Effect of Exit Pressure of Steam Turbine Last Stage Cascade Blade on Two Phases of Saturated Vapor and Water Droplet

Abstract

Experimental investigation was carried out in low pressure steam turbine cascade to determine the effect of exit pressure on two phases of saturated vapor and fine water droplet. Numerical investigation was also presented by assuming the flow is two dimensional, compressible, turbulent, viscous, with the aid of the classical nucleation model applied for the mass transfer in the transonic conditions to predict the two phases behavior in the cascade. Comparison between experimental and theoretical results for the cascade flow was found to be fairly acceptable. Experimentally it was found that the most important influence of rapid condensation on the pressure distribution is on the suction surface. Also when the outlet is termed supersonic the heat release causes a pressure rise in the zone of rapid condensation, therefore the term "condensation shock" for this feature is misleading. In the numerical approach when the flow is regard subsonic the rapid condensation zone occurs downstream the throat and not accompanied by a pressure rise, while in the experimental test for the same case there is no sign of this condensation.

Keywords

• cascade
• condensation
• two phases
• saturated
• vapor
• droplet
• exit pressure