Coalescence of Bubbles Generated from Single Nozzle in Stagnant Water

Rajendra Shrestha

Different conditions and phenomena for the coalescence of bubbles generated from single nozzle in pool water were studied and compared with the prior analysis. Research was done for the bubbles ranging 0.100 to 2.700 mm bubble diameter. It was found that the coalescence and non-coalescence processes of the bubbles depend upon size of the bubbles and bubble to bubble distances. For small bubbles 0.100 to 0.500 mm bubble diameter, the coalescence occurred for larger bubble distance and bubble diameter ratio than the coalescence between larger bubbles 0.500 to 2.700 mm bubble diameter. There were always a vertical and horizontal velocities of the bubbles rising in the water pool.  The vertical velocity of the upper coalescing pair became always slower and the velocity of the lower coalescing pair was higher than the non-coalescing bubbles of the same condition. The smaller horizontal displacement was favorable for the occurrence of the coalescence of the bubbles. The wakes of the bubbles influenced during the coalescence between the bubbles pairs. According to the horizontal displacement, bubble flow patterns were divided into TYPE I and TYPE II. In the TYPE I coalescence of the bubbles occurred in the line but in the TYPE II coalescence of the bubbles occurred after this line. When comparing the experimentally obtained vertical velocities of bubbles with the prior theories, the bubbles in the range 0.500 to 2.100 mm had higher velocities than the theoretically predicted. The higher velocities of these bubbles were found to be due to the larger horizontal fluctuations.