Development of composite wicks having different thermal conductivities for loop heat pipes

Xin, Gongming; Zhang, Peng; Chen, Yan; Cheng, Lin; Huang, Teng; Yin, Hongyi

doi:10.1016/j.applthermaleng.2018.03.005

Cited by 28 publications

(7 citation statements)

References 31 publications

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“…As mentioned above, a large heat leak can increase the LHP operating temperature, make it difficult to start up the LHP and is one of the biggest challenges in flat evaporator LHP production. One of the ideas for solving the parasitic heating problem in flat evaporator LHPs is to select a non-metallic wick material such as silicon, ceramic, composite and polytetrafluoroethylene (PTFE) [41][42][43][44][45][46][47][48][49][50][51]. Owning their low thermal conductivity, these non-metallic materials wicks could significantly reduce a heat leak in flat LHP.…”

Section: Non-metallic and Composite Wicksmentioning

confidence: 99%

“…Moreover, LHP with a PTFE wick could reach a critical heat load of 600 W, while that of the LHP with a nickel wick was only 500 W. Therefore, the applications of the non-metallic wicks in high heat transfer capacity cooling devices still need more studies to be validated. Xin et al [48] presented an LHP with a composite wick having two different effective thermal conductivities as a solution of the heat leak problem, that is, wick has a higher thermal conductivity on the side close to the vapor channels and lower thermal conductivity on the side close to the liquid in the compensation chamber. The wick was constructed with the higher thermal conductivity on the side close to the phase change region and the lower thermal conductivity on the side close to the liquid in the compensation chamber, which helped to increase the power absorbed by the working fluid for phase change and prevent heat leak from the evaporator to the CC.…”

Section: Non-metallic and Composite Wicksmentioning

confidence: 99%

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Recent Advances in Loop Heat Pipes with Flat Evaporator

Szymański

Law

McGlen

et al. 2021

Entropy

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The focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle) between component and evaporator. However, various challenges exist in the implementation of flat-evaporator, including (1) deformation of the evaporator due to high internal pressure and uneven stress distribution in the non-circular casing; (2) heat leak from evaporator heating zone and sidewall into the compensation chamber; (3) poor performance at start-up; (4) reverse flow through the wick; or (5) difficulties in sealing, and hence frequent leakage. This paper presents and reviews state-of-the-art LHP technologies; this includes an (a) review of novel manufacturing methods; (b) LHP evaporator designs; (c) working fluids; and (d) construction materials. The work presents solutions that are used to develop or improve the LHP construction, overall thermal performance, heat transfer distance, start-up time (especially at low heat loads), manufacturing cost, weight, possibilities of miniaturization and how they affect the solution on the above-presented problems and challenges in flat shape LHP development to take advantage in the passive cooling systems for electronic devices in multiple applications.

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Section: Non-metallic and Composite Wicksmentioning

confidence: 99%

Section: Non-metallic and Composite Wicksmentioning

confidence: 99%

Recent Advances in Loop Heat Pipes with Flat Evaporator

Szymański

Law

McGlen

et al. 2021

Entropy

View full text Add to dashboard Cite

show abstract

“…Figure 8 shows the experimental maximum superheat ΔTsh,max,exp as a function of the theoretical value ΔTsh,max,th, determined with Eq. (12). The ΔTsh,max,exp / ΔTsh,max,th ratio, plotted with lines, quantifies the agreement between the experimental optimum superheat and the predicted one, a 100 % ratio (plain line) corresponding to a perfect agreement.…”

Section: Thermal Behaviour Of the Wick Saturated With Watermentioning

confidence: 87%

“…It highlights the motivation of authors to work on the fabrication of new wicks with advanced features, able to delay the development of the vapour inside the porous structure or able to evacuate it more easily. They also aim at limiting the heat leak to the reservoir [12]. These wicks can be biporous (Yeh et al [13], Li et al [14], Liu et al [15], Chen et al, ([16], [17])), bidispersed (Yu and Cheng [18], Chen et al [19]), bi-layered (Wu et al [20], Xu et al [21]) or threelayered (Ji et al [22]).…”

Section: Introductionmentioning

confidence: 99%

Effect of the wick characteristics on the thermal behaviour of a LHP capillary evaporator

Giraudon

Lips

Fabrègue

et al. 2018

International Journal of Thermal Sciences

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The present work aims at investigating the effect of the characteristics of porous wicks integrated in a flat diskshaped LHP evaporator on their thermal performance and operating limits. Several wicks were manufactured by sintering of copper powder following a design of experiment, and characterised in terms of permeability, porosity, pore radius and thickness. A specific test bench was designed, consisting of a LHP evaporator uncoupled from the condenser. Water and pentane were used as the working fluids. The theoretical capillary and boiling limits of the wicks in the test bench were studied and compared to the experimental data. It was observed that a high permeable wick (K > 10 -13 m²) is likely to reach the boiling limit before the capillary limit because the fluid easily percolates through it. The heat transfer coefficient between the evaporator wall and the evaporating fluid is significantly higher with pentane than with water. It reaches a maximum value of 2340 W.m -2 .K -1 with water and 5310 W.m -2 .K -1 with pentane, but no clear tendency could be highlighted concerning the effect of the wick characteristics on this parameter. The maximum dissipated heat transfer rate before the wick dry-out varies in a smaller range with pentane than with water. The highest measured values are equal to 88 kW.m -² with water and 56 kW.m -² with pentane.

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“…To reduce the occurrence of heat leakage from evaporator to compensation chamber, Xin et al (2018) proposed a composite LHP with different thermal conductivity wick, using nickel and copper. On the side close to the steam channel, the copper with high thermal conductivity was used to improve the heat conduction from the heat source to the capillary wick while the nickel powder with poor thermal conductivity was used at the compensation chamber to suppress heat leakage.…”

Section: Types and Materials Of Porous Wickmentioning

confidence: 99%

Research and Development of Loop Heat Pipe – A Review

Ji¹,

Guo²,

Xu³

2020

Frontiers in Heat and Mass Transfer

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With fast development of electronic devices, novel strategies of thermal management have been received great attention to dissipate high heat fluxes. As an efficient heat transfer device, loop heat pipe (LHP) provides ideal solution for such purpose. Even though LHP was invented nearly half-century ago, challenges still exist on its design, fabrication and operation. The objective of this paper is to present a thorough review on LHPs, paying more attention on the working principle, advantage and configuration. The review is performed in three aspects. First, the macroscopic operation characteristics such as start-up, temperature fluctuations and anti-gravity operation are described. Second, effects of various parameters or factors such as porous wick material, pore size and micro-structure on LHPs are reviewed. Third, new concept LHPs using biporous wick and wettability modification are discussed. Finally, perspective of LHPs is presented, which guides future research and development activities, from both fundamental and application point of view.

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Development of composite wicks having different thermal conductivities for loop heat pipes

Cited by 28 publications

References 31 publications

Recent Advances in Loop Heat Pipes with Flat Evaporator

Recent Advances in Loop Heat Pipes with Flat Evaporator

Effect of the wick characteristics on the thermal behaviour of a LHP capillary evaporator

Research and Development of Loop Heat Pipe – A Review

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