Interferometric study of natural convection heat transfer phenomena around array of heated cylinders

摘要

Interferometric measurements of natural convection-based heat transfer rates around array(s) of heated cylinders have been presented. Experiments have been performed with single, two cylinders placed adjacent to each other with varying centre-to-centre distances and three cylinders arranged in a triangular configuration. Mach-Zehnder interferometer has been employed for recording the projection data of temperature field. The interferograms have first been qualitatively interpreted to understand the influence of buoyant plume of one cylinder on the convective phenomena of the other cylinder(s) of the array. Images have then been quantitatively analyzed to retrieve the whole field temperature distributions. Results have been presented in the form of interferometric images, temperature contours, local distribution of heat transfer rates as a function of Rayleigh numbers. Experiments involving two cylinders showed a strong dependence of the net convective phenomena on the relative spacing of the cylinders. While the buoyant plumes originating from each cylinder were almost independent of each other for larger centre-to-centre distances, the plumes were seen to be strongly coupled as the spacing between the cylinders was reduced. Wall heat transfer rates were found to be comparable with those of single cylinder for large cylinder centre-to-centre distances and showed a decreasing trend as the relative spacing is reduced. Experiments on the triangular array of cylinders revealed that the heat transfer rates from the top cylinder were strongly influenced by the thermal plumes rising from the bottom cylinders. The average Nusselt number around the top cylinder in triangular configuration was found to be significantly smaller than that of the single cylinder.