INTERACTIONS BETWEEN 2 BUBBLES UNDER ISOTHERMAL CONDITIONS AND IN A DOWNWARD TEMPERATURE-GRADIENT

Results from experiments on the motion of a pair of air bubbles in a s ilicone oil under isothermal conditions as well as in a downward tempe rature gradient are reported. Three situations were investigated: moti on driven by buoyancy, motion dominated by thermocapillarity, and moti on when the gravitational force and the thermocapillary force on the l arger bubble of the pair were comparable. The experimental results wer e found to be in good agreement with theoretical predictions from the method of reflections. When the gravitational force was slightly small er than the thermocapillary force on the larger bubble in the pair, th e larger bubble moved downward but the smaller bubble nearby was found to move upward. This counterintuitive behavior is actually consistent with expectation, and an explanation is given.