The Behaviour of Nucleation Fogs within the Nozzle Boundary Layer in the Wet Steam Turbine

Abstract

At low pressures the boundary layer within a turbine blade passage carrying a nucleation fog is very sparsely populated with droplets and its hydrodynamic behaviour is not materially influenced by their presence. The rate of energy dissipation within the boundary layer is only sufficient to evaporate a very small fraction of the total liquid entrained in the layer; nevertheless, superheat due to temperature recovery is almost completely suppressed by this evaporation. Thermal coagulation is active within the layer and gradient coagulation is very significant when the droplets are large. Any valid theory of deposition by diffusion must recognize this fact. Calculations were made for the concave surface of a typical low pressure turbine blade and boundary layer properties of interest are displayed.