An Analysis of Models Describing the Hideout Phenomenon in the Steam-Generating Equipment of Nuclear and Thermal Power Plants (a Review).

The salt hideout phenomenon of boiler water attracted the close attention of specialists as long ago as the 1940s–1950s. By the end of the 1980s, the majority of researches had arrived at the conclusion that the governing role in the hideout phenomenon is played by the deposits of structural material corrosion products (crud) on the steam-generating surfaces of the equipment of nuclear and thermal power plants. The steam-generation process takes place under confined conditions, which causes degraded mass transfer between the flow core and the heat-transfer surface. This results in that water impurities concentrate in the pores of deposits and even precipitate in a solid phase form. As the steam boiler/steam generator power output increases, the concentrations of certain impurities and chemical agents in boiler water decrease; this effect is called hideout, and as the load decreases, their concentrations increase (hideout return). In the last decades, a few physical and mathematical models have been developed in which the hideout phenomenon is considered from the viewpoint of boiler water impurities becoming concentrated not in the layer of permeable deposits but in the viscous sublayer of liquid at the steam-generating surface. Thus, the thermodynamic model rests on the postulates of nonequilibrium thermodynamics and is descriptive in nature. The mass-transfer model based on the laws of mass and energy conservation in the viscous sublayer incorporates an analytical expression for the impurity concentration ratio. However, this model also in fact contains only a qualitative description of the hideout process without performing its detailed comparison with experimental data. The article presents an analysis of these models and their comparison with reliable data obtained by domestic and foreign researchers, and it is shown that the key statements laid down at the essence of models based on impurity concentration in the liquid viscous sublayer are erroneous in nature. Adequate fundamental principles of mass transfer under hideout conditions are of significant theoretical and practical importance for working out operation regulations and securing reliable operation of installations with boiling coolant at nuclear and thermal power plants. [ABSTRACT FROM AUTHOR]