Dynamical regimes of thermally convective emulsions

Abstract

Emulsions are paramount in various interdisciplinary topical areas, yet a satisfactory understanding of their behavior in buoyancy-driven thermal flows has not been established. In the present work, we unravel the dynamical regimes of thermal convection in emulsions by leveraging a large set of mesoscale numerical simulations. Emulsions are prepared with a given volume fraction of the initially dispersed phase, $\varphi$, ranging from dilute (low values of $\varphi$) to jammed emulsions (high values of $\varphi$), resulting in different rheological responses of the emulsion, i.e., from Newtonian to non-Newtonian yield-stress behaviors, respectively. We then characterize the dynamics of the emulsions in the paradigmatic setup of the Rayleigh-Bénard convection, i.e., when confined between two parallel walls at different temperatures under the effect of buoyancy forces, the latter encoded in the dimensionless Rayleigh number Ra. We thoroughly investigated the dynamics of the emulsion in the changing of $\varphi$ and Ra. For a given $\varphi$, at increasing Ra, we observe that the emulsion exhibits convection states, where structural changes may appear (i.e., droplet breakup, coalescence or phase inversion), which inevitably impact the emulsion rheology. For sufficiently high values of Ra, two states of convection are observed: for low/moderate values of $\varphi$ (Newtonian emulsions), we observe breakup-dominated dynamics, whereas for high values of $\varphi$ (non-Newtonian emulsions), we observe phase-inverted states. For both scenarios, the droplet size distribution depends on Ra, and scaling laws for the average droplet size are analyzed and quantified. Our results offer insights into the rich dynamics of emulsions under thermal convection, offering the first detailed characterization of the various dynamic regimes to be expected and their relation with structural changes occurring in such complex fluids.

15 pages, 10 figures

References in corpus (16)

• Comparison between two and three dimensional Rayleigh-Bénard convection
• Relaxation in yield stress systems through elastically interacting activated events
• Heat transport in boiling turbulent Rayleigh-Bénard convection
• The interaction of droplet dynamics and turbulence cascade
• Ductile-to-brittle transition and yielding in soft amorphous materials: perspectives and open questions
• Stress Overshoots in Simple Yield Stress Fluids
• Heat transfer in turbulent Rayleigh-Bénard convection within two immiscible fluid layers
• Lattice Boltzmann simulation of deformable fluid-filled bodies: progress and perspectives
• Yield-stress transition in suspensions of deformable droplets
• Enhancing Heat Transport in Multiphase Rayleigh-Bénard Turbulence by Changing the Plate-Liquid Contact Angles
• Continuum modelling of shear start-up in soft glassy materials
• Rayleigh-Bénard convection of a model emulsion: anomalous heat-flux fluctuations and finite-size droplets effects
• TLBfind: a Thermal Lattice Boltzmann code for concentrated emulsions with FINite-size Droplets
• Analysis of the heat transfer fluctuations in the Rayleigh-Bénard convection of concentrated emulsions with finite-size droplets
• Build up of yield stress fluids via chaotic emulsification
• Intermittent thermal convection in jammed emulsions