1
|
Pelusi F, Ascione S, Sbragaglia M, Bernaschi M. Analysis of the heat transfer fluctuations in the Rayleigh-Bénard convection of concentrated emulsions with finite-size droplets. SOFT MATTER 2023; 19:7192-7201. [PMID: 37721416 PMCID: PMC10523216 DOI: 10.1039/d3sm00716b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Accepted: 08/26/2023] [Indexed: 09/19/2023]
Abstract
Employing numerical simulations, we provide an accurate insight into the heat transfer mechanism in the Rayleigh-Bénard convection of concentrated emulsions with finite-size droplets. We focus on the unsteady dynamics characterizing the thermal convection of these complex fluids close to the transition from conductive to convective states, where the heat transfer phenomenon, expressed in terms of the Nusselt number Nu, is characterized by pronounced fluctuations triggered by collective droplet motion [F. Pelusi et al., Soft Matter, 2021, 17(13), 3709-3721]. By systematically increasing the droplet concentration, we show how these fluctuations emerge along with the segregation of "extreme events" in the boundary layers, causing intermittent bursts in the heat flux fluctuations. Furthermore, we quantify the extension S and the duration of the coherent droplet motion accompanying these extreme events via a suitable statistical analysis involving the droplet displacements. We show how the increase in droplet concentration results in a power-law behaviour of the probability distribution function of S and and how this outcome is robust at changing the analysis protocol. Our work offers a comprehensive picture, linking macroscopic heat transfer fluctuations with the statistics of droplets at the mesoscale.
Collapse
Affiliation(s)
- Francesca Pelusi
- Istituto per le Applicazioni del Calcolo, CNR - Via dei Taurini 19, 00185 Rome, Italy.
| | - Stefano Ascione
- Department of Physics, Tor Vergata University of Rome - Via della Ricerca Scientifica 1, 00133 Rome, Italy
| | - Mauro Sbragaglia
- Department of Physics & INFN, Tor Vergata University of Rome -, Via della Ricerca Scientifica 1, 00133 Rome, Italy
| | - Massimo Bernaschi
- Istituto per le Applicazioni del Calcolo, CNR - Via dei Taurini 19, 00185 Rome, Italy.
| |
Collapse
|
2
|
Kobayashi M, Nakagawa N, Sasa SI. Control of Metastable States by Heat Flux in the Hamiltonian Potts Model. PHYSICAL REVIEW LETTERS 2023; 130:247102. [PMID: 37390420 DOI: 10.1103/physrevlett.130.247102] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Accepted: 05/15/2023] [Indexed: 07/02/2023]
Abstract
The local equilibrium thermodynamics is a basic assumption of macroscopic descriptions of the out of equilibrium dynamics for Hamiltonian systems. We numerically analyze the Hamiltonian Potts model in two dimensions to study the violation of the assumption for phase coexistence in heat conduction. We observe that the temperature of the interface between ordered and disordered states deviates from the equilibrium transition temperature, indicating that metastable states at equilibrium are stabilized by the influence of a heat flux. We also find that the deviation is described by the formula proposed in an extended framework of the thermodynamics.
Collapse
Affiliation(s)
- Michikazu Kobayashi
- School of Engeneering Science, Kochi University of Technology, Miyanoguchi 185, Tosayamada, Kami, Kochi 782-8502, Japan
| | - Naoko Nakagawa
- Department of Physics, Ibaraki University, Mito 310-8512, Japan
| | - Shin-Ichi Sasa
- Department of Physics, Kyoto University, Kyoto 606-8502 Japan
| |
Collapse
|
3
|
Sasa SI, Nakagawa N, Itami M, Nakayama Y. Stochastic order parameter dynamics for phase coexistence in heat conduction. Phys Rev E 2021; 103:062129. [PMID: 34271670 DOI: 10.1103/physreve.103.062129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 05/29/2021] [Indexed: 06/13/2023]
Abstract
We propose a stochastic order parameter model for describing phase coexistence in steady heat conduction near equilibrium. By analyzing the stochastic dynamics with a nonequilibrium adiabatic boundary condition, where total energy is conserved over time, we derive a variational principle that determines thermodynamic properties in nonequilibrium steady states. The resulting variational principle indicates that the temperature of the interface between the ordered region and the disordered region becomes greater (less) than the equilibrium transition temperature in the linear response regime when the thermal conductivity in the ordered region is less (greater) than that in the disordered region. This means that a superheated ordered (supercooled disordered) state appears near the interface, which was predicted by an extended framework of thermodynamics proposed in Nakagawa and Sasa [Liquid-Gas Transitions in Steady Heat Conduction, Phys. Rev. Lett. 119, 260602 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.260602.].
