A foam drainage equation generalized for all liquid contents

Abstract

Recently the study of liquid drainage through foams has generated considerable experimental and theoretical research. This research has usually made the assumptions that the liquid content is very low and that the viscous resistance is limited to occurring within either the Plateau borders or vertices. This paper presents a foam drainage model that not only describes the low-liquid-content extreme, but also takes account of liquid content effects. These include the increase in the foam volume with increasing liquid content and the increase in the liquid flowrate in the Plateau borders over the average flowrate brought about by the presence of vertices. The relative importance of the Plateau borders and vertices to viscous loss within the foam is also made dependent on the liquid content of the foam. This model is verified experimentally for two surfactant types and various bubble sizes using a standard forced drainage system.