Drainage induced convection rolls in foams:I. Convective bubble motion in a tilted tube

When liquid is added to a foam at sufficiently large flow rates, convective bubble motion will occur. Experiments are described in which the foam is confined in a tube which is tilted from the vertical. The theory of foam drainage is applied to this problem to show that the critical angle of tilt θc at which convection occurs is related to the liquid flow-rate Q by θc ∝ Q-3/4.