Turbulent dense gas flow characteristics in swirling conical diffuser

Diffusers placed at the exit of turbines are essential to recover pressure and increase turbine efficiency. This increase of efficiency is critical for the overall cycle efficiency of renewable power cycles based on low temperature renewable resources. Optimising the performance of a conical diffuser in renewable power cycles using high-density fluids can be established by examining the turbulence characteristics of both air considered as an ideal gas (IG) and R143a, a refrigerant with high-density in a non-ideal state, considered as a real gas (RG). Turbulence was firstly modelled and validated against experimental results from the ERCOFTAC swirling conical diffuser database and previous numerical results. The real gas thermodynamic and transport properties of refrigerant R143a were then obtained from the NIST REFPROP database. Investigating both RG and IG revealed that general trends remain, where the stronger wall components in RG help improve the diffuser performance. Furthermore, investigations regarding turbulence intensities indicated a clear effect on the flow behaviour for IG while being ineffective on the RG. The final application analysed the diffuser performance using the inlet conditions extracted directly from a potential radial-inflow turbine working with R143a. The change of conditions highlighted that radial components can be reduced, and thus the swirling number too. By implementing the first numerical study on real gas swirling conical diffuser, it was established that real gas flow regimes differ from the ones previously established for ideal gas, and thus preliminary flow regimes for R143a, specifically, are proposed.