Three-dimensional interfacial area transport in gas-dispersed two-phase flow up to churn-annular flow transition

Yang Liu, Purdue University

Abstract

The interfacial area transport equation (IATE) was developed to dynamically model the evolution of interfacial structures across the flow regime transition boundaries through mechanistic modeling of various fluid particle interaction phenomena. Previous researches largely focused on the one-dimensional phenomena where flow parameters were assumed to be uniformly distributed on the cross sectional plane. Nevertheless, a three-dimensional interfacial area transport equation is indispensable since the flow structures of multiphase flows are intrinsically multidimensional. Presented in the first part of the thesis is the experiment on the interfacial area transport in a narrow rectangular test section with strong multidimensional phenomena generated by various kinds of skewed inlet boundary conditions. The experiments consist of nine flow conditions with non-uniform gas injection and nine flow conditions with non-uniform liquid injection in bubbly, cap-turbulent and churn-turbulent flow regimes. Local two-phase parameters such as void fraction, bubble velocity, interfacial area concentration, etc., are measured using four-sensor conductivity probes at three axial locations. The local data were area averaged to evaluate the one-dimensional interfacial area transport equation. The agreement is satisfactory in general, however, deficiencies in the one-dimensional model were obvious and modification in the source sink terms was suggested. In the second part of the thesis, the experimental study of transition from churn-turbulent flow to annular flow is reported considering that the existing two-group interfacial area transport equation is only applicable up to churn-turbulent flows. Totally fifty-nine flow conditions around the transition region were tested on a test section equipped with local and global impedance probes and conductance probes. Data measured by those instrumentations were input into a self-organized neural network which can classify the given flow conditions based on a competitive learning algorithm and the characteristics of the signal. In this way the flow regimes were objectively identified. From the experimental results, the transition criterion based on onset of entrainment mechanism is found to be locally applicable and a transition boundary map varying with lateral locations is introduced. Finally, the three-dimensional two-fluid model with IATE is proposed to model two-phase flows covering the entire spectrum of flow regimes and to dynamically solve the transition problem. A new approach based on the local instant formulation of interfacial area is established in order to develop the IATE for flows near transition and in annular regime. It can handle the continuous interface between liquid film and gas core which cannot be modeled by the previous Boltzmann transport equation. Various source/sink terms have been analyzed for transition and annular flows. Detailed modeling, experiment and benchmarking need to be carried out in the future work.

Degree

Ph.D.

Advisors

Ishii, Purdue University.

Subject Area

Nuclear engineering

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