Turbulence-Induced Bubble Collision Force Model Development and Assessment for Adiabatic Dispersed Air-Water Two-phase Flow with the Two-Fluid Model

Abstract

The prediction capability of the two-fluid model for gas-liquid dispersed two-phase flow depends on the accuracy of the closure relations for the interfacial forces. In previous studies of two-phase flow Computational Fluid Dynamics (CFD), interfacial force models for a single isolated bubble has been extended to disperse two-phase flow assuming the effect in a swarm of bubbles is similar. Limited studies have been performed investigating the effect of the bubble concentration on the lateral phase distribution. Bubbles, while moving through the liquid phase, may undergo turbulence-driven random collision with neighboring bubbles without significant coalescence. The rate of these collisions depends upon the bubble approach velocity and bubble spacing. The bubble collision frequency is expected to be higher in locations with higher bubble concentrations, i.e., volume fraction. This turbulence-driven random collision causes the diffusion of the bubbles from high concentration to low concentration. Based on experimental observations, a phenomenological model has been developed for a "turbulence-induced bubble collision force" for use in the two-fluid model. For testing the validity of the model, two-phase flow data measured at Purdue University are utilized. The geometry is a 10 mm x 200 mm cross section channel. Experimentally, non-uniform inlet boundary conditions are applied with different sparger combinations to vary the volume fraction distribution across the wider dimension. Examining uniform and non-uniform inlet data allows for the influence of the volume fraction to be studied as a separate effect. The turbulence-induced bubble collision force has been implemented in ANSYS CFX. The assessment results show agreement with the measured data, correctly capturing the redistribution of volume fraction downstream with uniform and non-uniform inlet profiles. In particular, for the nonuniform data, the transverse redistribution of volume fraction at downstream locations is captured. This signifies the importance of bubble-bubble collision phenomena in correctly predicting volume fraction distributions.

Meeting Name

International Topical Meeting on Nuclear Reactor Thermal Hydraulics 2015, NURETH-16 (2015, Aug. 30-Sep. 4, Chicago, IL)

Department(s)

Nuclear Engineering and Radiation Science

Keywords and Phrases

Air; Computational fluid dynamics; Diffusion in liquids; Hydraulics; Nuclear reactors; Turbulence; Volume fraction; Air-water two phase flows; Bubble collision; Dispersed two-phase flows; Interfacial force models; Interfacial forces; Phenomenological modeling; Two fluid model; Volume fraction distribution; Two phase flow; Bubble collision based diffusion; CFD; Interfacial force; Turbulence; Two-fluid model

International Standard Book Number (ISBN)

978-1-5108-1184-3

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2015 American Nuclear Society (ANS), All rights reserved.

Publication Date

01 Aug 2015

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