Interfacial area measurement and transport modeling in air -water two -phase flow

Xinyu Fu, Purdue University

Abstract

In two-fluid model, the interfacial area concentration (IAC) is an important parameter that characterizes the interaction of two-phases at the interface. The accuracy of IAC modeling and local measurements largely affects the efficiency of designing and assessing two-phase flow systems. The prediction of the dynamical evolution of IAC is one of the most challenging tasks in research and application. This thesis is focused on developing advanced local measurement techniques to obtain reliable two-phase parameters and implementing efficient theoretical models for IAC source and sink terms in a two-group interfacial area transport equation based on experiments. In this study, an advanced local measurement technique using a four-sensor conductivity probe has been presented for obtaining IAC in air-water flows. It extends the existing conductivity probe method to slug and churn-turbulent flows with a unified probe design and comprehensive signal processing system. Sophisticated algorithm and software have been implemented that is robust in handling most practical conditions with high reliability. Systematic analyses on the issues of probe applications and benchmarks have been performed. The improved four-sensor method has also been applied to flow conditions with significant local recirculation, which was considered the most challenging situation for local measurement in two-phase flow. Using the well-established instrumentation, solid databases for a two-inch air-water loop have been built with sufficient information on the axial development and the radial distribution of the local parameters. Mechanistic models of major fluid particle interaction phenomena involving two bubble groups have been proposed, including the shearing-off of small bubbles from slug/cap bubbles, the wake entrainment of group-1 bubble into group-2 bubble, the wake acceleration and coalescence between group-2 bubbles, and the breakup of group-2 bubbles due to surface instability. Prediction of IAC evolution using the one-dimensional two-group transport equation and evaluation with experimental results are performed. The proposed model predicts a smooth transition across the bubbly-to-slug flow regime boundary and demonstrates mechanistic interactions for cap/slug bubble generation and developing processes. The finalized two-group interfacial area transport equation successfully covers a wide range from bubbly, slug, to churn turbulent flow regimes for adiabatic air-water upward flow in moderate diameter pipes.

Degree

Ph.D.

Advisors

Ishii, Purdue University.

Subject Area

Nuclear physics|Mechanical engineering|Chemical engineering

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