Investigation Of Hybrid Nanofluid Enhanced Thermal Conductivity Mechanism

As the preparation of nano materials has made great progress,the preparation and parameter measurement of hybrid nanofluids have been intensively studied by a large number of scholars.Nanofluids were first prepared by Argonne National Laboratory in 1995,followed by hybrid nanofluids by Jana et al.in 2007,and the concept of hybrid nanofluids was formally developed due to their good stability and good thermal conductivity.The hybrid nanofluid has been widely used as a good heat transfer medium,so it is necessary to grasp the intrinsic mechanism of its enhanced heat transfer.However,there is no conclusion on the law of enhancing the heat transfer performance of hybrid nanofluids under different nanoparticle hybrid,and due to the limitation of various factors in their experiments,this paper adopts molecular dynamics and Brownian dynamics methods to simulate the heat transfer phenomenon within hybrid nanofluids and investigate the intrinsic mechanism of their enhanced heat conduction.The general content of this paper includes:(1)Relying on the National Natural Science Foundation of China(NSFC)project,this paper presents the study background and significance of nanofluid and hybrid nanofluid,illustrates the current progress of nanofluid research by domestic and foreign scholars,as well as introduces the basic concepts of molecular dynamics method,and finally elaborates on the main research contents of the paper.(2)On the basis of the unknown internal heat transfer law of the hybrid nanofluid,firstly,the thermal conductivity and diffusion coefficient of the Cu-Ag/Ar hybrid nanofluid were calculated by molecular dynamics.The results show that the thermal conductivity of Cu-Ag 50%/Ar hybrid nanofluid can be increased by a greatest of 69.72% compared with liquid argon,and is greater than that of Ag/Ar and Cu/Ar nanofluids by 47.95% and 26.4%.Then,the Ar atoms on the surface of the nanoparticles are shown and tracked by the radial distribution function showing that the fluid is in dynamic equilibrium.At last,the nanosphere density and diffusion coefficient of the hybrid nanofluid in different hybrid ratios are analyzed in agreement with the thermal conductivity,and it is shown that the nanosphere structure and the diffusion of Ar are the two basic mechanisms.(3)Water-based as a very frequently used base fluid in nanofluidic applications,this paper constructs a hybrid nanofluid with water molecules base fluid based on the study of Ar fluid and simulates the heat transfer.As well,the pattern of thermal conductivity of the hybrid nanofluid with different volume fraction and particle size is quantitatively analyzed,and the reason for its elevated thermal conductivity is qualitatively explained by RDF and particle motion trajectory.The basis for the study of the enhanced heat transfer performance by particle aggregation within the hybrid nanofluid is laid.(4)In this paper,the laws of thermal conductivity between different particle numbers and different morphologies were analyzed based on ELBA coarse-grained water molecule model and Brownian dynamics.Multi-particle aggregation within a hybrid nanofluid is one of the factors that enhance heat transfer.In this paper,the laws of thermal conductivity between different particle numbers and different morphologies were analyzed based on ELBA coarse-grained water molecule model and Brownian dynamics.The results show that the aggregation structure between Cu-Ag in hybrid nanofluid is compact,and the fractal dimension is linearly related to the thermal conductivity;the aggregation between Cu-Cu in nanofluid is loose,and the fractal dimension is not linearly related to the thermal conductivity when the number of particles reaches 24.