Abstract
Although several forms of thermal conductivity models for nanofluid have been established, few models for nanofluids containing surfactants or columnar nanoparticles are found. This paper intends to consider the surfactants and particle shape effect in the thermal conductivity of TiO2 nanofluids. The thermal conductivity models for respectively spherical and columnar TiO2 nanofluids are proposed by considering the influences of solvation nanolayer and the end effect of columnar nanoparticles. The thicknesses of the solvation nanolayers are defined by the surfactant molecular length and a few atomic distances for nanofluid with and without surfactant respectively. The end effect of the columnar nanoparticles is considered by analyzing the different thermal resistances and probability of the heat conduction for the selected small element in axial direction and radial direction. Finally, the present models and some other existing models were compared with some available experimental data and the comparison results show the present models achieve higher accuracy and precision for all the four kinds of applications.
Highlights
Over the course of the past three decades, nanofluids have hit the scientific and industrial world because of their outstanding fluidity, stability[1] and thermal and transport characteristics[2] comparing to the fluids containing millimeter or micrometer particles
This paper proposed thermal conductivity models for respectively spherical and columnar TiO2 nanofluids by considering the influences of the solvation nanolayer and the end effect at the top and bottom side of columnar nanoparticles
The thickness of the solvation nanolayer is defined by a few atomic distances for the nanofluids without surfactant, and defined by the surfactant molecule length for nanofluid containing surfactant, respectively
Summary
Over the course of the past three decades, nanofluids have hit the scientific and industrial world because of their outstanding fluidity, stability[1] and thermal and transport characteristics[2] comparing to the fluids containing millimeter or micrometer particles. Many researchers have investigated the peculiar influence factors on the thermal conductivity of nanofluids. The current influence factors on the thermal conductivity of nanofluids are divided into three groups. The addition of surfactants can distinctly affect the dispersion and thermodynamic properties of nanofluids,[10] few thermal conductivity models have included the effect of surfactants. Most of the current thermal conductivity models are proposed for spherical or nano-tubes nanofluids, none was aimed at for nanofluids containing columnar nanoparticles. There is a great need of thermal conductivity models for nanofluids containing surfactants or columnar nanoparticles. Four thermal conductivity models for respectively spherical and columnar TiO2 nanofluids are proposed by considering the influences of solvation nanolayer and the end effect of columnar nanoparticles. It is expected that this study brings some supplementary ideas that can be helpful for the study of the thermal conductivity of some special shaped nanofluids
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