Thermophysical properties and heat transfer performance of carbon nanotubes water-based nanofluids

International audienceIn this paper, thermal conductivity and rheological properties of CNT water-based nanofluids were experimentally measured, whereas density and heat capacity were evaluated from appropriate theoretical correlations. The influence of nanoparticle content and base fluids on thermophysical properties of nanofluids was presented and discussed. Then, the thermal performance and convective heat transfer of such nanofluids were investigated in a coaxial heat exchanger working in cocurrent flow. Fixed wall temperature boundary condition and laminar regime were also considered during theexperiments. The results were presented discussing the effect of the entrance region, Reynolds number and nanofluids composition

Heat transfer properties of aqueous carbon nanotubes nanofluids in coaxial heat exchanger under laminar regime

International audienceThe thermal performance of water-based multi-wall carbon nanotubes nanofluids are measured in a coaxial heat exchanger under laminar regime within the range of Reynolds numbers 500-2500. The convective heat transfer properties with constant wall temperature are evaluated for four different multi-wall carbon nanotubes based nanofluids at low concentration of 0.05% in weight (0.026% in volume). The measurements of thermal and rheological properties of the nanofluids with operating temperature were investigated experimentally. The effects of the aspect ratio of carbon nanotubes, the type of base fluid and surfactant on viscosity, thermal conductivity and laminar convective heat transfer were studied. Based on the experimental results, we reported the shear-thinning behaviour of nanofluids, the nanofluid viscosity being dependant on the base fluid type in the Newtonian region. We also showed that the enhancement of the thermal conductivity and the average convective heat transfer of nanofluids increased with the aspect ratio of nanotubes and decreased when the thermal conductivity of the base fluid increases. This enhancement attains at least 10% in comparison to base fluid even with the low content of nanotubes used

Efficiency of carbon nanotubes water based nanofluids as coolants

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

Shear history effect on the viscosity of carbon nanotubes water-based nanofluid

International audienceExperimental results on the steady state rheological behaviour of carbon nanotube (CNT) water-based nanofluid are presented. We have investigated the influence of a controlled preshear history on the viscosity of CNT water-based nanofluid. Two types of preshear history effect are studied: the influence of stress rate during preshear and the effect of resting time before viscosity measurement. It is revealed that CNT water-based nanofluid behaves as a viscoelastic media at low shear rate and it is shear-thinning at higher shear rate. This behaviour is strongly dependent on shear history due to the breakdown in the structural network of nanofluid agglomerates. It is also observed that the nanofluid can reform at rest after preshear following the resting time and the rate or preshear applied to the nanofluid

Etude des performances thermiques en convection forcée des nanofluides à base de nanotubes de carbones dans un échangeur coaxial

International audienceLe présent travail s'attache à caractériser expérimentalement les propriétés thermo-physiques ainsi que les performances thermiques de quatre types de nanofluides à base de nanotubes de carbone à la fraction massique 0.01% afin d'évaluer les effets liés à leurs compositions dont le type de surfactant, le rapport d'aspect des NTC et l'ajout de l'antigel. Une section d'essais constituée d'un échangeur coaxial a été conçue et instrumentée finement avec des thermocouples au niveau de la paroi d'échange et à l'entrée/sortie du fluide, ainsi qu'avec des capteurs de pression afin de permettre une détermination précise des flux échangés au sein de cette section d'essais. Les mesures de la conductivité thermique et de la viscosité dynamique des nanofluides ont été effectuées expérimentalement. Le coefficient d'échange convectif dans l'échangeur ont été déterminés en fonction de la distance axiale

Optimisation des performances thermiques et hydrauliques d'un nanofluide à base de nanotubes de carbone dans un dissipateur de chaleur à microcanaux rectangulaires

International audienceCe travail s'attache à étudier l'optimisation d'un dissipateur de chaleur à microcanaux rectangulaires en utilisant un nanofluide à base de nanotubes de carbone comme liquide de refroidissement. La concentration massique de nanotubes de carbone utilisée dans cette étude est 0,01%. La masse volumique, la conductivité thermique et la viscosité dynamique du nanofluide sont mesurées expérimentalement afin d'évaluer la résistance thermique et la puissance de pompage dans le dissipateur de chaleur en régime laminaire. L'optimisation des performances thermiques (résistance thermique) et des pertes de charge (puissance de pompage) est basée sur l'algorithme génétique multi-objectifs NSGA-2 (Non Dominated Sorting Algorithm 2). Les effets de la température, des dimensions des canaux et l'utilisation du nanofluide à base de nanotubes de carbone sur la résistance thermique et la puissance de pompage sont étudiés. Les résultats montrent que l'utilisation optimisée du nanofluide étudié permet de réduire la résistance thermique totale et peut améliorer significativement les performances thermiques du fluide de refroidissement à haute température

Consideration of carbon nanotube-based nanofluid in thermal transfer

In the current trend towards demand for effective heat removal of high density heat flux, research into nanofluids have escalated due to the rise in thermal conductivity associated with the coolants. Are nanofluids a solution for a better thermal management? Does the application of nanofluids as coolants have limitations? This article presents a review of the thermophysical properties of carbon nanotube-water nanofluids, in particular the desired properties of low viscosity and high thermal conductivity. The effects of the concentration, temperature, aspect ratio, and surfactant on the thermal conductivity and viscosity of carbon nanotube nanofluid have been studied experimentally. These effects are thendiscussed for evaluation of the applicability of carbon nanotube-based nanofluidas a coolant for heat removal purposes

Viscosity of carbon nanotubes water based nanofluids: Influence of concentration and temperature

International audienceExperimental results on the steady-state viscosity of carbon nanotubes water-based nanofluids are presented considering the influence of particle volume fraction and temperature ranging from 0 to 40 C. The suspensions consist of multi-walled carbon nanotubes dispersed in de-ionized water and they are stabilized by a surfactant. The aspect ratio of nanotubes is close to 160 and the particle volume fraction varies between 0.0055% and 0.55%. It is shown that the nanofluids behave as shear-thinning materials for high particle content. For lower particle content, the nanofluids are quite Newtonian. It is also observed that the relative viscosity of nanofluids at high shear rate does not vary with temperature. Moreover, the evolution of relative viscosity at high shear rate is well predicted by the Maron-Pierce model considering the effect of nanoparticles agglomerates

Comparison of the thermal performances of two nanofluids at low temperature in a plate heat exchanger

International audienceThe 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 (Al2O3) 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

Experimental investigations of the viscosity of nanofluids at low temperatures

Special Issue on Energy Solutions for a Sustainable World - Proceedings of the Third International Conference on Applied Energy, May 16-18, 2011 - Perugia, Italy Guest Editors: Umberto Desideri, Jinyue YanInternational audienceThe effects due to temperature and shearing time on viscosity for Al2O3/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 non-Newtonian behaviour, depending on shear rate. CNT water based nanofluid behaves as Newtonian fluid at high shear rate whereas Al2O3 water based nanofluid is non-Newtonian within the range of low temperatures investigated