Design method and performance comparison of plenum and volute delivery systems for radial inflow turbines

Radial inflow turbines are the preferred architecture for energy extraction from the organic Rankine cycle and the supercritical CO2 Brayton cycle at smaller scales. For such turbines it is possible for fluid to be delivered to the first stage by either a volute or plenum delivery system. For high pressure supercritical CO2 turbines, there are no fully documented fluid delivery systems in literature and it remains unclear as to which architecture results in higher performance with the highly dense working fluid. The aim of this paper is to present a performance comparison between a new plenum based fluid delivery system and conventional volute for a 100 kW supercritical CO2 radial inflow turbine. Numerical simulations of the fluid delivery systems are conducted and compared in terms of flow uniformity, total pressure loss and entropy rise. It is demonstrated that fluid can be delivered to the stator vanes with a plenum style inlet for a radial inflow supercritical CO2 turbine without re-circulation regions and minimal total pressure loss. Entropy rise for the plenum is reduced more than tenfold in comparison to the volute, however fluid velocities are not matched and there is a periodic variation in in velocity generated by the multiple inlets.