New Measurements of the Apparent Thermal Conductivity of Nanofluids and Investigation of Their Heat Transfer Capabilities

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• 作者：Georgia J. Tertsinidou ; Chrysi M. Tsolakidou ; Maria Pantzali ; Marc J. Assael ; Laura Colla ; Laura Fedele ; Sergio Bobbo ; William A. Wakeham
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2017
• 出版时间：January 12, 2017
• 年：2017
• 卷：62
• 期：1
• 页码：491-507
• 全文大小：862K
• ISSN：1520-5134

文摘

The aim of this paper is to investigate in depth whether adding nanoparticles or nanotubes to a fluid enhances its heat transfer capabilities. For this reason, the thermal conductivities and viscosities of a selection of nanofluids were thoroughly examined. The systems studied were (a) ethylene glycol with added CuO, TiO₂, or Al₂O₃ nanoparticles and (b) water with TiO₂ or Al₂O₃ nanoparticles or multiwall carbon nanotubes (MWCNTs). All of the measurements were conducted at 298.15 K. In a very recent paper, it was shown that instruments employing the transient hot-wire technique can produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the geometry of the hot wire. Furthermore, it was shown that an approximate analytic solution can be employed with equal success over the time range from 0.1 to 1 s, provided that four specific criteria are satisfied. Subsequently a transient hot-wire instrument was designed, constructed, and employed for the measurement of the thermal conductivities of nanofluids with an uncertainty of about 2%. A second, validated technique, namely, a hot-disk instrument, was also employed to conduct measurements on some of the systems to provide mutual support for the results of the thermal conductivity measurements. To investigate the effect of any enhancement of the thermal conductivity of the fluids on their application in practical heat transfer, the viscosities of typical concentrations of several of the nanofluids were also measured. A parallel-plate rotational rheometer, able to measure the viscosities of Newtonian and non-Newtonian liquids with an uncertainty of better than 5%, was employed for these measurements because most of the nanofluids considered showed behavior comparable to a Bingham plastic. All of these measurements have allowed an investigation of the change in the heat transfer capability of the base fluid when nanoparticles or MWCNTs are added to it for a typical heat exchanger. It is shown that in general the combined changes in physical properties that accompany suspension of nanoparticles in fluids mean that the heat transfer benefits are all rather modest, even when they are achieved.