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Castonguay AC, Kailasham R, Wentworth CM, Meredith CH, Khair AS, Zarzar LD. Gravitational settling of active droplets. Phys Rev E 2023; 107:024608. [PMID: 36932547 DOI: 10.1103/physreve.107.024608] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 01/23/2023] [Indexed: 06/18/2023]
Abstract
The gravitational settling of oil droplets solubilizing in an aqueous micellar solution contained in a capillary channel is investigated. The motion of these active droplets reflects a competition between gravitational and Marangoni forces, the latter due to interfacial tension gradients generated by differences in filled-micelle concentrations along the oil-water interface. This competition is studied by varying the surfactant concentration, the density difference between the droplet and the continuous phase, and the viscosity of the continuous phase. The Marangoni force enhances the settling speed of an active droplet when compared to the Hadamard-Rybczynski prediction for a (surfactant free) droplet settling in Stokes flow. The Marangoni force can also induce lateral droplet motion, suggesting that the Marangoni and gravitational forces are not always aligned. The decorrelation rate (α) of the droplet motion, measured as the initial slope of the velocity autocorrelation and indicative of the extent to which the Marangoni and gravitational forces are aligned during settling, is examined as a function of the droplet size: correlated motion (small values of α) is observed at both small and large droplet radii, whereas significant decorrelation can occur between these limits. This behavior of active droplets settling in a capillary channel is in marked contrast to that observed in a dish, where the decorrelation rate increases with the droplet radius before saturating at large values of droplet radius. A simple relation for the crossover radius at which the maximal value of α occurs for an active settling droplet is proposed.
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Affiliation(s)
- Alexander C Castonguay
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - R Kailasham
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Ciera M Wentworth
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Caleb H Meredith
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Aditya S Khair
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Lauren D Zarzar
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Chen X, Sun S, Tian X, Liu L, Yang J. A quasi-two-dimensional fluid experimental apparatus based on tank-in-tank configuration. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:015115. [PMID: 36725545 DOI: 10.1063/5.0125679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 01/04/2023] [Indexed: 06/18/2023]
Abstract
The fluid tank is an essential facility for experimental research on fluid mechanics. However, owing to the hydrostatic fluid pressure, a fine uniformity of the narrow channel is difficult to be maintained in a tall narrow-channel tank. To address this issue, we proposed a quasi-two-dimensional fluid experimental apparatus based on a "tank-in-tank" configuration and built with an outer tank and an inner tank. The outer tank was cuboid-shaped and used to load the fluid medium, while the inner tank, consisting of two parallel glass plates, was embedded into the outer tank and served as the experimental channel. The hydrostatic pressure acting on the channel was balanced so that a high level of uniformity was maintained over the whole channel. The available height and width of the channel were 2800 and 1500 mm, respectively, while its gap distance could be adaptive from 0 to 120 mm. Experimental research on motion characteristics of circular disks falling in the quasi-2D channel was implemented to investigate the effects of the falling environment and disk geometry. Four distinct falling types were observed, and the wake flow fields of the falling disks were visualized. The Reynolds numbers of falling disks ranged from 400 to 63 000 presently. Chaotic motion and regular motion were demarcated at Re ≈ 30 000. An analytical model was established to predict the final average falling velocity and Reynolds number. Finally, potential directions for future research and improvements to the apparatus were suggested.
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Affiliation(s)
- X Chen
- State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - S Sun
- State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - X Tian
- State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - L Liu
- State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - J Yang
- State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
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Will JB, Krug D. Rising and Sinking in Resonance: Mass Distribution Critically Affects Buoyancy-Driven Spheres via Rotational Dynamics. PHYSICAL REVIEW LETTERS 2021; 126:174502. [PMID: 33988413 DOI: 10.1103/physrevlett.126.174502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 04/07/2021] [Indexed: 06/12/2023]
Abstract
We present experimental results for spherical particles rising and settling in a still fluid. Imposing a well-controlled center of mass offset enables us to vary the rotational dynamics selectively by introducing an intrinsic rotational timescale to the problem. Results are highly sensitive even to small degrees of offset, rendering this a practically relevant parameter by itself. We further find that, for a certain ratio of the rotational to a vortex shedding timescale (capturing a Froude-type similarity), a resonance phenomenon sets in. Even though this is a rotational effect in origin, it also strongly affects translational oscillation frequency and amplitude, and most importantly, the drag coefficient. This observation equally applies to both heavy and light spheres, albeit with slightly different characteristics for which we offer an explanation. Our findings highlight the need to consider rotational parameters when trying to understand and classify path properties of rising and settling spheres.
