Molecular Dynamics Study On The Thermophysical Properties Of Nanofluids Considering Particle Agglomeration

Nanofluid has a wide application prospect because of its good thermophysical properties and has become a research hotspot in various fields.At present,the influence of particle size and particle shape on the thermophysical properties of nanofluids in the research results is still inconsistent,and the internal mechanism of the change of physical properties also needs to be further explored.In addition,the influence of particle agglomeration in nanofluids also needs to be further studied.Molecular dynamics simulation(MD)has become an important way to develop nanofluid-related topics due to the complex movement of nanoscale fluids,unstable experimental conditions,and difficult observation of experimental results,and its research results can provide a theoretical basis for improving the thermal properties of nanofluids.In this paper,molecular dynamics method was used to study the effects of temperature,volume fraction,particle size,particle shape,potential energy parameters,particle agglomeration,and other factors on the thermophysical properties of nanofluids.(1)The molecular dynamics software LAMMPS was used to simulate the copper-water nanofluid,and the thermal and physical properties of the nanofluid were calculated.The effects of volume fraction,temperature,particle size,and particle shape were analyzed.The results show that the thermal conductivity and dynamic viscosity increase with the increase of the volume fraction of nanoparticles.When the temperature increases from 283 K to 323 K,the thermal conductivity of the nanofluids with different volume fractions increases slightly,while the dynamic viscosity decreases significantly.The thermal conductivity decreases with the increase of particle radius,while the dynamic viscosity is basically unchanged.In the case of cylindrical and disk-shaped nanoparticles,the thermal conductivity of the nanofluids is not much different within the range of the calculated volume fraction,which is higher than that of spherical nanoparticles.The dynamic viscosity of the fluid containing non-spherical nanoparticles is higher than that of the fluid containing spherical nanoparticles.(2)At the coarse-grained size,the process of particle agglomeration with different shapes in nanofluids was simulated,and the accuracy of particle agglomeration model in nanofluids was verified.The effects of different system sizes,agglomeration morphology,potential energy parameters and temperature on the thermal physical properties and agglomeration characteristics were obtained.The results show that the description of the logarithmic relationship between the rotation radius and the number of particles in the agglomeration model is basically the same as that in the DLCA model.The morphology of the agglomerated particles tends to be chain-like,and the agglomeration behavior occurs from near to far.The agglomeration behavior is irreversible,and each atom in the cluster does not have relative displacement after a certain time.The formation of large clusters increases the thermal conductivity and decreases the viscosity of nanofluids,which is beneficial to enhance heat transfer and reduce flow resistance.The thermal conductivity of nanofluids increases with the increase of potential energy parameters,while the viscosity has little change with the increase of potential energy parameters.The large increase of thermal conductivity and the obvious decrease of viscosity are the results of agglomeration.When the temperature increases,the thermal conductivity of the nanofluid increases,the viscosity decreases,and the degree of agglomeration increases.