The limiting behavior of the thermal conductivity of nanoparticles and nanofluids

Abstract

We present experimental evidence of negative thermal conductivity enhancement in nanofluids consisting of 2 nm titania nanoparticles dispersed in 50% ͑w/w͒ water+ ethylene glycol. This behavior is unlike that of other nanofluids, which have been shown to exhibit positive thermal conductivity enhancements. Our results for titania nanofluids suggest that the thermal conductivity of 2 nm titania nanoparticles is smaller than the thermal conductivity of the base fluid at the same temperature, indicating a dramatic decrease in the thermal conductivity of titania particles as the particle size becomes of the same order as the phonon mean free path. Although such a decrease has been predicted for semiconductor nanoparticles by theory and simulation, experimental evidence has hitherto been lacking. Our results provide indirect experimental evidence for this decrease in metal oxide particles, and validate our previous work on alumina nanofluids that showed an exponential decrease in the thermal conductivity of alumina particles with decreasing particle size, from a limiting value for large ͑micron-sized͒ particles.

Co3O4 ethylene glycol-based nanofluids: Thermal conductivity, viscosity and high pressure density

“…4. A similar trend j nf decrease with the increase in temperature was observed previously by other authors [37][38][39][40]. From a modelling perspective, Maxwell [41] was the first to propose an equation to estimate the thermal conductivity of colloids composed by solid spherical particles suspended in a fluid, as follows:…”

Heat conduction at micro and nanoscales: A review through the prism of Extended Irreversible Thermodynamics

“…was used with success to describe nano uids with dispersed solid particles [50,51]. Another category of models has proved to be more adapted to the description of carbon nanotubes (CTN) dispersed in a base uid.…”

Rheological and volumetric properties of TiO2-ethylene glycol nanofluids

“…Therefore, with the aim to improve the heat transfer properties of nanofluids, a considerable amount of research efforts are being devoted to the analysis of their thermal conductivity and convective heat transfer properties. Although it is possible to tailor nanofluids exhibiting negative thermal conductivity enhancement, or a decrease in the effective thermal conductivity of the dispersion if compared with that of the base liquid [6], in most cases, nanofluids exhibit a significant enhancement in thermal conductivity. Therefore, nanofluids are expected to provide optimized convective heat transfer coefficients.…”