Molecular Dynamics Simulations of Interfacial Heat and Mass Transfer at Nanostructured Surface

Abstract

The nanoscale heat and mass transport phenomena play important roles on the applications of nanotechnologies with great attention to its differences from the continuum mechanics. In this paper, the breakdown of the continuum assumption for nanoscale flows has been verified based on the molecular dynamics simulations and the heat transfer mechanism at the nanostructured solid-liquid interface in the nanochannels is studied from the microscopic point of view. Simple Lennard-Jones (LJ) fluids are simulated for thermal energy transfer in a nanochannel using nonequilibrium molecular dynamics techniques. Multi-layers of platinum atoms are utilized to simulate the solid walls with arranged nanostructures and argon atoms are employed as the LJ fluid. The results show that the interface structure (i.e. the solid-like structure formed by the adsorption layers of liquid molecules) between solid and liquid are affected by the nanostructures. It is found that the hydrodynamic resistance and thermal resistance dependents on the surface wettability and for the nanoscale heat and fluid flows, the interface resistance cannot be neglected but can be reduced by the nanostructures. For the hydrodynamic boundary condition at the solid-liquid interface, the no-slip boundary condition holds good at the super-hydrophilic surface with large hydrodynamic resistance. However, apparent slip is observed at the low hydrodynamic resistance surface when the driving force overcomes the interfacial resistance. For the thermal boundary condition, it is found that the thermal resistance at the interface depends on the interface wettability and the hydrophilic surface has lower thermal resistance than that of the hydrophobic surfaces. The interface thermal resistance decreases at the nanostructed surface and significant heat transfer enhancement has been achieved at the hydrophilic nanostructured surfaces. Although the surface with nanostrutures has larger surface area than the flat surface, the rate of heat flux increase caused by the nanostructures is remarkable.