Interfacial area transport for bubbly-to-slug transition flows in small diameter pipes

TL;DR

This paper experimentally investigates interfacial area transport during bubbly-to-slug flow transition in small pipes, revealing significant intergroup transfer influenced by bubble size and developing models to predict this phenomenon.

Contribution

The study introduces new models predicting the onset of drastic intergroup transfer based on bubble size and void fraction in small diameter pipes.

Findings

Intergroup transfer can be drastic in small pipes under low liquid velocities.

Large relative bubble size causes significant intergroup transfer.

The developed models accurately predict the transition in small pipes.

Abstract

This study aims to experimentally investigate the two-group interfacial area transport in small diameter pipes. Experimental data focusing on the bubbly to slug transition regime, namely one-group to two-group transport region, are collected in a 12.7 mm vertical pipe under adiabatic, air-water conditions. The result shows the intergroup transfer in the small diameter pipe can be drastic, especially under low superficial liquid velocities. The cause of this phenomenon is mainly due to the large relative bubble size comparing to the pipe cross-sectional area. The wake entrainment effect could be enhanced by the small spherical bubbles that are acting like cap or slug bubbles in a medium-size pipe. Based on the experimental observation, a throughout analysis of the dependence of the drastic intergroup transfer is provided in this study. The models predicting the initiation of drastic intergroup transfer in small diameter pipes in terms of the bubble diameter and the void fraction are developed. These models are compared with the two-phase data among the different pipe sizes and the results show a good agreement. These newly developed models are applied to the IATE wake entrainment model by developing a transition function analogous to the sigmoid function. With the transition function, the revised IATE model is given the new ability on predicting the drastic intergroup transfer phenomenon.