Numerical simulation of CO₂ centrifugal compressor near condensation line using real gas models

This investigation evaluates the performance of a carbon dioxide centrifugal compressor operating near the condensation line to validate real-gas modeling approaches in computational fluid dynamics (CFD) simulations. The study focuses on an experimentally characterized CO2 compressor comprising an axial inlet chamber, mixed-flow impeller, vaneless diffuser, and discharge volute, tested under both subcritical and supercritical conditions. Numerical simulations conducted in Ansys CFX incorporated the Peng-Robinson and Redlich-Kwong equations of state, demonstrating maximum deviations of 4.1% for outlet pressures and temperatures compared to experimental data across an inlet pressure range of 4.166-4.424 MPa. Additional thermodynamic analysis using NIST mini-REFPROP with Peng-Robinson and Span-Wagner models revealed localized liquid formation at inlet pressures exceeding 4.35 MPa, a phenomenon not captured by single-phase CFD simulations. The results indicate that while single-phase gas modeling achieves reasonable accuracy for global thermodynamic parameters, it inadequately represents local condensation effects. Enhanced prediction of phase-transition behavior requires implementation of two-phase CFD methodologies with optimized phase-interaction parameters, refined mesh resolution, and improved boundary condition specification.