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19Fax: +33 (0) 2 23 23 40 51 20 21Abstract: 22 23Experimental results on the steady state viscosity of carbon nanotubes water-based nanofluids 24 are presented considering the influence of particle volume fraction and temperature ranging 25 from 0 to 40°C. The suspensions consist of multi-walled carbon nanotubes dispersed in de-26 ionized water and they are stabilized by a surfactant. The aspect ratio of nanotubes is close to 27 160 and the particle volume fraction varies between 0.0055% and 0.55%. It is shown that the 28 nanofluids behave as shear-thinning materials for high particle content. For lower particle 29 content, the nanofluids are quite Newtonian. It is also observed that the relative viscosity of 30

International audienceThe thermo-physical properties of water-based nanofluids containing carbon nanotubes, stabilized by SDBS as surfactant, are experimentally studied. The effect of low nanoparticle volume fraction, ranging from 0.0055% to 0.278%, on density, thermal conductivity and viscosity of nanofluids is investigated for temperature range of 20°C to 40°C. Enhancement in density, thermal conductivity and viscosity of nanofluids with volume fraction in nanotubes is shown in comparison to base fluids and modelled from simple theoretical relationships. The influence of temperature on the thermo-physical properties of tested nanofluids is also discussed, as well as the shear rate dependence on the nanofluids viscosity. Finally, the efficiency of the tested nanofluids as cooling fluids is evaluated under laminar and turbulent flows regimes from the thermo-physical values previously determined. This may be helpful for using these nanofluids in real cooling systems

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.

The effects due to temperature and shearing time on viscosity for Al 2 O 3 /water and CNT/water based nanofluids at low concentration and low temperatures are experimentally investigated. The viscosity data were collected using a stress-controlled rheometer equipped with parallel plate geometry under up and down shear stress ramp. CNT and Al2O3 water based nanofluids exhibited hysteresis behaviour when the stress is gradually loaded and unloaded, depending also on shearing time. Experiments also showed that the nanofluid suspensions indicated either Newtonian or nonNewtonian behaviour, depending on shear rate. CNT water based nanofluid behaves as Newtonian fluid at high shear rate whereas Al 2 O 3 water based nanofluid is non-Newtonian within the range of low temperatures investigated.

The objective of this study is to compare experimentally the thermal performances of two types of commercial nanofluids. The first is composed of oxides of alumina ((γAl 2 O 3 )) dispersed in water and the second one is aqueous suspensions of nanotubes of carbons (CNTs). The viscosity of the nanofluids is measured as a function of the temperature between 2 and 10°C. An experimental device, containing three thermal buckles controlled in temperature and greatly instrumented permits to study the thermal convective transfers. The evolution of the convective coefficient permits to study the convective thermal transfers. The evolution of the convective coefficient is presented according to the Reynolds number, at low temperature from 0 to 10°C and for the two aforementioned nanofluids. An assessment of the pressure drops in the circuit as well as of the powers of the circulator and outputs is dealt with.

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