Numerical prediction of the performance of radial inflow turbine designed for ocean thermal energy conversion system

Abstract

Ocean thermal energy conversion (OTEC) is a source of renewable energy that employs temperature difference existing between water surface and some depth inside ocean. In this work, a small laboratory scale model radial turbine was designed with 2kWe power output for OTEC application. Working fluid chosen for this turbine is refrigerant R134a. The turbine is designed for inlet and exit temperatures of 24.5°C and 14°C respectively. Speed of the turbine is chosen as 22000rpm in order to avoid the use of gearbox. A comprehensive one-dimensional mean line design approach for radial-inflow turbine is adopted in this work. Important dimensions of R134a turbine are 35.5mm and 22mm for rotor tip and shroud radii respectively and blade widths at rotor inlet and outlet are 6mm and 13mm respectively. Detailed numerical simulation predicts the performance of the baseline turbine geometry described above. Further investigations were performed to bring out the effects of different geometric parameters on turbine performance. It is shown that blade edge filleting is very important to improve turbine performance over a wide range of operating parameters. Effect of tip clearance was found to be more significant than that in conventional large-sized turbines. Two phase flow calculation involving non-equilibrium condensation of vapor shows the effect of liquid wetness fraction to be of limited influence because of restricted range of pressure ratio that the turbine goes through.