Study on the spontaneous condensation of moist air in the high-speed turbo-expander

Spontaneous condensation processes are common in the industry and have a significant impact on the aero-dynamic characteristics of turbines. The spontaneous condensation process of moist air in a high-speed turbo -expander was investigated experimentally and numerically. Temperature and humidity of the moist air into the turbo-expander were controlled independently in a psychrometric chamber. A liquid fraction of 0.8% was achieved at the turbo-expander outlet which was corresponding to a relative humidity of 76.9% at 303.2 K. The non-equilibrium condensation model was validated against the experimental results, and the maximum relative deviations of outlet temperature, absolute humidity, and moist efficiency were 0.16%, 3.23%, and 2.15%, respectively. Based on numerical simulations, the nucleation process and droplet distribution in the turbo -expander were studied. Compared with the suction surface, the nucleation region near the pressure surface was more extensive. The effect of inlet temperature, humidity, and pressure was compared. The inlet pressure had the most significant impact on the nucleation initial position, and the inlet temperature mainly determined the nucleation rate and droplet number. The wetness loss due to the vapor condensation mainly occurred in the impeller, and the efficiency drop could reach 2.17% when the pressure ratio was 2.1.