Experiments on the Identification of the Onset of Buoyancy-Driven Convection in High Aspect Ratio Top Open Cavities

Experimental analysis of the onset of buoyancy-driven convection in a top facing high aspect ratio cavity is reported. Bottom surface of the cavity is heated, with its two vertical side walls being insulated. Thermal field in the cavity has been non-intrusively mapped using a Mach-Zehnder interferometer. The cavity has been subjected to two different temperature differences, Delta T=3 degrees C (Ra similar or equal to 300) and Delta T=15 degrees C (Ra similar or equal to 1400). Sudden change in the heat transfer coefficient as well as the formation of thermally stratified layers at the bottom part of the cavity was not observed for the applied cavity temperature differences, which in turn, indicates that there is no such phenomenon of onset of buoyancy-driven convection in high aspect ratio cavities. Corner flow, induced due to the temperature difference between the atmosphere and the cavity, is the dominant flow inside the cavity. Almost identical profiles of flow in both the cases of the applied temperature potentially signify that the flow profile is independent of the Rayleigh number or the temperature differences. These observations have been supported by whole field temperature distribution profiles, spatial distributions of local Nusselt number, and nondimensional temperature at different position of the cavity.