Nonintrusive Diagnostics of Nanofluids-Based Natural Convection Heat Transfer over a Heated Cylinder

Abstract

The phenomena of nanofluids-based natural convection heat transfer around a heated cylinder have been studied using nonintrusive real-time diagnostics. Experiments have been performed with a horizontally placed heated cylinder immersed in bulk ambient conditions with water and alumina oxide/water-based dilute nanofluids as the working fluids. Volumetric concentrations of alumina nanoparticles have been varied from 0.005 to 0.02%. A classical Mach–Zehnder interferometer has been used to record the line-of-sight projection data of the convective field around the heated cylinder. The strength of thermal gradients prevailing around the surface of the heated cylinder was seen to be clearly affected by the variations in the nanofluid concentration, thus indicating the plausible role of nanoparticles in disrupting the thermal boundary-layer profiles around the cylinder surface. Significant enhancement in the heat transfer coefficient was observed at the highest levels of concentration of the dilute nanofluids employed, whereas the spatially averaged Nusselt numbers around the cylinder surface showed a marginal deterioration at the lower range of volumetric concentrations. With a further increase in nanoparticles concentration, the Nusselt numbers showed an increasing trend, although not as significant as observed in the case of the heat transfer coefficient. Plausible mechanisms responsible for these observations have been delved upon using purely nonintrusive whole field measurements.