Impact of discharge volute on parameters in control sections of CO₂ centrifugal compressor

Carbon dioxide (CO 2 ) serves as a crucial refrigerant in both transcritical and subcritical commercial and industrial cooling systems, with centrifugal CO 2 compressors playing a vital role in these applications and in heat pump technologies. This investigation examines through numerical simulation the influence of discharge volute configuration on centrifugal compressor impeller performance within a laboratory-scale transcritical energy cycle. The research quantitatively assesses variations in outlet pressure, temperature, and isentropic efficiency at impeller and diffuser outlets, comparing configurations with and without discharge volute in the subcritical gaseous region of CO 2 . Three real-gas modeling approaches were implemented in Ansys CFX simulations: the integrated Peng-Robinson and Redlich-Kwong equations of state, along with real-gas property tables derived from the Span-Wagner equation. Results indicate that volute removal causes marginal reductions in static pressure (≤0.1%) and temperature (≤0.03%), while increasing impeller outlet velocity (≤0.51%) and decreasing diffuser outlet velocity (≤0.38%). Numerical predictions of outlet pressure and temperature demonstrate agreement with experimental data within 5% deviation. These findings provide valuable insights for optimizing CO 2 compressor designs across various applications including refrigeration systems, power cycles, heat pumps, and transcritical CO 2 systems.