Thermal conductivity of CNT water based nanofluids: Experimental trends and models overview

Abstract

Thermal conductivity measurement of carbon nanotubes water-based nanofluids is here reported. We have considered in particular the influence of nanoparticle volume fraction, temperature, carbon nanotube aspect ratio and different kind of surfactant (SDBS, Lignin, Sodium polycarboxylate) on thermal conductivity enhancement of nanofluids. The experiments show that TC enhancement of nanofluids produces at very low volume fraction. It is also mainly governed by both volume fraction and temperature increase. However, TC enhancement of nanofluids is weakly affected by carbon nanotubes aspect ratio and surfactant type used in the study.In addition, various theoretical thermal conductivity models are used to possibly correlate the experimental data and explain the TC enhancement of nanofluids. The selected models do not capture the experimental findings within the range of this parametric study, evidencing the need to develop appropriate model for TC enhancement prediction of CNT nanofluids and measure TC of this kind of nanofluids before performing numerical studies in heat exchangers and cavities.

Thermal Conductivity of Suspension of Aggregating Nanometric Rods

“…The reported values show the increase of relative conductivity k suspension /k particle from 0.001 when there are no particles to 0.014 at 2% of volume fraction. These orders of magnitude are the same that are found in some existing works (e.g., [3,18]). Regarding this figure, modification of conductivity is almost the same for random distribution or MD simulation (they almost give the same values of conductivity because low concentration does not promote percolation).…”

“…Moreover, the approach here proposed could be useful to explain thermal conductivity enhancements for some fluids where the viscosity effects are preponderant. In fact, in [3,18], we observe almost the same enhancement at a low concentration. Even if it is shown in [19] that high enhancements of the thermal conductivity can be found for low concentrations, compared to our simulations, it is not in contradiction with our study because we only focused here on structuration effects and not on the other different factors previously mentioned that could promote an extra-thermal conductivity enhancement.…”

Thermal Conductivity and Specific Heat Capacity of Dodecylbenzenesulfonic Acid-Doped Polyaniline Particles—Water Based Nanofluid

“…The enhancement in thermal conductivity of water was achieved when the amount of dispersed carbon nanotubes was increased [18,19]. It was also reported that 5% volume fraction of TiO2 nanoparticles and 7.5% of volume fraction of CuO enhanced thermal conductivity of water by 33% and 32%, respectively [20,21], whereas 5% volume of ZnO enhanced thermal conductivity of water by 12% [22].…”

Unexpected sharp peak in thermal conductivity of carbon nanotubes water-based nanofluids

“…As an extension of our previous works [17,[22][23][24], we study the effect of nanoparticle volume fraction and temperature on thermal conductivity, considering unusually very low volume fraction below the critical concentration of theoretical percolation threshold. Unexpectedly, we find here the existence of a very small optimal concentration leading to a peak in thermal conductivity where the enhancement is similar to the one obtained at high volume fraction.…”

“…The physical mechanisms responsible of thermal conductivity enhancement were also investigated [10]. Many attempts have also been made to model and predict the enhancement of nanofluids thermal conductivity [11][12][13][14][15][16][17] taking into account the presence of nanoparticle aggregates [18,19] and the influence of chain-like structures [20,21]. It is usually recognized that thermal conductivity enhancement of nanofluids produces under percolation threshold, i.e., for a critical nanoparticle loading when the conductive nanoparticles start to form a continual connected network.…”