Collapse
Affiliation(s)
- Shin-Ichi Sasa
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Naoko Nakagawa
- Department of Physics, Ibaraki University, Mito 310-8512, Japan
| | - Masato Itami
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
| | - Yohei Nakayama
- Department of Applied Physics, Tohoku University, Sendai 980-8579, Japan
| |
Collapse
|
4
|
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.
Collapse
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.
| |
Collapse
|
5
|
Urban P, Hanzelka P, Králík T, Macek M, Musilová V, Skrbek L. Elusive transition to the ultimate regime of turbulent Rayleigh-Bénard convection. Phys Rev E 2019; 99:011101. [PMID: 30780350 DOI: 10.1103/physreve.99.011101] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Indexed: 11/07/2022]
Abstract
By using cryogenic ^{4}He gas as the working fluid in a cylindrical cell 0.3 m in both height and diameter, we study the influence of non-Oberbeck-Boussinesq (NOB) effects on the heat transfer in turbulent Rayleigh-Bénard convection (RBC). We show that the NOB effects increase the heat transfer efficiency when the top plate temperature closely approaches the saturation vapor curve even far away from the critical point. Viewed in this light, our analysis points to the likelihood that the claim of having observed the transition to Kraichnan's ultimate regime, under nominally similar conditions in the experiments with SF_{6} [Phys. Rev. Lett. 108, 024502 (2012)PRLTAO0031-900710.1103/PhysRevLett.108.024502], is probably an NOB effect and the important issue of the transition to the ultimate state of RBC remains open.
Collapse
Affiliation(s)
- P Urban
- Institute of Scientific Instruments, The Czech Academy of Sciences, Královopolská 147, Brno, Czech Republic
| | - P Hanzelka
- Institute of Scientific Instruments, The Czech Academy of Sciences, Královopolská 147, Brno, Czech Republic
| | - T Králík
- Institute of Scientific Instruments, The Czech Academy of Sciences, Královopolská 147, Brno, Czech Republic
| | - M Macek
- Institute of Scientific Instruments, The Czech Academy of Sciences, Královopolská 147, Brno, Czech Republic
| | - V Musilová
- Institute of Scientific Instruments, The Czech Academy of Sciences, Královopolská 147, Brno, Czech Republic
| | - L Skrbek
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague, Czech Republic
| |
Collapse
|
6
|
Nakagawa N, Sasa SI. Liquid-Gas Transitions in Steady Heat Conduction. PHYSICAL REVIEW LETTERS 2017; 119:260602. [PMID: 29328708 DOI: 10.1103/physrevlett.119.260602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Indexed: 06/07/2023]
Abstract
We study liquid-gas transitions of heat conduction systems in contact with two heat baths under constant pressure in the linear response regime. On the basis of local equilibrium thermodynamics, we propose an equality with a global temperature, which determines the volume near the equilibrium liquid-gas transition. We find that the formation of the liquid-gas interface is accompanied by a discontinuous change in the volume when increasing the mean temperature of the baths. A supercooled gas near the interface is observed as a stable steady state.
