Natural convection in shear-thinning fluids: Experimental investigations by MRI

Darbouli, Mohamed; Métivier, Christel; Leclerc, Sébastien; Nouar, Chérif; Bouteera, Mondher; Stemmelen, Didier

doi:10.1016/j.ijheatmasstransfer.2015.12.056

Cited by 35 publications

(35 citation statements)

References 43 publications

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“…It is interesting to note that when the characteristic timeλ of the fluid is larger than the advection time d /R 1 Ω −1 1 , the Carreau model tends towards the power-law modelμ =KΓ (nc−1)/2 with a consistency K =μ 0λ (nc−1)/2 . Examples of the values of the Carreau parameters can be found in the literature, particularly for solutions of xanthan gum, stiff-rode-like polymer [21,34,35].…”

Section: Ii2 Carreau Modelmentioning

confidence: 99%

Taylor-vortex flow in shear-thinning fluids

et al. 2019

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The present paper deals with the Taylor-Couette flow of shear-thinning fluids. It focuses on the first principles understanding the influence of the viscosity stratification and the nonlinear variation of the effective viscosity µ with the shear rateγ on the flow structure in the Taylor vortex flow regime. A wide gap configuration (η = 0.4) is mainly considered. A weakly nonlinear analysis, using the amplitude expansion method at high order is adopted as a first approach to study nonlinear effects. For the numerical computation, the shear-thinning behavior is described by the Carreau model. The rheological parameters are varied in a wide range. The results indicate that the flow field undergoes a significant change as shear-thinning effects increase. First, vortices are squeezed against the inner wall and the center of the patterns are shifted axially towards the radial outflow boundaries (z = 0, z/λ z = 1). This axial shift leads to increasing concentration of vorticity at these positions. The outflow becomes more stronger than the inflow and the inflow zone, where the vorticity is low, increases accordingly. Nevertheless, the strength of the vortices relative to the velocity of the inner cylinder is weaker. Second, the pseudo-Nusselt number, ratio of the torque to that obtained in the laminar flow, decreases. Third, higher harmonics become more relevant and grow faster with Reynolds number. Finally, the modification of the viscosity field is described.

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Section: Ii2 Carreau Modelmentioning

confidence: 99%

Taylor-vortex flow in shear-thinning fluids

et al. 2019

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“…Generally, non-Newtonian fluids are highly viscous and thermodependent. The thermodependency of the fluid properties leads to hexagonal patterns at the onset [45][46][47]. Analysis of the stability of this convective pattern is the next step of our work, dealing with the influence of the rheology on the pattern selection.…”

Section: Discussionmentioning

confidence: 96%

Instabilities of convection patterns in a shear-thinning fluid between plates of finite conductivity

2017

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Rayleigh-Bénard convection in a horizontal layer of a non-Newtonian fluid between slabs of arbitrary thickness and finite thermal conductivity is considered. The first part of the paper deals with the primary bifurcation and the relative stability of convective patterns at threshold. Weakly nonlinear analysis combined with Stuart-Landau equation is used. The competition between squares and rolls, as a function of the shear-thinning degree of the fluid, the slabs' thickness, and the ratio of the thermal conductivity of the slabs to that of the fluid is investigated. Computations of heat transfer coefficients are in agreement with the maximum heat transfer principle. The second part of the paper concerns the stability of the convective patterns toward spatial perturbations and the determination of the band width of the stable wave number in the neighborhood of the critical Rayleigh number. The approach used is based on the Ginzburg-Landau equations. The study of rolls stability shows that: (i) for low shear-thinning effects, the band of stable wave numbers is bounded by zigzag instability and cross-roll instability. Furthermore, the marginal cross-roll stability boundary enlarges with increasing shear-thinning properties; (ii) for high shear-thinning effects, Eckhaus instability becomes more dangerous than cross-roll instability. For square patterns, the wave number selection is always restricted by zigzag instability and by "rectangular Eckhaus" instability. In addition, the width of the stable wave number decreases with increasing shear-thinning effects. Numerical simulations of the planform evolution are also presented to illustrate the different instabilities considered in the paper.

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“…Considering our experimental setup, we obtain a velocity uncertainty of 5 times the resolution [17]. It means that we cannot measure velocity magnitudes below the value 5.10…”

Section: Mr Velocitymentioning

confidence: 96%

“…Velocity images are obtained using a protocol detailed in [17]. This protocol uses a classical spin-echo imaging sequence with additional bipolar gradient pulses in order to encode the velocity [24].…”

Section: Mr Velocitymentioning

confidence: 99%

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MRI temperature and velocity measurements in a fluid layer with heat transfer

Leclerc

Métivier

2018

Exp Fluids

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To cite this version:Sébastien Leclerc, C. Métivier. MRI temperature and velocity measurements in a fluid layer with heat transfer. Experiments in Fluids, Springer Verlag (Germany), 2018, 59 (2), 10.1007/s00348-018-2494-3. hal-01693075Noname manuscript No. Résumé Magnetic Resonance Thermometry (MRT) is an innovative technique which can provide 2D and 3D temperature measurements using Magnetic Resonance Imaging (MRI). Despite the powerful advantages of MRT, this technique is sparcely developed and used in the engineering sciences. In this paper, we investigate the possibility to measure temperatures with MRI in a fluid layer submitted to heat transfer. By imposing a vertical temperature gradient, we study the temperature fields in both conductive and convective regimes. The temperature fields are obtained by measuring the transverse relaxation time T 2 in glycerol, a Newtonian fluid. The MRT protocol is described in detail and the results are presented. We show that for a conductive regime, temperature measurements are in very good agreement with the theoretical profile. In the convective regime, when comparing the temperature and velocity fields obtained by MRI, we get an excellent agreement in terms of flow structure. Temperature uncertainties are found to be less than 1• C for all our results.

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Natural convection in shear-thinning fluids: Experimental investigations by MRI

Cited by 35 publications

References 43 publications

Taylor-vortex flow in shear-thinning fluids

Taylor-vortex flow in shear-thinning fluids

Instabilities of convection patterns in a shear-thinning fluid between plates of finite conductivity

MRI temperature and velocity measurements in a fluid layer with heat transfer

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