Analysis of enhancement mechanism for thermal conductivity of nanofluids by inelastic X-ray scattering

The inelastic X-ray scattering for the nanofluid composed of silicon dioxide (SiO2) nanoparticles (various sizes exceeding 100 nm) and ethylene glycol aqueous solution has revealed one of the mechanisms for the thermal conductivity enhancement of nanofluids, which the addition of a small amount of nanoparticles can improve the thermal conductivity of nanofluids beyond the theoretical value. The high-frequency sound velocity derived from the inelastic X-ray scattering spectra of nanofluids may be generally correlated with the structural relaxation of solvent molecules and corresponding thermal conductivity. It can also clarify the effect of nanoparticles on the thermal transport in nanofluids and the molecular dynamics of the solvent around nanoparticles. The size of the SiO2 particles in the nanofluid, which are 100, 30 0, 50 0, and 1000 nm, is approximately 10 times larger than the typical size of nanoparticles considered in research. Nevertheless, the experimental results indicate that SiO2 particles may increase the high-frequency sound velocity in the ethylene glycol aqueous solution because of the highly restricted movement of the solvent molecules around these nanoparticles. The high-frequency sound velocity in the SiO2 nanofluid is proportional to the thermal conductivity and that containing particles 300 nm in size is higher than those of other nanofluids containing particles 100, 500, and 1000 nm in size. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study demonstrates that adding a small amount of SiO2 nanoparticles to nanofluids can enhance thermal conductivity beyond theoretical values, and the high-frequency sound velocity can provide insights into the relationship between solvent molecular relaxation and thermal conductivity. Different sizes of SiO2 particles have varying effects on the high-frequency sound velocity and thermal conductivity of ethylene glycol aqueous solution.