Interface Deformation and Convective Transport in Horizontal Differentially Heated Air-Oil Layers

Abstract

Convection in a differentially heated cavity partly filled with silicone oil has been experimentally studied. The air-oil layers are subjected to a temperature difference in the vertical direction, with the lower wall being heated with respect to the top. The overall geometry is that of an enclosed cavity that is octagonal in plan. Heights of oil layers considered for experiments correspond to 30, 50, and 70% of the vertical cavity dimension. Measurements have been carried out using a shadowgraph technique. A limited number of interferograms have also been recorded. The shadowgraph technique has been validated against interferograms under identical experimental conditions. The temperature fields in silicone oil along with the deformation of the interface have been obtained from measurements. The thrust of the study is on establishing the relationship between the interface deformation and the local heat flux, the latter measured at the interface as well as the lower hot wall. The correlation has been examined under steady as well as unsteady conditions. Nusselt number distribution over the entire air-oil interface has been determined using principles of tomography. For this purpose, the thermal field in the cavity has been mapped at four angles, namely 0, 45, 90 and 135 . When the cavity is filled up to 30 and 50% of its height with silicone oil, the Nusselt number distribution at the interface is seen to correlate directly with interface deformation. This result is seen in the instantaneous as well as the timeaveraged shadowgraph images. The correlation is reversed for the lower heated wall. No interface deformation was recorded for a cavity 70% filled with silicone oil, even when the overall temperature difference was quite high. 1 Department of Mechanical Engineering, Indian Institute of Technology Kanpur,Kanpur 208 016 UP (India). Keyword: Convection, buoyancy, interface deformation, shadowgraph, tomography, Nusselt number.