Study on two-phase nozzle and turbine

Abstract

Low temperature thermal energy included in hot spring or waste-heat at factories has been abandoned until now. It is reported that geothermal heat of up to 120 degrees corresponds to the energy of 7.4GW. Among them, a new technology that attempts to recover the thermal energy by driving turbine with two-phase flow which is generated by flashing hot water has been developed. The high momentum and low velocity two-phase flow drives the turbine at synchronous speed to the generator. This eliminates the need for the expensive gearbox required for the conventional steam turbine systems and thereby improves the reliability and reduces the maintenance. However, the improvement of efficiency and stability is required to put to the practical use. Therefore, the basic experiment to understand the performance of two-phase turbine and flashing nozzle was conducted and discussed by using water instead of organic fluid. Water is expected to be used to prevent the environmental destruction. The visualization of two-phase flow at the nozzle exit was conducted and the power output of two-phase turbine was measured. The experimental and analytical results showed that: (1) the non-equilibrium degree changed from nozzle throat to exit.; (2) steel wool in the convergent part of nozzle could effectively reduce the non-equilibrium and suppressed the pulsation of two-phase jet; (3) the practical two-phase jet velocity was obtained from the maximum turbine efficiency and compared with the prediction with non-equilibrium model.