The highly efficient expansion turbine plays an important role in the Organic Rankine cycle for low-grade heat energy recovery. It is known that the proper preliminary design is essential for the expansion turbine. The present paper focuses on the preliminary design for a 590 kW radial inflow turbine with organic working fluid R134a. An in-house code of the preliminary design for the radial inflow turbine is programmed with MATLAB language, and the physical properties of the organic working fluid are acquired from NIST REFPROP software. The validity of the current code is firstly proven in comparison with the published data. The influences of seven design parameters, including velocity ratio, reaction degree, nozzle velocity coefficient, rotor velocity coefficient, absolute flow angle at rotor inlet, relative flow angle at rotor outlet, and wheel diameter ratio, are then discussed on the total-to-static efficiency. The optimization work is finally performed to find the maximum total-to-static efficiency and the relevant design parameters using the particle swarm optimization algorithm. It is shown that the total-to-static efficiency is improved by performing the optimization work, and the value of 84.84 is achieved. The rotor inlet and outlet velocity triangles, meridian geometries, and energy loss coefficients are compared and analyzed between the initial and optimum designs.
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