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Research Papers: Experimental Techniques

Critical Invalidation of Temperature Dependence of Nanofluid Thermal Conductivity Enhancement

[+] Author and Article Information
Kisoo Han

Mechanical Engineering Department,
Kyung Hee University,
Yongin 449-701, South Korea

Wook-Hyun Lee

Korea Institute of Energy Research,
Daejon 305-343, South Korea

Clement Kleinstreuer

Mechanical and Aerospace Engineering Department,
North Carolina State University,
Raleigh, NC 27695-7910

Junemo Koo

Mechanical Engineering Department,
Kyung Hee University,
Yongin 449-701, South Korea
e-mail: jmkoo@khu.ac.kr

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 15, 2012; final manuscript received January 18, 2013; published online April 11, 2013. Assoc. Editor: Oronzio Manca.

J. Heat Transfer 135(5), 051601 (Apr 11, 2013) (9 pages) Paper No: HT-12-1435; doi: 10.1115/1.4023544 History: Received August 15, 2012; Revised January 18, 2013

Of interest is the accurate measurement of the enhanced thermal conductivity of certain nanofluids free from the impact of natural convection. Owing to its simplicity, wide range of applicability and short response time, the transient hot-wire method (THWM) is frequently used to measure the thermal conductivity of fluids. In order to gain a sufficiently high accuracy, special care should be taken to assure that each measurement is not affected by initial heat supply delay, natural convection, and signal noise. In this study, it was found that there is a temperature limit when using THWM due to the incipience of natural convection. The results imply that the temperature-dependence of the thermal conductivity enhancement observed by other researchers might be misleading when ignoring the impact of natural convection; hence, it could not be used as supporting evidence of the effectiveness of micromixing due to Brownian motion. Thus, it is recommended that researchers report how they keep the impact of the natural convection negligible and check the integrity of their measurements in the future researches.

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Figures

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Fig. 1

Definitions of temperature history, start- and end-time in the data

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Fig. 2

Schematics of the apparatus for data collection using the transient hot-wire method

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Fig. 3

SEM images of nanoparticles used in the nanofluids

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Fig. 4

Effects of temperature data-range selections on thermal conductivity determination for: (a) water; (b) water-based Ag nanofluid at 313 K; (c) EG; and (d) EG-based ZnO nanofluid at 303 K

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Fig. 5

Comparison of measurement margins for different fluids

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Fig. 6

Comparison of thermal conductivity measurements between pure base fluids and nanofluids versus the predictions by Maxwell's model

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Fig. 7

Comparison between research groups concerning the temperature dependence of effective thermal conductivity enhancement of nanofluids: (a) other groups; and (b) current study

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Fig. 8

Effect of temperature data-range selection on the estimation of the nanofluid effective thermal conductivity

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Fig. 9

Effect of particle volume fraction on the incipience of natural convection for EG-based ZnO nanofluids

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Fig. 10

Thermal conductivity enhancement with the variation of the ZnO particle volume fraction in EG-based nanofluids

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