Collapse
Affiliation(s)
- Naoko Nakagawa
- Department of Physics, Ibaraki University, Mito 310-8512, Japan
| | - Shin-Ichi Sasa
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| |
Collapse
|
7
|
Weiss S, Wei P, Ahlers G. Heat-transport enhancement in rotating turbulent Rayleigh-Bénard convection. Phys Rev E 2016; 93:043102. [PMID: 27176385 DOI: 10.1103/physreve.93.043102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Indexed: 06/05/2023]
Abstract
We present new Nusselt-number (Nu) measurements for slowly rotating turbulent thermal convection in cylindrical samples with aspect ratio Γ=1.00 and provide a comprehensive correlation of all available data for that Γ. In the experiment compressed gasses (nitrogen and sulfur hexafluride) as well as the fluorocarbon C_{6}F_{14} (3M Fluorinert FC72) and isopropanol were used as the convecting fluids. The data span the Prandtl-number (Pr) range 0.74<Pr<35.5 and are for Rayleigh numbers (Ra) from 3×10^{8} to 4×10^{11}. The relative heat transport Nu_{r}(1/Ro)≡Nu(1/Ro)/Nu(0) as a function of the dimensionless inverse Rossby number 1/Ro at constant Ra is reported. For Pr≈0.74 and the smallest Ra=3.6×10^{8} the maximum enhancement Nu_{r,max}-1 due to rotation is about 0.02. With increasing Ra, Nu_{r,max}-1 decreased further, and for Ra≳2×10^{9} heat-transport enhancement was no longer observed. For larger Pr the dependence of Nu_{r} on 1/Ro is qualitatively similar for all Pr. As noted before, there is a very small increase of Nu_{r} for small 1/Ro, followed by a decrease by a percent or so, before, at a critical value 1/Ro_{c}, a sharp transition to enhancement by Ekman pumping takes place. While the data revealed no dependence of 1/Ro_{c} on Ra, 1/Ro_{c} decreased with increasing Pr. This dependence could be described by a power law with an exponent α≃-0.41. Power-law dependencies on Pr and Ra could be used to describe the slope S_{Ro}^{+}=∂Nu_{r}/∂(1/Ro) just above 1/Ro_{c}. The Pr and Ra exponents were β_{1}=-0.16±0.08 and β_{2}=-0.04±0.06, respectively. Further increase of 1/Ro led to further increase of Nu_{r} until it reached a maximum value Nu_{r,max}. Beyond the maximum, the Taylor-Proudman (TP) effect, which is expected to lead to reduced vertical fluid transport in the bulk region, lowered Nu_{r}. Nu_{r,max} was largest for the largest Pr. For Pr=28.9, for example, we measured an increase of the heat transport by up to 40% (Nu_{r}-1=0.40) for the smallest Ra=2.2×10^{9}, even though we were unable to reach Nu_{r,max} over the accessible 1/Ro range. Both Nu_{r,max}(Pr,Ra) and its location 1/Ro_{max}(Pr,Ra) along the 1/Ro axis increased with Pr and decreased with Ra. Although both could be given by power-law representations, the uncertainties of the exponents are relatively large.
Collapse
Affiliation(s)
- Stephan Weiss
- Department of Physics, University of California, Santa Barbara, California 93106, USA
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), D-37077 Göttingen, Germany
| | - Ping Wei
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - Guenter Ahlers
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| |
Collapse
|
8
|
Huisman SG, van der Veen RCA, Bruggert GWH, Lohse D, Sun C. The boiling Twente Taylor-Couette (BTTC) facility: Temperature controlled turbulent flow between independently rotating, coaxial cylinders. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:065108. [PMID: 26133874 DOI: 10.1063/1.4923082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A new Taylor-Couette system has been designed and constructed with precise temperature control. Two concentric independently rotating cylinders are able to rotate at maximum rates of f(i) = ± 20 Hz for the inner cylinder and f(o) = ± 10 Hz for the outer cylinder. The inner cylinder has an outside radius of r(i) = 75 mm, and the outer cylinder has an inside radius of r(o) = 105 mm, resulting in a gap of d = 30 mm. The height of the gap is L = 549 mm, giving a volume of V = 9.3 L. The geometric parameters are η = r(i)/r(o) = 0.714 and Γ = L/d = 18.3. With water as working fluid at room temperature, the Reynolds numbers that can be achieved are Re(i) = ω(i)r(i)(r(o) - r(i))/ν = 2.8 × 10(5) and Re(o) = ω(o)r(o)(r(o) - r(i))/ν = 2 × 10(5) or a combined Reynolds number of up to Re = (ω(i)r(i) - ω(o)r(o))(r(o) - r(i))/ν = 4.8 × 10(5). If the working fluid is changed to the fluorinated liquid FC-3284 with kinematic viscosity 0.42 cSt, the combined Reynolds number can reach Re = 1.1 × 10(6). The apparatus features precise temperature control of the outer and inner cylinders separately and is fully optically accessible from the side and top. The new facility offers the possibility to accurately study the process of boiling inside a turbulent flow and its effect on the flow.
