Theoretical Investigations on Water Condensation in Main Steam Pipe

摘要

Condensation in the main steam pipe is harmful for the downstream steam turbine. If the condensation water has not been completely drained from the main pipeline, the droplet will lead to the water hammer and cause unstable operations for the power station. As a result, accurate predictions of the water condensation during the startup and stable running processes are helpful for the drainage system operations and controls. In the power station, the main pipeline consists of pipe and outside insulation layer which prevents the heat loss thus improves the thermal efficiency. In this case, complex heat transfers including heat convection, conduction and radiation occur from the water-steam side to the atmospheric environment. In the current study, by using the theoretical methods, heat transfer and water condensation rate in the main steam pipe for the nuclear power station are calculated. Firstly, heat convection from the steam to the pipe, heat conduction in the pipe and insulation layer, and natural convection outside the insulation layer are computed and analyzed based on heat transfer theory and empirical correlation expressions. Secondly, in order to visualize the wetness distributions and pressure loss, the corresponding CFD computations with equilibrium condensation model is additionally utilized. Compared to the theoretical predictions, numerical result shows the same trend of the condensation and heat transfer loss. Finally, a new theoretical method without specifying the outer wall temperature of the insulation layer is developed. It shows that this method can predict a reasonable condensation rate and is convenient for the industrial applications.