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

Abstract

This study aims to experimentally investigate the two-group interfacial area transport in small diameter tubes. 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 tube under adiabatic, air-water condition. Result shows the intergroup transfer in the small diameter tube can be drastic, especially under low superficial liquid velocities. The cause of this phenomenon is mainly due to the large relative bubble size to the pipe cross-sectional area. The wake entrainment effect could be enhanced by these bubbles that are acting like cap or slug bubbles in a medium-size tube. Based on the experimental observation, a throughout analysis of the dependence of the drastic intergroup transfer is provided in this study. The criteria of the initiation of drastic intergroup transfer in small diameter tubes in terms of the bubble relative diameter and the void fraction are developed. These criteria are compared the two-phase data among the different tube sizes and the results show a good agreement. The criteria are to be used towards the development of a generalized interfacial area transport equation for small diameter tubes.