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Research Papers: Two-Phase Flow and Heat Transfer

Derivation and Validation of a Figure of Merit for Loop Heat Pipes With Medium Temperature Working Fluids

[+] Author and Article Information
Wukchul Joung

Center for Thermometry,
Division of Physical Metrology,
Korea Research Institute of Standards
and Science,
267 Gajeong-Ro, Yuseong-Gu,
Daejeon 305-340, South Korea
e-mail: wukchul.joung@kriss.re.kr

Jinho Lee

School of Mechanical Engineering,
Yonsei University,
50-1 Yonsei-Ro, Seodaemun-Gu,
Seoul 120-749, South Korea
e-mail: jinholee@yonsei.ac.kr

Sanghyun Lee

Center for Thermometry,
Division of Physical Metrology,
Korea Research Institute of Standards
and Science,
267 Gajeong-Ro, Yuseong-Gu,
Daejeon 305-340, South Korea
e-mail: leesh@kriss.re.kr

Joohyun Lee

Center for Thermometry,
Division of Physical Metrology,
Korea Research Institute of Standards
and Science,
267 Gajeong-Ro, Yuseong-Gu,
Daejeon 305-340, South Korea
e-mail: joohyun.lee@kriss.re.kr

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 14, 2015; final manuscript received January 4, 2016; published online February 17, 2016. Assoc. Editor: Amitabh Narain.

J. Heat Transfer 138(5), 052901 (Feb 17, 2016) (10 pages) Paper No: HT-15-1280; doi: 10.1115/1.4032534 History: Received April 14, 2015; Revised January 04, 2016

The working fluids of loop heat pipes (LHPs) play an important role in the operation of the LHPs by influencing the operating temperatures and the heat transfer limits. Therefore, the proper selection of a working fluid is a key practice in LHP fabrication, and there has been a high demand for an appropriate index that enables the quantitative comparison of the steady-state thermal performance of the working fluids. In this work, a figure of merit for LHPs was theoretically derived and experimentally verified. In particular, the pressure losses in the LHP operation were balanced with the saturation pressure difference between the evaporator and the compensation chamber to derive the figure of merit. This derived figure of merit for LHPs successfully predicted the steady-state thermal performance of the tested working fluids within the variable conductance regime. In the constant conductance regime, the differences in the condenser cooling capacity and in the liquid subcooling for different working fluids determined the thermal performance of each working fluid. The limitations and prospects of the proposed figure of merit were discussed in detail.

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References

Figures

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Fig. 2

Thermodynamic operation curve (P–T diagram) of a conventional LHP

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Fig. 1

Schematic of a conventional LHP

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Fig. 9

Evaporator temperature variations for the selected working fluids

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Fig. 10

Compensation chamber temperature variations for the selected working fluids

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Fig. 11

Condenser outlet temperature variations for the selected working fluids

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Fig. 12

Liquid inlet temperature variations for the selected working fluids

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Fig. 3

Variation of the figure of merit for laminar vapor flows

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Fig. 4

Variation of the figure of merit for turbulent vapor flows

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Fig. 5

Variations of the figure of merit for conventional heat pipes

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Fig. 6

External and section views of the evaporator–wick–compensation chamber assembly (dimensions in millimeter)

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Fig. 7

External view of the flat evaporator LHP and locations of the temperature readings

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Fig. 8

Schematic of the experimental apparatus

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Fig. 13

Heat leak variations for the selected working fluids

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Fig. 14

Thermal resistance variations for the selected working fluids

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