Turbulent velocity profiles in a tilted heat pipe

Salort, Julien; Riedinger, Xavier; Rusaouen, Eleonore; Tisserand, Jean-Christophe; Seychelles, Fanny; Castaing, B.; Chillà, Francesca

doi:10.1063/1.4824852

Cited by 3 publications

(2 citation statements)

References 19 publications

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“…An attempt based on the mixing length approximation was recently reported by Salort et al (2013) in the case of a prescribed axial density gradient. This model emphasizes the crucial role of the stabilizing stratification as Θ increases and introduces empirical corrections to the usual mixing length definition to cope with this influence.…”

Section: Final Remarksmentioning

confidence: 99%

“…For Θ 20 • , the corresponding mean velocity and shear stress profiles are similar to those of Znaien et al (2009), and the smaller Θ the lower the critical Rayleigh number required to reach the 'hard' regime. New data by the same group in the range 5 • Θ 20 • (Salort et al 2013) were interpreted in the light of a mixing length model, but the observed Θ-dependence of the mean velocity profile could only be recovered by altering the usual time scale of Prandtl's original model (i.e. the inverse of the mean shear) with contributions resulting from both the stabilizing and destabilizing buoyancy components.…”

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Buoyancy-induced turbulence in a tilted pipe

Hallez

Magnaudet

2014

J. Fluid Mech.

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Numerical simulation is used to document the statistical structure and better understand energy transfers in a low-Reynolds-number turbulent flow generated by negative axial buoyancy in a long circular tilted pipe under the Boussinesq approximation. The flow is found to exhibit specific features which strikingly contrast with the familiar characteristics of pressure-driven pipe and channel flows. The mean flow, dominated by an axial component exhibiting a uniform shear in the core, also comprises a weak secondary component made of four counter-rotating cells filling the entire cross-section. Within the cross-section, variations of the axial and transverse velocity fluctuations are markedly different, the former reaching its maximum at the edge of the core while the latter two decrease monotonically from the axis to the wall. The negative axial buoyancy component generates long plumes travelling along the pipe, yielding unusually large longitudinal integral length scales. The axial and crosswise mean density variations are shown to be respectively responsible for a quadratic variation of the crosswise shear stress and density flux which both decrease from a maximum on the pipe axis to near-zero values throughout the near-wall region. Although the crosswise buoyancy component is stabilizing everywhere, the crosswise density flux is negative in some peripheral regions, which corresponds to apparent counter-gradient diffusion. Budgets of velocity and density fluctuations variances and of crosswise shear stress and density flux are analysed to explain the above features. A novel two-time algebraic model of the turbulent fluxes is introduced to determine all components of the diffusivity tensor, revealing that they are significantly influenced by axial and crosswise buoyancy effects. The eddy viscosity and eddy diffusivity concepts and the Reynolds analogy are found to work reasonably well within the central part of the section whereas non-local effects cannot be ignored elsewhere.

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Section: Final Remarksmentioning

confidence: 99%

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confidence: 99%

Buoyancy-induced turbulence in a tilted pipe

Hallez

Magnaudet

2014

J. Fluid Mech.

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A review on heat transfer characteristics of cryogenic heat pipes

Haghighi

Maleki

Assad

et al. 2021

J Therm Anal Calorim

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Non-isothermal buoyancy-driven exchange flows in inclined pipes

et al. 2017

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We study non-isothermal buoyancy-driven exchange flow of two miscible Newtonian fluids in an inclined pipe experimentally. The heavy cold fluid is released into the light hot one in an adiabatic small-aspect-ratio pipe under the Boussinesq limit (small Atwood number). At a fixed temperature, the two fluids involved have the same viscosity. Excellent qualitative and quantitative agreement is first found against rather recent studies in literature on isothermal flows where the driving force of the flow comes from salinity as opposed to temperature difference. The degree of flow instability and mixing enhances as the pipe is progressively inclined towards vertical. Similar to the isothermal limit, maximal rate of the fluids interpenetration in the non-isothermal case occurs at an intermediate angle, β. The interpenetration rate increases with the temperature difference. The degree of fluids mixing and diffusivity is found to increase in the non-isothermal case compared to the isothermal one. There has also been observed a novel asymmetric behavior in the flow, never reported before in the isothermal limit. The cold finger appears to advance faster than the hot one. Backed by meticulously designed supplementary experiments, this asymmetric behavior is hypothetically associated with the wall contact and the formation of a warm less-viscous film of the fluid lubricating the cold more-viscous finger along the pipe. On the other side of the pipe, a cool more-viscous film forms decelerating the hot less-viscous finger. Double diffusive effects associated with the diffusion of heat and mass (salinity) are further investigated. In this case and for the same range of inclination angles and density differences, the level of flow asymmetry is found to decrease. The asymmetric behaviour of the flow is quantified over the full range of experiments. Similar to the study of Salort et al. [“Turbulent velocity profiles in a tilted heat pipe,” Phys. Fluids 25(10), 105110-1–105110-16 (2013)] for tilted heat pipes, a small Richardson number of Ri≈0.05 is found, above which flow laminarization occurs. In terms of the dimensionless numbers of the problem, it is found that the interpenetrative speeds of the heavy and light fluid layers in non-isothermal and double-diffusive cases increase with the dimensionless temperature difference, rT, Atwood number, At, Grashof number, Gr, Reynolds number, Re, Nahme number, Na, and Péclet number, Pe but decreases with Prandtl number, Pr, and Brinkman number, Br.

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Turbulent velocity profiles in a tilted heat pipe

Cited by 3 publications

References 19 publications

Buoyancy-induced turbulence in a tilted pipe

Buoyancy-induced turbulence in a tilted pipe

A review on heat transfer characteristics of cryogenic heat pipes

Non-isothermal buoyancy-driven exchange flows in inclined pipes

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