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2 Transactions of the Institute of Fluid-Flow Machinery

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Gas-liquid and liquid-liquid stratified flows: exact analytical solutions and mechanistic models

Ullmann A., Goldstein A., Brauner N.

Transactions of the Institute of Fluid-Flow Machinery

2005

nr 117

59-79

An exact analytical solution has been obtained for fully developed laminar stratified flow in inclined pipes with a plane or curved interface. This solution is of practical significance mainly for studying liquid-liquid flows. However, it is also needed as a benchmark for testing the validity of numerical methods, and for testing closure relations for two-fluid models. Two-fluid models may yield poor predictions in inclined co-current and counter-current flows. The commonly used closure relations for the wall and interfacial shear stresses do not correctly represent the fine balance between the gravity body forces and viscous shear in inclined flows. The exact solution obtained for laminar flows is used to establish and validate new closure relations, which account for the interaction between the phases and are applicable also for turbulent stratified flows.

Prediction of holdup in liquid slugs

Brauner N., Ullmann A.

Transactions of the Institute of Fluid-Flow Machinery

2003

nr 112

75--90

Correlations and models from the literature for the prediction of void fraction in liquid slugs are reviewed. It is shown that a mechanism that can explain the slug aeration in vertical, horizontal and inclined tubes has not yet been established. A new model that attributes the aeration of the liquid slug to a recurrent bubble entrainment from the Taylor bubble (TB) tail is introtuced. The bubble fragmentation is related to the rate of turbulent kinetic energy in the shear layer, which is formed at the TB wake as the liquid film plunges into the slug front. The model has been tested against experimental data available from the literature and was found to predict the effects of liquid and gas flow rates and physical properties, as well as tube diameter and inclination on the void fraction.