Collapse
Affiliation(s)
- Sander G Huisman
- Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Roeland C A van der Veen
- Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Gert-Wim H Bruggert
- Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Detlef Lohse
- Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Chao Sun
- Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| |
Collapse
|
9
|
Zhang X, Lhuissier H, Sun C, Lohse D. Surface nanobubbles nucleate microdroplets. PHYSICAL REVIEW LETTERS 2014; 112:144503. [PMID: 24765973 DOI: 10.1103/physrevlett.112.144503] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Indexed: 05/13/2023]
Abstract
When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.
Collapse
Affiliation(s)
- Xuehua Zhang
- Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville, Victoria 3010, Australia and Physics of Fluids Group, Department of Applied Physics, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Henri Lhuissier
- Physics of Fluids Group, Department of Applied Physics, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Chao Sun
- Physics of Fluids Group, Department of Applied Physics, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Detlef Lohse
- Physics of Fluids Group, Department of Applied Physics, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| |
Collapse
|
10
|
Oresta P, Prosperetti A. Effects of particle settling on Rayleigh-Bénard convection. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:063014. [PMID: 23848779 DOI: 10.1103/physreve.87.063014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2013] [Revised: 05/06/2013] [Indexed: 06/02/2023]
Abstract
The effect of particles falling under gravity in a weakly turbulent Rayleigh-Bénard gas flow is studied numerically. The particle Stokes number is varied between 0.01 and 1 and their temperature is held fixed at the temperature of the cold plate, of the hot plate, or the mean between these values. Mechanical, thermal, and combined mechanical and thermal couplings between the particles and the fluid are studied separately. It is shown that the mechanical coupling plays a greater and greater role in the increase of the Nusselt number with increasing particle size. A rather unexpected result is an unusual kind of reverse one-way coupling, in the sense that the fluid is found to be strongly influenced by the particles, while the particles themselves appear to be little affected by the fluid, despite the relative smallness of the Stokes numbers. It is shown that this result derives from the very strong constraint on the fluid behavior imposed by the vanishing of the mean fluid vertical velocity over the cross sections of the cell demanded by continuity.
Collapse
Affiliation(s)
- Paolo Oresta
- Department of Mathematics, Mechanics and Management, Polytechnic of Bari, 70126 Bari, Italy
| | | |
Collapse
|
11
|
Abstract
Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to numerous mechanisms, many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubble compounds with that of the liquid to give rise to a much-enhanced natural convection. In this article, we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh-Bénard convection process in a cylindrical cell with a diameter equal to its height. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping this difference constant, we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between 2 × 10(6) and 5 × 10(9). We find a considerable enhancement of the heat transfer and study its dependence on the number of bubbles, the degree of superheat of the hot cell bottom, and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the cell bottom, and the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experiments on boiling Rayleigh-Bénard convection.
