Buoyancy induced convective heat transfer in particle, tubular and flake type of nanoparticle suspensions

This paper reports the experimental study to investigate the buoyancy-induced convective heat transfer in a square cavity using different types of nanofluids. Three types of nanofluids namely, particle based (Al2O3/Water), tube based (MWCNT/Water) and flake based (Graphene/Water) are used. A square cavity with the dimensions (40×40×200) mm3 is used as the test section. Experiments are performed for 0.1%, 0.3%, and 0.5% volume fractions with varying Rayleigh number over a range of 7 ×105 to 1 ×107. For the comparison of heat transfer characteristics of different nanofluids normalized Nusselt number is estimated. It has been observed that an enhancement in natural convective heat transfer is obtained using MWCNT/Water and Graphene/Water nanofluids at 0.1% volume fraction. However for higher concentration, a deterioration in heat transfer is observed. The relative changes in thermophysical properties of nanofluids are insufficient to explain the reported results. It is proposed that the contribution of various slip mechanisms between the nanoparticle suspension and basefluid are responsible for the enhancement.