Experimental study in a natural convection cavity using nanofluids

Abstract

This experimental paper is about the implementation of two types of nanofluid in a three-liter natural convection cavity (H = 20 cm, L = 15 cm and W = 10 cm) and to investigate the effect on the heat transfer. In this experiment, the left wall has constant heat (80 W) and the right wall has a constant temperature that is being cooled by using a fabricated constant temperature water bath. In electronics cooling, this kind of natural convection can be found and the left wall is the location where electronics equipment is mounted and releases constant heat. This surface is getting cooled by the natural convection cavity. ZnO and Al2O3 nanoparticles (both of them create whitish aqueous solution) of low volume fraction (up to 0.05% to maintain the stability in the cavity) are chosen for this purpose so that fluid flow visualization can be observed. Initially, flow visualizations are carried out using smoke and water with color dye. The natural convection loop is observed for both the cases at steady state condition but the water case takes a much longer time. The eye of the vortex is found in both cases. In the case of air, it stays at the center but for water, there is a gradual shift of the vortex eye towards the cold wall over time. However, initially, ZnO nanoparticles are formed from micro-particle by manually grinding but this leads to a very unstable solution (even at 0.01% volume fraction) in distilled water solution even after three hours of ultra-sonication. So, in-house nanoparticle preparation (without using any surfactant in the nanofluid) fails the purpose and thus vendor-supplied nanoparticles will be used for all future investigations.