48 research outputs found
Self-Sustained Cascading Coalescence in Surface Condensation
No full textISSN:1944-8244ISSN:1944-8252ISSN:1944-825
Thermal control for the two-beam module of the compact linear collider with computational fluid dynamics simulations of conjugate heat transfer problems, with subsidiary finite-element simulations
No full textConjugate heat transfer simulations were performed for the two-beam module of the Compact Linear Collider (CLIC). A full approach using ANSYS Fluent is presented for the determination of heat dissipation values from the main beam portion of the module to the cooling air and water. A transient model for heat dissipated through the tunnel to the outside soil is presented as well. Structural stress-strain simulations and modal analyses were performed for the adjustable supports with the finite-element method using ANSYS Mechanical. The operating range of the adjustable supports was determined
Self-Sustained Cascading Coalescence in Surface Condensation
No full textSustained
dropwise condensation of water requires rapid shedding of condensed
droplets from the surface. Here, we elucidate a microfluidic mechanism
that spontaneously sweeps condensed microscale droplets without the
need for the traditional droplet removal pathways such as use of superhydrophobicity
for droplet rolling and jumping and utilization of wettability gradients
for directional droplet transport among others. The mechanism involves
self-generated, directional, cascading coalescence sequences of condensed
microscale droplets along standard hydrophobic microgrooves. Each
sequence appears like a spontaneous zipping process, can sweep droplets
along the microgroove at speeds of up to ∼1 m/s, and can extend
for lengths more than 100 times the microgroove width. We investigate
this phenomenon through high-speed in situ microscale condensation
observations and demonstrate that it is enabled by rapid oscillations
of a condensate meniscus formed locally in a filled microgroove and
pinned on its edges. Such oscillations are in turn spontaneously initiated
by coalescence of an individual droplet growing on the ridge with
the microgroove meniscus. We quantify the coalescence cascades by
characterizing the size distribution of the swept droplets and propose
a simple analytical model to explain the results. We also demonstrate
that, as condensation proceeds on the hydrophobic microgrooved surface,
the coalescence cascades recur spontaneously through repetitive dewetting
of the microgrooves. Lastly, we identify surface design rules for
consistent realization of the cascades. The hydrophobic microgrooved
textures required for the activation of this mechanism can be realized
through conventional, scalable surface fabrication methods on a broad
range of materials (we demonstrate with aluminum and silicon), thus
promising direct application in a host of phase-change processes
Inhibition of condensation-induced droplet wetting by nano-hierarchical surfaces
No full textSuperhydrophobic nanostructured surfaces can enhance water condensation efficiency by facilitating droplet departure via coalescence-induced jumping. However, condensed droplets tend to transit from a mobile jumping mode to a highly pinned state at high condensation heat flux because excessive water nucleates within the nanostructures and anchors the condensed droplets. The large pinned droplets act as a thermal barrier and insulate the cooling surface, thus severely degrading its heat transfer efficiency. This work developed a nano-hierarchical structured surface by growing branched TiO2 nanorod arrays to prevent condensation-induced droplet pinning. After hydrophobization, the nano-hierarchical structure can spontaneously push the water out of nanostructures with an outward Laplace capillary pressure gradient when the droplet size is only at the nanoscale level. This effective de-wetting process maintains the high droplet mobility on the nano-hierarchical surface over a wide subcooling range, resulting in an up to ∼ 90 % increase in heat transfer coefficient at a high heat flux of 132 kW∙m−2 compared to the single-tier nanorod surface. Our investigation of how the nano-hierarchical structures fundamentally suppress the condensation-induced wetting on superhydrophobic surfaces represents a significant advance in understanding multiphase wetting phenomena and paves the way for the rational design of cooling surfaces.</p
Self-Sustained Cascading Coalescence in Surface Condensation
No full textSustained
dropwise condensation of water requires rapid shedding of condensed
droplets from the surface. Here, we elucidate a microfluidic mechanism
that spontaneously sweeps condensed microscale droplets without the
need for the traditional droplet removal pathways such as use of superhydrophobicity
for droplet rolling and jumping and utilization of wettability gradients
for directional droplet transport among others. The mechanism involves
self-generated, directional, cascading coalescence sequences of condensed
microscale droplets along standard hydrophobic microgrooves. Each
sequence appears like a spontaneous zipping process, can sweep droplets
along the microgroove at speeds of up to ∼1 m/s, and can extend
