Investigation of Gas-Liquid Two-Phase Flow Using Three-Field Two-Fluid Model and Two-Group Interfacial Area Transport Equation in CFD Code

Subash L Sharma, Purdue University

Abstract

Prior work has shown that a two-fluid model with a single set of constitutive relations is required to predict a wide range of two-phase flow conditions. The current work is a step in that direction. The 3-D three-field two-fluid model with a two-group Interfacial Area Transport Equation (IATE) has been selected as the required framework with the Computational Fluid Dynamics (CFD) code ANSYS-CFX. The objectives of this proposed work are the following: select a set of constitutive relations and implement these models into CFX; evaluate these models for a wide range of test conditions; if required, develop better models for the interfacial transfer mechanisms. Models and constitutive relations were validated against experimental data. The following difference between CFD simulations and experimental results were observed: insufficient diffusion of bubbles; and physically unrealistic void fractions for small bubbles in the near-wall region for highly turbulent flow cases. Bubble diffusion is hypothesized to be insufficient because an important mechanism for diffusion by turbulence-driven random collision of bubbles was not modeled. A diffusion force model based on turbulence induced bubble collision is formulated and assessed against experimental data from bubbly to churn-turbulent flow with uniform and non-uniform inlet injection conditions. Although the overall predictions of void fraction improved with bubble collision diffusion force, a relatively high void fraction is still predicted for smaller Group-1 bubbles in the near-wall region for highly turbulent flow cases belonging to the high liquid velocity regime. A model for lift coefficient with dependency on channel liquid Reynolds number has been proposed; this is found to solve the unrealistic peak near the wall region. Discrepancies were also found in predictions of the coalescence and breakup models of the IATE, especially near flow regime transitions. Therefore, new experiments were performed in the flow transition region with the objective of obtaining accurate flow transition data for assessing the IATE models. The new data were used for evaluation of IATE models in one-dimensional form and possible reasons for discrepancies are discussed.

Degree

Ph.D.

Advisors

Ishii, Purdue University.

Subject Area

Engineering|Nuclear engineering

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