Optimization of capillary flow through square micropillar arrays

Hale, Renee; Bonnecaze, Roger T.; Hidrovo, Carlos

doi:10.1016/j.ijmultiphaseflow.2013.08.003

Cited by 40 publications

(23 citation statements)

References 29 publications

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“…Figure 5b plots the measured and theoretically calculated imbibition times for the micro-textured surfaces at different micropillar spacings b corresponding to an imbibed length of L =2.5 mm. First, we note that the predictions of the scaling imbibition model, which are almost the same as that of a more complex solution 45 49 50 based on the Brinkman equation, agree reasonably well with the experimental data at low to moderate micropillar spacings ( b ≤10 μm). For larger micropillar spacings, the thickness of the imbibed liquid microlayer t i is expected to be less than the height of the micropillars.…”

Section: Resultssupporting

confidence: 69%

“…( b ) Plot of the experimentally measured and theoretically calculated imbibition time τ i for 10 cSt silicone oil to imbibe to a length of 2.5 mm versus the micropillar spacing b of the micro-textured surfaces. The predictions of the simpler scaling imbibition model are almost the same as that of a more complex Brinkman model 45 49 50 . The imbibition models agree with the experimental data corresponding to an imbibed liquid microlayer thickness t i equal to the micropillar height h for b ≤10 μm and t i ∼4 μm for b >10 μm.…”

Section: Figurementioning

confidence: 60%

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Critical heat flux maxima during boiling crisis on textured surfaces

2015

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Enhancing the critical heat flux (CHF) of industrial boilers by surface texturing can lead to substantial energy savings and global reduction in greenhouse gas emissions, but fundamentally this phenomenon is not well understood. Prior studies on boiling crisis indicate that CHF monotonically increases with increasing texture density. Here we report on the existence of maxima in CHF enhancement at intermediate texture density using measurements on parametrically designed plain and nano-textured micropillar surfaces. Using high-speed optical and infrared imaging, we study the dynamics of dry spot heating and rewetting phenomena and reveal that the dry spot heating timescale is of the same order as that of the gravity and liquid imbibition-induced dry spot rewetting timescale. Based on these insights, we develop a coupled thermal-hydraulic model that relates CHF enhancement to rewetting of a hot dry spot on the boiling surface, thereby revealing the mechanism governing the hitherto unknown CHF enhancement maxima.

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Section: Resultssupporting

confidence: 69%

Section: Figurementioning

confidence: 60%

Critical heat flux maxima during boiling crisis on textured surfaces

2015

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“…Micro-pins in a rectangular arrangement are also more permeable compared to other pin arrangements and sintered-powder wicks, shown in Figure 11. This is due to the presence of larger flow channels in a rectangular pin arrangement, which results in larger permeability to liquid flow, and with the combination of small pin-to-pin spacing, a higher overall capillary performance is achievedthis also reinforces the findings of Hale et al (2014a) and Hale et al (2014b).…”

Section: Capillary Performance Comparisonsupporting

confidence: 67%

“…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. However, rectangular pins show significant anisotropy in fluid flow; in comparison, hexagonal arrangement performed most similarly to sintered wicks in isotropy of capillary flow.…”

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

confidence: 59%

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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“…Permeability is a key parameter to determine and optimize the liquid flow rate through the micropillar array. Hale et al [18] had a comprehensive study on the micropillar array permeability by comparing several permeability models including Yazdchi et al [19], Tamayol and Bahrami [20], Xiao et al [21] and an analytical solution derived from a 2dimensional velocity profile with appropriately varying boundary conditions. In the present work, a combination of Xiao with Yazdchi's models is used to predict the micropillar array permeability [18]:…”

Section: Modelingmentioning

confidence: 99%

Modeling the Performance of Bi-Textured Micropillar Array as a Wicked Evaporator

Azarkish

Behzadmehr

Fréchette

2016

Volume 2: Heat Transfer in Multiphase Systems; Gas Turbine Heat Transfer; Manufacturing and Materials Processing; Heat Transfer

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In the present work, the performance of bi-textured micro pillar arrays has been modeled as a wicked evaporator to provide steam flow via the thin film evaporation mechanism. Bi-textured micro pillar evaporator consists of an array with rough hydrophilic pillar bases and smooth hydrophobic tips. Water wicks between the rough hydrophilic sections of the micro pillar array to cover the surface, and vaporizes from the thin films that are formed in the vicinity of the pillar walls. The stability of the phase change mechanism is increased due to the change in direction of the capillary forces at the rough-smooth interface of micro pillars. The experimental results show that the pure evaporation mechanism occurs for a surface temperature above saturation on the bi-textured micro pillar array. The numerical analysis shows that there are optimal micro pillar dimensions for each surface temperature. The evaporation mass flow rate at the optimum dimensions is higher than the pool boiling mass flow rate on a bare surface at the same surface temperature. However, the wicked evaporator performance decreases for larger evaporator sizes.

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Optimization of capillary flow through square micropillar arrays

Cited by 40 publications

References 29 publications

Critical heat flux maxima during boiling crisis on textured surfaces

Critical heat flux maxima during boiling crisis on textured surfaces

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

Modeling the Performance of Bi-Textured Micropillar Array as a Wicked Evaporator

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