Development of Moisture Loss Models in Steam Turbines

This paper describes physics-based moisture loss models for designing wet-steam turbines. Steam turbines in wet-steam conditions experience thermodynamic and mechanical losses caused by the presence of moisture. The developed moisture loss models are composed of six categories : supersaturation loss, condensation loss, accelerating loss, braking loss, capturing loss and pumping loss. These losses are calculated according to the wetness levels in the nozzle & bucket rows, and defined by the functions of steam properties and design factors of turbine stages. The supersaturation loss produced by the non-equilibrium expansion of the wet steam is modeled using the pressure ratio and the isentropic exponent in the supersaturated steam. The loss models are applied to the full-size test turbine data for the prediction of the overall moisture losses. As a result, the developed loss models are found to be very effective for estimating the moisture losses of turbine stages.