@article{SalamaKouDawoudetal., author = {Salama, Amgad and Kou, Jisheng and Dawoud, Belal and Rady, Mohamed and El Morshedy, Salah}, title = {Investigation of the self-propulsion of a wetting/nonwetting ganglion in tapered capillaries with arbitrary viscosity and density contrasts}, series = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, volume = {664}, journal = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, publisher = {Elsevier}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2023.131151}, abstract = {The movement of a meniscus inside a capillary tube has been extensively studied in the context of displacing one fluid with another immiscible one. This phenomenon exists in many applications including pharmaceutical, oil production, filtration and separation processes, and others. When one of the phases is entrapped inside a capillary tube, it forms what is called a ganglion with two menisci between the two fluids. In a straight uniform capillary tube, a stagnant entrapped ganglion is symmetric. The situation is different if the capillary tube is tapered in which case the two menisci assume different curvatures. Such inhomogeneity of the capillary pressure self-propels the ganglion to move. The fate of the ganglion inside the tapered tube depends on whether it is wetting or nonwetting to the tube wall. That is, after the initial movement, a wetting ganglion accelerates towards the tapered end of the tube while a nonwetting one decelerates towards the wider end before reaching a terminal configuration. Such fates are linked to the variations of the capillary pressure, which continuously increases for a wetting ganglion and decreases for the nonwetting one. In this work, a generalized model is developed that not only describes capillary-driven dynamics over a wide range of viscosity and density contrasts but also pressure-driven scenarios with/without gravity. The model, however, neglects the inertial effect of the two fluids on account of the fact that it is confined to the very early time of the movement process. A first-order nonlinear ordinary differential equation is developed that describes the dynamic behavior of both the wetting and nonwetting ganglions. A fourth-order Runge-Kutta algorithm is developed to solve the model equations. Furthermore, a computational fluid dynamics (CFD) analysis was used to provide a comparison and verification framework.}, language = {en} }