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Research Papers: Heat Transfer Enhancement

Formation of Nano-Adsorption Layer and Its Effects on Nanofluid Spray Heat Transfer Performance

[+] Author and Article Information
Tong-Bou Chang

Department of Mechanical and
Energy Engineering,
National Chiayi University,
No. 300, Syuefu Road,
Chiayi City 600, Taiwan
e-mail: tbchang@mail.ncyu.edu.tw

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 22, 2014; final manuscript received October 11, 2014; published online November 18, 2014. Assoc. Editor: Zhixiong Guo.

J. Heat Transfer 137(2), 021901 (Feb 01, 2015) (11 pages) Paper No: HT-14-1336; doi: 10.1115/1.4028903 History: Received May 22, 2014; Revised October 11, 2014; Online November 18, 2014

For spray cooling using nanofluid as the working fluid, a nano-adsorption layer is formed on the heated surface and affects the heat transfer performance of the cooling system. This study performs an experimental investigation into the formation of this nano-adsorption layer and its subsequent effects on the spray heat transfer performance of a cooling system using Al2O3–water nanofluid as the working fluid. The experiments consider four different nanoparticle volume fractions (i.e., 0 vol. %, 0.001 vol. %, 0.025 vol. %, and 0.05 vol. %) and two different surface roughnesses (i.e., 0.1 μm and 1.0 μm). The experimental results show that the 0.001 vol. % nanofluid yields the optimal heat transfer performance since most of the nanoparticles rebound from the heated surface directly on impact or are washed away by subsequently arriving droplets. The surface compositions of the spray-cooled specimens are examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results reveal that for all of the nanofluids, a nano-adsorption layer is formed on the surface of the spray-cooled test pieces. Moreover, the layer thickness increases with an increasing nanoparticle concentration. A greater nano-adsorption layer thickness not only results in a higher thermal resistance but also reduces the effect of the surface roughness in enhancing the heat transfer performance. In addition, the nano-adsorption layer absorbs the nanofluid droplets under the effects of capillary forces, and therefore reduces the contact angle, which induces a hydrophilic surface property.

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Figures

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Fig. 1

Schematic illustration of experimental spray cooling system

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Fig. 2

Schematic illustration of heating module

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Fig. 3

Comparison of present experimental results for spray cooling heat transfer performance of DI water with results presented by Lin et al. [15]

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Fig. 4

Variation of spray cooling heat transfer performance with heat flux as function of Al2O3 nanoparticle concentration given surface roughness of 0.1 μm

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Fig. 5

Variation of spray cooling heat transfer performance with heat flux as function of Al2O3 nanoparticle concentration given surface roughness of 1.0 μm

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Fig. 6

Morphology and composition of test pieces with surface roughness values of (a) 0.1 μm and (b) 1.0 μm before spray cooling experiments

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Fig. 7

Morphology and composition of test pieces with surface roughness of 0.1 μm after spray cooling experiments using nanofluid with particle volume fractions of (a) 0 vol. %, (b) 0.001 vol. %, (c) 0.025 vol. %, and (d) 0.05 vol. %

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Fig. 8

Morphology and composition of test pieces with surface roughness of 1.0 μm after spray cooling experiments using nanofluid with particle volume fractions of (a) 0 vol. %, (b) 0.001 vol. %, (c) 0.025 vol. %, and (d) 0.05 vol. %

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Fig. 9

Photographs of pre-experiment contact angles on test pieces with surface roughness of 0.1 μm given particle volume fractions of (a) 0 vol. %, (b) 0.001 vol. %, (c) 0.025 vol. %, and (d) 0.05 vol. %

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Fig. 10

Photographs of pre-experiment contact angles on test pieces with surface roughness of 1.0 μm given particle volume fractions of (a) 0 vol. %, (b) 0.001 vol. %, (c) 0.025 vol. %, and (d) 0.05 vol. %

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Fig. 11

Photographs of post-experiment contact angles on test pieces with surface roughness of 0.1 μm given particle volume fractions of (a) 0 vol. %, (b) 0.001 vol. %, (c) 0.025 vol. %, and (d) 0.05 vol. %

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Fig. 12

Photographs of post-experiment contact angles on test pieces with surface roughness of 1.0 μm given particle volume fractions of (a) 0 vol. %, (b) 0.001 vol. %, (c) 0.025 vol. %, and (d) 0.05 vol. %

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