Journal of Nano Research Vol. 11 (2010) pp 101-106 Online available since 2010/May/04 at www.scientific.net © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/JNanoR.11.101
Thermodynamic and Transport Properties of CNT- Water Based Nanofluids J. Ponmozhi1,a, F.A.M.M. Gonçalves1,b, A.G.M. Ferreira2,c, I.M.A. Fonseca2,d, S. Kanagaraj3,e, N. Martins1,f, M.S.A. Oliveira1,g 1
Departmento de Engenharia Mecânica, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal
2
Departmento de Engenharia Química, Universidade de Coimbra, Pólo II, Rua Sílvio Lima, 3030790 Coimbra, Portugal 3
Mechanical Engineering Department, IIT Guwahati, Assam, India
a
[email protected],
[email protected],
[email protected],
[email protected] , e
[email protected],
[email protected];
[email protected]
Keywords: CNTs, nanofluids, thermal conductivity, viscosity.
Abstract. Carbon nanotubes (CNTs) – perhaps the most enticing class of nano-materials, can be added in small volume fractions to enhance the thermal properties of fluids when process intensification or even device miniaturization is required. This work reports on the results obtained when measuring viscosity, and thermal conductivity of homogenous CNTs – water based nanofluids. The influence of CNTs volume concentration on the nanofluid thermo-physical properties is studied and measurements are undertaken at different temperatures, ranging from 283.15 K to 333.15 K. The nanofluids have been prepared by adding different volume concentrations of treated CNTs to water. The latter has been then sonicated for one hour and the colloidal stability monitored via UV – vis spectrophotometer. The absorbance of the nanofluid was observed at 263 nm, and the average concentration of CNTs was maintained at 9.35 mg/l, even after 200 hours, over 97% when compared with the initial concentration. The viscosity was measured using a controlled stress rheometer, and the measurements were performed in the shear rate ranging from 0 to 600 sec-1. At the same shear rate and temperature, the viscosity was observed to rise with increasing CNTs volume concentration. In what concerns thermal conductivity, it was assessed with a KD2 pro thermal property tester from Decagon Devices and the results clearly show that thermal conductivity rises with CNTs volume fraction, reaching its maximum at 2.5%vol where it represents more than 100% enhancement when the comparison is established with the corresponding value for the base fluid, at the same temperature conditions (i.e. 283.15 – 303.15 K). Furthermore, at higher temperatures (i.e. 313.15 – 333.15 K), the latter, for up to 1%vol concentration represents a 70% enhancement in thermal conductivity. Introduction Heating or cooling fluids are of major importance to many industrial sectors including transportation, energy supply and production, electronics, nuclear and biomedical instrumentation and equipment. However, conventional heat transfer fluids have poor heat transfer properties compared to most solids. Despite considerable previous research and development focusing on industrial heat transfer requirements, major improvements in heat transfer capabilities have been lacking. As a result, a clear need exists to develop new strategies for improving the effective heat transfer behaviour of conventional heat transfer fluids. Effective thermal conductivity measurements of dispersed nanotubes in synthetic poly-oil were carried out [1] and a 160% increase in the thermal conductivity of oil at 1% volume fraction of CNTs was found. The thermal conductivity of Cu-ethylene glycol nanofluids was assessed [2], and it was observed a 40% enhancement containing approximately 0.3 vol% of Cu nanoparticles with mean diameter, 10 nm. A thermal conductivity increase of 35% to 79% for 0.5 to 1.0 vol% of carbon nanoparticles in water was also observed, [3]. The viscosity of CNT nanofluids as a function of shear rate was also All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 210.212.8.62-06/07/11,06:29:21)
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measured at different temperatures and concentrations, at pH = 6. It was observed a shear thinning behavior, at low shear rates, but a slightly shear thickening is seen at shear rates greater than 200 s-1. It was observed that the thermal conductivity enhancement reaches up to 17.5% at the volume fraction of 0.01 (1 vol%) for CNTs - ethylene glycol based nanofluids, [4]. At low volume fractions (
