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MICRO/NANOSCALE HEAT TRANSFER—PART I

Nanofluids: Synthesis, Heat Conduction, and Extension

[+] Author and Article Information
Liqiu Wang1

Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Konglqwang@hku.hk

Xiaohao Wei

Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong

1

Corresponding author.

J. Heat Transfer 131(3), 033102 (Jan 13, 2009) (7 pages) doi:10.1115/1.3056597 History: Received January 30, 2008; Revised May 05, 2008; Published January 13, 2009

We synthesize eight kinds of nanofluids with controllable microstructures by a chemical solution method (CSM) and develop a theory of macroscale heat conduction in nanofluids. By the CSM, we can easily vary and manipulate nanofluid microstructures through adjusting synthesis parameters. Our theory shows that heat conduction in nanofluids is of a dual-phase-lagging type instead of the postulated and commonly used Fourier heat conduction. Due to the coupled conduction of the two phases, thermal waves and possibly resonance may appear in nanofluid heat conduction. Such waves and resonance are responsible for the conductivity enhancement. Our theory also generalizes nanofluids into thermal-wave fluids in which heat conduction can support thermal waves. We emulsify olive oil into distilled water to form a new type of thermal-wave fluids that can support much stronger thermal waves and resonance than all reported nanofluids, and consequently extraordinary water conductivity enhancement (up to 153.3%) by adding some olive oil that has a much lower conductivity than water.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

CSM for synthesis of nanofluids: flowchart

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Figure 2

TEM images of some nanoparticles from “drying” samples of nanofluids synthesized by the CSM ((a) spherical Fe3O4 nanoparticles, (b) elliptic Cu nanorods, (c) needlelike CuO nanoparticles, (d) octahedral Cu2O nanoparticles, (e) CePO4 nanofibers, (f) hollow CuS nanoparticles, (g) hollow and wrinkled Cu2O nanoparticles, and (h) Cu2O(core)/CuS(shell) nanoparticles)

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Figure 3

Variation of k/kw with reactant concentration and temperature for CePO4-nanofibers/water nanofluids in Fig. 2 (k: nanofluids thermal conductivity; kw: water thermal conductivity)

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Figure 4

Nanofluids and representative elementary volume (REV)

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Figure 5

Oil/water emulsion (oil volume fraction from 0.5 vol % to 16.7 vol %)

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Figure 6

Oil/water emulsion under microscope (oil volume fraction=3.33%; temperature=50°C; oil droplet mean diameter of 192.1 nm with a coefficient of variation (CV) of 4.99%)

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Figure 7

Variation of k/kw with oil volume fraction and emulsion temperature (k: emulsion thermal conductivity; kw: water thermal conductivity)

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