MOLECULAR STUDY OF CORE-SHELL RATIO EFFECT ON THERMOPHYSICAL PROPERTIES OF SIO2@AU-WATER NANOFLUID

Abstract

Thermal conductivity (λ) and specific heat capacity (<i>c<sub>p</sub></i>) are essential thermophysical properties related to thermal storage systems. Molecular simulations of the shell-to-total-radius ratios (Φ) of SiO<sub>2</sub>@ Au nanoparticle (NP) are used to investigate their impact on the <i>c<sub>p</sub></i> and λ of water nanofluids (NFs) containing this NP. The roles of solid/liquid and solid/solid interfaces on <i>c<sub>p</sub></i> and λ are identified by using the calculations of the vibrational density of state (VDOS) of the SiO<sub>2</sub>@Au nanoparticle, the core (SiO<sub>2</sub> molecule), the shell (Au atom), and the thin layer of water molecules next to the particle surface. The effects of core-shell NPs on the characteristics of the base fluid are further understood by using the VDOS mismatch between the NP and the thin water layer and the radial distribution function of water molecules. The heat current contribution is discussed to view the λ increase mechanism of NF. It is found that <i>c<sub>p</sub></i> increases with increasing Φ, while λ increases with decreasing Φ. The convection component and the virial term consisting of the heat current are considerable contributions. New correlations are proposed for calculating the <i>c<sub>p</sub></i> and λ of NFs containing core-shell NPs, thus explaining the contributions of the components to <i>c<sub>p</sub></i> and λ of NFs. The study of the effect of Φ on the thermophysical characteristics of these NFs provides molecular insight into the roles of the solid/liquid and solid/solid interfaces. These results contribute to the understanding of the thermophysical properties of core-shell NFs and their uses in solar thermal applications.