The polymer effect on turbulent Rayleigh-Bénard convection based on PIV experiments

Cai, Weihua; Wei, Tai‐Huei; Tang, Xiaojing; Liu, Yao; Li, Biao; Li, Feng‐Chen

doi:10.1016/j.expthermflusci.2019.01.011

Cited by 13 publications

(7 citation statements)

References 30 publications

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“…of the HTR and HTE experiments [2][3][4][5] is speculative. Nonetheless, the detailed identification of interactions between polymers and natural convection cells at a low Rayleigh number allows for new insights into the mechanism driving HTM.…”

Section: Please Cite This Article As Doi:101063/15143275mentioning

confidence: 99%

“…For polymer parameters, the viscosity ratio β is kept constant, β = 0.9, matching previous viscoelastic channel flow simulations performed in previous studies 19,20,22 . The parameter space under investigation is a matrix (L,Wi) with L = (10, 25, 50, 100) and Wi = (1,5,10,15,20,25,30,35,40,45), with a few additional simulations for L = 15, 20, 30, 40 at Wi = 10 and L = 25, 40 at Wi = 40.…”

Section: Resolution and Parameter Spacementioning

confidence: 99%

“…Their effect on turbulent heat transport is far less documented, even though polymer solutions may be of interest in the management of heat transfer for instance. Recent experimental studies [2][3][4][5] demonstrated that dilute solutions of polymers may cause heat transfer reduction (HTR) or enhancement (HTE) in turbulent natural convection flow. The flow of interest here, specifically the Rayleigh-Bénard convection (RBC) flow, is generated by a vertical negative gradient of temperature between two horizontal plates.…”

Section: Introductionmentioning

confidence: 99%

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Heat transfer enhancement and reduction in low-Rayleigh number natural convection flow with polymer additives

Dubief

Terrapon

2020

Physics of Fluids

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The effects of viscoelasticity, here caused by polymer additives, on Rayleigh Bénard convection flows are investigated via direct numerical simulations at a marginally turbulent Rayleigh number. Simulations with a range of polymer length and relaxation time scales show heat transfer enhancement (HTE) and reduction (HTR). The selection of HTE and HTR depends strongly on the maximum extensional viscosity of the solution, whereas the magnitude of heat transfer modification is a function of both the maximum extensional viscosity and relaxation time of the polymer solution. The underlying physics of HTE and HTR are explored and a mechanism of the interaction between convection cells and polymers is proposed. The findings are extrapolated to high Ra to shed some new light onto experimental observations of HTR.

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Section: Please Cite This Article As Doi:101063/15143275mentioning

confidence: 99%

Section: Resolution and Parameter Spacementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Heat transfer enhancement and reduction in low-Rayleigh number natural convection flow with polymer additives

Dubief

Terrapon

2020

Physics of Fluids

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“…Rayleigh-B enard convection problems have been widely studied by taking into account the Newtonian fluids, while the focus on non-Newtonian fluids is comparatively less. Non-Newtonian fluids have applications in petroleum drilling, polymer engineering, and the importance of non-Newtonian fluids are studied by a few prominent researchers (Ahlers and Nikolaenko, 2010;Wei et al, 2012Wei et al, , 2018Cai et al, 2019;Xie et al, 2015;Cheng et al, 2017Cheng et al, , 2019Benzi et al, 2012). One among the non-Newtonian fluid is the couple-stress fluid, and the concept was introduced by Stokes (1966).…”

Section: Stability Of the Fluid In Convection 1019mentioning

confidence: 99%

Convective instability analysis of couple-stress dielectric fluid saturated anisotropic porous medium with radiation effect

Myson

Nagouda

2020

MMMS

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PurposeThe effects of anisotropy and radiation cannot be considered negligible while investigating the stability of the fluid in convection. Hence, the purpose of this paper is to analyze how these effects could affect the system while considering a couple-stress dielectric fluid. Therefore, the study establishes the effect of thermal radiation in a couple-stress dielectric fluid with an anisotropic porous medium using Goody's approach (Goody, 1956).Design/methodology/approachTo analyze the effect of radiation on the onset of convection, the Milne–Eddington approximation is employed to convert radiative heat flux to thermal heat flux. The equations are further developed to approximate for transparent and opaque medium. Stability of the quiescent state within the framework of linear theory is performed. The principle of exchange of stabilities is shown to be valid by means of single-term Galerkin method. Large values of conduction–radiation and absorptivity parameters are avoided as fluid is considered as liquid rather than gas.FindingsThe radiative heat transfer effect on a couple-stress dielectric fluid saturated anisotropic porous medium is examined in terms of Milne–Eddington approximation. The effect of couple-stress, dielectric, anisotropy and radiation parameters are analyzed graphically for both transparent and opaque medium. It is observed that the conduction–radiation parameter stabilizes the system; in addition, the critical Darcy–Rayleigh number also shows a stabilizing effect in the absence of couple-stress, dielectric and anisotropy parameters, for both transparent and opaque medium. Furthermore, the absorptivity parameter stabilizes the system in the transparent medium, whereas it exhibits a dual effect in the case of an opaque medium. It was also found that an increase in thermal and mechanical anisotropy parameters shows an increase in the cell size, whereas the increase in Darcy–Roberts number and conduction–radiation parameter decreases the cell size. The validity of principle of exchange of stability is performed and concluded that marginal stability is the preferred mode than oscillatory.Originality/valueThe effects of anisotropy and radiation on Rayleigh–Bénard convection by considering a couple-stress dielectric fluid has been analyzed for the first time.

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“…Wang et al [8] firstly introduced the wavelet method into the study of flow structures of polymer drag-reducing flow. Cai’s group studied polymer effects on turbulent Rayleigh-Benard convection and oscillating grid turbulence by both numerical simulation and experiment using particle image velocimetry [9,10,11].…”

Section: Introductionmentioning

confidence: 99%

Direct Numerical Simulation of Gas-Liquid Drag-Reducing Cavity Flow by the VOSET Method

Wang

Wang²,

Cheng

2019

Polymers

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Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method—coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.

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The polymer effect on turbulent Rayleigh-Bénard convection based on PIV experiments

Cited by 13 publications

References 30 publications

Heat transfer enhancement and reduction in low-Rayleigh number natural convection flow with polymer additives

Heat transfer enhancement and reduction in low-Rayleigh number natural convection flow with polymer additives

Convective instability analysis of couple-stress dielectric fluid saturated anisotropic porous medium with radiation effect

Direct Numerical Simulation of Gas-Liquid Drag-Reducing Cavity Flow by the VOSET Method

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