Study On The Effect Mechanism Of Morphology Of Nanoparticles On The Thermal Conductivity Of Nanocomposites

Nano-composite material has great potential and research value for improving energy efficiency.The modeling of effective thermal conductivity of nanocomposites and the analysis of its influencing mechanism are one of the important topics in the research on nanocomposites.This topic aims at the structure and morphology of graphene nanoparticles and explores the mechanism of their influence on the thermal conductivity of nanocomposites through theory and experiment.The work of this paper is summarized as follows:(1)In this paper,a new model considering the effects of graphene’s length and thickness,interface layer and anisotropic characteristics is established.The model is further modified by considering the possibility of absence of graphene in the actual thermal conduction path,that is only bulk matrix along the heat conduction path in some cases.It is found that the thermal conductivity predicted by the present model is positively correlated with the temperature,concentration and length of nanoparticles,while is slightly negatively correlated with thickness.This model is applied to predict thermal conductivities of graphene nanocomposites in different cases compared to other models.The results indicate that the present model has a strong ability to predict graphene nanocomposites especially at relatively low concentrations(<0.1 vol%).(2)The effects of surfactants,binders,ultrasonic oscillation time and storage time on the dispersion stability of graphene nanofluids are investigated experimentally.An experimental device for measuring thermal conductivity by transient hot wire method is built to measure the thermal conductivity of nanocomposites and explore the effects of graphene nanoparticle concentration,surfactant,binder,ultrasonic oscillation time,storage time and other factors.The results show that polyethylene(K90)can improve the stability of graphene nanofluids.The synergistic effect of K90 and PVA can further improve the stability of graphene nanofluids.The thermal conductivity of graphene nanocomposites is positively correlated with particle concentration and ultrasonic oscillation time,while other factors have little influence on the thermal conductivity.(3)In this experiment,directional graphene nanocomposites are prepared by bidirectional freezing method,and the thermal conductivity in different directions is measured.The results show that a wedge with an Angle of 30° and a faster freezing rate can make graphene nanocomposites more oriented.At a low concentration(0.001wt%),the thermal conductivity of graphene nanocomposites in different directions is basically the same,while at a high concentration,the thermal conductivity of graphene nanocomposites presents obvious anisotropy,and the greater the concentration,the greater the difference in thermal conductivity in different directions.