Thermodynamic losses of hetero and homogeneous condensation in steam turbine cascades

Abstract

The approach used in this paper for the condensation of flowing steam is based on the homogeneous condensation of steam and also on the heterogeneous (binary) nucleation of water droplets with a representative chemical impurity NaCl. The physical and mathematical models are briefly described. The homogeneous and binary nucleation numerical models are then used for the calculation of steam flow with condensation in the two-dimensional nozzle-blade cascade of the first wet stage of the low-pressure part of a fossil-fuelled condensing 200-MW steam turbine and in a similar cascade of the low-pressure part of a nuclear 1000-MW turbine. Results of the calculations of the flow in the cascades and of the thermodynamic loss are presented and analysed. It is recommended to situate the salt solution zone of NaCl upstream of a turbine nozzle cascade, to use a lower expansion rate on the cascade, and to realise there, primarily, a heterogeneous process (binary nucleation of steam and NaCl) for the initial condensation.