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The Fundamental Role of Extreme Environmental Conditions on Surface Icing and on the Design of Icephobic Surfaces

Titel Englisch The Fundamental Role of Extreme Environmental Conditions on Surface Icing and on the Design of Icephobic Surfaces
Gesuchsteller/in Poulikakos Dimos
Nummer 162565
Förderungsinstrument Projektförderung (Abt. I-III)
Forschungseinrichtung Institut für Energietechnik ETH Zürich
Hochschule ETH Zürich - ETHZ
Hauptdisziplin Maschineningenieurwesen
Beginn/Ende 01.02.2016 - 31.01.2019
Bewilligter Betrag 382'155.00
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Keywords (6)

Droplet impact; Superhydrophobic; Supericephobic; Thermofluidics; Surface morphology engineering; Stratospheric

Lay Summary (Deutsch)

Lead
Ziel dieses Projekts ist unser grundlegendes Verständnis von Eisbildung an Oberflächen in stratosphärischen Bedingungen zu vertiefen, sowie, basiert auf die gewonnene Kenntnisse, verlässliche Strategien zu erarbeiten, um eine solche Eisbildung zu vermeiden.
Lay summary

Wir werden den Einfluss von stratosphärischen Umgebungsbedingungen, wie sie beispielsweise in der Luftfahrt anzutreffen sind, mit Drücken zwischen 10-3 und 1 bar sowie Temperaturen zwischen 0 und -40°C, auf die Eisbildung an Oberflächen untersuchen. Zu diesem Zweck entwickeln wir Oberflächen, die wasserabweisende und eisabweisende Eigenschaften haben. Es werden Experimente durchgeführt, bei denen unterkühlte Wassertropfen, die aufgrund der niedrigen Temperaturen deutlich viskoser als bei Raumtemperatur sind, auf superhydrophobe, mit Mikro- und Nano-Rauigkeit ausgestattete Oberflächen unter stratosphärischen Bedingungen auftreffen. Ein besonderer Fokus liegt auf der Untersuchung der Stabilität der Gasschicht, die sich in den Vertiefungen der rauen Oberfläche befindet und verantwortlich für die wasserabweisenden Eigenschaften ist. Darüber hinaus werden wir in einer Reihe von Experimenten die Keimbildung und die Ausbreitung der Gefrierfront, sowie deren Einfluss auf die Haftung von unterkühlten Tropfen an der Oberfläche untersuchen. Bei diesen Experimenten werden die Temperatur, der Druck und die Luftfeuchtigkeit kontrolliert. Im Besonderen sind wir daran interessiert, die schlagartige Freisetzung von Wasserdampf im Moment des Gefrierens zu nutzen, um den gerade gefrierenden Tropfen von der Oberfläche zu entfernen. Wir wollen das grundlegende Verständnis von Eisbildung an Oberflächen in stratosphärischen Bedingungen vertiefen, sowie verlässliche Strategien erarbeiten, um eine Eisbildung zu vermeiden.

Direktlink auf Lay Summary Letzte Aktualisierung: 12.10.2015

Verantw. Gesuchsteller/in und weitere Gesuchstellende

Mitarbeitende

Verbundene Projekte

Nummer Titel Start Förderungsinstrument
135479 Towards Supericephobic Surfaces - A Fundamental Study into the Effects of Morphology and Surface Functionality on Ice Formation and Adhesion 01.11.2011 Projektförderung (Abt. I-III)
170724 Initiated chemical vapor deposition (iCVD) system for rational and durable surface functionalization 01.01.2017 R'EQUIP

