Condensation on the Surface of a Low-Pressure Steam Turbine Suction Blade

Abstract

A 2·54 cm length of low-pressure turbine suction blade mounted between perspex walls to form a test section was used to determine the distribution of static pressure and surface temperature when passing near-saturated live steam at realistic turbine conditions. The distribution of static pressure conformed closely to that applicable to one-dimensional isentropic expansion with γ = 1·326. Working surface temperatures were taken for ‘steam-only’ flow with and without blade suction and for ‘steam-with-surface-water’ flow with and without suction. For dry flow with no suction, recovered values of temperature approximated to stagnation values, but with suction applied, a temperature reduction was promoted by the inward heat transfer due to the colder blade interior. Liquid film thickness was measured by electrical conductivity probes and values obtained were compared with predictions from turbulent film flow theories. Condensation on the blade surface was measured by three experimental methods and the results compared with predictions from turbulent-film condensation theories. A correlating equation is proposed which enables prediction of condensation rates from the average values of the steam Mach number and Reynolds number over the blade, and the Prandtl number of the water.