  Conventional heat carrier liquids have demonstrated remarkable enhancement in
heat and mass transfer when nanoparticles were suspended in them. These
liquid-nanoparticle suspensions are now known as Nanofluids. However the
relationship between nanoparticles and the degree of enhancement is still
unclear, thus hindering the large scale manufacturing of them. Understanding of
the energy and flow behaviour of nanofluids is therefore of wide interest in
both academic and industrial context. In this paper we first model the heat
transfer of a nanofluid in convection in a circular tube at macro-scale by
using CFD code of OpenFoam. Then we zoon into nano-scale behaviour using the
Molecular Dynamics (MD) simulation. In the latter we considered a system of
water and Gold nanoparticles. A systematic increase of convective heat transfer
was observed with increasing nanoparticle concentration. A maximum enhancement
of 7.0% was achieved in comparison to base fluid water. This occurred when the
gold volume fraction was 0.015. Subsequent MD simulations confirmed a dense
water layer formed 2nm away from the gold nanoparticle boundary. It is
speculated that the observed increase in thermal conductivity was principly
caused by this dense water layer formed around each nanoparticle.
