Calculation Method of Moisture Flow Discharge Coefficient in Steam Turbines

This paper describes a calculation method of moisture flow discharge coefficient for designing wet-steam turbines. The flow discharge coefficient in wet-steam conditions is different from that in dry-steam conditions, because the former is affected by supersaturation phenomenon and wetness fraction. An accurate prediction of the flow discharge coefficient is required for flow-pattern design in turbine stages. The developed calculation method is divided four models according to the wetness levels in the nozzle & bucket rows, and defined by the functions of wet-steam properties, such as saturated & supersaturated isentropic exponents, wetness fraction, and pressure ratio in the nozzle & bucket rows. The calculation method is applied to a full-size & a model test turbine data for the prediction of the moisture flow discharge coefficient. As a result, the developed calculation method is found to be very effective for estimating the moisture flow discharge coefficient in a wide range of wetness fractions.