A STUDY OF THE BUBBLE-TO-SLUG TRANSITION IN VERTICAL GAS-LIQUID FLOW IN COLUMNS OF DIFFERENT DIAMETER

The aim of this study is to investigate the structure of upwards air-w ater flow and its variation as the bubble-to-slug transition is approa ched, with a view to understanding the mechanism of the transition. Th e development of bubble size with column height is measured with a dou ble needle resistivity probe, and of void fraction waves with an Imped ance Void Fraction Meter (IVFM) with quadrant electrodes in a 150 mm d iameter column. The results are compared with some experimental data g athered in a 28.9 mm column. Traditional slug flow does not exist in t he 150 mm diameter column; instead there is a gradual transition to ch urn flow. Possible instabilities of void fraction waves are detected d uring the transition from bubble to churn at constant liquid rate, but not at constant gas rate. In the 28.9 mm column at constant liquid ra te, an abrupt transition from bubble-to-slug flow occurs, with strong indications of associated void fraction wave instabilities. (C) 1998 E lsevier Science Ltd. All rights reserved.