The Creeping Motion of Immiscible Drops Through a Converging/Diverging Tube: I. Non-Newtonian Effects of Viscoelastic Drops. II. Effects of Constant Pressure Gradient Condition for the Flow. III. Motion of Drops Through a Parallel Channel

Experimental results are presented for the motion of neutrally buoyant drops of non-Newtonian fluid through a wavy wall tube within a Newtonian suspending fluid. The motion of these drops exhibits very different behavior with respect to both Newtonian drop-Newtonian suspending fluid system and Newtonian drop-viscoelastic suspending fluid system. In particular, drop breakup behavior is strongly modified. At small flow rates (small capillary numbers) viscoelastic drops undergo drop breakup. At large flow rates (large capillary numbers) breakup phenomena do not occur and axial drop elongation is inhibited. For the cases in which drop breakup occurs, it produces important effects on the time-dependent response of the extra pressure drop and on the drop mobility. For high polymer concentration (1%) in the viscoelastic drop, the resulting elastic effects are overshadowed by the increase in viscosity which accompanies the addition of polymer. The effects of flow type on the dynamics of the drop motion in a wavy wall tube are investigated. According to the nature of the driving mechanism there are two types of flow, each one of them presenting different properties (though identical for non-drop conditions). One flow is susceptible to changes in flow resistance that may appear in the experimental setup, the other is such that the volumetric flow rate is constant. The former is generated by imposing a constant pressure gradient (CPG conditions), the latter is generated by a gear pump (CFR conditions). Drop deformation in a CPG experiment is less severe than it is in a CFR experiment. Also, under CPG conditions, the axial elongation and the mobility of a moving drop are independent of the viscosity ratio, whereas under CFR conditions they depend on it. In addition, the magnitude of the extra pressure drop caused by the passage of the drop through the test section is smaller under CPG conditions than it is under CFR conditions. Finally, a more realistic simulation of flow dynamics in porous media is considered. For this purpose, a parallel channel device was tested under constant pressure gradient conditions. Measurements were taken in both arms of this device for the extra pressure drop caused by the passage of drops through one of the channels (a wavy wall tube). The ratio of the mean value of such measurements is nearly constant regardless of the value of the total volumetric flow, drop size or viscosity ratio. Obviously, the pressure drop measured in the bypass tube is a tangible indication of the increase (or decrease) in the volumetric flow through it, due to the motion of the drop through the other arm of the experimental apparatus.