Анализ моделей силового взаимодействия пара и жидкости в барботажном слое для двухскоростного описания пароводяной смеси

Abstract

Тhe article analyzes the effect the interfacial force interaction models developed for different types of bubble flows have on the bubble layer description. The analysis is performed in the framework of a stationary 1D two-velocity mathematical model describing the flow of steam-water mixture with the liquid phase velocity assumed equal to zero. A conjecture was made based on the results from studying the qualitative flow pattern in the bubble layer that an emulsion flow mode takes place in it for practically important steam loads. The calculated values were compared with the typical actual values for horizontal steam generators used in nuclear steam supply systems built around VVER-type reactors. The calculated void fraction value in the bubble layer’s main part was found to be significantly higher than the experimental values. The same picture was also obtained for other values of reduced steam velocity and void fraction in the ranges obtained in these steam generators, which is attributed to the way in which the interfacial interaction force is simulated. It is shown that the use of the considered models leads either to a significant overestimation of the interfacial interaction force and, consequently, the void fraction in the bubble layer, or to lack of solution for the values of parameters characteristic for the horizontal steam generators of nuclear power plants equipped with VVER-type reactors. The correlations investigated in this study were derived proceeding from the flow friction coefficient of a single bubble as a function of the Reynolds number and introduction of the mixture viscosity that depends on the volume fraction of the dispersed phase. A steady flow of the two-phase mixture was considered under such conditions. Possibly, such a steady flow does not have enough time to be formed in steam generators. The steam entering from the bottom into the bubble layer through the submerged perforated sheet (SPS) holes initially ascends as a jet through the liquid layer. The steam-liquid interface separating the steam jet from the liquid may experience instability according to the Kelvin-Helmholtz mechanism. Estimates show that the time for which disturbances develop on the jet surface is essentially shorter than the time taken for the steam to pass through the bubble layer, a circumstance due to which perturbations may grow significantly up to reaching a nonlinear stage and appearance of complex two-phase structures.