Droplet arrangement and coalescence in diverging/converging microchannels

Abstract

We experimentally examine the dynamics of droplet assembly and recombination processes in a twodimensional pore-model system. Monodisperse trains of droplets are formed by focusing streams of immiscible fluids into a square microchannel that is connected to a diverging/ converging slit microfluidic chamber. We focus on the limit of dilute emulsions and investigate the formation and stability of crystal-like structures when droplets are hydrodynamically coupled in the chamber. The minimal distance between droplets and the spread of droplet lattices are measured as a function of initial control parameters and the relationship between droplet velocity and trajectory is discussed. We demonstrate that the onset of coalescence depends on both the capillary number based on the viscosity of the external phase and the droplet concentration. The draining time of the thin film between droplets in apparent contact is found to depend on fluid characteristics. Such property allows us to examine the crossover between noncoalescing and coalescing droplet microflows by varying the residence time of the dispersion in the microfluidic chamber. This work characterizes droplet interaction and coalescence phenomena during multiphase transport in a simple extensional microgeometry.

Motion of Deformable Drops Through Porous Media

“…In Aul & Olbricht (1991), a pair of oil drops in apparent contact in a microchannel of diameter 50 μm had to travel approximately 100 tube diameters to coalesce. In Jose & Cubaud (2012), the film drainage time to coalescence between drops in a diverging/converging microchannel was approximately 10 3 times larger than the hydrodynamical scale. Presumably, in many practical situations, drop coalescence is a slow process compared to the drop's motion through a porous medium; hence, the assumption of no coalescence is reasonable, at least as the first approximation.…”

Investigating Arrangement of Composite Drops in Two-Dimensional Microchannels Using Multiagent Simulations: A Design Perspective

“…These interacting drop traffic models are incorporated in a multiagent simulation framework that solves Newton's second law of motion along with the creeping flow approximation as shown in eq (1) for all the drops, to estimate the time evolution of the velocity and position of each of those drops inside the microchannel. The MAS is validated using the experiments of Jose and Cubaud, 28 where organization of drops is studied in a tiltedsquare shaped microchannel as shown in Figure 1a. Though the models for forces are simple, the MAS is able to capture the dynamic pattern formation of drops to a considerable extent: one can observe the match in the ordered arrangement of drops in Figure 1 (panels b and d).…”

“…Jose and Cubaud in an attempt to analyze drop inlet and exit sequence, tracked individual drop trajectories ( Figure 6 of their article 28 ). We infer from that plot (although the authors do now account for it in their article) that six drops, sent one after the other, can arrange in a single (almost) vertical row.…”

Bubble Motion in a Converging–Diverging Channel

“…Thus, several researchers studied the motion of bubbles and drops due to buoyancy in vertical channels and pipes [4] as well as in unbounded domains [5,6]. At smaller scales, spatially varying walls are frequently encountered, and play a vital role in the resultant flow dynamics [7,8]. First, the studies of flows associated with spatially varying geometries, which have received considerable attention in the recent past, mainly, in the context of small-scale flows are briefly discussed below.…”