for lengths more than 100 times the microgroove width. We investigate
this phenomenon through high-speed in situ microscale condensation
observations and demonstrate that it is enabled by rapid oscillations
of a condensate meniscus formed locally in a filled microgroove and
pinned on its edges. Such oscillations are in turn spontaneously initiated
by coalescence of an individual droplet growing on the ridge with
the microgroove meniscus. We quantify the coalescence cascades by
characterizing the size distribution of the swept droplets and propose
a simple analytical model to explain the results. We also demonstrate
that, as condensation proceeds on the hydrophobic microgrooved surface,
the coalescence cascades recur spontaneously through repetitive dewetting
of the microgrooves. Lastly, we identify surface design rules for
consistent realization of the cascades. The hydrophobic microgrooved
textures required for the activation of this mechanism can be realized
through conventional, scalable surface fabrication methods on a broad
range of materials (we demonstrate with aluminum and silicon), thus
promising direct application in a host of phase-change processes
Inhibition of condensation-induced droplet wetting by nano-hierarchical surfaces
No full textISSN:0300-9467ISSN:1385-8947ISSN:1873-3212ISSN:0923-0467ISSN:1385-8947ISSN:1873-3212ISSN:0923-046
Self-Sustained Cascading Coalescence in Surface Condensation
No full textSustained
dropwise condensation of water requires rapid shedding of condensed
droplets from the surface. Here, we elucidate a microfluidic mechanism
that spontaneously sweeps condensed microscale droplets without the
need for the traditional droplet removal pathways such as use of superhydrophobicity
for droplet rolling and jumping and utilization of wettability gradients
for directional droplet transport among others. The mechanism involves
self-generated, directional, cascading coalescence sequences of condensed
microscale droplets along standard hydrophobic microgrooves. Each
sequence appears like a spontaneous zipping process, can sweep droplets
along the microgroove at speeds of up to ∼1 m/s, and can extend
for lengths more than 100 times the microgroove width. We investigate
this phenomenon through high-speed in situ microscale condensation
observations and demonstrate that it is enabled by rapid oscillations
of a condensate meniscus formed locally in a filled microgroove and
pinned on its edges. Such oscillations are in turn spontaneously initiated
by coalescence of an individual droplet growing on the ridge with
the microgroove meniscus. We quantify the coalescence cascades by
characterizing the size distribution of the swept droplets and propose
a simple analytical model to explain the results. We also demonstrate
that, as condensation proceeds on the hydrophobic microgrooved surface,
the coalescence cascades recur spontaneously through repetitive dewetting
of the microgrooves. Lastly, we identify surface design rules for
consistent realization of the cascades. The hydrophobic microgrooved
textures required for the activation of this mechanism can be realized
through conventional, scalable surface fabrication methods on a broad
range of materials (we demonstrate with aluminum and silicon), thus
promising direct application in a host of phase-change processes
Self-Sustained Cascading Coalescence in Surface Condensation
No full textSustained
dropwise condensation of water requires rapid shedding of condensed
droplets from the surface. Here, we elucidate a microfluidic mechanism
that spontaneously sweeps condensed microscale droplets without the
need for the traditional droplet removal pathways such as use of superhydrophobicity
for droplet rolling and jumping and utilization of wettability gradients
for directional droplet transport among others. The mechanism involves
self-generated, directional, cascading coalescence sequences of condensed
microscale droplets along standard hydrophobic microgrooves. Each
sequence appears like a spontaneous zipping process, can sweep droplets
along the microgroove at speeds of up to ∼1 m/s, and can extend
for lengths more than 100 times the microgroove width. We investigate
this phenomenon through high-speed in situ microscale condensation
observations and demonstrate that it is enabled by rapid oscillations
of a condensate meniscus formed locally in a filled microgroove and
pinned on its edges. Such oscillations are in turn spontaneously initiated
by coalescence of an individual droplet growing on the ridge with
the microgroove meniscus. We quantify the coalescence cascades by
characterizing the size distribution of the swept droplets and propose
a simple analytical model to explain the results. We also demonstrate
that, as condensation proceeds on the hydrophobic microgrooved surface,
the coalescence cascades recur spontaneously through repetitive dewetting
of the microgrooves. Lastly, we identify surface design rules for
consistent realization of the cascades. The hydrophobic microgrooved
textures required for the activation of this mechanism can be realized
through conventional, scalable surface fabrication methods on a broad
range of materials (we demonstrate with aluminum and silicon), thus
promising direct application in a host of phase-change processes
