Investigation of the convective heat transfer in waterbased Alumina nanofluid

Recent research has suggested that nanofluids have great potential in thermal applications due to their significantly high thermal conductivity [1]. But the buoyancy- driven convective flow would play an important role in the heat transport process. We have conducted an experimental measurement of the convective heat transfer in water-based Al$_2$O$_3$ nanofluid in a cylindrical cell (19 cm in both height and diameter). The nominal diameter of Al$_2$O$_3$ particle is 45 nm. At the fixed heating power, $Q =513 W$, 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 the volume fraction of nanoparticle, $\phi$, increases from 0.03{\%} to 1.1{\%}. At $\phi =1.1{\%}$, we examined the relationship between Nusselt number ($Nu$) and Rayleigh number ($Ra$) of nanofluid. It has been found that the $Nu-Ra$ scaling of nanofluid follows that of pure water at higher $Ra$ ($>3\times10^{9}$). At lower $Ra$ ($<3\times10^{9}$), a deviation occurs, and it becomes more pronounced with decreasing $Ra$.// [1]. J. A. Eastman {\it et. al.}, Annu. Rev. Mater. Res. {\bf 34} 219, (2004).