Macro-size drop encapsulation

Abstract

Viscoplastic fluids do not flow unless they are sufficiently stressed. This property can be exploited in order to produce novel flow features. One example of such flows is viscoplastically lubricated (VPL) flow, in which a viscoplastic fluid is used to stabilize the interface in a multi-layer flow, far beyond what might be expected for a typical viscous-viscous interface. Here we extend this idea by considering the encapsulation of droplets within a viscoplastic fluid, for the purpose of transportation, e.g. in pipelines. The main advantage of this method, compared to others that involve capillary forces is that significantly larger droplets may be stably encapsulated, governed by the length scale of the flow and yield stress of the encapsulating fluid. We explore this set-up both analytically and computationally. We show that sufficiently small droplets are held in the unyielded plug of a Poiseuille flow (pipe or plane channel). As the length or radius of the droplets increases, the carrier fluid eventually yields, potentially breaking the encapsulation. We study this process of breaking and give estimates for the limiting size of droplets that can be encapsulated.

Elastoviscoplastic flows in porous media

“…The data reveal that the yielded part of the flow is the one mostly responsible for the shear flow behavior, whereas shear and elongation flows are almost equally distributed in the unyielded regions. Similar feature is also observed in flows of ideal visco-plastic fluids in anfractuous configurations [76,13].…”

Progress in numerical simulation of yield stress fluid flows

“…The third class of problems that has been extensively studied over the past 20 years is the gravity-driven motion of dispersed droplet/bubble or solid particle in an otherwise quiescent yield stress fluid (Roquet and Saramito, 2003;Nirmalkar et al, 2013Nirmalkar et al, , 2014Bose et al, 2014;Singh and Denn, 2008;Tsamopoulos et al, 2008;Prashant and Derksen, 2011;Dimakopoulos et al, 2013;Tripathi et al, 2015;Maleki et al, 2015;Wachs and Frigaard, 2016). Actually, numerical works can be sorted into two sub-categories: (i) methods that really treat freely-moving droplet/bubble or solid particle, and (ii) methods in which the problem is formulated in the droplet/bubble/particle frame of reference or as the flow past a motionless droplet/bubble/particle.…”

Long bubbles in tubes filled with viscoplastic fluid

“…For thicker films, one can imagine that the bubble might break free of the wall, forcing the film to yield all along its length. At yet higher film thickness, one can then envision encapsulating the bubble within the plug of the background flow [29].…”