Publisher Summary Slug flow is a highly complex type of flow with an unsteady nature The prediction of pressure drop, heat, and mass transfer for such flow is often considered a difficult task The chapter deals with steady slug flow The chapter introduces several options of modeling the hydrodynamic parameters and pressure drop using a unified approach that is applicable for the vertical, horizontal, and inclined cases The chapter also reviews transient phenomena in slug flow by illustrating an example of severe slugging in a pipeline-riser system It is noted that heat transfer in slug flow is of major importance for practical applications The treatment of the two-phase flow is usually considered as a two-phase mixture The severe slugging that consists of one riser and one pipeline is one of the simplest example of slug flow under nonsteady conditions The Boe criterion differentiates between steady and cyclic operations with two exceptions At high liquid flow rates, a steady flow can also exist within the severe slugging region predicted by the Boe criterion There is a region outside the Boe criterion that is in an unsteady state and leads to unsteady oscillations

Two-Phase Slug Flow

Two-phase flow hydrodynamics in vertical capillaries of circular and square cross sections were experimentally studied, using air as the gas phase and water, ethanol, or an oil mixture as the liquid phase. The capillary hydraulic diameters ranged from 0.9 mm to 3 mm, with the superficial gas and liquid velocities covering a span of 0.008−1 m/s, which is typical of that obtained in monolith reactors. Using a high-speed video camera, four distinct flow regimes were observed within the range at which experiments were conducted:  bubbly, slug-bubbly, Taylor, and churn flows. Annular flow was observed at excessively high gas and low liquid flow rates, well beyond those of interest to this study. Based on the definition of a two-class flow regime, the combination of two parametersthe slip ratio (S) and the ratio of the superficial gas velocity to two-phase superficial velocity (UG/UTP)was observed to be suitable for determining the transition from homogeneous flow to nonhomogeneous flow. The influence of capill...

Hydrodynamics of Taylor Flow in Vertical Capillaries: Flow Regimes, Bubble Rise Velocity, Liquid Slug Length, and Pressure Drop

A unified hydrodynamic model is developed for predictions of flow pattern transitions, pressure gradient, liquid holdup and slug characteristics in gas-liquid pipe flow at all inclination angles from -90° to 90° from horizontal. The model is based on the dynamics of slug flow, which shares transition boundaries with all the other flow patterns. By use of the entire film zone as the control volume, the momentum exchange between the slug body and the film zone is introduced into the momentum equations for slug flow. The equations of slug flow are used not only to calculate the slug characteristics, but also to predict transitions from slug flow to other flow patterns. Significant effort has been made to eliminate discontinuities among the closure relationships through careful selection and generalization. The flow pattern classification is also simplified according to the hydrodynamic characteristics of two-phase flow.

D.J. Nicklin

Papers

Two-phase bubble flow