| Microfluids have good transport and heat performance,which play an important role in the preparation of microelectronic devices and heat transfer elements with high heat flux density.To further explore the nature of fluid transport and heat transfer at the microscale.In this paper,the molecular dynamics method is used to numericaly simulate the flow and heat transfer characteristics of fluids in restricted-flow nanochannels.The effects of wall structure and wall wettability on the boundary slip of nanochannels with rough inner walls,and the effects of changes in wall physical properties and driving force on interface thermal resistance in nanochannels were mainly analyzed.The effect of wall asymmetry on the interface slip in the nanochannels is studied by changing the wall structure.The roughness is used to define the roughness of the wall.The results show that the asymmetric upper and lower wall can lead to an asymmetric distribution of flow parameters.The change of wall roughness and wettability would affect the flow characteristics of fluid atoms near the wall.Due to the influence of wall grooves,the number density distribution near the rough wall is lower than that on the smooth wall side.As the rib height and wall wettability increase,the number density of fluid atoms in the groove increases gradually,and the change of the rib spacing does not substantially affect the number density distribution of fluid atoms near the rough wall.For different structure types of walls,the real solid-liquid boundary positions are determined by simulating the velocity field distribution in the channel under both Couette flow and Poiseuille flow,which can help us to better analyze the interface slip effect.The variation of wall roughness and wettability can affect the position of the solid-liquid interface.The change of rib height and wettability can greatly influence the velocity distribution in channel,and the position of the solid-liquid boundary as well.Conversely,the rib spacing has a less effect on the boundary position.The difference in boundary position can affect the interface slip effect.We can find the slip velocity and the slip length on one side of the rough wall to be smaller than those on the smooth wall side,and as the rib height and wall wettability increase,the slip velocity and the slip length significantly decrease near the rough wall side.The effect of rib spacing on fluid flow is trivial,and the interface slip velocity and length are relatively stable.The variation of interface thermal resistance in asymmetric nanochannels is investigated by changing the wall temperature and wettability.The difference of interface thermal resistance between static fluid and flowing fluid is calculated and compared.The present results show that changes in wettability only affect the thermal resistance of the corresponding interface.As well,the effect of wall temperature on thermal resistance is limited.For example,in the current results,when the wall wettability was the weakest,the thermal resistance at the interface of the hot wall was higher than that of the interface of the cold wall.In the case of stronger wettability,the influence of the wall temperature on the thermal resistance of the interface was relatively small.The addition of external forces causes frictional viscous heating at the solid-liquid interface,which reduces the temperature jump and increases the heat flux through the interface,thereby reducing the interface thermal resistance.The present results show that the effect of solid-liquid interaction strength on thermal resistance is more significant than that of the external force.The fluid molecules adsorbed on the wall of the static fluid were compared with those adsorbed on the wall of the flowing fluid to study the relationship between the thermal resistance and the fluid molecules adsorbed on the wall.It was found through this approach that almost the same number of fluid molecules was adsorbed,even when the external force was changed.Interestingly,a significant change in thermal resistance was observed between static and flowing fluid. |
