Generation of Controlled Liquid–Liquid Slug Flow by Interlocking Two Diaphragm Pumps

From the viewpoint of resource and energy-saving, the high extraction rate of alternating liquid–liquid flow (slug flow) is important given that it enables its novel use in extraction. Additionally, a specific extraction rate must be maintained for the practical application of slug flow to chemical extraction. Although slug flow is easily generated, controlling the slug length is difficult. In this study, two diaphragm pumps were interlocked to generate a slug flow. By linking the movement of the diaphragms of the two pumps, we could successfully and efficiently control the slug length, and the interlocking diaphragms could easily control the length of the aqueous and oil phase segments of the slug flow. The lengths of the aqueous and oil phases of the slug flow, which could not be quantitatively controlled, could be expressed in terms of the linear velocity of the liquid, the kinematic viscosity, and the tube diameter using the Reynolds number. This relation aids the extraction equipment design using slug flow. Furthermore, the mass transfer coefficient of extraction obtained using the slug flow generated by the developed device was similar to that obtained by the conventional method of a syringe pump. These results indicate that slug flow can be successfully applied to extraction processes.