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dc.contributor.author
Graeber, Gustav
dc.contributor.supervisor
Poulikakos, Dimos
dc.contributor.supervisor
Quéré, David
dc.contributor.supervisor
Shih, Chih-Jen
dc.contributor.supervisor
Schutzius, Thomas M.
dc.date.accessioned
2020-03-27T10:58:46Z
dc.date.available
2019-03-26T12:54:40Z
dc.date.available
2019-03-26T13:22:07Z
dc.date.available
2020-03-27T10:58:46Z
dc.date.issued
2019
dc.identifier.uri
http://hdl.handle.net/20.500.11850/333899
dc.identifier.doi
10.3929/ethz-b-000333899
dc.description.abstract
Droplet freezing is important both in nature and in technology. In this thesis I investigate the fundamentals of freezing water droplets and derive design criteria for the development of intrinsically ice-repellent materials. Such icephobic surfaces could improve the performance and safety of a multitude of technical processes in energy and transport. This includes for example heat exchangers, where ice built-up reduces thermal transport, and airplane flight, where freezing of water on airfoils can result in catastrophic events. The thesis consists of three individual studies. In the first study we investigated how the environmental conditions during droplet freezing affect the freezing outcome. We found that evaporatively or convectively supercooled water droplets resting on solid substrate can self-remove during freezing. This phenomenon, which we termed self-dislodging, requires that the heat removal from the droplet’s free surface dominates the heat removal through the solid substrate. Consequently, the freezing front moves from the outside of the droplet towards the center and from the top to the bottom, resulting in a solid ice shell with an unsolidified core and an unfrozen droplet-substrate interface. We observed experimentally that the inward motion of the phase boundary near the substrate drives a gradual reduction in droplet-substrate contact. Concurrently, due to the volumetric expansion associated with freezing, semi-frozen water is displaced towards the droplet-substrate interface lifting the freezing droplet away from the substrate. The combined effects of dewetting and lifting result in droplet self-removal. We found that the more the substrate is hydrophobic the more robust self-dislodging occurs. In the second study we examined how multiple water droplets interact during freezing in a low-pressure environment. Understanding droplet interactions during freezing is important as droplets do not appear in isolation, but always in groups. We found that the freezing of a supercooled droplet results in self-heating and induces strong vaporization. The resulting, rapidly propagating vapor front causes immediate cascading freezing of neighboring supercooled droplets upon reaching them. We suggest that as the vapor approaches cold neighboring droplets, it can lead to local supersaturation and formation of airborne microscopic ice crystals, which act as freezing nucleation sites. The sequential triggering and propagation of this mechanism results in the rapid freezing of an entire droplet ensemble resulting in ice coverage of the solid surface. In the third study we introduced a controllable and upscalable method to fabricate superhydrophobic surfaces with a 3D-printed architecture for improved repellency of viscous liquids. We show a more than threefold contact time reduction of impacting viscous droplets up to a fluid viscosity of 3.7mPa s, which covers the viscosity of supercooled water down to -17 °C. Based on the combined consideration of the fluid flow within and the simultaneous droplet dynamics above the texture, we recommend future pathways to rationally architecture such surfaces that can repel supercooled water before it freezes and sticks to the surface. The three studies presented in this thesis address the topic of surface icing from three different angles, collaboratively covering a broad range of the problem. Only when taking into account the environmental conditions, freezing group dynamics and liquid solid interactions, robust icephobic surfaces can be designed in the future. With my thesis I contribute to this development process.
en_US
dc.format
application/pdf
en_US
dc.language.iso
en
en_US
dc.publisher
ETH Zurich
en_US
dc.rights.uri
http://rightsstatements.org/page/InC-NC/1.0/
dc.subject
Freezing
en_US
dc.subject
Sublimation
en_US
dc.subject
Icephobicity
en_US
dc.subject
Nanotextures
en_US
dc.subject
Phase change
en_US
dc.subject
Recalescence freezing
en_US
dc.subject
Superhydrophobicity
en_US
dc.subject
Vaporization
en_US
dc.subject
3D Printing
en_US
dc.subject
Thermodynamics
en_US
dc.subject
Droplet impact
en_US
dc.title
Freezing Physics and Derived Surface Nano-Engineering for Spontaneous Deicing
en_US
dc.type
Doctoral Thesis
dc.rights.license
In Copyright - Non-Commercial Use Permitted
dc.date.published
2019-03-26
ethz.size
194 p.
en_US
ethz.code.ddc
DDC - DDC::5 - Science::530 - Physics
en_US
ethz.grant
The Fundamental Role of Extreme Environmental Conditions on Surface Icing and on the Design of Icephobic Surfaces
en_US
ethz.grant
Pathways to Intrinsically Icephobic Surfaces
en_US
ethz.identifier.diss
25649
en_US
ethz.publication.place
Zurich
en_US
ethz.publication.status
published
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02130 - Dep. Maschinenbau und Verfahrenstechnik / Dep. of Mechanical and Process Eng.::02627 - Institut für Energietechnik / Institute of Energy Technology::03462 - Poulikakos, Dimos / Poulikakos, Dimos
en_US
ethz.leitzahl.certified
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02130 - Dep. Maschinenbau und Verfahrenstechnik / Dep. of Mechanical and Process Eng.::02627 - Institut für Energietechnik / Institute of Energy Technology::03462 - Poulikakos, Dimos / Poulikakos, Dimos
en_US
ethz.grant.agreementno
162565
ethz.grant.agreementno
669908
ethz.grant.fundername
SNF
ethz.grant.fundername
EC
ethz.grant.funderDoi
10.13039/501100001711
ethz.grant.funderDoi
10.13039/501100000780
ethz.grant.program
H2020
ethz.relation.cites
10.1021/acsnano. 8b05921
ethz.relation.cites
10.1073/pnas.1705952114
ethz.relation.cites
10.1021/acsami.8b16893
ethz.date.deposited
2019-03-26T12:54:49Z
ethz.source
FORM
ethz.eth
yes
en_US
ethz.availability
Open access
en_US
ethz.date.embargoend
2020-03-26
ethz.rosetta.installDate
2019-03-26T13:23:15Z
ethz.rosetta.lastUpdated
2020-03-27T10:59:07Z
ethz.rosetta.versionExported
true
ethz.COinS
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