Heat Transfer in Porous Media Considering Phase Change, Capillarity and Gravity. Application to Capillary Evaporator

Figus, C.; Bray, Y. Le; Bories, Serge; Prat, Marc

doi:10.1615/ihtc11.4000

Cited by 4 publications

(3 citation statements)

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“…This achieves several advantages such as the ability to operate without electric power, a high heat-transfer capability, and a flexible framework. In previous research [1][2][3][4], various approaches have been proposed to enhance the thermal performance of an evaporator. In our work, a material of low thermal conductivity was used as the wick bulk to enhance the thermal performance of a miniature LHP [5].…”

Section: Introductionmentioning

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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Section: Introductionmentioning

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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“…The conditions promoting the easy flow of vapor into the groove have been investigated. For example, a biporous structure wick [12], a two-layer cylindrical wick in which the outer wick has higher permeability [13], and circumferential grooves on the wick outer diameter and microgrooves on the evaporator inner diameter [4] have been proposed and evaluated. In this work, a gap between the wick and the evaporator casing, which was initially proposed by Figus [14], is introduced and investigated experimentally.…”

Section: Introductionmentioning

confidence: 99%

“…Fig 13. Evaporator temperature and pressure difference of the evaporator on ethanol, acetone and R134a.…”

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confidence: 99%

Parametric experiments on a miniature loop heat pipe with PTFE wicks

Nishikawara

Nagano

2014

International Journal of Thermal Sciences

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A miniature loop heat pipe (LHP) with polytetrafluoroethylene (PTFE) wicks was fabricated and its evaporator thermal performance was investigated with parametric experiments. The variables considered were the clearance between the cylindrical evaporator casing and the wick, the working fluid inventory, the properties of the working fluids, and the sink temperature. Micro-gaps between the outer surface of the wick and inner surface of the evaporator casing were included in the experiments with variables of clearance to investigate their effect on the evaporator heat-transfer coefficient. Ethanol, acetone, and R134a were charged in the LHP to evaluate the effect of the properties of the working fluids. The LHP tests were conducted with several W/cm 2 of applied heat flux to the evaporator under controlled sink temperature. The clearance seriously affected the evaporator heat-transfer coefficient, with a gap of 20 μm between the wick and casing having the best effect on the evaporator heat transfer across a range of tested heat fluxes. The effects of the working fluid inventory and fluid properties on the evaporator heat transfer were also clarified.Finally, the developed LHP was tested using ethanol as a working fluid under a stepwise heat load and sink temperature.

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