Molecular Dynamics Study On The Velocity Slip Of Micro/nano Scale Gas Flow

With the progress of science and technology and the development of nanotechnology,the applications of various micro and nano devices are becoming more and more widely.A lot of micro and nano devices are involved in the flow of gas.Because of the small scale and the influence of wall effect and rarefaction effect,the gas flow in micro nano scale channel is different from the macroscopic flow.The conclusions obtained based on the macroscopic flow theory will not always be correct,which will greatly affect the measurement accuracy of the instrument.Therefore,it is very necessary to study the characteristics of gas flow in micro and nano scale,and this paper is mainly carried out from this aspect.When the channel size is small,the gas near the wall will deviate from the equilibrium state,so that the velocity slip phenomenon will appear on the wall,which will have great influence on the flow.In this paper,we use the molecular dynamics method to study the velocity slip phenomenon under the smooth wall and the rough wall,and consider the two kinds of flow of Poiseuille flow and Couette flow.For the Poiseuille flow on a smooth wall,the effects of different driving forces,density,temperature and gas-solid force on velocity slip are investigated.The driving force is large,slip velocity is bigger,and the increasing trend of linear velocity slip;The velocity slip decreases with the increase of the density,and the velocity slip increases with the increase of Kn;At a small density,the higher the temperature,the greater the slip velocity;Velocity slip with the increase of gas and solid the force first decreased,then increased.The effect of combined study of various factors on the velocity slip,obtained in different density,temperature and gas-solid interaction energy,velocity slip is along with the increase of driving pressure increasing;in the study of different temperature slip velocity with the density change,in low velocity slip with the increasing temperature the increase,but when the density is high,the velocity slip continuously decreased with temperature increasing;effect of different density on the potential role of gas-solid slip velocity,the gas-solid interaction energy is small,the velocity slip decreases with the increase of density and.When the potential energy of gas solid interaction is large,negative slip is generated with the increase of density.The velocity slip increases with the increase of the gas solid potential energy in the case of small density;for the larger density,the increase of the potential energy of gas-solid interaction almost does not affect the velocity slip.When the strength of fluid solid is small,the velocity slip increases with the increase of temperature.When the intensity of fluid solid interaction is large and the temperature is low,the condensation of gas molecules leads to the increase of velocity slip.For smooth wall Couette flow,the conclusion is basically consistent with that of Poiseuille flow.Research on roughness surface,first proposed the rough wall virtual wall method,virtual wall simulation results and real simulation results consistent with the same conditions,but the simulation time is increased by 200 times.Secondly,the method is used to study the velocity slip of two kinds of roughness wall,which are divided into three aspects: aspect ratio,spacing and height.The results of two kinds of flow agree well with the aspect ratio,spaceing and height of different roughness elements.The velocity slip of the two kinds of flow increases with the decrease of the aspect ratio of the roughness element,and increases with the increase of roughness element spacing,and decreases with the increase of roughness element height.