Heat transfer measurements in an inclined low aspect ratio Rayleigh–Bénard convection cell under feedback control

Abstract

We report experimental results on the inclined Rayleigh–Bénard convection of a moderate aspect ratio convection cell using a high Prandtl aqueous solution of glycerol. The main goal of the present work is to measure continuously the transition from a convective condition into a purely conduction regime by a smooth quasi-static variation of the tilt angle of the convection cell with respect to the gravity vector in 180° at Rayleigh numbers just above of convection onset. Flow circulation inside the convection cell is indirectly detected by temperature sensors located at the bounding active plates. Changes in the temporal evolution of the heat transfer curve appear directly related to flow transitions between characteristic flow patterns from transversal rolls evolving into an unicellular single roll convective pattern and then a conductive state. For small tilt angles 6°≤γ≤20° time signal fluctuations on both the Nusselt number and temperature readings were observed. Flow visualizations and PIV measurements provided a complementary view of the convective flow pattern being associated to transitions in the Nusselt number evolution with the tilt angle of the cell. For small tilt angle transitions, we observed a loss of rolls process followed by a reorganization of the flow which might be the responsible of the Nusselt unsteadiness.