Collapse
|
12
|
Anomalous heat transport and condensation in convection of cryogenic helium. Proc Natl Acad Sci U S A 2013; 110:8036-9. [PMID: 23576759 DOI: 10.1073/pnas.1303996110] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
When a hot body A is thermally connected to a cold body B, the textbook knowledge is that heat flows from A to B. Here, we describe the opposite case in which heat flows from a colder but constantly heated body B to a hotter but constantly cooled body A through a two-phase liquid-vapor system. Specifically, we provide experimental evidence that heat flows through liquid and vapor phases of cryogenic helium from the constantly heated, but cooler, bottom plate of a Rayleigh-Bénard convection cell to its hotter, but constantly cooled, top plate. The bottom plate is heated uniformly, and the top plate is cooled by heat exchange with liquid helium maintained at 4.2 K. Additionally, for certain experimental conditions, a rain of helium droplets is detected by small sensors placed in the cell at about one-half of its height.
Collapse
|
13
|
Chillà F, Schumacher J. New perspectives in turbulent Rayleigh-Bénard convection. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2012; 35:58. [PMID: 22791306 DOI: 10.1140/epje/i2012-12058-1] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 06/15/2012] [Accepted: 06/15/2012] [Indexed: 06/01/2023]
Abstract
Recent experimental, numerical and theoretical advances in turbulent Rayleigh-Bénard convection are presented. Particular emphasis is given to the physics and structure of the thermal and velocity boundary layers which play a key role for the better understanding of the turbulent transport of heat and momentum in convection at high and very high Rayleigh numbers. We also discuss important extensions of Rayleigh-Bénard convection such as non-Oberbeck-Boussinesq effects and convection with phase changes.
Collapse
Affiliation(s)
- F Chillà
- Laboratoire de Physique, École Normale Supérieure de Lyon, Lyon, France.
| | | |
Collapse
|
14
|
Biferale L, Perlekar P, Sbragaglia M, Toschi F. Convection in multiphase fluid flows using lattice Boltzmann methods. PHYSICAL REVIEW LETTERS 2012; 108:104502. [PMID: 22463414 DOI: 10.1103/physrevlett.108.104502] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Indexed: 05/31/2023]
Abstract
We present high-resolution numerical simulations of convection in multiphase flows (boiling) using a novel algorithm based on a lattice Boltzmann method. We first study the thermodynamical and kinematic properties of the algorithm. Then, we perform a series of 3D numerical simulations changing the mean properties in the phase diagram and compare convection with and without phase coexistence at Rayleigh number Ra∼10(7). We show that in the presence of nucleating bubbles non-Oberbeck-Boussinesq effects develop, the mean temperature profile becomes asymmetric, and heat-transfer and heat-transfer fluctuations are enhanced, at all Ra studied. We also show that small-scale properties of velocity and temperature fields are strongly affected by the presence of the buoyant bubble leading to high non-gaussian profiles in the bulk.
Collapse
Affiliation(s)
- L Biferale
- Department of Physics and INFN, University of Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
| | | | | | | |
Collapse
|
15
|
Bosbach J, Weiss S, Ahlers G. Plume fragmentation by bulk interactions in turbulent Rayleigh-Bénard convection. PHYSICAL REVIEW LETTERS 2012; 108:054501. [PMID: 22400934 DOI: 10.1103/physrevlett.108.054501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Indexed: 05/31/2023]
Abstract
Using compressed gases with Prandtl numbers near 0.7, we obtained flow visualizations of turbulent Rayleigh-Bénard convection in a cylindrical sample with an aspect ratio Γ≡D/L≅10 (D is the diameter and L the height) by the shadowgraph method. Focusing on the plumes under the top plate, we found that their length had a log-normal distribution, suggesting a fragmentation process. Fragmentation events could be visually identified in the images and involved plume interactions with bulk fluctuations or upwelling domain walls. We found the mean spacing between plumes to vary with the Rayleigh number in proportion to the volume-averaged Kolmogorov length of the turbulent bulk fluctuations, providing further evidence for plume-bulk interactions.
