ABSTRACT
S. P. S. Andrew proposed a frothing mechanism different from that of F. J. Zuiderweg and A. Harmens but essentially equivalent to the traditional explanation for foam stabilization by surface-active agents. This chapter describes how liquid surface tension level effects the flow structure, ignoring for the moment the existence of surface tension gradients which necessarily exist in the multicomponent interfaces present in distillation. It presents a brief description of the distillation process, and discusses the interfacial and capillary phenomena in distillation in the absence of surfactants. The chapter focuses on the behavior of pure liquids or liquid mixtures, which do not produce significant surface tension gradients in order to separate out the influence of capillary effects in the absence of tension gradients. The explanation of Zuiderweg and Harmens for the difference in behavior between the two types of systems relies on the development of surface tension gradients as described for unsupported-area and supported-area equipment.
