Molecular Dynamics Simulation of Nanochannel Flows.

摘要

Nanoscale fluid flow systems involve both microscopic and macroscopic parameters, which may couple with each another and lead to many special properties. The primary objective of this thesis is, through molecular dynamics simulation, to understand the physical and dynamic properties of nanoscale flows, which are special and different from the classical fluid mechanics. We first explore the flow regimes by illustrating the fluid flux of nanoscale Poiseuille flows as a function of a dimensionless number, which represents the effective surface effect on the fluid; it is shown that the fluid motion in nanochannels falls into different regimes, each of which is associated with a distinct mechanism. To consider the effects of high shear rate and fluid heating, nanoscale Poiseuille flows under large external force are also investigated, and many intriguing nonlinear flow behaviors are observed. In addition, the transitions of the nanoflows from the regime where the surface effects are significant to the continuum regime where the classical fluid mechanics is valid with increasing channel size are depicted. It is shown that when the channel size is larger than about 150 molecular diameters (∼ 50 nm) the Navier-Stokes equations are valid regardless of the strength of the fluid-wall interaction. Furthermore, motivated by the potential applications of nanoflows for electronic device cooling, the interfacial thermal resistance is investigated, and its dependence on the external force under different fluid-wall interactions and temperatures are disclosed. Finally, based on the understanding of nanoscale flows, we propose a composite nanochannel with heterogeneous surface energies in which fluids is shown to be pumped by a symmetric temperature gradient. The mechanisms that govern the flow are explained and the conditions required to guarantee the flow and its possible applications are discussed.