Physics of Fluid Transport in Hybrid Biporous Capillary Wicking Microstructures

Ravi, Saitej; Dharmarajan, R.; Moghaddam, Saeed

doi:10.1021/acs.langmuir.6b01611

Cited by 32 publications

(16 citation statements)

References 34 publications

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“…Woven screens have attracted considerable attention due to their physical durability and superior thermal resistance. − Ravi et al analyzed the physics of the capillary limit and dry out in a copper screen suspended over a homogeneous micropillar array, where the mass transport capacity is affected by the global change in the curvature of the liquid–vapor meniscus. Radial capillary transport within a metal woven screen was theoretically and experimentally investigated by Conrath et al An analytical solution is obtained in terms of time versus the wicking radius.…”

Section: Introductionmentioning

confidence: 99%

Flow Physics of Wicking into Woven Screens with Hybrid Micro-/Nanoporous Structures

et al. 2021

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Wicking within woven screens has attracted considerable attention due to its important role in applications concerning phase-change heat transfer and phase separation. In the present study, horizontal spreading experiments are conducted to investigate the wicking performance of woven screens by measuring the volumetric liquid intake into the screens and the liquid propagation fronts through two perpendicular high-speed cameras. Woven screens with micro (single- and multilayer)- and nano (plain, etched, and fluoridated)-porous structures are manipulated through diffusion bonding and chemical processes. The macroscopic observation indicates the substantial enhancement of the wicking capability in multilayer structures, where the interlayer microchannels could compensate for the essential deficiency of single-layer screens by providing low-resistance flow passages. Wicking capability of water is enhanced by the hydrophilic nanograsses along the wires. Furthermore, flow mechanisms within the screens are analyzed by comparisons between apparent and saturated wicking distances. In multilayer structures, the liquid spreads along the entire cross-sectional area in etched screens, while it spreads primarily along the interlayer microchannels in plain and fluoridated screens. The influence of various fluids on the wicking behavior within the woven screens is found to be fully represented by a unique parameter that captures the effects of surface tension and dynamic viscosity in the radial flow model. This work deepens the understanding of the capillary-driven flow within the woven screens with hybrid micro-/nanoporous structures and provides guidance for the design and manufacture of highly efficient wicking structures.

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Section: Introductionmentioning

confidence: 99%

Flow Physics of Wicking into Woven Screens with Hybrid Micro-/Nanoporous Structures

et al. 2021

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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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“…al. [13] investigated the fluid transportation in in-plane hybrid biporous evaporator and out-of-plane biporous evaporator with a porous mesh suspended over uniform micropillar arrays. Out-of-plane biporous evaporators' dryout performance was found to be profoundly influenced by the mesh thickness.…”

Section: Introductionmentioning

confidence: 99%

A Comprehensive Study of Silicon Micropillar Based Biporous Evaporator

Wei¹,

He²,

Liang³

et al. 2017

World Congress on Mechanical, Chemical, and Material Engineering

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-Silicon micropillar based evaporators were proven to be good candidates in advanced vapor chambers, due to their high permeability, excellent capillary performance and ease of control over the fabrication process. In this paper, biporous silicon micropillar based evaporator with microchannels to shorten the fluid transportation distance was studied comprehensively. Semianalytical model in predicting the dryout heat flux of biporous evaporator was developed. Evaporator samples with different microchannel widths were fabricated and tested. Sample with geometries of d = 3.4 μm, h = 9.00 μm, l=6 μm, l i =101.0 μm, w = 58.5 μm was able to demonstrate a dryout heat flux q''= 55.9 W/cm 2. This has a difference of only 9.0 % compared to the model predicted dryout heat flux. The biporous evaporator was found to have a gentle drop of heat transfer coefficient after dryout, owing to the existence of microchannels that can shorten the fluid propagation distance. Samples with wider microchannels were found to have larger superheat values, due to the smaller thin film evaporation areas of these sample. This paper provided great insights into the investigation of biporous evaporators and can serve as important design guidance for biporous evaporator utilized in advanced vapor chamber.

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Physics of Fluid Transport in Hybrid Biporous Capillary Wicking Microstructures

Cited by 32 publications

References 34 publications

Flow Physics of Wicking into Woven Screens with Hybrid Micro-/Nanoporous Structures

Flow Physics of Wicking into Woven Screens with Hybrid Micro-/Nanoporous Structures

Stable and Efficient Nanofilm Pure Evaporation on Nanopillar Surfaces

A Comprehensive Study of Silicon Micropillar Based Biporous Evaporator

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