Study On The Role Of Rough Solid Surface On Fluid Flow And Heat Transfer By Molecular Dynamics Simulation

Nanoscale fluid flow and heat transfer have a wide range of applications in fields like micro electromechanical systems, space technology, biomedical sciences, etc., and such researches have a very significant academic value in the exploration of microscopic motion and transportation. The decrease in the channel dimension leads to larger surface-to-volume ratio, causing surface roughness effects on nanoscale fluid flow and heat transfer to be significantly more important. As an important property of the solid surface, study on the role of surface roughness on the fluid flow and heat transfer has been ranked as one of the frontier and hot problems, and it is of great significance for academic research and engineering application.In nanoscale systems, mass transport and energy transfer occurred in a limited nanoscale structure, which leads to surface roughness effect, velocity slip and temperature jump effect and viscous dissipative effect. In order to reveal these nanoscale effects and the mechanism, the molecular dynamics models of heat conduction of fluid in a rough nanochannel, coupled fluid flow and heat transfer in a rough nanochannel and granular flow down a rough inclined plane are developed to investigate the role of surface roughness on the nanoscale fluid flow and heat transfer, velocity slip and temperature jump. A series of results and conclusions are obtained as follows:(1) The molecular dynamics simulation of heat conduction of fluid in a rough nanochannel indicates that, the temperature profile deviates from the linear fashion in the wall-neighboring region and the temperature jump is observed at the rough solid surface. Compared with the smooth surface, the presence of the roughness decreases the temperature jump length at the boundary. A large roughness height increases the contact area between the liquid and the solid, which enhances the energy transfer at liquid-solid interface and hence decreases the temperature jump length. In addition, the increase in liquid-solid interaction strength or reduction in wall stiffness leads to a smaller temperature jump length.(2) The molecular dynamics simulation of coupled fluid flow and heat transfer in a rough nanochannel indicates that, the velocity of the fluid flow under an external force in a nanochannel in a bulk region is of a parabolic distribution, and the viscous dissipation due to shear flow induces the fourth-order temperature profile in the nanochannel. And the velocity slip and temperature jump will occur at the fluid-solid interface. The presence of roughness may introduce an extra viscous dissipation in shear flow, leading to a reduction of overall velocity and an increase in temperature in the nanochannel when compared with the smooth nanochannel. In addition, the degree of velocity slip and temperature jump at a rough liquid-solid interface is smaller than that at a smooth interface. In particular, the increase in fluid-solid interaction strength and reduction in wall stiffness will lead to a small velocity slip and temperature jump.(3) The molecular dynamics simulation of granular flow down a rough inclined plane indicates the presence of roughness leads to a reduction of overall velocity and velocity slip past rough surface when compared with the smooth surface. The velocity is large in the near free surface region, and velocity slip occurs near the solid surface. The packing fraction remains constant as a function of depth. Differing from the conventional fluid flow, the orderly oscillation of the density distribution near the solid surface is not observed. In addition, the tilt angle, internal coefficient of friction and the particle spacing of the solid surface have a great influence on the behavior of the granular flow.