The Classical Nature of Thermal Conduction in Nanofluids

Abstract

We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating fractal configuration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluid

The thermal conductivity of clustered nanocolloids

“…10,11 The classical theory of heat conduction in inhomogeneous media was developed by Maxwell, originally in the context of electrical conduction, and gives the thermal conductivity of a two-phase system that consists of a dispersion of non-interacting spheres in a continuous medium. 12 At fixed volume fraction of phases, Maxwell's theory predicts in fact two limits: 13,14 1…”

Thermal behaviour of nanofluids confined in nanochannels

“…Structured layers of liquid atoms located both, experimentally [12] and computationally [13] have been theorized to possess higher thermal conductivities due to their solid-like nature, significantly enhancing the overall heat transfer capacity of the fluid [14,15]. The counterargument for this thermal transport mechanism is that the minute size of these nanolayers (with thickness ) cannot possibly produce such severe enhancements [8,7]. Finally, a number of studies suggest that the inability of classical models to make accurate predictions lies on their regularly false assumption of a uniform distribution of particles [11,8,7].…”

“…The energy transfer due to the collision between nanoparticles as a result of their Brownian motion was one such theory attempting to attach a physical explanation to the unexpected enhancement of the thermal conductivity of nanofluids [5,6,7]. It was, however, deemed insignificant due to the low frequency of collisions compared to the orders-of-magnitude larger thermal diffusion [8,5,7]. The motion of the nanoparticles was considered to affect the motion of the liquid, inducing nanoscale convective affects which transferring energy, with arguments both in favour [6,9,10] and against [11,8] its importance.…”

“…The counterargument for this thermal transport mechanism is that the minute size of these nanolayers (with thickness ) cannot possibly produce such severe enhancements [8,7]. Finally, a number of studies suggest that the inability of classical models to make accurate predictions lies on their regularly false assumption of a uniform distribution of particles [11,8,7]. The investigations conclude that the nanoparticles can form long chains of low thermal resistance which allows for a more optimal transfer of energy.…”

“…It was, however, deemed insignificant due to the low frequency of collisions compared to the orders-of-magnitude larger thermal diffusion [8,5,7]. The motion of the nanoparticles was considered to affect the motion of the liquid, inducing nanoscale convective affects which transferring energy, with arguments both in favour [6,9,10] and against [11,8] its importance. Structured layers of liquid atoms located both, experimentally [12] and computationally [13] have been theorized to possess higher thermal conductivities due to their solid-like nature, significantly enhancing the overall heat transfer capacity of the fluid [14,15].…”