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.