The wake effect on bubble rising velocity in one-component systems

The present paper reports an experiment of bubble rising velocity in a liquid column using R-114 and FC-72. Vapour bubbles are generated at the bottom of the saturated liquid column by a tiny electric heater and their evolution is recorded with high speed cinematography from the generation point until they reach the terminal velocity in the liquid column. Single bubble and bubble train (with controlled frequency) tests are carried out to ascertain the wake effect on the bubble rising velocity in the range of bubble diameter from 0.1 to 0.7 mm, showing a negligible wake effect on the tested bubbles. Prediction of bubble terminal rising velocity with available correlations has been attempted. Though most of them have been developed for two-component systems (gas and liquid), some of them provide with a fairly good prediction. A recent drag coefficient model, specifically derived for distorted spheroidal bubbles in infinite stagnant liquids under a surface tension dominant regime, looks promising although the agreement with the present experimental data is not completely satisfactory, as being similar to Fan and Tsuchiya correlation. A reasonable prediction of bubble shape has been obtained using available correlations and models, and specifically the Taylor and Acrivos model and the Vakhrushev and Efremov correlation. (C) 2004 Published by Elsevier Ltd.