Analogy between Vertical Upward Cap Bubble and Horizontal Plug Flow

Abstract

SummaryThe intermittent gas-liquid flow can be seen in both vertical upward and horizontal pipes. In a vertical pipe, the gas pockets of intermittent flow can be present as cap bubbles (cap bubble flow) or Taylor bubbles (slug flow), while in a horizontal configuration, the intermittent flow can be as plug or slug flows. Extensive literature survey has shown a lack of deep understanding of the difference between the vertical upward cap bubble and horizontal plug flow regimes.This paper explains the hydrodynamic similarities between vertical cap bubble flow and horizontal plug flow regimes. Moreover, the differences between the cap bubble and slug flow in vertical pipes are explained in detail. The study was carried out using a collected database from the open literature of different flow parameters. A comparison between the behavior of the void fraction, bubble structure velocity, slippage number, slug frequency, and slug length demonstrated the similarity between cap bubble and plug flows. It was also demonstrated, from the evolution of the void fraction, that the gas-to-liquid superficial velocities ratio plays a significant role in the cap bubble-to-slug flow transition. These results highlight the existence of an analogy between vertical cap bubble and horizontal plug flow. In addition, the difference between the flow structures and flow parameters behavior between cap bubble and slug flow, demonstrated in this study, highlights the need to differentiate between the two flow patterns.