Whole field measurements to understand the effect of nanoparticle concentration on heat transfer rates in a differentially-heated fluid layer

Experimental study on natural convection in a nanofluid-filled differentially heated cavity has been presented. Experiments have been conducted in an octagonal cavity with water and Al2O3/water-based dilute nanofluids of varying concentrations. A Mach Zehnder interferometer has been employed to record the projection data of convective field from four view angles (0, 45, 90 and 135°). The two-dimensional temperature fields determined through the quantitative analysis of the interferometric images have been employed to reconstruct the local field information using the principles of tomography. Results of the three-dimensional reconstructions clearly brought out the mechanisms of possible fluid movement in the differentially-heated cavity and its dependence on nanoparticle concentration. Near wall surface distributions of temperature fields as well as local Nusselt numbers indicated towards possible breakdown of large scale fluid structures into small length scale multiple roll-like circulatory loops at higher volumetric concentrations of dilute nanofluids. Local disturbances thus induced in the fluid layer due to the addition of nanoparticles resulted into better fluid mixing, which in turn led to an enhancement in the heat transfer rates with increasing concentration of nanofluids. Surface plots of Nusselt numbers obtained in the vicinity of the two thermally active walls of the cavity established an overall energy balance in the fluid layer.