Application of Invariant Turbulence Modeling of the Density Gradient Correlation in the Phase Change Model for Steam Generators

Abstract

Predictions of the amount of steam generated on evaporation plates are mostly done by empirical algebraic models or semi-algebraic one equation models. However, the accuracy of the methods fully depends on the equipment and the environment. A new method that directly installs the phase change model into the system of fluid dynamics equations is studied for improvement. First, a turbulence model for the phase field model below the boiling point or near the boiling point is constructed. The model consists of the density gradient correlations, which are shown in the set of the phase field equation (C-H equation). The density gradient correlation is obtained with the Reynolds decomposition from the compressible continuity equation. Second, to import the effect of viscosity, the pseudo stress tensor in the momentum equation is modified in a semi-direct simulation, which covers mainly large eddies on coarse grids. A steam generator is modeled with a three-layer problem: the water layer, the humid air layer, and the environmental boundary in nearly homogeneous turbulence with strong acoustical disturbances, which are common in the multi-phase flows in pipes. The density gradient correlation equation is closed by the invariant modeling technique with many unknown constants. In the present work, one constant appearing in the invariant model is determined theoretically. The set of equations allows stable computations during prediction for the steam generator.