Impact of frother on the terminal velocity of small bubbles

Using a circulating flow that balances buoyancy and drag, small bubbles (< 1 mm) are held in a column that classifies them according to their terminal velocities. Without frother, the terminal velocities fall between the values predicted by Hadamard–Rybczynski for fluid spheres, and those predicted by Stokes for hard spheres. Although it is commonly believed that industrial surfactants have little to no impact on such small bubbles, this study demonstrates a trend comparable to that of larger bubbles, namely that the addition of frother can retard the bubbles even beyond the predictions of the hard sphere model. Hence the motion of small bubbles appears to be impeded by mechanisms similar to those acting on larger bubbles. The frothers studied were MIBC and Dowfroth 250.