Numerical study on natural convection of MWCNT nanofluids in a enclosure based on experimental conductivity and viscosity

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.

This study is motivated by the much reported enhancement in thermal conductivity of nanofluids and their potential as a replacement for conventional coolant fluids. Among the various factors considered in the selection of a coolant fluid, this study focused on the convective behaviour of nanofluids as demonstrated in a square enclosure with differentially heated side walls at low particle concentrations of 0 – 1 % and Ra number range of 104 to 106. Therefore, the study consists of numerical investigation by using experimentally determined thermal conductivities and viscosities of the nanofluid. A theoretical model was used for higher (though less practical) particle concentration of up to 8 %. The simulations were done by using CD Adapco’s Star-CCM+ Code (v 8.06) revealed an initial enhancement in the Nusselt number with varying particle concentration before rapidly falling to an average value that continues to diminish for the concentration range tested. This was true for different Ra numbers. The variation was attributed to the counteracting, non-linear effects of thermal conductivity and viscosity both of which increases by increasing particle concentration. The thermal conductivity effect were observed to be more dominant for a very narrow range of low particle concentration below 0.1 % while the viscous effect was found to be the more dominant at higher particle concentration above 0.1 %.