MATHEMATICAL RELATIONSHIPS OF MODELS OF TWO-PHASE FLOWS IN CHANNELS OF REACTORS AND STEAM GENERATORS OF NPP’s FOR CALCULATION OF THEIR HYDRODYNAMIC CHARACTERISTICS

Abstract

Two-phase flows of the working substance in the steam-generating channels of reactors of single-circuit NPP’s and steam generators of two- and three-circuit NPP’s represent the joint movement of liquid (feed water) and steam in the form of a steam-water mixture. The forms of movement of two-phase flows are much more diverse, and the laws of their movement are much more complicated than flows of single-phase media, and they are characterized by a large number of parameters. This is due to the fact that when the flow of the steam-water mixture moves in the steam-generating channels, mass exchange processes occur between the liquid and vapor phases of the mixture, in which the volumes of the phases change; the interfaces between the phases of the mixture vary along the length of the channel and often do not have a distinct character. The cross-sectional mean velocities of the liquid and vapor phases of the flow are not equal to each other, and the difference in the velocities of the phases in the steady-state mode of motion of the two-phase flow depends on the mass flow rate of the steam-water mixture, its pressure, direction of flow, heating intensity, and other indicators. All this complicates experimental studies and calculations of parameters and hydrodynamic (gas-dynamic) characteristics of two-phase flows of a steam-water mixture of a working substance in reactors and steam generators of nuclear power plants. The article discusses mathematical relationships for calculating the hydraulic characteristics of two-phase flows of different structures during the movement of a steam-water mixture in the steam-generating channels of reactors and steam generators of nuclear power plants, namely bubble, slug, rod, dispersed. The ratios are given for various designs of the channels of reactors and steam generators.