Nanofiber coating of surfaces for intensification of drop or spray impact cooling

Srikar, R.; Gambaryan‐Roisman, Tatiana; Steffes, Clarissa; Stephan, Peter; Tropea, Cameron; Yarin, Alexander L.

doi:10.1016/j.ijheatmasstransfer.2009.07.021

Cited by 86 publications

(63 citation statements)

References 25 publications

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“…Related to this, the gas film equation for a flat plate (38) is parabolically degenerate, as the diffusion coefficient tends to zero for f small. For a permeable substrate, this is regularized by any non-zero product kh in (36), with the behaviour for f small being given by the parabolic equation…”

Section: Gas Behaviour In the Substratementioning

confidence: 99%

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Gas-cushioned droplet impacts with a thin layer of porous media

Hicks

Purvis

2015

J Eng Math

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The pre-impact gas cushioning behaviour of a droplet approaching touchdown onto a thin layer of porous substrate is investigated. Although the model is applicable to droplet impacts with any porous substrate of limited height, a thin layer of porous medium is used as an idealized approximation of a regular array of pillars, which are frequently used to produced superhydrophobic and superhydrophilic textured surface. Bubble entrainment is predicted across a range of permeabilities and substrate heights, as a result of a gas pressure build-up in the viscous-gas squeeze film decelerating the droplet free-surface immediately below the centre of the droplet. For a droplet of water of radius 1 mm and impact approach speed 0.5 m s −1 the change from a flat rigid impermeable plate to a porous substrate of height 5 µm and permeability 2.5 µm 2 reduces the initial horizontal extent of the trapped air pocket by 48%, as the porous substrate provides additional pathways through which the gas can escape. Further increases in either the substrate permeability or substrate height can entirely eliminate the formation of a trapped gas pocket in the initial touchdown phase, with the droplet then initially hitting the top surface of the porous media at a single point.Droplet impacts with a porous substrate are qualitatively compared to droplet impacts with a rough impermeable surface, which provides a second approximation for a textured surface. This indicates that only small pillars can be successfully modelled by the porous media approximation. The effect of surface tension on gas-cushioned droplet impacts with porous substrates is also investigated. In contrast to the numerical predictions of a droplet free-surface above flat plate, when a porous substrate is included the droplet free-surface touches down in finite time. Mathematically this is due to the regularization of the parabolic degeneracy associated with the small gas-film-height limit the gas squeeze film equation, by non-zero substrate permeability and height, and physically suggests that the level of surface roughness is a critical parameter in determining the initial touchdown characteristics.

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Section: Gas Behaviour In the Substratementioning

confidence: 99%

“…These correspond to no slip in the substrate (δ = 0) and the absence of velocity shear in the gas film (δ = 0 and α → ∞). In these cases the Reynolds lubrication equation (36) simplifies to give…”

Section: A Gas Cushioning With Alternative Forms Of the Beavers-josepmentioning

confidence: 99%

Gas-cushioned droplet impacts with a thin layer of porous media

Hicks

Purvis

2015

J Eng Math

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“…19,20 A recent ramification of such investigations encompassed drop impact onto nano-textured porous surfaces. [14][15][16][17][18][21][22][23][24][25][26] Such impacts are accompanied by nontrivial physical effects, which require understanding. In addition to the interesting physical aspects, the attention to drop impacts onto nano-textured porous surfaces was fueled by the interest in developing novel water-repelling surfaces, with electrospun Teflon nanofiber mats being a natural candidate.…”

Section: Introductionmentioning

confidence: 99%

Drop impacts on electrospun nanofiber membranes

et al. 2012

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This work reports a systematic study of drop impacts of polar and non-polar liquids onto different electrospun nanofiber membranes (of 8-10 mm thickness and pore sizes of 3-6 mm) with an increasing degree of hydrophobicity. The liquids studied were water, FC 7500 (Fluorinert fluid) and hexane. The nanofibers used were electrospun from polyacrylonitrile (PAN), nylon 6/6, polycaprolactone (PCL) and Teflon. It was found that for any liquid/fiber pair there exists a threshold impact velocity ($1.5 to 3 m s À1 ) above which water penetrates membranes irrespective of their hydrophobicity. The other liquids (FC 7500 and hexane) penetrate the membranes even more easily. The low surface tension liquid, FC 7500, left the rear side of sufficiently thin membranes as a millipede-like system of tiny jets protruding through a number of pores. For such a high surface tension liquid as water, jets immediately merged into a single bigger jet, which formed secondary spherical drops due to capillary instability. No mechanical damage to the nanofiber mats after liquid perforation was observed. A theoretical estimate of the critical membrane thickness sufficient for complete viscous dissipation of the kinetic energy of penetrating liquid is given and corroborated by the experimental data.

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“…A novel approach in drop and spray cooling of microelectronic devices employs coating of hot surfaces with electrospun non-woven polymer nanofiber mats [8,9]. Electrospun nanofiber mats are nano-textured permeable materials comprising of individual polymer nanofibers (with diameter of about several hundred nanometers) which are randomly orientated in the mat plane.…”

Section: Introductionmentioning

confidence: 99%

Nonisothermal drop impact and evaporation on polymer nanofiber mats

et al. 2011

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The work describes the experimental and theoretical investigation of water drop impact onto electrospun polymer nanofiber mats deposited on heated stainless steel foils. The measurements encompass water spreading over and inside the mat, as well as the corresponding thermal field. The results show that the presence of polymer nanofiber mats prevents receding motion of drops after their complete spreading and promotes the moisture spreading inside the mat over a large area of the heater, which facilitates a tenfold enhancement of heat removal as the latent heat of drop evaporation.

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Nanofiber coating of surfaces for intensification of drop or spray impact cooling

Cited by 86 publications

References 25 publications

Gas-cushioned droplet impacts with a thin layer of porous media

Gas-cushioned droplet impacts with a thin layer of porous media

Drop impacts on electrospun nanofiber membranes

Nonisothermal drop impact and evaporation on polymer nanofiber mats

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