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Technical Brief

Thermal Conductivity Enhancement of Ethylene Glycol-Based Suspensions in the Presence of Silver Nanoparticles of Various Shapes

[+] Author and Article Information
Li-Wu Fan

Mem. ASME
e-mail: liwufan@zju.edu.cn
Institute of Thermal Science and Power Systems,
Department of Energy Engineering, Zhejiang University,
Hangzhou, Zhejiang 310027, China;
Key Laboratory of Efficient Utilization of Low
and Medium Grade Energy (Tianjin University),
Ministry of Education of China,
Tianjin 300072, China

Zi-Tao Yu

Institute of Thermal Science and Power Systems,
Department of Energy Engineering, Zhejiang University,
Hangzhou, Zhejiang 310027, China;
State Key Laboratory of Clean Energy Utilization,
Department of Energy Engineering, Zhejiang University,
Hangzhou, Zhejiang 310027, China

Xu Xu

Institute of Energy Engineering,
College of Metrological and Measurement Engineering,
China Jiliang University,
Hangzhou, Zhejiang 310018, China

Guan-Hua Cheng

Zhejiang Provincial Key Laboratory of Solar Energy
Utilization and Energy Conversation Technologies,
Zhejiang Energy and Radiation Institute,
Hangzhou, Zhejiang 310012, China

Ya-Cai Hu

Institute of Thermal Science and Power Systems,
Department of Energy Engineering, Zhejiang University,
Hangzhou, Zhejiang 310027, China

Ke-Fa Cen

State Key Laboratory of Clean Energy Utilization,
Department of Energy Engineering, Zhejiang University,
Hangzhou, Zhejiang 310027, China

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 30, 2013; final manuscript received August 26, 2013; published online November 21, 2013. Assoc. Editor: Andrey Kuznetsov.

J. Heat Transfer 136(3), 034501 (Nov 21, 2013) (7 pages) Paper No: HT-13-1222; doi: 10.1115/1.4025663 History: Received April 30, 2013; Revised August 26, 2013

In this technical brief, the effect of adding silver (Ag) nanoparticles of various shapes on the thermal conductivity enhancement of ethylene glycol (EG)-based suspensions was investigated experimentally. These included Ag nanospheres (Ag NSs), Ag nanowires (Ag NWs), and Ag nanoflakes (Ag NFs). Measurements of the thermal conductivity of the suspensions were performed from 10 to 30 °C at an increment of 5 °C. It was shown that the thermal conductivity of the EG-based suspensions increases with raising the temperature. The Ag NWs of a high aspect ratio (∼500) caused greatest relative enhancement up to 15.6% at the highest loading of nearly 0.1 vol. %, whereas the other two shapes of nanoparticles, Ag NSs and Ag NFs with much smaller aspect ratios, only led to enhancements up to 5%. The formation of a network of Ag NWs that facilitates heat conduction was likely responsible for their better performance. The relative enhancement was also predicted by the Hamilton-Crosser model that takes the particle shape effect into consideration. It was shown that the predictions far underestimate the thermal conductivity enhancements but are qualitatively consistent with their shape dependence. As a penalty, however, the presence of Ag NWs was shown to give rise to significant increase in the viscosity of the EG-based suspensions.

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Figures

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Fig. 1

XRD patterns for the (a) Ag NSs, (b) Ag NWs and (c) Ag NFs, showing diffraction peaks corresponding to the (111), (200), (220), (311) and (222) crystallographic planes of face-centered cubic Ag crystals

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Fig. 2

Shapes of the (a) Ag NSs, (b) Ag NWs and (c) Ag NFs as characterized by SEM images. The inset in (c) shows the thicknesses of isolated Ag NFs as determined by AFM image

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Fig. 3

TEM images of the (a) Ag NSs, (b) Ag NWs and (c) Ag NFs in the EG-based suspensions, and (d) comparison of hydrodynamic clustering size distributions of the Ag nanoparticles as determined by DLS technique, where the insets show the photographs of the EG-based suspensions (10 mg/mL) with the corresponding Ag nanoparticles

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Fig. 4

Measured thermal conductivity of the EG-based suspensions in the presence of (a) Ag NSs, (b) Ag NWs and (c) Ag NFs as a function of temperature, and (d) comparison of the relative enhancement of thermal conductivity among the Ag nanoparticles

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Fig. 5

Comparison between the measured and predicted thermal conductivity of the EG-based suspensions in the presence of the various Ag nanoparticles

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