like phase becomes highest in the experiment, which is well simulated by the method. The calculated pressure ratio shows excellent matching with experimental data in the supercritical liquid-like phase. However overestimation is recognized at the off-design point in the supercritical gaslike or subcritical region. Experiments also show that the compressor performance improves with reduction of the compressibility coefficient, which the Meanline method has well predicted.