A novel method for characterization of liquid transport through micro-wicking arrays

Ravi, Saitej; Horner, David A.; Moghaddam, Saeed

doi:10.1007/s10404-013-1301-y

Cited by 21 publications

(24 citation statements)

References 32 publications

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“…Since the capillary and viscous pressures are coupled to pore size, the highest critical heat flux (CHF) are typically for sintered wicks with particle sizes of 250-355 µm using water. This CHF is~500 W/cm 2 with nucleate boiling in the wicking structure and 50-80 W/cm 2 with pure evaporation [13][14][15][16] , that is, without nucleate boiling. Similarly, the overall heat transfer coefficient (h = q″/ΔT) in traditional capillary-driven evaporation structures is dominated by heat conduction in the wicking structure as well as through the evaporating liquid film.…”

Section: Introductionmentioning

confidence: 99%

Nanoporous membrane device for ultra high heat flux thermal management

et al. 2018

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High power density electronics are severely limited by current thermal management solutions which are unable to dissipate the necessary heat flux while maintaining safe junction temperatures for reliable operation. We designed, fabricated, and experimentally characterized a microfluidic device for ultra-high heat flux dissipation using evaporation from a nanoporous silicon membrane. With~100 nm diameter pores, the membrane can generate high capillary pressure even with low surface tension fluids such as pentane and R245fa. The suspended ultra-thin membrane structure facilitates efficient liquid transport with minimal viscous pressure losses. We fabricated the membrane in silicon using interference lithography and reactive ion etching and then bonded it to a high permeability silicon microchannel array to create a biporous wick which achieves high capillary pressure with enhanced permeability. The back side consisted of a thin film platinum heater and resistive temperature sensors to emulate the heat dissipation in transistors and measure the temperature, respectively. We experimentally characterized the devices in pure vaporambient conditions in an environmental chamber. Accordingly, we demonstrated heat fluxes of 665 ± 74 W/cm 2 using pentane over an area of 0.172 mm × 10 mm with a temperature rise of 28.5 ± 1.8 K from the heated substrate to ambient vapor. This heat flux, which is normalized by the evaporation area, is the highest reported to date in the pure evaporation regime, that is, without nucleate boiling. The experimental results are in good agreement with a high fidelity model which captures heat conduction in the suspended membrane structure as well as non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work suggests that evaporative membrane-based approaches can be promising towards realizing an efficient, high flux thermal management strategy over large areas for high-performance electronics.

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Section: Introductionmentioning

confidence: 99%

Nanoporous membrane device for ultra high heat flux thermal management

et al. 2018

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“…This approach allows access to the main liquid bodies in the manifolds rather a limited amount of liquid left at the channel corners. Prior studies 32 33 34 35 on wicking characteristics of water within silicon micropillars have indicated that the optimal pillars spacing depends on the wicking length. Hence, the experimental studies discussed in the following section aim at finding the optimal spacing between pillars that can wick water along the channel length from the inlet and exit manifolds.…”

Section: Implementation Of Model In Design Of Full-scale Heat Sinksmentioning

confidence: 99%

Physics of microstructures enhancement of thin film evaporation heat transfer in microchannels flow boiling

Bigham

Fazeli

Moghaddam

2017

Sci Rep

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Performance enhancement of the two-phase flow boiling heat transfer process in microchannels through implementation of surface micro- and nanostructures has gained substantial interest in recent years. However, the reported results range widely from a decline to improvements in performance depending on the test conditions and fluid properties, without a consensus on the physical mechanisms responsible for the observed behavior. This gap in knowledge stems from a lack of understanding of the physics of surface structures interactions with microscale heat and mass transfer events involved in the microchannel flow boiling process. Here, using a novel measurement technique, the heat and mass transfer process is analyzed within surface structures with unprecedented detail. The local heat flux and dryout time scale are measured as the liquid wicks through surface structures and evaporates. The physics governing heat transfer enhancement on textured surfaces is explained by a deterministic model that involves three key parameters: the drying time scale of the liquid film wicking into the surface structures (τd), the heating length scale of the liquid film (δH) and the area fraction of the evaporating liquid film (Ar). It is shown that the model accurately predicts the optimum spacing between surface structures (i.e. pillars fabricated on the microchannel wall) in boiling of two fluids FC-72 and water with fundamentally different wicking characteristics.

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“…where 2 is the permeability from Sangani and Acrivos [17]. The expression in the bracket is a correction factor for the porous nature of the transporting medium (i.e., Brinkman equation) where as 1 and 2 are correction factors for the variation in wetted and cross-sectional areas, respectively [18,19]. Depending on the heat flux and the evaporation rate, the liquid meniscus dynamically adjusts its curvature to maintain steady-state evaporation.…”

Section: Modelingmentioning

confidence: 99%

Experimental Characterization and Modeling of Capillary-Pumped Thin-Film Evaporation From Micropillar Wicks

Adera

Antao

Raj

et al. 2016

ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels

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Generation of concentrated heat load in confined spaces in integrated circuits and advanced microprocessors has presented a thermal management challenge for the semiconductor industry. Compared to state-of-the-art single phase cooling strategies, phase-change based approaches are promising for cooling the next generation microelectronic devices. In particular, thin-film evaporation from engineered surfaces has received significant attention in the last few decades as a potential candidate since it enables passive transport of the working fluid via capillarity in addition to increasing the evaporation area via extending the liquid meniscus and three-phase contact line. Thin-film evaporation, however, is coupled with nucleate boiling making experimental characterization as well as modeling of the fluidic and thermal transport a challenging task for thermal engineers. Furthermore, quantifying the relative contributions of nucleate boiling and thin-film evaporation from the experimentally reported heat fluxes has been difficult. Unlike previous studies, our work experimentally characterizes thin-film evaporation in the absence of nucleate boiling from arrays of silicon micropillars. In particular, we characterize the capillary-limit where the microstructured surface dries out due to liquid starvation when the capillary pressure that is generated due to the meniscus shape cannot overcome the viscous losses within the micropillar wick. We modeled the fluidic and thermal transport of the evaporating meniscus by solving the coupled heat and mass transfer equations. Compared to experiments, our model predicts the dryout heat flux with ±20% accuracy. The insights gained from this study provide a suitable platform to design and optimize micropillar wicks for phase-change based thermal management devices such as heat pipes and vapor chambers.

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A novel method for characterization of liquid transport through micro-wicking arrays

Cited by 21 publications

References 32 publications

Nanoporous membrane device for ultra high heat flux thermal management

Nanoporous membrane device for ultra high heat flux thermal management

Physics of microstructures enhancement of thin film evaporation heat transfer in microchannels flow boiling

Experimental Characterization and Modeling of Capillary-Pumped Thin-Film Evaporation From Micropillar Wicks

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