The heat transfer of water-based Al$_2$O$_3$ nanofluid in turbulent Rayleigh-B\'{e}nard convection*

We report experimental measurements of the convective heat transfer in water-based Al$_2$O$_3$ nanofluid in a cylindrical convection cell, which has 19 cm in both height and diameter. The nanofluid has been supplied by Nanophase Technologyies Inc. with an initial volume fraction ($\phi$) 22{\%}. It has been diluted into deionized water to obtain nanofluid of low volume fraction. The nominal diameter of Al$_2$O$_3$ particle is 45 nm. At the fixed heating power, $Q =500 W$, it has been found that the convective heat transfer coefficient ($h=Q/{\Delta T} $, $\Delta T$ is the temperature difference across the cell.) decreases to 2{\%} when $\phi$ varies from 0.03{\%} to 1.1{\%}. At $\phi =1.1{\%}$, we have measured the Nusselt number ($Nu$) as a function of Rayleigh number ($Ra$). It has been found that $Nu$ of nanofluid collapses on the $Nu \sim Ra$ scaling curve of pure water at higher $Ra$ ($4\times10^{9}$ to $1\times10^{10} $). While the deterioration of convective heat transfer has been observed at lower $Ra$ ($8\times10^{8}$ to $4\times10^{9} $), and the deterioration becomes more pronounced with decreasing $Ra$. Additional measurement on the thermal and flow structures is in progress to understand the convective heat transport in nanofluid.