Numerical Study of Thermal Performance of a Capillary Evaporator in a Loop Heat Pipe with Liquid-Saturated Wick

Nishikawara, Masahito; Nagano, Hosei; Mottet, Laetitia; Prat, Marc

doi:10.4236/jectc.2014.44013

Cited by 12 publications

(4 citation statements)

References 21 publications

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“…So, vapor pocket generation because of bubble nucleation as reported in refs. [7][8][9], is unlikely to occur. The liquidvapor interface recedes into the wick only at capillary limit.…”

Section: Numerical Modelingmentioning

confidence: 99%

Numerical simulation of capillary evaporator with microgap in a loop heat pipe

Nishikawara

Nagano

2016

International Journal of Thermal Sciences

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A mathematical model to investigate the heat transfer characteristics of a capillary evaporator in a loop heat pipe with a microgap between the case and the wick was developed, and the gap effect on the evaporator heat-transfer coefficient is discussed.The model was validated by comparison with experimental results obtained for a polytetrafluoroethylene-ethanol loop heat pipe.Calculated and experimental results agreed well below a 100 µm gap distance, with both approaches indicating the existence of an optimal gap between 0 and 50 µm. We clarify why the heat-transfer coefficient had a local maximum against the gap distance. The effect of the gap is determined for a change in heat flux to the evaporator, wick shape, working fluid, and thermal conductivity of the wick. The simulation showed that an optimal gap exists on the evaporator, except for the stainless steel wick. The microgap evaporator was workable for a wick made from a low thermal conductivity material. When a microgap is introduced in the loop heat pipe, the evaporator heat-transfer coefficient can be enhanced, hysteresis of the liquid-vapor interface in a porous structure can be prevented, and the evaporator thermal performance can be predicted easily. Therefore, the microgap is an effective approach for thermal performance enhancement.

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“…So, vapor pocket generation because of bubble nucleation as reported in refs. [7][8][9], is unlikely to occur. The liquidvapor interface recedes into the wick only at capillary limit.…”

Section: Numerical Modelingmentioning

confidence: 99%

Numerical simulation of capillary evaporator with microgap in a loop heat pipe

Nishikawara

Nagano

2016

International Journal of Thermal Sciences

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“…Evaporation behavior and vapor-liquid interface shift in the wick have been visualized with microscale thermal imaging [23]. The pore network model has also been developed to simulate detailed liquid and vapor flow in the porous structure of the wick [24]. As an application, an LHP with a 10 m heat transport distance has been developed by the use of advanced wicks, and its performance has been demonstrated [25].…”

Section: Introductionmentioning

confidence: 99%

Thermofluid Characteristics in Microporous Structure With Different Flow Channels for Loop Heat Pipe

Nagano

Kuroi

Nishikawara

2016

Heat Transfer Engineering

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The use of two-phase heat transfer devices using capillary action in a microscale porous structure such as a loop heat pipe (LHP) is a promising heat transport technology. It is because they have characteristics of higher heat transfer power and longer heat transport distances with no electrical power compared with conventional heat pipes. The thermal performance of an LHP is governed by the thermo-fluid behavior in a microscale porous structure called the wick. In this research, high-performance wicks made of polymer has been developed, and its pore distribution and permeability were evaluated. The effects of the vapor channel's shape on the loop's thermal performance have been investigated by calculation and experiment to enhance evaporator performance. A mathematical model of the evaporator considering super heat in the channel, pressure drop across the wick, and two-phase pressure loss on the boundary face between the wick and the evaporator case was newly developed. The experiment was also conducted as a function of the groove shapes. From calculation and test results, it was found that in order to increase the maximum heat transport capability and decrease the operating temperature, the groove should be well distributed.

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“…Additionally, several studies have been carried out over the last decades to recognize how the use insulation material can reduce the heat losses [Lewkowicz et al 2018]. Modeling of individual segments of thermal pumps was performed in the articles [Chen et al 2002, Cao and Faghri 1994, Nishikawara et al 2014. In the article [Chen et al 2002], a modeling of compressors was carried out and in the articles [Cao andFaghri 1994, Nishikawara et al 2014] a research on evaporators of thermal pumps was conducted.…”

Section: Introductionmentioning

confidence: 99%