Laminar flow of two phases through a capillary tube with variable square cross-section

Abstract The angularity of the channels in a porous medium and the variation in their cross-section can be schematized by a constricted capillary tube of square cross-section. The flow of a nonwetting droplet in such a capillary, already filled with an immiscible fluid, is described by approximated equations derived from Stokes equations. The droplets flows through the constriction if the ratio of the viscosity forces to the interfacial forces is greater than a critical value which depends on the contact angle, and on the viscosity ratio. The greater the droplet viscosity, the more easily the droplet flows through the throat whatever the boundary conditions. This phenomenon, due to the internal flow in the droplet, remains unchanged in a pore doublet. Experiments performed with various capillary tubes and various fluids are in good agreement with theory. Results are compared with experiments performed with porous media.