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Abstract

The aim of this paper is to conduct a preliminary comparison of different turbine architectures for a small-scale 100 kW supercritical CO 2 Rankine cycle. The turbine is required to expand supercritical CO2 from 650°C and 170 bar, down to 50 bar. For such an application, it is not immediately clear which turbine architecture is the most suitable design when considering both aerodynamic and mechanical design constraints. Within this paper, three different turbine architectures are considered, namely radial-inflow, single-stage axial, and two-stage axial turbines. For each architecture, a preliminary design model is constructed which is based on conventional turbomachinery design parameters such as the loading coefficient, flow coefficient and degree of reaction. Using this model, a parametric investigation on the effect of the rotational speed on the required rotor diameter and blade height is conducted and the different turbine architectures are compared. This is completed with the view of establishing the feasible design space for a small-scale supercritical CO2 turbine. For all three architectures, it is found that in order to obtain feasible blade heights it is necessary to maximise the loading coefficient whilst m inimising the flow coefficient, and design the turbine with the minimum allowable diameter. Typically, this results in a turbine design w ith a rotor diameter of 30 mm, a rotor-inlet blade height in the range of 1.74 to 2.47 mm, and a rotational s peed between 150 and 250 kRPM for a single-stage radial or axial turbine, and 75 and 175 kRPM for a two-stage axial turbine. Ultimately, nine candidate turbine designs have been identified, which should be studied further using more advanced 3D CFD and FEA simulations.

Publication Type:	Conference or Workshop Item (Paper)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering

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