Annular flow of two immiscible liquids I. Mechanisms

A study was made of the flow mechanisms of two immiscible liquids with a small density difference introduced at a horizontal-pipe inlet in initial concentric flow. Extent of the annular flow, its break-up mechanisms and the subsequent flow patterns encountered were investigated with the aid of high-speed photography. Annular-flow break-up was found to occur by one of two mechanisms: collapse of the core-liquid by varicose Rayleigh-type waves or rupture of the top-wall liquid-film, attenuated by the ascent of the lighter core-liquid. Flow patterns observed after break-up involve fine dispersions, slugs or stratified layers. Charts mapping flow-pattern zones show conditions under which annular-flow holds over a considerable extent.