Abstract

Icing of surfaces is common in nature and technology, affecting everyday life and often causing catastrophic events. Despite progress in recent years in the area of hydrophobicity, engineered surfaces that can be used in applications based on their inherent (passive) icephobicity for realistic anti-icing applications, going beyond classical additional chemical coatings or heating treatments, are not a reality. This is due in part to the lack of thorough understanding of the physics of icing under more extreme conditions, that is, departing from classical characterization under tropospheric conditions where a majority of research has been done to-date. Therefore, this project will investigate the role of stratospheric conditions -a term used to summarily describe environmental conditions with pressure and temperature ranges of 10-3 to 1 bar and 0 to -40°C, respectively, and covering a range of important operating conditions relevant for example to aviation applications- in the formation of surface ice. The results will aid the development of robust strategies towards inhibiting surface icing and ultimately help attain the goal of a supericephobic surface. Specifically, since in such challenging environments ice nucleation in supercooled water is practically inevitable, we seek to incorporate its inherent physics toward designing icephobic surfaces, functioning based on their a-priori engineered composition and texture. Our goal is to identify anti-wetting phenomena and to explore the role of nucleation initiation and freezing dynamics (first/recalescent and second stages of freezing) on the resulting ice adhesion. This will lead to the development of surfaces having low water contact and retention and spontaneous de-wetting/de-icing properties. The current proposal is aimed at addressing the open fundamental questions related to inhibiting surface icing through theoretical and experimental considerations. The proposed project can be divided into two parts:1.Supercooled water fluid dynamics: A series of experiments will be performed whereby supercooled droplets -which at -25°C for example have a 5x higher viscosity compared with their room temperature state- are impacted onto multitier superhydrophobic surfaces under stratospheric conditions. The emphasis will be on studying the stability of the gaseous intervening layer -which is responsible for the superhydrophobic property- and using this knowledge to better engineer surfaces for a wider (than tropospheric) range of operating conditions (relevant for example to aviation and ice formation under partial vacuum applications). This droplet impact process will be characterized by using a chamber which can selectively control each of the environmental parameters (e.g., pressure); macro-scale imaging will be performed with high-speed optical and infrared cameras (visualizing the bulk droplet transport and heat transfer characteristics); micro-scale imaging of liquid meniscus penetration into the surface texture (displacement of the intervening air layer) will be performed with the aid of X-ray imaging and epi-illumination microscopy so that the behavior of the liquid meniscus within the surface texture can be observed. The mechanical and chemical durability of the surface will also form an important component of this portion of the study.2.Recalescent freezing thermodynamics: For operating conditions with water well in the supercooled (metastable) temperature range for extended exposure times, ice nucleation is inevitable. For metastable liquids that are in a condition far from equilibrium, their solidification will result in a rapid release of latent heat-so-called recalescent freezing.[1-3] This heat release is associated with a simultaneous rapid vaporization. Understanding the interaction of such phenomena, inherent to freezing from a supercooled state, with the surface texture at the abovementioned environmental conditions, can play a significant role toward designing surfaces with extreme resistance to icing. We will perform a series of experiments to study the physics of nucleation and ice-front propagation (freezing dynamics) on the retention of a supercooled droplet on a surface under controlled temperature, humidity, and pressure conditions. Specifically, we aim to exploit the sudden release of vapor for the purposes of propelling and ejecting freezing droplets from the solid substrate. Characterization of this process will be achieved with an environmental chamber, which has optical and infrared access to facilitate high-speed imaging of the fast dynamics.In closing, the goal of this proposal is to advance the fundamental understanding of surface ice formation under stratospheric conditions on engineered surfaces (e.g., multi-tier superhydrophobic) in order to develop more robust strategies for inhibiting surface icing. Systematic coupling of the inherent physics at these environmental conditions and surface texture design will be performed hand-in-hand in order to establish a well understood and rationally engineered de-icing/anti-wetting performance. [1] P. Eberle, M. K. Tiwari, T. Maitra, D. Poulikakos, Nanoscale 2014, 6, 4874.[2] S. Jung, M. K. Tiwari, N. V. Doan, D. Poulikakos, Nat. Commun. 2012, 3, 615.[3] S. Jung, M. K. Tiwari, D. Poulikakos, Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 16073.
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