Capillary Performance of Micropillar Arrays in Different Arrangements

Cho, Sangbeom; Tummala, Rao; Joshi, Yogendra

doi:10.1080/15567265.2018.1431749

Cited by 20 publications

(10 citation statements)

References 27 publications

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“…Micro-pin wicks with rectangular pin arrangement and 450-600 m m pin spacing showed the best capillary performance and were similar to the performance of electroplated copper micropins (Cho et al, 2018). Micro-pins in a rectangular arrangement are also more permeable compared to other pin arrangements and sintered-powder wicks, shown in Figure 11.…”

Section: Capillary Performance Comparisonmentioning

confidence: 66%

Section: Manufacturing Process Of Porous Wicks Via Laser Powder Bed Fusionmentioning

confidence: 99%

“…Non-AM wick fabrication processes for periodic microstructures, such as electroplating of square, hexagonal and rectangular pin arrangements (Cho et al, 2018), as well as micro machining of v-grooves, Zeng et al (2017) have been demonstrated. Cho et al (2018) found that, among silica-plated copper micro-pin structures with 45-80% porosity, rectangular arrangement provided the highest permeability, capillary performance and directionality in fluid flow (highest permeability along widest tracks). Other works have confirmed these findings (Hale et al, 2014a;Hale et al, 2014b), showing that rectangular arrangement provide higher capillary performance than the square arrangement due to a higher permeability with similar capillary pressure.…”

Section: Manufacturing Process Of Porous Wicks Via Laser Powder Bed Fusionmentioning

confidence: 99%

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Laser powder bed fusion additive manufacturing of copper wicking structures: fabrication and capillary characterization

Mezghani

Nassar

Dickman

et al. 2021

RPJ

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Purpose An integral component in heat pipes (HPs) and vapor chambers (VCs) is a porous wicking structure. Traditional methods for manufacturing wicking structures within HPs and VCs involve secondary manufacturing processes and are generally limited to simple geometries. This work aims to leverage the unprecedented level of design freedom of laser powder bed fusion (LPBF) additive manufacturing (AM) to produce integrated wicking structures for HPs and VCs. Design/methodology/approach Copper wicking structures are fabricated through LPBF via partial sintering and via the formation of square, hexagonal and rectangular arrangements of micro-pins and micro-grooves, produced in multiple build directions. Wicks are characterized by conducting capillary performance analysis through the measurement of porosity, permeability and capillary rate-of-rise. Findings Copper wicking structures were successfully fabricated with capillary performance, K/reff, ranging from 0.186–1.74 µm. The rectangular-arrangement micro-pin wick presented the highest performance. Originality/value This work represents the first published report on LPBF AM of copper wicking structures for HPs/VCs applications and represents foundational knowledge for fabricating complete assemblies of copper VCs and HPs through LPBF AM.

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Section: Capillary Performance Comparisonmentioning

confidence: 66%

Section: Manufacturing Process Of Porous Wicks Via Laser Powder Bed Fusionmentioning

confidence: 99%

Section: Manufacturing Process Of Porous Wicks Via Laser Powder Bed Fusionmentioning

confidence: 99%

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Laser powder bed fusion additive manufacturing of copper wicking structures: fabrication and capillary characterization

Mezghani

Nassar

Dickman

et al. 2021

RPJ

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“…For dense structures, . A variety of models have been proposed to predict the permeability of square micropillar arrays [23,31,32], among which the one by Yazdchi et al [32] has been shown to agree with experimental results for square micropillar arrays having both high and low porosities [33]. The capillary pressure calculated…”

Section: Superhydrophilicity Metric Calculationmentioning

confidence: 82%

A coupled wicking and evaporation model for prediction of pool boiling critical heat flux on structured surfaces

Weibel

Garimella

2019

International Journal of Heat and Mass Transfer

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Boiling is an effective heat transfer mechanism that is central to a variety of industrial processes including electronic systems, power plants, and nuclear reactors. Micro-/nanostructured surfaces have been demonstrated to significantly enhance the critical heat flux (CHF) during pool boiling, but there is no consensus on how to predict the structure-induced CHF enhancement. In this study, we develop an analytical model that takes into consideration key mechanisms that govern CHF during pool boiling on structured surfaces, namely, capillary wicking and evaporation of the liquid layer underneath the bubble. The model extends existing wicking-based CHF theories by introducing the competing evaporation mechanism. The model reveals a wicking-limited regime where CHF increases monotonically with the wicking flux, and an evaporation-limited regime where additional increases in the wicking flux do not significantly affect CHF. The model predictions are shown to agree with experimental CHF data from the literature for boiling of water on surfaces structured with square micropillar arrays. A parametric study is performed for such micropillared surfaces and has identified the optimal structure based on the competition between wicking and evaporation, capillary pressure and viscous resistance, and conduction and liquid-vapor interfacial resistance.

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“…Many efforts have tried to understand the governing physics and improve device performance. − Ravi et al fabricated different micropillar array wicks to assess the accuracy of various existing models for permeability and capillary pressure. An overall model for predicting the liquid mass flow rate was developed by combining two of the most accurate models.…”

Section: Introductionmentioning

confidence: 99%

Stable and Efficient Nanofilm Pure Evaporation on Nanopillar Surfaces

Wang

Sun

et al. 2021

Langmuir

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Molecular dynamics simulations were conducted to systematically investigate how to maintain and enhance nanofilm pure evaporation on nanopillar surfaces. First, the dynamics of the evaporation meniscus and the onset and evolution of nanobubbles on nanopillar surfaces were characterized. The meniscus can be pinned at the top surface of the nanopillars during evaporation for perfectly wetting fluid. The curvature of the meniscus close to nanopillars varies dramatically. Nanobubbles do not originate from the solid surface, where there is an ultrathin nonevaporation film due to strong solid–fluid interaction, but originate and evolve from the corner of nanopillars, where there is a quick increase in potential energy of the fluid. Second, according to a parametric study, the smaller pitch between nanopillars (P) and larger diameter of nanopillars (D) are found to enhance evaporation but also raise the possibility of boiling, whereas the smaller height of nanopillars (H) is found to enhance evaporation and suppress boiling. Finally, it is revealed that the nanofilm thickness should be maintained beyond a threshold, which is 20 Å in this work, to avoid the suppression effect of disjoining pressure on evaporation. Moreover, it is revealed that whether the evaporative heat transfer is enhanced on the nanopillar surface compared with the smooth surface is also affected by the nanofilm thickness. The value of nanofilm thickness should be determined by the competition between the suppression effect on evaporation due to the decrease in the volume of supplied fluid and the existence of capillary pressure and the enhancement effect on evaporation due to the increase in the heating area. Our work serves as the guidelines to achieve stable and efficient nanofilm pure evaporative heat transfer on nanopillar surfaces.

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Capillary Performance of Micropillar Arrays in Different Arrangements

Cited by 20 publications

References 27 publications

Laser powder bed fusion additive manufacturing of copper wicking structures: fabrication and capillary characterization

Laser powder bed fusion additive manufacturing of copper wicking structures: fabrication and capillary characterization

A coupled wicking and evaporation model for prediction of pool boiling critical heat flux on structured surfaces

Stable and Efficient Nanofilm Pure Evaporation on Nanopillar Surfaces

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