| As the rapid development of the global economy,the demand of electronic components is gradually increasing,and the characteristic size of components is developing toward miniaturization,which is leading to the heat generation per unit area increased dramatically.Therefore,high heat flux heat sinks are needed to dissipate heat in the miniaturization device application.The commonly used air-cooled and liquid-cooled heat dissipation methods involve only single-phase natural convection heat transfer and single-phase forced convection heat transfer,which cannot meet the requirements of high heat dissipation with the heat dissipation requirements.Heat pipe,as a spontaneous phase change heat dissipation element,owns the advantages of high heat transfer efficiency,good isothermal properties and simple internal structure,which is widely used in cooling system.Its heat dissipation capacity has exceeded single-phase natural convection heat transfer by 1-3 orders of magnitude.Furthermore,in the work of heat pipe,the thermal conductivity of heat transfer medium determines the efficiency of heat exchange in heat pipe,and the thermal conductivity of nano fluid is higher than the heat transfer performance of general fluid,which has better application prospects.Besides,it also involves the flow of fluid,the transfer of heat at the interface and the conversion between multiple phases,so it is important to investigate the fluid flow,interfacial heat transfer and phase transition heat transfer processes in heat pipes.In this paper,we investigate the nanofluid flow in a rough channel,the heat transfer between the solid-liquid interface and the phase transition mechanism of nanofluid based on molecular dynamics simulation.Firstly,the flow process of nanofluid over rough walls and the influencing factors are investigated,and the model construction and simulation methods are introduced.The thermal physical parameters are calculated for hemispherical,triangular and rectangular cross-sectional roughness and smooth walls,and compared to the results,we can find that increasing the height of roughness drives the temperature and flow velocity;decreasing the cross-sectional area increases the velocity and temperature of the nanofluid for the same height;meanwhile,the presence of roughness decreases the density amplitude at the near-wall due to the presence of roughness decreases the number of particles at the near-wall.The triangular roughness has the greatest effect on the flow characteristics of the nanofluid.The roughness of the walls affects the flow characteristics of the nanofluid,however,the flow of the nanofluid is accompanied by heat transfer,which is hindered by the presence of thermal resistance between the interfaces.Monolayer graphene has high thermal conductivity,and it is found that the addition of a monolayer graphene layer between solid and liquid significantly reduces the interfacial thermal resistance by up to48%,and the phonon mismatch between graphene and base fluid particles is lower than that between metal wall surface and base fluid particles,which is revealing the enhanced heat transfer at the solid-liquid interface.The weak force between graphene and metal wall surface also leads to an increase in the degree of velocity slip at the solid-liquid wall surface.The flow process of nanofluid is accompanied by multi-phase interconversion.The shape and number of nanoparticles play an important role in the boiling phase transition process.It is found that nanoparticles with small specific surface area shorten the time of phase transition occurrence,and the thermal conductivity of the system increases with the larger specific surface area.In addition,it is found that the larger the number of nanoparticles,accompanied by the longer the phase transition time,and the larger the thermal conductivity.In this paper,we systematically study the Poiseuille flow of nanofluid,the heat transfer between the solid-liquid walls,and the phase transition mechanism of nanofluid.The above theoretical studies are important for the practical application of heat pipes. |