Collapse
Affiliation(s)
- Johannes Bosbach
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | | | | |
Collapse
|
16
|
Weidauer T, Pauluis O, Schumacher J. Rayleigh-Bénard convection with phase changes in a Galerkin model. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 84:046303. [PMID: 22181257 DOI: 10.1103/physreve.84.046303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2011] [Revised: 05/25/2011] [Indexed: 05/31/2023]
Abstract
The transition to turbulence in Rayleigh-Bénard convection with phase changes and the resulting convective patterns are studied in a three-dimensional Galerkin model. Our study is focused on the conditionally unstable regime of moist convection in which the stratification is stable for unsaturated air parcels and unstable for saturated parcels. We perform a comprehensive statistical analysis of the transition to convection that samples the dependence of attractors (or fixed points) in the phase space of the model on the dimensionless parameters. Conditionally unstable convection can be initiated either from a fully unsaturated linearly stable equilibrium or a fully saturated linearly unstable equilibrium. Highly localized moist convection can be found in a steady state, in an oscillating recharge-discharge regime, or turbulent in dependence of the aspect ratio and the degree of stable stratification of the unsaturated air. Our phase-space analysis predicts parameter ranges for which self-sustained convective regimes in the case of subcritical conditional instability can be observed. The observed regime transitions for moist convection bear some similarities to transitions to turbulence in simple shear flows.
Collapse
Affiliation(s)
- Thomas Weidauer
- Institut für Thermo- und Fluiddynamik, Technische Universität Ilmenau, Postfach 100565, D-98684 Ilmenau, Germany
| | | | | |
Collapse
|
17
|
Lakkaraju R, Schmidt LE, Oresta P, Toschi F, Verzicco R, Lohse D, Prosperetti A. Effect of vapor bubbles on velocity fluctuations and dissipation rates in bubbly Rayleigh-Bénard convection. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 84:036312. [PMID: 22060497 DOI: 10.1103/physreve.84.036312] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Indexed: 05/31/2023]
Abstract
Numerical results for kinetic and thermal energy dissipation rates in bubbly Rayleigh-Bénard convection are reported. Bubbles have a twofold effect on the flow: on the one hand, they absorb or release heat to the surrounding liquid phase, thus tending to decrease the temperature differences responsible for the convective motion; but on the other hand, the absorbed heat causes the bubbles to grow, thus increasing their buoyancy and enhancing turbulence (or, more properly, pseudoturbulence) by generating velocity fluctuations. This enhancement depends on the ratio of the sensible heat to the latent heat of the phase change, given by the Jakob number, which determines the dynamics of the bubble growth.
Collapse
Affiliation(s)
- Rajaram Lakkaraju
- Physics of Fluids Group, Faculty of Science and Technology, Impact and Mesa+ Institutes, and J. M. Burgers Center for Fluid Dynamics, University of Twente, NL-7500 AE Enschede, The Netherlands.
| | | | | | | | | | | | | |
Collapse
|
18
|
|
19
|
Oresta P, Verzicco R, Lohse D, Prosperetti A. Heat transfer mechanisms in bubbly Rayleigh-Bénard convection. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:026304. [PMID: 19792246 DOI: 10.1103/physreve.80.026304] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2008] [Indexed: 05/28/2023]
Abstract
The heat transfer mechanism in Rayleigh-Bénard convection in a liquid with a mean temperature close to its boiling point is studied through numerical simulations with pointlike vapor bubbles, which are allowed to grow or shrink through evaporation and condensation and which act back on the flow both thermally and mechanically. It is shown that the effect of the bubbles is strongly dependent on the ratio of the sensible heat to the latent heat as embodied in the Jakob number Ja. For very small Ja the bubbles stabilize the flow by absorbing heat in the warmer regions and releasing it in the colder regions. With an increase in Ja, the added buoyancy due to the bubble growth destabilizes the flow with respect to single-phase convection and considerably increases the Nusselt number.
Collapse
Affiliation(s)
- Paolo Oresta
- Physics of Fluids Group, Department of Science and Technology, J. M. Burgers Centre for Fluid Dynamics, and Impact Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | | | | | | |
Collapse
|