Electrostatically induced mixing in confined stratified multi-fluid systems

Abstract

Electrostatic control mechanisms underpin a wide range of modern industrial processes, from lab-ona-chip devices to microfluidic sensors for security applications. During the last decades, the striking impact of fluid interface manipulation in contexts such as polymer self-assembly, micromanufacturing and mixing in viscous media has established the field of electrically driven interfacial flows as invaluable.This work investigates electrostatically induced interfacial instabilities and subsequent generation of nonlinear coherent structures in immiscible, viscous, dielectric multi-layer stratified flows confined in channels with plane walls. The present study demonstrates theoretically that interfacial instabilities can be utilized to achieve efficient mixing in different immiscible fluid regions. This is accomplished by electrostatically driving stable flows far from their equilibrium states to attain time-oscillatory and highly nonlinear flows producing mixing. The nonlinear electrohydrodynamic instabilities play the role of imposed background velocity fields or moving device parts in more traditional mixing protocols.Initially, simple yet efficient on-off voltage protocols are investigated and subsequently symmetrybreaking voltage distributions are considered and shown to considerably enhance the achieved level of mixing. Both two and three-dimensional flows, containing realistic fluid configurations (water and oils), are computed using direct numerical simulations based on the Navier-Stokes equations. Such numerical investigations facilitate the quantitative study of the flow into the fully nonlinear regime and constitute the basis of optimization methods in the context of microfluidic mixing applications in two-and three-dimensional geometries.

Electric field stabilization of viscous liquid layers coating the underside of a surface

“…In addition, direct numerical simulations that necessarily use finite slab geometries were found to be in excellent agreement with the model. We also demonstrated the possibility of using the imposed electric field as an active control parameter to induce sustained time-periodic nonlinear oscillations of the interface that may have relevance in mixing in small-scale geometries (see [24] for related approaches).…”

“…Simple control protocols have already been investigated in a geometry of infinite vertical extent [18] and then tailored towards mixing studies in two and three dimensions [24] when the walls were placed far away from the undisturbed position of the interface. The latter study uses vertical electric fields to introduce instability in otherwise stably stratified flows; here we use horizontal electric fields to arrest gravitational instabilities.…”

Instability and dripping of electrified liquid films flowing down inverted substrates

“…In both [42] and [43], the authors demonstrate numerically the possibility of active control of the underlying Rayleigh-Taylor instability and production of sustained nonlinear interfacial oscillations for arbitrarily long times. Such oscillations can enhance mixing, for example, as in [44]. Importantly, we note that such varying electric fields are required for this particular problem to give bounded nontrivial solutions at large times; for constant field strengths, either the flat state is stable or finger formation accompanied by film rupture occurs.…”

Motion of liquid Droplets in gas channels in a SO2 Module

“…Instead, the work here is built on the basis of source code implementation in a transparent environment suitable for both fundamental scientific studies, as well as advances in practical directions. For example, the author has published mathematical work aimed at high-impact high-risk applications in a variety of areas ranging from electrohydrodynamic control of interfaces at small scales (Cimpeanu et al (2014); Cimpeanu & Papageorgiou (2015)) to high speed drop impact studies for the study of icing in the aircraft industry (Cimpeanu & Papageorgiou (2018)).…”