Developing Cross Drag Expressions for Nanotube Bundles Using Molecular Dynamics

The nonequilibrium molecular dynamics (NEMD) simulations are performed to calculation the cross drag over a nanotube located in a uniform liquid argon flow. As is known, the behavior of fluid flows in nano-scale sizes is very different from that in microscopic and macroscopic sizes. In this work, our concern is on the flow of argon molecules over a nanotube which occurs in nanoscale sizes. We calculate the cross drag enforced the nanotube at Re≤1.0. In this regard, we use the molecular dynamics and simulate the flow of argon molecules over (6,0), (8,0) and (10,0) nanotubes. The simulations are performed at different velocities and the cross drag coefficient is computed at different Reynolds numbers. To improve the efficiency of simulations, we use USHER algorithm and examin the insertion of molecules at the end of the simulation box, the argon molecules are located out of box. Using the power trend line, we derived a formula, which approximates the cross drag of chosen nanotube. In all simulations, only the first two and the last two rings of the nanotube are frozen. All non-bonded interactions are calculated based on the Lennard-Jones potential. The results if molecular dynamics are compared with two empirical expressions provided by experiments performed on the flow over a macro-scale cylinder. The results show that the cross drag force on a single-walled nanotube calculated from MD simulations is larger than that provided by the empirical expressions in slow flows (Re≪ 1.0). As is expected the results of continuum flow calculations cannot be trusted to predict the drag of a nanotubes if Re≪1.0. The difference increases as the flow velocity decreases.