Design of an efficient space constrained diffuser for supercritical CO2 turbines

1st International Seminar on Non-Ideal Compressible-Fluid Dynamics for Propulsion & Power

物理学;力学

Keep, Joshua A.^1 ; Head, Adam J.^2 ; Jahn, Ingo H.^1

University of Queensland, Brisbane, Australia^1

Delft University of Technology, Delft, Netherlands^2

关键词: Cantilevered rotor;    Design constraints;    Energy extraction;    Geometric characteristics;    Radial inflow turbine;    Static-pressure recovery;    Supercritical CO2;    Turbine inlet pressure;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/821/1/012026/pdf
DOI  :  10.1088/1742-6596/821/1/012026

学科分类：力学，机械学

来源: IOP

【 摘 要 】

Radial inflow turbines are an arguably relevant architecture for energy extraction from ORC and supercritical CO2power cycles. At small scale, design constraints can prescribe high exit velocities for such turbines, which lead to high kinetic energy in the turbine exhaust stream. The inclusion of a suitable diffuser in a radial turbine system allows some exhaust kinetic energy to be recovered as static pressure, thereby ensuring efficient operation of the overall turbine system. In supercritical CO2Brayton cycles, the high turbine inlet pressure can lead to a sealing challenge if the rotor is supported from the rotor rear side, due to the seal operating at rotor inlet pressure. An alternative to this is a cantilevered layout with the rotor exit facing the bearing system. While such a layout is attractive for the sealing system, it limits the axial space claim of any diffuser. Previous studies into conical diffuser geometries for supercritical CO2have shown that in order to achieve optimal static pressure recovery, longer geometries of a shallower cone angle are necessitated when compared to air. A diffuser with a combined annular-radial arrangement is investigated as a means to package the aforementioned geometric characteristics into a limited space claim for a 100kW radial inflow turbine. Simulation results show that a diffuser of this design can attain static pressure rise coefficients greater than 0.88. This confirms that annular-radial diffusers are a viable design solution for supercritical CO2radial inflow turbines, thus enabling an alternative cantilevered rotor layout.