The supercritical carbon dioxide (sCO2) Brayton cycle has gained significant attention as an emerging
power cycle for Waste heat recovery applications. The cycle’s unique properties, such as the
supercritical behavior of carbon dioxide, result in improved efficiency, compactness, and the potential
for higher power density than traditional power cycles. Turbo-expander analysis has been the critical
element in increasing the efficiency of the whole power cycle. Higher power and densities lead to very
compact and high-speed turbomachinery, challenging its design. The KW scale Radial Inflow turbine
(RIT) development has not been prominent and has been challenging due to higher rotational speeds
and small rotor sizes. The aim is to develop and optimize an RIT in KW to MW scale with a feasible
design and higher efficiencies.
A physics-based one-dimensional mean-line modeling technique and required loss models are
integrated with material, frequency, geometrical, and kinematic constraints to obtain a feasible design
space. Parametric studies are followed by optimization studies using a Genetic Algorithm for a power
range of 85 kW to 1.2 MW and pressure ratios ranging from 2 to 3. Results obtained from the above
studies predict that a back-swept blade configuration is preferred over radial blades for a lower power
range (up to 300 kW) compared to higher power ranges. The efficiency deviation for lower power
ranges has been up to 3-4 % compared to 1-2 % for higher power ranges.
The RPM restrictions result in infeasible solutions for higher pressure ratios and lower power range
turbines. Two-stage turbines splitting the pressure ratio into an HP turbine stage and an LP turbine
stage for these cases increase the efficiency by 2.5-4.5 % for both back-swept and radial cases and
work output by 7.7% and 6.8% for back-swept and radial cases, respectively. Thus back-swept blade
rotor configuration is preferred for both single-stage and two-stage turbines for lower power ranges.