Performance of compressed nickel foam wicks for flat vertical heat pipes

Hansen, Geir Karsten; Næss, Erling

doi:10.1016/j.applthermaleng.2015.02.040

Cited by 15 publications

(7 citation statements)

References 19 publications

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“…From a series of capillary rise experiments with nickel foam wicks and heptane the contact angle of heptane on nickel was determined to 58.4° [23]. For potassium on nickel a contact angle of 0° was assumed [21].…”

Section: The Contact Anglementioning

confidence: 99%

Sintered Nickel Powder Wicks for Flat Vertical Heat Pipes

2015

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Abstract:The fabrication and performance of wicks for flat heat pipe applications produced by sintering a filamentary nickel powder has been investigated. Tape casting was used as an intermediate step in the wick production process. Thermogravimetric analysis was used to study the burn-off of the organic binder used and to study the oxidation and reduction processes of the nickel. The wicks produced were flat, rectangular and intended for liquid transport in the upwards vertical direction. Rate-of-rise experiments using heptane were used to test the flow characteristics of the wicks. The wick porosities were measured using isopropanol. The heat transfer limitation constituted by the vapour static pressure and the capillary pressure was discussed. The influence on wick performance by using pore former in the manufacturing was studied. When Pcap/Psat > 1, the use of a pore former to increase the wick permeability will always improve the wick performance. When Pcap/Psat < 1, it was shown that if the effective pore radius and the permeability increase with an equal percentage the overall influence on the wick capacity is negative. A criterion for a successful pore former introduction is proposed and the concept of a pore former evaluation plot is presented.

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Section: The Contact Anglementioning

confidence: 99%

Sintered Nickel Powder Wicks for Flat Vertical Heat Pipes

2015

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“…Ji et al and Hansen et al [13,22] explored the performance of highly porous copper and nickel foam wicks that were sintered to the inner surface of their vapour chambers. Ji et al [13] showed that the high porosity and multiscale size of the copper foams enhanced the heat transfer rate and delayed the onset of CHF.…”

Section: Introductionmentioning

confidence: 99%

A novel ultra-large flat plate heat pipe manufactured by thermal spray

Feng

Gibbons

Marengo

et al. 2020

Applied Thermal Engineering

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An ultra-large flat plate copper heat pipe (180 x 180 mm 2) was constructed using a thermal spray technique, and it was then thermally characterized. A porous copper wick was fabricated by using a flame spray torch to deposit a mixture of copper and aluminum particles onto the target substrate. A stainless-steel wire mesh acts as a mask so that the coating deposited is in the form of an array of microstructures with channels between them. After spraying, the aluminum deposit is leached away by immersing the plate in a dilute NaOH solution to produce a porous structure. A second copper plate was placed on top of the coated surface, and their edges were vacuum brazed to form a sealed enclosure. The enclosed volume was evacuated and partially filled with water to form a heat pipe. The heat pipe was centrally heated from its bottom and cooled along its top outer edge. Three liquid filling ratios and six heat fluxes from 2.5 W/cm 2 to 15 W/cm 2 were investigated. A decreasing lateral thermal resistance for an increasing applied heat flux was noted for all filling ratios until central dry-out. Central dry-out corresponds to the point where the evaporation rate outpaces the wicking of the working fluid at the centre of the heat pipe. Dry-out of the central wick results in a large thermal resistance compared to the pre-dry-out condition. Delayed dry-out onset was noted for increasing working fluid filling ratios. In the pre-dry-out condition, a peak average radial thermal conductivity of 920 W/m K was noted for a 65% filling ratio, and 7.5 W/cm 2 applied heat flux. A model was generated to calculate dry-out of the thermally sprayed porous wick for a given filling ratio and applied heat flux. The present research represents two highly novel advances in heat pipe technology. The first is the development of a new innovative manufacturing technique for the generation of a porous wick structure within a heat pipe. This new manufacturing technique enables the production of large metal vapour chambers with complex 3D geometries. When applied in conjunction with copper compatible working fluids, this techniques facilitates the realization of skin thermal conductors. Second, the fabrication of an ultra-large flat plate heat pipe that is significantly larger than that previously reported in the literature is demonstrated.

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“…The large uncertainty indicated in Figure 6 by the high and low vapor static pressure limit curves and the high and low capillary pressure limit curves is a result of the uncertainty of the permeability of the compressed wick, which was calculated to˘26% [12]. In general, from Equation (5), the heat transfer capacity will increase by decreased effective pore radius and/or increased permeability.…”

Section: Performance Limitations Of the Wick Analytical And Experimmentioning

confidence: 99%

“…The total heat transfer capacity (in Watts) of a vertical flat wick exposed to a uniform heat flux is obtained by inserting Equations (2)- (4) into Equation (1) [12]:…”

Section: Wick Performancementioning

confidence: 99%

“…Faghri [3] divided wicks into two groups; homogeneous and composite, and stated that homogeneous wicks are usually chosen due to simple design, manufacture, and installation (i.e., lower costs), even though the composite wicks usually have better performance. Wicks can be made of compressed nickel foam, and the development and testing of such wicks were reported in an earlier paper [12]. This type of wick has the advantage that the wick properties can be selected within a wide range by choosing the degree of compression [13].…”

Section: Introductionmentioning

confidence: 99%

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Analysis of a Vertical Flat Heat Pipe Using Potassium Working Fluid and a Wick of Compressed Nickel Foam

2016

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Heat at high temperatures, in this work 400-650˝C, can be recovered by use of cooling panels/heat pipes in the walls of aluminum electrolysis cells. For this application a flat vertical heat pipe for heat transfer from a unilateral heat source was analyzed theoretically and in the laboratory, with special emphasis on the performance of the wick. In this heat pipe a wick of compressed nickel foam covered only the evaporator surface, and potassium was used as the working fluid. The magnitudes of key thermal resistances were estimated analytically and compared. Operating temperatures and wick performance limits obtained experimentally were compared to predictions. Thermal deformation due to unilateral heat flux was analyzed by the use of COMSOL Multiphysics ® . The consequences of hot spots at different locations on the wick were analyzed by use of a numerical 2D model. A vertical rectangular wick was shown to be most vulnerable to hot spots at the upper corners.

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Performance of compressed nickel foam wicks for flat vertical heat pipes

Cited by 15 publications

References 19 publications

Sintered Nickel Powder Wicks for Flat Vertical Heat Pipes

Sintered Nickel Powder Wicks for Flat Vertical Heat Pipes

A novel ultra-large flat plate heat pipe manufactured by thermal spray

Analysis of a Vertical Flat Heat Pipe Using Potassium Working Fluid and a Wick of Compressed Nickel Foam

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