The Numerical Simulation On The Transport Properties Of Fluid Regulated By The Nanoparticle Properties

Nanofluids are colloidal suspensions composed of nanoparticles and base fluid,which can be used as novel carriers for mass transfer and energy storage in modern industrial equipment,such as microelectronic chips,solar energy collection devices,etc.Generally,the addition of nanoparticles can induce a concurrent change for both of heat and mass transfer performance of fluid.This concurrent change of thermal conductivity,viscosity and other physical properties of nanofluids is closely related to the nanoparticle properties,which provides a challenge for the design of modern industrial equipment with consideration of the change in the physical properties.Therefore,it is of great significance to study the influence of nanoparticle properties on the heat transfer and viscosity of nanofluids for the design of high-performance equipment containing nanofluids.In this study,a numerical model of the fullerene-water nanofluids is established,in which a single nanoparticle is adopted to avoid the influence of aggregation on the simulation results.Based on molecular dynamics simulation,the thermal conductivity and viscosity of nanofluids are studied.Meanwhile,the mechanism of the effect of the nanoparticle properties on the transport properties is revealed by the structural characteristics of base fluid characterized by radial distribution function and the movement of base fluid around nanoparticles in heterogeneous phase characterized by persistence time.According to the study of the regulation of the nanoparticle properties on thermal conductivity of nanofluids,the variations of thermal conductivity of nanofluids with temperature,volume fraction,nanoparticle size and surface wettability are revealed.Under the condition of the same nanoparticle size,the thermal conductivity increases with the increase of the volume fraction of the nanoparticle,and the increase of temperature can further promote the thermal conductivity of nanofluids with different volume fractions.Under the condition of the same volume fraction,the thermal conductivity increases with an increase of the nanoparticle size,and the higher the volume fraction of nanoparticles is,the faster rate of thermal conductivity with the nanoparticle size is.In terms of wettability,it is adjustable for wettability through altering the interaction between nanoparticles and fluid molecules.The effect of wettability on thermal conductivity of nanofluids indicates that the more hydrophobic the surface of nanoparticles is,the higher the heat transfer of nanofluids is.In the light of the study of the regulation of nanoparticle properties on viscosity of nanofluids,the variations of viscosity of nanofluids with temperature,volume fraction,nanoparticle size and surface wettability are revealed and the mechanisms of viscosity of nanofluids regulated by nanoparticle properties are presented.Under the condition of the same nanoparticles size,the regulation of the volume fraction on the viscosity is as same as that on the thermal conductivity,i.e.,the viscosity is enhanced with the increase of the volume fraction,and the viscosity of nanofluids with different volume fractions can be further increased with the decrease of temperature.Under the condition of the same volume fraction,the regulation of viscosity by the nanoparticle size is as same as that by the thermal conductivity,i.e.,the viscosity decreases with the enhancement of the nanoparticle size.In the aspect of wettability,the results show that the higher the hydrophobicity of particle surface is,the lower the viscosity of nanofluids is,which is contrary to the regulation of thermal conductivity.In terms of mechanism,the local viscosity of the molecular layer around nanoparticles is closely related to the viscosity of nanofluids.In conclusion,the molecular model of nanofluid established in the simulation can effectively solve the problem of nanoparticle aggregation.The variations of heat transfer and viscosity of nanofluid with nanoparticle properties are investigated by molecular dynamics simulation.The mechanism of nanoparticle properties regulating the transport properties of nanofluid is revealed on the basis of the structure and motion of base fluid in nanoscale.The results of this study can provide support for the parametric design of the nanofluids treating as transport media in the novel equipment.