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Affiliation(s)
- Jelle B Will
- Physics of Fluids Group and Max Planck Center Twente, J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
| | - Dominik Krug
- Physics of Fluids Group and Max Planck Center Twente, J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
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Wang Z, Mathai V, Sun C. Self-sustained biphasic catalytic particle turbulence. Nat Commun 2019; 10:3333. [PMID: 31350393 PMCID: PMC6659658 DOI: 10.1038/s41467-019-11221-w] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 07/01/2019] [Indexed: 11/30/2022] Open
Abstract
Turbulence is known for its ability to vigorously mix fluid and transport heat. Despite over a century of research for enhancing heat transport, few have exceeded the inherent limits posed by turbulent-mixing. Here we have conceptualized a kind of "active particle" turbulence, which far exceeds the limits of classical thermal turbulence. By adding a minute concentration (ϕv ∼ 1%) of a heavy liquid (hydrofluoroether) to a water-based turbulent convection system, a remarkably efficient biphasic dynamics is born, which supersedes turbulent heat transport by up to 500%. The system operates on a self-sustained dynamically equilibrated cycle of a "catalyst-like" species, and exploits several heat-carrier agents including pseudo-turbulence, latent heat and bidirectional wake capture. We find that the heat transfer enhancement is dominated by the kinematics of the active elements and their induced-agitation. The present finding opens the door towards the establishment of tunable, ultra-high efficiency heat transfer/mixing systems.
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Affiliation(s)
- Ziqi Wang
- Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, 100084, Beijing, China
| | - Varghese Mathai
- School of Engineering, Brown University, Providence, RI, 02912, USA
| | - Chao Sun
- Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, 100084, Beijing, China.
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Mathai V, Huisman SG, Sun C, Lohse D, Bourgoin M. Dispersion of Air Bubbles in Isotropic Turbulence. PHYSICAL REVIEW LETTERS 2018; 121:054501. [PMID: 30118276 DOI: 10.1103/physrevlett.121.054501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Indexed: 06/08/2023]
Abstract
Bubbles play an important role in the transport of chemicals and nutrients in many natural and industrial flows. Their dispersion is crucial to understanding the mixing processes in these flows. Here we report on the dispersion of millimetric air bubbles in a homogeneous and isotropic turbulent flow with a Taylor Reynolds number from 110 to 310. We find that the mean squared displacement (MSD) of the bubbles far exceeds that of fluid tracers in turbulence. The MSD shows two regimes. At short times, it grows ballistically (∝τ^{2}), while at larger times, it approaches the diffusive regime where the MSD∝τ. Strikingly, for the bubbles, the ballistic-to-diffusive transition occurs one decade earlier than for the fluid. We reveal that both the enhanced dispersion and the early transition to the diffusive regime can be traced back to the unsteady wake-induced motion of the bubbles. Further, the diffusion transition for bubbles is not set by the integral timescale of the turbulence (as it is for fluid tracers and microbubbles), but instead, by a timescale of eddy crossing of the rising bubbles. The present findings provide a Lagrangian perspective towards understanding mixing in turbulent bubbly flows.
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Affiliation(s)
- Varghese Mathai
- Physics of Fluids Group, Department of Science and Technology, Max Planck Center Twente for Complex Fluid Dynamics, MESA+Institute, and J. M. Burgers Center for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
| | - Sander G Huisman
- Physics of Fluids Group, Department of Science and Technology, Max Planck Center Twente for Complex Fluid Dynamics, MESA+Institute, and J. M. Burgers Center for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
- Université Lyon, ENS de Lyon, Université Claude Bernard, CNRS, Laboratoire de Physique, F-69342 Lyon, France
| | - Chao Sun
- Physics of Fluids Group, Department of Science and Technology, Max Planck Center Twente for Complex Fluid Dynamics, MESA+Institute, and J. M. Burgers Center for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
- Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, 100084 Beijing, China
| | - Detlef Lohse
- Physics of Fluids Group, Department of Science and Technology, Max Planck Center Twente for Complex Fluid Dynamics, MESA+Institute, and J. M. Burgers Center for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
- Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany
| | - Mickaël Bourgoin
- Université Lyon, ENS de Lyon, Université Claude Bernard, CNRS, Laboratoire de Physique, F-69342 Lyon, France
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