The effect of wall temperature fluctuations on the heat transfer and fluid flow occuring in a liquid enclosure

A numerical study of the effect of thermal fluctuations, similar to those encountered during directional solidification in Vertical Bridgman configuration (VB), on the heat transfer and fluid flow in a liquid enclosure has been undertaken. The VB when heated from the top is characterized by a stable flow regime maintained for a larger range of Rayleigh numbers than can be obtained with an Inverted Vertical Bridgman configuration (IVB) heated from below. In order to qualify the effect of thermal fluctuations on the heat and flow transfers, investigations are conducted for the range of Rayleigh numbers maintaining a stable flow (Ra ∈ [104, 106]). The results show that the thermal oscillations at low frequency can destabilize the flow regime. A characteristic frequency at which the average heat transfer rate reaches a minimum value is identified. This minimum value is dependent on the amplitude of thermal fluctuation. The critical frequency increases linearly with the intensity of the convection (Rayleigh number).