The local measurement of the size and velocity of bubbles rising in liquids
An experimental study of the rise of small air bubbles (0.1 to 1.0 mm in diameter) in a quiescent pool is described. Local measurements of rise velocity were obtained as a function of height above the source nozzle using a laser-Doppler method. In addition, the bubble diameter was determined simultaneously from the same optical signals. Data are presented for various bubble diameters and spacings in bubble columns for both distilled water and a dilute polymer solution.
It was found that for distilled water the rise velocity near the nozzle reaches the maximum observed in other studies before decelerating to its terminal velocity due to surfactant accumulation at its interface. The maximum rise velocity in dilute polymer was much lower for the same bubble diameter and reached its terminal velocity much faster. The results are shown to be in closer agreement with predictions for a solid sphere in this case.
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