# Dynamic modeling of interfacial structure in two-phase flow using interfacial area transport equation in CFD code

#### Abstract

The dynamic modeling of the interfacial structure in two-phase flows is accomplished by using the interfacial area transport equation with various bubble interaction mechanisms as the source and sink terms. In the present study, the one-group interfacial area transport equation and two-group interfacial area transport equation are implemented into a commercial 3-D CFD code, ANSYS CFX. The one-group interfacial area transport equation is directly coupled with the conventional two-fluid model. On the other hand, the two-group interfacial area transport equation is implemented with a modification of the conventional two-fluid model. In view of the implementation of the two-group interfacial area transport equation, the conventional two-fluid model needs to be modified as either the three-field two-fluid model or modified two-fluid model. The three-field two-fluid model treats the Group-1 and Group-2 bubbles separately for the gas phase. So the three-field two-fluid model solves two gas momentum equations. The modified two-fluid model treats the combined mixture gas phase for the Group-1 and Group-2 bubbles. Thus, the modified two-fluid model solves the one mixture gas momentum equation with the constitutive relation for the relative velocity between the Group-1 and Group-2 bubbles, while it deals with two gas continuity equations for the Group-1 and Group-2 bubbles. The implemented one-group interfacial area transport equation with the two-fluid model is benchmarked against the experimental data for the bubbly flow conditions in the rectangular test section with narrow channel gap. The simulation results with the interfacial area concentration, void fraction, bubble Sauter mean diameter, and gas velocity show reasonable agreement with the experimental data in terms of the area-averaged values along the axial direction and the transverse local phase distribution. The benchmark for the local phase distribution by using the one-group interfacial area transport equation is performed with the lift force, wall lubrication force and turbulent dispersion force to close the interfacial momentum transfer. On the other hand, the implemented two-group interfacial area transport equation in the framework of the modified two-fluid model which is based on the mixture gas momentum equation is benchmarked against the experimental data beyond the bubbly flows. The advanced interfacial forces such as the lift force with physics-based lift coefficient, bubble induced turbulent diffusion force, turbulent lift force (corner force) and Basset force as well as bubble induced turbulence model are applied to the benchmark against beyond the bubbly flows. It is found that the lift force with physics-based lift coefficient, bubble induced turbulent diffusion force and bubble induced turbulence model show enough capability to predict the local phase distribution beyond the bubbly flow conditions. These interfacial forces and bubble induced turbulence model are also applied to the benchmark against various non-uniform flow conditions and show prediction capability with the two-group interfacial area transport equation for the local phase distribution in the framework of the modified two-fluid model. It is expected that the prediction capability against non-uniform flow conditions can be improved with separate treatment of the Group-1 and Group-2 bubble momentum equations called the three-field two-fluid model.

#### Degree

Ph.D.

#### Advisors

Ishii, Purdue University.

#### Subject Area

Nuclear engineering

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