Development of a closed-loop sCO2 experimental cycle and modelling methods for CO2 condensing flows

Abstract

Supercritical CO2 (sCO2) power cycles represent a promising technology for sustainable energy generation due to their potential for high efficiency and reduced emissions. However, the large nonlinear variations in fluid properties near the critical point significantly impact the fluid behaviour in this region. Experimental characterisation of sCO2 is crucial for developing these cycles. In order to address these challenges, a closedloop sCO2 experimental facility was designed and constructed to characterise sCO2 behaviour in supercritical and two-phase regions. A dynamic model of the experimental loop was developed to predict its behaviour under varying operating conditions, including the use of CO2-SO2 mixtures, providing a valuable tool for studying loop performance.

This dissertation investigates key challenges associated with sCO2 flows, particularly the phenomenon of non-equilibrium condensation and shock wave interactions in supersonic two-phase flows. A novel advanced numerical approach for simulating non-equilibrium condensation in sCO2 flows was developed. This approach includes models that account for real gas effects at high pressures encountered in sCO2 cycles. Furthermore, the research investigates shock wave behaviour in two-phase CO2 flows within nozzles. Three-dimensional CFD simulations analyse the interaction between shock waves and the boundary layer, along with the impact of shock waves on droplet evaporation rates. Finally, the dissertation explores moment-based methods for simulating polydispersed droplet size distributions in CO2 condensing flows. These methods are integrated into the existing phase-change model and applied to simulations of nozzles and turbine cascades.

The findings of this research contribute significantly to the development and optimization of sCO2 power cycles by providing valuable insights into the behaviour of two-phase CO2 flows. The numerical models presented can be used for the design and analysis of critical components within sCO2 cycles, ultimately leading to improved efficiency and performance.