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Research Papers: Heat and Mass Transfer

Effects of Hydrophilic and Hydrophobic Surfaces on Start-Up Performance of an Oscillating Heat Pipe

[+] Author and Article Information
Tingting Hao

Institute of Chemical Engineering,
Dalian University of Technology,
Dalian 116024, Liaoning, China
e-mail: haotingting224@mail.dlut.edu.cn

Xuehu Ma

Mem. ASME
Institute of Chemical Engineering,
Dalian University of Technology,
Dalian 116024, Liaoning, China
e-mail: xuehuma@dlut.edu.cn

Zhong Lan

Institute of Chemical Engineering,
Dalian University of Technology,
Dalian 116024, Liaoning, China
e-mail: lanzhong_dut@sohu.com

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 31, 2016; final manuscript received April 27, 2017; published online August 16, 2017. Assoc. Editor: Chun Yang.

J. Heat Transfer 140(1), 012002 (Aug 16, 2017) (9 pages) Paper No: HT-16-1337; doi: 10.1115/1.4037341 History: Received May 31, 2016; Revised April 27, 2017

Slug oscillations and heat transfer performance in the start-up stage of oscillating heat pipes (OHPs) with different surface wetting characteristics were investigated experimentally. The inner surfaces of the OHPs were superhydrophilic surface, hydrophilic surface, copper, hydrophobic surface, and superhydrophobic surface, respectively. There was a thin liquid film between the vapor bubble and the surface in the hydrophilic OHP which was different from hydrophobic OHP. Results showed that start-up performance was improved in hydrophilic OHP due to the low flow resistance and deteriorated in hydrophobic OHP as opposed to the copper OHP. Heat transfer results showed that wall temperature fluctuations were observed at the start-up stage. Compared with the copper OHP, start-up time and start-up temperature were reduced by 100 s and 3.32–4.41 °C in the hydrophilic OHP at the start-up stage. Slug oscillation frequency and temperature oscillation amplitude increased with heat input; however, slug oscillation amplitude increased first and then decreased with heat input. Compared with the copper OHP, with the increasing of 0–57% in slug oscillation amplitude and 0–100% in slug oscillation frequency, the thermal performance was enhanced by 0–67% in the hydrophilic OHP. Although the slug oscillation frequency in the superhydrophobic OHP was higher than that in the copper OHP, with the decreasing of 0–70% in the slug oscillation amplitude, the thermal resistance in superhydrophobic OHP was significantly increased and was 1.5–5 times higher than that in the copper OHP.

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References

Figures

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Fig. 1

Schematic of the experimental setup

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Fig. 2

Photos of the OHPs for (a) visualization, (b) surface temperature measurement, and (c) locations of the thermocouple (all units in mm)

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Fig. 3

Contact angles on (a) superhydrophilic, (b) hydrophilic, (c) copper, (d) hydrophobic, and (e) superhydrophobic surfaces

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Fig. 4

ESEM images of (a) superhydrophilic and superhydrophobic, (b) hydrophilic, and (c) copper and hydrophobic surfaces

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Fig. 5

Schematic drawing of flow patterns in the evaporation section with (a) superhydrophilic, hydrophilic, and copper, (b) hydrophobic, and (c) superhydrophobic surfaces at the start-up stage

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Fig. 6

Slug oscillation positions in the copper OHP

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Fig. 7

Slug oscillations with time in the OHPs

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Fig. 8

Maximum slug oscillation amplitudes with heat input in the OHPs

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Fig. 9

Slug oscillation frequencies with heat input in the OHPs

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Fig. 10

Temperature variations of the OHPs at the start-up state (heat input: 100 W)

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Fig. 11

Temperature oscillations of (a) evaporation and (b) condensation section at the steady stage (heat input: 100 W)

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Fig. 12

Maximum temperature oscillation differences in the condensation section of OHPs

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Fig. 13

Hydrophilic and hydrophobic surfaces on thermal resistances of OHPs

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