Experimental Study of the Real Gas Effects of CO₂ on the Aerodynamic Performance Characteristics of a 1.5-Stage Axial Compressor

The thermodynamic properties of CO₂ do not obey the ideal gas law and the simplified equation of state. The enthalpy and sonic speed depend on both temperature and pressure whereas the enthalpy and the speed of sound of ideal gas, like atmospheric air, depend only on its temperature. These effects add additional complexity to the design and operation of CO₂ compressors compared to compressors utilizing air as their working fluid. For example, if the compressor inlet pressure changes during operation, its flow Mach number changes due to the change of the sonic speed which is followed by the change of corrected speed and the performance. This paper focused on the experimental investigation of the performance parameters of a 1.5 stage axial compressor with CO₂ gas. The design speed and the design pressure ratio of the compressor are 19,800 rpm and 1.41, respectively. The testing was completed using a 10 MW closed CO₂ compressor test loop at the University of Notre Dame Turbomachinery Laboratory. The compressor performance was measured at various compressor inlet conditions to demonstrate the effectiveness of the generalized corrected speed and the corrected flow coefficient in the CO₂ compressor performance. Additionally, it is shown that the Reynolds number is connected to other performance parameters through the sonic speed and a set of experimental data is presented with an attempt to separate the effect of the Reynolds number and the effect of the corrected speed on the compressor performance.