On the performance of a cascade of improved turbine nozzle blades in nucleating steam – Part 3: theoretical analysis

Abstract

This article is the last of a set and describes the analysis of the performance of an improved steam turbine nozzle blade profile. In the course of expansion of steam in turbines, the state path crosses the saturation line, the fluid nucleates to become wet, and the succeeding stages have to operate on a two-phase mixture. The formation and subsequent behaviour of the liquid phase lowers the performance of turbine wet stages. Following earlier studies of typical profiles in nucleating steam, the performance of a new design of blades is examined. A substantially improved aerodynamic performance is achieved by the new design. The effect of heat release by condensation in increasing the aerodynamic losses is not intrinsic to the system and can be avoided by design but the losses resulting from the internal heat transfer are intrinsic and considerable.