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Research Papers: Heat and Mass Transfer

Maximum Heat Transfer and Operating Temperature of Oscillating Heat Pipe

[+] Author and Article Information
Naoko Iwata

Japan Aerospace Exploration Agency,
2-1-1, Sengen,
Tsukuba 305-8505,
Ibaraki, Japan
e-mail: iwata.naoko@jaxa.jp

Hiroyuki Ogawa

Japan Aerospace Exploration Agency,
3-1-1, Yoshinodai,
Chuoku,
Sagamihara 252-5210,
Kanagawa, Japan
e-mail: ogawa.hiroyuki@jaxa.jp

Yoshiro Miyazaki

Reinetsu,
7-6-13-608, Bunkyo 910-0017,
Fukui, Japan
e-mail: miyazfam@lapis.plala.or.jp

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received November 1, 2015; final manuscript received June 8, 2016; published online August 2, 2016. Editor: Portonovo S. Ayyaswamy.

J. Heat Transfer 138(12), 122002 (Aug 02, 2016) (5 pages) Paper No: HT-15-1685; doi: 10.1115/1.4034054 History: Received November 01, 2015; Revised June 08, 2016

It is reported that the operating temperature of an oscillating heat pipe (OHP) at an operating limit is not dependent on the ambient temperature but that the maximum heat transfer is dependent on this. In this study, using different ambient temperature conditions, a 15-turn OHP filled with HFC-134a as a working fluid was operated until it dries out. The maximum heat transfer was found to vary with changes in the ambient temperature, but the operating temperature at an operating limit, which depends on the filling ratio (FR) of the working fluid, was found to be constant. At the operating limit, the operating temperature decreased with an increase in the FR when the ratio was greater than 50 wt.%. Visualization experiments and calculations were used to confirm that there is an increase in the liquid volume in the OHP in accordance with an increase in the heat input and that ultimately the OHP fills with the liquid, resulting in the failure of OHP operation. In contrast, at the operating limit, when the FR was less than 50%, the operating temperature increased in line with an increase in the FR. In this case, it is assumed that the volume of liquid slugs decreases as the heat input increases, thus causing the OHP to dry out. This theory is explained using a P–V diagram of the working fluid in the OHP. The OHP thermodynamic cycle reaches a saturated liquid or vapor line before it reaches a critical point if a specified volume is shifted from the specified volume at the critical point. The optimum FR for maximum heat transfer is therefore decided by the void ratio at the critical point of the working fluid.

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References

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Figures

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Fig. 2

Experimental setup

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Fig. 3

Maximum heat transfer

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Fig. 4

TH at operating limit

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Fig. 5

HFC-134a liquid density at saturation condition

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Fig. 6

Liquid volume in OHP at operating limit

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Fig. 7

Relation between TH and FR

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Fig. 9

Visualization experiment results (FR = 85 wt.%). Left: low heat input (16.0 W) and right: high heat input (32.4 W).

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Fig. 10

Visualization experiment results (FR = 39 wt.%). Left: low heat input (16.0 W) and right: high heat input (55.2 W).

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Fig. 11

P–V diagram of the working fluid

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