Analytical and numerical investigation of a small-scale radial-inflow steam turbine

Abstract

This thesis compares experiments to the analytical and numerical investigation of a small-scale radial-inflow turbine (diameter of 15 mm). This turbine is part of the Fan-Turbine Unit (FTU). The turbine of this FTU propels the fan that recirculates the unused hydrogen and water vapor from the anode off-gas of a Solid Oxide Fuel Cell (SOFC) to its inlet. This recirculation improves the electrical efficiency of the SOFC system due to higher global fuel utilization and allows for an operation without external water supply for the steam reformer. Due to its high efficiencies, also at small-scale and the possibility for heat cogeneration, it is competitive compared with other energy generation systems. The main objective of this thesis is to improve the existing analytical and numerical models of the turbine and compare their respective results with experimental measurements. Good results are obtained with the analytical (38 Watt) and the numerical investigation (43 Watt), if the gas film bearing mechanical loss (18 Watt) is added to the experimental measurement (22 Watt). The turbine power at the design point is very low (40 Watt) compared to the bearing mechanical losses (18 Watt), so heat fluxes to the turbine impeller domain have a high impact.