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Hydrodynamics and Thermodynamics of Ice Accretion through Impact of Supercooled Large Droplets: Experiments, Simulations and Theory

Schremb, Markus (2018):
Hydrodynamics and Thermodynamics of Ice Accretion through Impact of Supercooled Large Droplets: Experiments, Simulations and Theory.
Darmstadt, Technische Universität, [Online-Edition: http://tuprints.ulb.tu-darmstadt.de/7398],
[Ph.D. Thesis]

Abstract

Icing of solid surfaces is an ever-present problem for many engineering applications. In particular ice accretion due to the impact and freezing of supercooled water drops is rich in various physical processes and of relevance for aviation, road traffic, shipping, wind turbines, and high-voltage power lines and insulators. It is initiated by the impact of water drops being in a thermodynamic meta-stable state, followed by nucleation of the impacting drops and ending up with solidification of the liquid, potentially influenced by the impact surface. All of these processes have been separately the focus of extensive experimental, theoretical and numerical studies for many decades. However, for the first time the present work attempts to consolidate the understanding of all involved mechanisms, and to examine them in the context of icing of surfaces. Following the aforementioned subdivision, the subprocesses of ice accretion are separately examined using experimental, theoretical and numerical approaches. Non-isothermal impact of both supercooled water drops and water drops initially at room temperature onto surfaces below the freezing point of water is studied experimentally and numerically, and the heat transfer during drop impact is theoretically modeled. Nucleation during drop impact is experimentally studied and theoretically modeled. The freezing process of supercooled water drops with wall contact is investigated, employing a novel experimental approach, and the influence of the wall is theoretically modeled. Finally, the mutual influence between fluid flow during drop impact and freezing of the impinging liquid is experimentally examined and theoretically modeled. Due to its comprehensive nature and the application of new experimental approaches, the present work constitutes a fundamental contribution to a better understanding of the processes taking place during ice accretion by supercooled water drops. It provides theoretical models which allow the prediction of heat transfer during non-isothermal drop impact, the quantitative analysis of experiments aimed at nucleation during drop impact, the prediction of the characteristic solidification velocity for the case of water freezing with wall contact, and the prediction of the residual ice layer thickness after impact of an individual supercooled water drop.

Item Type: Ph.D. Thesis
Erschienen: 2018
Creators: Schremb, Markus
Title: Hydrodynamics and Thermodynamics of Ice Accretion through Impact of Supercooled Large Droplets: Experiments, Simulations and Theory
Language: English
Abstract:

Icing of solid surfaces is an ever-present problem for many engineering applications. In particular ice accretion due to the impact and freezing of supercooled water drops is rich in various physical processes and of relevance for aviation, road traffic, shipping, wind turbines, and high-voltage power lines and insulators. It is initiated by the impact of water drops being in a thermodynamic meta-stable state, followed by nucleation of the impacting drops and ending up with solidification of the liquid, potentially influenced by the impact surface. All of these processes have been separately the focus of extensive experimental, theoretical and numerical studies for many decades. However, for the first time the present work attempts to consolidate the understanding of all involved mechanisms, and to examine them in the context of icing of surfaces. Following the aforementioned subdivision, the subprocesses of ice accretion are separately examined using experimental, theoretical and numerical approaches. Non-isothermal impact of both supercooled water drops and water drops initially at room temperature onto surfaces below the freezing point of water is studied experimentally and numerically, and the heat transfer during drop impact is theoretically modeled. Nucleation during drop impact is experimentally studied and theoretically modeled. The freezing process of supercooled water drops with wall contact is investigated, employing a novel experimental approach, and the influence of the wall is theoretically modeled. Finally, the mutual influence between fluid flow during drop impact and freezing of the impinging liquid is experimentally examined and theoretically modeled. Due to its comprehensive nature and the application of new experimental approaches, the present work constitutes a fundamental contribution to a better understanding of the processes taking place during ice accretion by supercooled water drops. It provides theoretical models which allow the prediction of heat transfer during non-isothermal drop impact, the quantitative analysis of experiments aimed at nucleation during drop impact, the prediction of the characteristic solidification velocity for the case of water freezing with wall contact, and the prediction of the residual ice layer thickness after impact of an individual supercooled water drop.

Place of Publication: Darmstadt
Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA)
Date Deposited: 20 May 2018 19:55
Official URL: http://tuprints.ulb.tu-darmstadt.de/7398
URN: urn:nbn:de:tuda-tuprints-73984
Referees: Tropea, Prof. Dr. Cameron and Weigand, Prof. Dr. Bernhard and Jakirlic, Apl. Prof. Suad
Refereed / Verteidigung / mdl. Prüfung: 16 April 2018
Alternative Abstract:
Alternative abstract Language
Vereisung von Oberflächen ist ein allgegenwärtiges Problem in vielen technischen Bereichen. Vor allem die Vereisung aufgrund unterkühlter Wassertropfen beinhaltet verschiedenste physikalische Vorgänge und ist relevant für die Luftfahrt, den Straßenverkehr, die Schifffahrt, Windkraftanlagen sowie Hochspannungsleitungen und -isolatoren. Der Vorgang wird durch den Aufprall von Wassertropfen im thermodynamisch metastabilen Zustand initiert und Nukleation der aufprallenden Tropfen führt schließlich zur Erstarrung der Flüssigkeit. Obwohl diese Teilprozesse im einzelnen jeweils seit einigen Jahrzehnten Gegenstand experimenteller, theoretischer und numerischer Untersuchungen sind, stellt die hier vorliegende Arbeit den ersten Versuch einer umfangreichen Untersuchung aller Teilprozesse vor dem Hintergrund der Vereisung dar. Entsprechend der vorangegangenen Beschreibung werden die Teilprozesse mittels experimenteller, theoretischer und numerischer Methoden separat erforscht. Der nicht-isotherme Aufprall von Wassertropfen auf Oberflächen unterhalb des Schmelzpunktes von Wasser wird experimentell und numerisch untersucht, und die Wärmeübertragung während des Aufpralls theoretisch modelliert. Nukleation während des Aufpralls sowie die Erstarrung unterkühlter Tropfen mit Wandkontakt werden experimentell beobachtet und mathematisch modelliert. Die Interaktion von Fluidströmung und Erstarrung während des Tropfenaufpralls wird experimentell untersucht und mathematisch beschrieben. Aufgrund ihres Umfangs und der Anwendung neuer experimenteller Ansätze, stellt die vorliegende Arbeit einen fundamentalen Beitrag zu einem besseren Verständniss der Vorgänge während der Vereisung aufgrund unterkühlter Wassertropfen dar. Die daraus resultierenden Modelle ermöglichen die Vorhersage der Wärmeübertragung während des nichtisothermen Tropfenaufpralls, die quantitative Beschreibung der Nukleation während des Aufpralls, die Vorhersage der charakteristischen Erstarrungsgeschwindigkeit im Falle von Wasser mit Wandkontakt sowie die Vorhersage der resultierenden Eisschichtdicke nach dem Aufprall eines einzelnen unterkühlten Wassertropfens.German
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