Rayleigh–Bénard convection of a model emulsion: anomalous heat-flux fluctuations and finite-size droplet effects
| Autor: | Sauro Succi, Francesca Pelusi, Massimo Bernaschi, Andrea Scagliarini, Mauro Sbragaglia, Roberto Benzi |
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| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Convection
Materials science Condensed Matter - Soft Condensed Matter 01 natural sciences 010305 fluids & plasmas Physics::Fluid Dynamics Viscosity Rheology 0103 physical sciences Newtonian fluid Thermal Convection ddc:530 010306 general physics Condensed Matter - Statistical Mechanics Rayleigh–Bénard convection Settore FIS/02 General Chemistry Mechanics Physics - Fluid Dynamics Condensed Matter Physics Heat flux Soft Matter Heat transfer Emulsion Emulsions |
| Zdroj: | Soft matter 17(13), 3709-3721 (2021). doi:10.1039/D0SM01777A Soft matter 17 (2021): 3709–3721. doi:10.1039/d0sm01777a info:cnr-pdr/source/autori:Pelusi F.; Sbragaglia M.; Benzi R.; Scagliarini A.; Bernaschi M.; Succi S./titolo:Rayleigh-Bénard convection of a model emulsion: anomalous heat-flux fluctuations and finite-size droplet effects/doi:10.1039%2Fd0sm01777a/rivista:Soft matter (Print)/anno:2021/pagina_da:3709/pagina_a:3721/intervallo_pagine:3709–3721/volume:17 |
| DOI: | 10.1039/D0SM01777A |
| Popis: | We present mesoscale numerical simulations of Rayleigh-B\'enard (RB) convection in a two-dimensional model emulsion. The systems under study are constituted of finite-size droplets, whose concentration Phi_0 is systematically varied from small (Newtonian emulsions) to large values (non-Newtonian emulsions). We focus on the characterisation of the heat transfer properties close to the transition from conductive to convective states, where it is known that a homogeneous Newtonian system exhibits a steady flow and a time-independent heat flux. In marked contrast, emulsions exhibit a non-steady dynamics with fluctuations in the heat flux. In this paper, we aim at the characterisation of such non-steady dynamics via detailed studies on the time-averaged heat flux and its fluctuations. To understand the time-averaged heat flux, we propose a side-by-side comparison between the emulsion system and a single-phase (SP) system, whose viscosity is constructed from the shear rheology of the emulsion. We show that such local closure works well only when a suitable degree of coarse-graining (at the droplet scale) is introduced in the local viscosity. To delve deeper into the fluctuations in the heat flux, we propose a side-by-side comparison between a Newtonian emulsion and a non-Newtonian emulsion, at fixed time-averaged heat flux. This comparison elucidates that finite-size droplets and the non-Newtonian rheology cooperate to trigger enhanced heat-flux fluctuations at the droplet scales. These enhanced fluctuations are rooted in the emergence of space correlations among distant droplets, which we highlight via direct measurements of the droplets displacement and the characterisation of the associated correlation function. The observed findings offer insights on heat transfer properties for confined systems possessing finite-size constituents. Comment: 15 pages, 22 figures. arXiv admin note: substantial text overlap with arXiv:2010.02139, arXiv:2010.02138 |
| Databáze: | OpenAIRE |
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