Experimental investigation of the Rayleigh-B茅nard convection in a yield stress fluid

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• 作者：Zineddine Kebiche ; Cathy Castelain ; Teodor Burghelea
• 关键词：Carbopol® ; Rayleigh&ndash ; Bé ; nard convection ; Yielding ; Rheological hysteresis ; Supercritical bifurcation
• 刊名：Journal of Non-Newtonian Fluid Mechanics
• 出版年：January, 2014
• 年：2014
• 卷：203
• 期：Complete
• 页码：9-23
• 全文大小：3622 K

文摘

An experimental study of the Rayleigh-B茅nard convection in a yield stress fluid (Carbopol庐 980) uniformly heated from below in a rectangular cavity with high aspect ratio is presented. By combined integral measurements of the temperature difference between two parallel plates and the local flow velocity within a wide range of heating powers P two distinct regimes are observed. For heating powers smaller then a critical value a purely conductive regime is observed. A gradual increase of the heating power beyond this onset reveals a convective regime manifested through a nonlinear dependence of the temperature difference between plates on the heating power. Simultaneously with this, local measurements of the flow fields reveal a nonlinear increase of the roll pattern amplitude. Regardless the concentration of Carbopol庐 and in spite of a significant shear thinning behaviour, the Rayleigh-B茅nard convection in the Carbopol庐 gel is found to emerge as an imperfect bifurcation that can be correctly modelled by the Landau theory of phase transitions. A critical slowing down phenomenon is observed corresponding to the onset of convection. The scaling laws of the convective onset and of the corresponding temperature difference with the relevant material properties are discussed. The onset of the instability can be described in terms of a critical yield number rather than in terms of a critical Rayleigh number. The paper closes with a comparison of our findings with existing previous works.