Air bubble changes from 6–7 kHz ultrasonic exposure in 20°C plain water

Rectified heat and mass transfer in rising air bubbles in water are studied to assess bubble management by insonation, a possibility which might be useful in various applications which use generated air bubbles of comparable size in processes below boiling. A model is presented to predict volume and mass change in ultrasonically insonated 0·2–0·8 mm air bubbles in water. Comparison of model results to experimental data of tracked bubble streams rising at 20–30 cm s−1 shows the model predicts the experimental trends capturing rapid growth and shrinkage as a function of insonation frequency to bubble resonant frequency. Rectified heat and mass transfer in altering bubble size involving only sensible heat is much less than when latent heat is a factor, but it can be significant near a match between the bubble’s resonant frequency and the insonation frequency. Contributing mechanisms for oscillating bubble mass change are examined.