Session: 38-01 Radial & Mixed Flow Turbines

Paper Number: 102556

102556 - Loss Analysis in Radial Inflow Turbines for Sco2 Mixtures 

Supercritical carbon dioxide (sCO₂) and sCO₂ mixtures are viable working fluids for future power plants with enhanced thermal efficiency. Based on aerodynamic and cost considerations, radial inflow turbines (RIT) are a reasonable choice for small to medium sized power plants (100 kW to 10 MW).  Therefore, a better understanding of sCO₂ RIT design is beneficial to the advancement of sCO₂ technology. In this paper, we compare between RIT mean-line designs of three sCO₂ mixtures containing tetrachloride (TiCl₄), sulphur dioxide (SO₂), and hexaflourobenzene (C₆F₆) by analysing aerodynamic losses.

Turbine performance is predicted using loss equations that are frequently used in the literature, these include nozzle passage, rotor incidence, rotor passage, rotor tip clearance, rotor trailing edge, exit, and windage losses. Previous studies have described the trends in loss contribution with changes in the turbine design. However, the cause of these trends is rarely explicitly explained, which we aim to do here. This is achieved by taking a purely mathematical approach and assuming that all terms in the loss equations are mutually exclusive, and thus can be changed independently of each other. Ultimately, by understanding the effect each term has on the losses we may better explain the change in turbine performance across the turbine design space.

Mean-line RIT designs for the three sCO₂ mixtures are then presented and compared considering the results from the loss analysis. To accentuate the differences between the mixtures, turbine designs from the sub-MW (100 kW) to higher power capacities (10 MW) are analysed. In all cases, turbine boundary conditions are set assuming that the turbines operate within power blocks of concentrated solar power plants.

Results show that the loss models, and hence turbine performance, are predominantly determined by geometric and kinematic parameters such as the inlet and outlet radiuses, the number of rotor blades, and the relative velocities in the rotor, not by thermophysical properties such as the kinematic viscosity. Therefore, turbines designed to optimise aerodynamic performance will have similar designs regardless of the sCO₂ mixture used. However, results from the power-scaling study show that mixtures for which turbines have a larger rotor blade height will be able to achieve higher efficiencies at sub 10 MW scales. For example, 100 kW turbines for CO₂/TiCl₄, CO₂/C₆F₆, and CO₂/SO₂ mixtures achieve total-to-static efficiencies of 79%, 77.9%, and 76.3%, respectively. However, a total-to-static efficiency of 87% is achievable at the 10 MW, regardless of the sCO₂ mixture used.

Presenting Author: Omar Aqel City, University of London

Presenting Author Biography: Omar Aqel is currently a PhD student at City, University of London. He is investigating radial inflow turbine design optimization within power cycles utilizing CO2-based working fluids.

Authors:

Omar Aqel City, University of London
Martin White University of Sussex
Abdulnaser Sayma City University of London