Abstract:
Due to the improvement of heat transfer by nanofluids, an understanding of the interactions between nanoparticles
and the base fluid is essential for simulation. The relative or slip velocity between nanoparticles and the
base fluid is one of the main factors in choosing the multiphase mixture model approach. In this paper, a new
slip velocity is proposed and used to compare the simulation result to the experimental results of natural convective
flow in a cavity filled with an alumina nanofluid. Therefore, the ANSYS-Fluent 15.0 software is employed and
the new slip velocity is applied as a user-defined function. The new slip velocity is a result of the combination of
Brownian and thermophoretic diffusions, lift, buoyancy and centrifugal forces, virtual mass, pressure gradient,
Van der Waals attraction and electric double layer repulsion forces. The comparison between these forces and induced
drag force will provide the corresponding slip velocity. The simulation results were in good agreement
with the flow pattern and heat transfer features of the experimental studies in the literature. It was found that
thermophoretic and electrostatic slip mechanisms should essentially be considered in simulations, as well as
buoyancy force. The major effects of electrostatic slip velocity are mainly seen in concentration higher than
1 vol.%, while thermophoresis could not be ignored in any concentration. Therefore, the implemented slip velocity
reveals some critical aspects of nanoparticle and base fluid interactions compared to an algebraic velocity.
