Abstract
Nanofluids are two-phase mixtures consisting of small percentages of nanoparticles (sub 1–10 %vol) inside a carrier fluid. The typical size of nanoparticles is less than 100 nm. These fluids have been exhibiting experimentally a significant increase of thermal performance compared to the corresponding carrier fluids, which cannot be explained using the classical thermodynamic theory. This study deciphers the thermal heat transfer mechanism for the conductive heat transfer mode via a molecular dynamics simulation code. The current findings are the first of their kind and conflict with the proposed theories for heat transfer propagation through micron-sized slurries and pure matter. The authors provide evidence of a complex new type of heat transfer mechanism, which explains the observed abnormal heat transfer augmentation. The new mechanism appears to unite a number of popular speculations for the thermal heat transfer mechanism employed by nanofluids as predicted by the majority of the researchers of the field into a single one. The constituents of the increased diffusivity of the nanoparticle can be attributed to mismatching of the local temperature profiles between parts of the surface of the solid and the fluid resulting in increased local thermophoretic effects. These effects affect the region surrounding the solid manifesting interfacial layer phenomena (Kapitza resistance). In this region, the activity of the fluid and the interactions between the fluid and the nanoparticle are elevated. Isotropic increased nanoparticle mobility is manifested as enhanced Brownian motion and diffusion effects
Highlights
IntroductionNanofluids are binary mixtures containing solid nanoparticles (usually below 100 nm in size) and a carrier/base fluid (usually conventional coolants) invented by U.S Choi during the 1990s [1]
Nanofluids are binary mixtures containing solid nanoparticles and a carrier/base fluid invented by U.S Choi during the 1990s [1]
The concentration of nanoparticles in the mixture is of the order of sub 1 %vol up to 10 %vol Despite the small concentration of nanoparticles and their small size, it has been proven experimentally that the measured thermal performance exceeds the thermal enhancement predicted by classical thermodynamic models
Summary
Nanofluids are binary mixtures containing solid nanoparticles (usually below 100 nm in size) and a carrier/base fluid (usually conventional coolants) invented by U.S Choi during the 1990s [1]. Recent work was published on nanofluids in peristaltic flows and porous channels [13,14,15] These applications are of high importance for biology and biomedicine that will help understand several physical processes which are yet unknown. Several other applications considered the flow of nonNewtonian nanofluids in the presence of magnetohydrodynamics, radiation and porous media to derive analytic solutions to describe them. This has a great importance for several industrial applications we are currently using but have not yet streamlined and fully understood or are future candidates for nanofluid applications, for example, the flow of liquid metals, cosmic plasmas, MHD pumps and power generators, electrostatic precipitation
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