Stability of annular flow and slugging

Abstract

In this work we propose an effective viscosity criterion for the stabilization of annular gas-liquid and liquid-particle flows and an inertial mechanism which drives waves into slugs in slugging gas-liquid flows. Annular flow is stable when the fluid having the higher effective viscosity occupies the core region and the lower viscosity fluid is the annulus. The eddy viscosity criterion is shown to be very consistent with published work on annular flow transitions in horizontal and vertical gas-liquid flows. It also applies to a variety of liquid-solid and gas-solid flows. In the second part of the paper we propose a mechanism for explaining the growth of initially small waves and initiation of slugs in gas-liquid flow.

Core-Annular Flows

“…On the other hand, for some operating conditions the lubricating PCAF with the less viscous fluid (water) outside can be stable to both axisymmetric and non-axisymmetric disturbances. Annular gas-liquid and gas-solid flows can also be stable if the effective gas eddy viscosity in turbulant gas flow is larger than the viscosity of the liquid of solid particles at the wall (Joseph et al 1996). In general, only thin lubricating layers are stable, but even in this case the stability depends on flow conditions.…”

Two-Phase Annular Flow in Vertical Pipes: A Critical Review of Current Research Techniques and Progress

“…For an annular two-phase flow in a vertical pipe, the peripheral liquid film generally includes ripple and disturbance waves and acts as a thin wall for the gaseous core flow with entrained drops, as shown in Figure 11. Annular flow gets stable when the fluid has higher effective viscosity (molecular and turbulent viscosity) in the core region and lower viscosity fluid in the annulus [208]. Several definitions are frequently used in the field to describe the flow, such as instantaneous film thickness, the average thickness of base film/substrate, average film thickness, and local maximum thickness.…”