Boundary effects on forced drainage through aqueous foam

The flow of liquid through foam confined in vertical tubes was investigated by measuring the velocity v(f) of the liquid front forced down by gravity for various flow rates Q. The power law relating the velocity to how rate o f the incoming liquid (v(f) proportional to Q(alpha)) was observed for tube s of various cross-sectional areas A. The exponent alpha was found to vary linearly with the reciprocal of the area: alpha = 0.325 + 13.7 mm(2)/A. Thi s further supports the node-dominated foam drainage model, which predicts a lpha = 1/3 in the limit of infinite cross-sectional area. This relation app ears to be independent of bubble size, suggesting that using smaller foam b ubbles may not alleviate boundary effects. The results of these experiments also partially explain the discrepancies in measurements of alpha reported in previous studies.