The flow of liquid through foam confined in vertical tubes was investigated by measuring the velocity υ_f of the liquid front forced down by gravity for various flow rates Q. The power law relating the velocity of flow rate of the incoming liquid (250L訽r ∝ Q~α) was observed for tubes of various cross-sectional areas A. The exponent α was found to vary linearly with the reciprocal of the area: α = 0.325 + 13.7 mm~2/A. This further supports the node-dominated foam drainage model, which predicts α = 1/3 in the limit of infinite cross-sectional area. This relation appears to be independent of bubble size, suggesting that using smaller foam bubbles may not alleviate boundary effects. The results of these experiments also partially explain the discrepancies in measurements of α reported in previous studies.
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