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Research Papers: Heat Exchangers

Effect of Sink Temperature on the Stability of the Pressure-Controlled Loop Heat Pipe

[+] Author and Article Information
Wukchul Joung

Division of Physical Metrology,
Korea Research Institute of
Standards and Science,
267 Gajeong-ro, Yuseong-gu,
Daejeon 34113, South Korea
e-mail: wukchul.joung@kriss.re.kr

Joohyun Lee

Division of Physical Metrology,
Korea Research Institute of
Standards and Science,
267 Gajeong-ro, Yuseong-gu,
Daejeon 34113, 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 September 3, 2018; final manuscript received June 3, 2019; published online July 22, 2019. Assoc. Editor: Manfred Groll.

J. Heat Transfer 141(9), 091805 (Jul 22, 2019) (8 pages) Paper No: HT-18-1571; doi: 10.1115/1.4043956 History: Received September 03, 2018; Revised June 03, 2019

Recently, a novel temperature control technique utilizing the unique thermohydraulic operating principles of the pressure-controlled loop heat pipes (PCLHPs) was proposed and proved its effectiveness, by which a faster and more stable temperature control was possible by means of the pressure control. However, due to its recent emergence, the proposed hydraulic temperature control technique has not been fully characterized in terms of the various operating parameters including the sink temperature. In this work, the effect of the sink temperature on the loop heat pipe (LHP)-based hydraulic temperature control was investigated to improve the stability of the proposed technique. Start-up characteristics and transient responses of the operating temperatures to different pressure steps and sink temperatures were examined. From the test results, it was found that there was a minimum sink temperature, which ensured a steady-state operation after the start-up and a stable hydraulic temperature control with the increasing pressure steps, due to the unstable balance between the heat leak and the liquid subcooling in the compensation chamber at low sink temperatures. In addition, the range of the stable hydraulic temperature control was extended with the increasing coolant temperature due to the decreased heat leak, which resulted in the increased pressure difference between the evaporator and the compensation chamber. Therefore, it was found and suggested that for a stable hydraulic temperature control in an extended range, it was necessary to operate the PCLHP at higher sink temperatures than the low limit.

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References

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Maydanik, Y. F. , Fershtater, Y. G. , and Solodovnik, N. N. , 1994, “ Design and Investigation of Methods of Regulation of Loop Heat Pipes for Terrestrial and Space Application,” SAE Paper No. 941407.
Romera, F. , Mishkinis, D. , Kulakov, A. , and Torres, A. , 2010, “ Control of LHP Operation Temperature by a Pressure Regulating Valve,” 15th International Heat Pipe Conference, Clemson, SC, Apr. 25–30, pp. 1–8. https://www.researchgate.net/publication/257023004_Control_of_LHP_operation_temperature_by_a_pressure_regulating_valve
Joung, W. , Kim, Y. , Yang, I. , and Gam, K. , 2013, “ Operating Characteristics of a Loop Heat Pipe-Based Isothermal Region Generator,” Int. J. Heat Mass Transfer, 65, pp. 460–470. [CrossRef]
Joung, W. , Gam, K. , Kim, Y. , and Yang, I. , 2015, “ Hydraulic Operating Temperature Control of a Loop Heat Pipe,” Int. J. Heat Mass Transfer, 86, pp. 796–808. [CrossRef]
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Figures

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Fig. 1

External view of the pressure-controlled loop heat pipe (dimensions in mm) [10]. Reproduced with thepermission of IOP Publishing. Copy right by 2014 Bureau International des Poids et Mesures and IOP Publishing Ltd.

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Fig. 2

Schematic of the experimental apparatus

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Fig. 3

Start-up behavior of the pressure-controlled loop heat pipe at low coolant temperatures: (a) start-up at a coolant temperature of 80 °C and (b) start-up at a coolant temperature of 90 °C

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Fig. 4

Unstable behavior of the pressure-controlled loop heat pipe during the hydraulic temperature control. (a) Response of the isothermal region temperature to the increasing pressure changes of the control gas (coolant temperature: 90 °C). (b) Temperature variations of the components during the hydraulic temperature control (coolant temperature: 90 °C). (c) Temperature variations of the components during the hydraulic temperature control (coolant temperature: 140 °C). (d) Variations of thetemperature difference between the evaporator and the compensation chamber during the hydraulic temperature control (coolant temperature: 90 °C and 140 °C).

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Fig. 5

Responses of the isothermal region temperature to control gas pressure change for different coolant temperatures. (a) Coolant temperature: 100 °C. (b) Coolant temperature: 110 °C. (c) Coolant temperature: 120 °C. (d) Coolant temperature: 130 °C. (e) Coolant temperature: 140 °C.

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Fig. 6

Plot of the pressure increments at which temporary operation failure occurred for different coolant temperatures

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Fig. 7

Plot of the isothermal region temperatures at different control gas pressures for different coolant temperatures. Each symbol represents an average value from three repeated test results. The error bars indicate measurement uncertainties at a 95% level of confidence.

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Fig. 8

Variation of the compensation chamber temperature during the hydraulic temperature control at difference coolant temperatures

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Fig. 9

Variations of the temperature difference between the evaporator and the compensation chamber during the hydraulic temperature control at different coolant temperatures

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