Can Wicking Control Droplet Cooling?

Auliano, Manuel; Auliano, Damiano; Fernandino, María; Asinari, Pietro; Dorao, Carlos Alberto

doi:10.1021/acs.langmuir.9b00548

Cited by 20 publications

(16 citation statements)

References 61 publications

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“…A high-speed camera is mounted overhead the arrangement to visualize wicking from the top, while a side camera at an inclination of 12 o is used to monitor the temporal variation of the amount of liquid sitting on the top. As the nanochannels are mostly closed (buried) with openings only at micropores, water wicks to much larger distances compared to open structures ,,,, as we have reduced evaporation compared to capillary flow; this allows us to visualize and detect the wicking front with ease. The two cameras are synchronized based on the instant when the droplet touches the surface, and the maximum error in synchronization is estimated to be 0.053 s based on the frame rates.…”

Section: Methodsmentioning

confidence: 99%

“…Thin-film evaporation manifests itself in nearly all evaporation processes, − and surfaces are designed to amplify its occurrence to achieve high heat flux removal. ,, For example, over the past few years, micro/nanostructures have been fabricated on surfaces to passively wick the liquid and augment thin-film meniscus area, thus enhancing heat transfer. ,,,− The way in which liquid is supplied to such structured surfaces gives rise to two distinct scenarios, first where the surface is partially submerged in a pool of bulk liquid thus providing unlimited supply of liquid to the structures , and second where liquid supply to the structured surface is limited but recurs at regular intervals. An example of the latter is spray cooling ,, where micro/macrosized droplets are dispersed, at a desired frequency, onto a heated surface where the droplets wick into the structures creating thin-film regions.…”

Section: Introductionmentioning

confidence: 99%

“…Challenges arise due to the dynamic and transient nature of interaction between the thin-film menisci present within the structures with the continuously changing droplet’s interfacial curvature as well as decreasing droplet volume. Consequently, wicking experiments to study droplet evaporation dynamics on heated structured surfaces at temperatures below nucleation have been sparsely conducted, ,− as structures are open to the environment resulting in small wicking distances. In order to optimize structure/liquid supply design and maximize heat flux removal, estimations of heat flux in micro/nanostructures as well as at the surface, along with dryout limits, are important.…”

Section: Introductionmentioning

confidence: 99%

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Droplet Evaporation on Porous Nanochannels for High Heat Flux Dissipation

Poudel

Zou

Maroo

2020

ACS Appl. Mater. Interfaces

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Droplet wicking and evaporation in porous nanochannels is experimentally studied on a heated surface at temperatures ranging from 35 o C to 90 o C. The fabricated geometry consists of cross-connected nanochannels of height 728 nm with micropores of diameter 2 µm present at every channel intersection; the pores allow water from a droplet placed on the top surface to wick into the channels. Droplet volume is also varied and a total of 16 experimental cases are conducted. Wicking characteristics such as wicked distance, capillary pressure, viscous resistance and propagation coefficient are obtained at the high surface temperatures. Evaporation flux from the nanochannels/micropores is estimated from the droplet experiments, but is also independent confirmed via a new set of experiments where water is continuously fed to the sample through a microtube such that it matches the evaporation rate. High heat flux as high as ~294 W/cm 2 is achieved from channels and pores. The experimental findings are applied to evaluate the use of porous nanochannels geometry in spray cooling application, and is found to be capable of dissipating high heat fluxes upto ~77 W/cm 2 at temperatures below nucleation, thus highlighting the thermal management potential of fabricated geometry.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Droplet Evaporation on Porous Nanochannels for High Heat Flux Dissipation

Poudel

Zou

Maroo

2020

ACS Appl. Mater. Interfaces

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“…This typical example can be considered as a base line for studying capillary flow in micro/nano structured surface in association with phase change heat transfer enhancement. Similar concept for studying the magnitude of liquid spread/rise has been applied and proved experimentally and computationally by various researchers [15][16][17][18][19][20][21][22][23] which is elaborated in Table I.…”

Section: A Role Of Micro/nano Structures In Chf Enhancementmentioning

confidence: 98%

Advances in Boiling Heat Transfer Enhancement using Micro/Nano Structured Surfaces

Agarwal¹,

Kumar²

2019

EJERS

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In this article we present an inclusive review of research carried out in the field of phase change heat transfer enhancement. First, we discuss about different kinds of conventional heat transfer enhancement techniques performed in convection heat transfer related heat exchangers. Next, we present the advantages of implementing phase change heat transfer and report a brief introduction to the physics behind the phase change (boiling) heat transfer phenomenon. We present a well explained data about different kinds of enhancement techniques using micro and nano scale structures on heat transfer surface/device to increase the limit of boiling heat transfer. The entire review article is broadly divided into two categories: first the investigation related to fluid flow or transport mechanism over the micro/nano structured surface which is of crucial importance, second is the actual computational and experimental methods to achieve higher heat transfer capability in terms of critical heat flux (CHF) for a given surface/device. From the ongoing work, we are able to conclude and put forward three major stages of doing research in CHF enhancement using micro/nano structures/devices viz.: (i) selection and construction of micro/nano structures, (ii) perceiving the fluid transport through capillary over the micro/nano structured surface and (iii) actual experiment/computation to compare CHF of modified device with the base device.

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“…Superior wettability of wicking surfaces marks their potential to be used in the field of thermal management and various lab-on-a-chip applications. , Porosity is a major factor in determining the extent of wicking in such surfaces, along with surface tension, viscous forces, gravity, and evaporation . The design and fabrication of a wicking surface can result in an approximate (random porous structures − such as nanowires) or accurate (uniform geometries − such as micropillars) theoretical estimation of its porosity. This work focuses on the latter as precise knowledge of porosity is critical for modeling, understanding, and predicting the wicking phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Evaporation Dynamics in Buried Nanochannels with Micropores

2020

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Cross-connected buried nanochannels of height ∼728 nm, with micropores of ∼2 μm diameter present at each intersection, are used in this work to numerically and experimentally study droplet-coupled evaporation dynamics at room temperature. The uniformly structured channels/pores, along with their well-defined porosity, allow for computational fluid dynamics simulations and experiments to be performed on the same geometry of samples. A water droplet is placed on top of the sample causing water to wick into the nanochannels through the micropores. After advancing, the meniscus front stabilizes when evaporation flux is balanced with the wicking flux, and it recedes once the water droplet is completely wicked in. Evaporation flux at the meniscus interface of channels/pores is estimated over time, while the flux at the water droplet interface is found to be negligible. When the meniscus recedes in the channels, local contact line regions are found to form underneath the pores, thus rapidly enhancing evaporation flux as a power-law function of time. Temporal variation of wicking flux velocity and pressure gradient in the nanochannels is also independently computed, from which the viscous resistance variation is estimated and compared to the theoretical prediction.

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Can Wicking Control Droplet Cooling?

Cited by 20 publications

References 61 publications

Droplet Evaporation on Porous Nanochannels for High Heat Flux Dissipation

Droplet Evaporation on Porous Nanochannels for High Heat Flux Dissipation

Advances in Boiling Heat Transfer Enhancement using Micro/Nano Structured Surfaces

Evaporation Dynamics in Buried Nanochannels with Micropores

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