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

Abstract : An experimental investigation of the Rayleigh–Bénard convection in shear-thinning fluids using MRI technics is presented. The experimental setup consists on a cylindrical cavity defined by a finite aspect ratio A = D/d = 6. Qualitative and quantitative results are provided. Flow structure is determined from velocity mapping for a Newtonian fluid, Glycerol and for shear-thinning fluids, Xanthan gum aqueous solutions with weight concentrations ranging from 0.1% to 0.2%. In the case of the Glycerol and the Xanthan solution at 0.1%, one recovers similar results in terms of criticality with Rac ≈ 1800 and patterns since the convection is characterized by rolls. When the Xanthan concentration is increased, the critical Rayleigh number is not modified, however the onset occurs with hexagonal pattern. Because the critical temperature differences increase with the concentrations due to an increase in viscosity, one can think that hexagonal patterns are due to variations of physical properties with temperature (non Oberbeck–Boussinesq effects). Similarities with some results obtained in the Newtonian case are highlighted. We have observed a transition from hexagonal patterns to rolls by increasing the Rayleigh number. This pattern transition is characterized by a discrepancy in the maximal velocity values. By using shear-thinning fluids, results show an increase in the intensity of convection compared with the Newtonian case.
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International Journal of Heat and Mass Transfer, Elsevier, 2016, 95, pp.742-754. 〈10.1016/j.ijheatmasstransfer.2015.12.056〉
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Mohamed Darbouli, Christel Métivier, Sébastien Leclerc, Chérif Nouar, Mondher Bouteera, et al.. Natural convection in shear-thinning fluids: Experimental investigations by MRI. International Journal of Heat and Mass Transfer, Elsevier, 2016, 95, pp.742-754. 〈10.1016/j.ijheatmasstransfer.2015.12.056〉. 〈hal-01408983〉

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