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Multiscale simulation and statistical analysis of nanoparticles size effect on nanofluids effective thermal conductivity

University of British Columbia

Recent developments in nanofluids have led to a renewed interest in the nanoparticles effect on the effective thermal conductivity (ETC) of nanofluids. There are three parameters that define the nanoparticles properties: size, shape, and material. The effect of nanoparticle shape is simplified to the nanoparticle’s aspect ratio. Although the experimental data for the effect of nanoparticles aspect ratio and material on ETC are quite consistent, there are still controversial results regarding the effect of the nanoparticles size. Limitations in nano-scale experimental observations would make it even harder to approach into this topic. Thus, researchers have proposed many different macroscopic (continuum-based)/microscopic (molecular scale) numerical schemes as an alternative for experimental investigations. However, these studies are sporadic, meaning that there is not a consistent methodology to investigate the effect of the same type of a nanoparticle property in multiple scales. Here, a multiscale numerical analysis, is implemented to study the effect of nanoparticle properties on the nanofluids thermal conductivity. The multiscale analysis consists of macroscale (Navier-Stokes equation), mesoscale (Lattice Boltzmann method), and microscale (Molecular Dynamics). A Finite Element Method is implemented for the continuum-based method. At the mesoscale, results of a Lattice Boltzmann method (LBM) are taken into further statistical analysis. Using the statistical analysis on LBM results would further improve the acceptability of this method. At the microscale, a Molecular Dynamic simulation is used to investigate the effect of nanoparticles size, aspect ratio, and material on thermal energy conduction. The results demonstrate that the nanofluids thermal conductivity and the nanoparticles volume fraction can be linearly correlated. In addition, increasing the nanoparticles aspect ratio can improve ETC of nanofluids. However, the nanoparticle size is not statistically significant (P-Value > 0.050) to be considered as an influencing parameter when the interfacial phenomena (interfacial thermal resistance, nano-liquid layering, etc.) are not taken into account as they are largely affected by other parameters such as nanoparticles/base fluids material. The pure effect of nanoparticles size is compensated by other parameters such as the distribution regime. This leads to the conclusion that nanoparticles size cannot play an important role in enhancing the thermal properties of nanofluids.

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2020-09-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/76065

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/