Boundary-layer thickness and instabilities in Benard convection of a liquid with a temperature-dependent viscosity

New and published experimental measurements of spatial and temporal aspects of variable-viscosity convection are compared with boundary layer models. Viscosity μ is assumed to decrease with increasing temperature T so that convection occurs beneath a relatively stagnant layer. Of particular interest to applications involving asymptotically large viscosity variations, is the result that both the temperature difference across the hot thermal boundary layer and the frequency of thermal formation scale with the rheological temperature scale −(d log μ/dT)−1. Measurements indicate that for large Rayleigh numbers, viscosity varies by less than a factor of ≈37 across the actively convecting region.

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