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Rotary Atomizer: Investigation of the Internal and External Liquid Flow and Atomization

Kuhnhenn, Maximilian (2019):
Rotary Atomizer: Investigation of the Internal and External Liquid Flow and Atomization.
Darmstadt, Technische Universität, [Online-Edition: https://tuprints.ulb.tu-darmstadt.de/7414],
[Ph.D. Thesis]

Abstract

Rotary atomizers are the preferred instrument of drying of many materials such as dairy products, foods, pharmaceuticals, polymers, etc. and are therefore often used in spray drying applications in the chemical and food industry. They are able to atomize complex, highly viscous, multicomponent liquids. Rotary atomizers have been successfully used in the spray drying industry for over 90 years, but increasing awareness for environmental concerns leads to the request for a higher energy efficiency. Based on the initial idea to improve the state-of-the-art design of rotary atomizers, this study tries to deliver an extensive insight into the underlying functional principle of rotary atomizers. Understanding and controlling the resultant droplet size distribution is crucial for the design process of spray dryers, since it is instrumental in determining the resultant powder size distribution.

In this thesis the internal flow inside a rotary atomizer, the mechanisms of primary atomization, the outer flow of the jets, rivulets and drops are studied experimentally and analyzed theoretically. The flow is observed using a high resolution video system, while the size, velocity vector and the number density of the drops in the spray are characterized using a phase Doppler measurement system.

Two main regions of the internal flow in the insert are identified: a thin film flow and a single rivulet flow. Correspondingly, the drops in the spray are formed as a result of the film and rivulet atomization processes.

Finally it is shown, that the average dimensionless drop diameter, scaled by the jet thickness, correlates very well with the dimensionless stretching parameter. A semi-empirical model for the average diameter of drops in the spray is developed.

Item Type: Ph.D. Thesis
Erschienen: 2019
Creators: Kuhnhenn, Maximilian
Title: Rotary Atomizer: Investigation of the Internal and External Liquid Flow and Atomization
Language: English
Abstract:

Rotary atomizers are the preferred instrument of drying of many materials such as dairy products, foods, pharmaceuticals, polymers, etc. and are therefore often used in spray drying applications in the chemical and food industry. They are able to atomize complex, highly viscous, multicomponent liquids. Rotary atomizers have been successfully used in the spray drying industry for over 90 years, but increasing awareness for environmental concerns leads to the request for a higher energy efficiency. Based on the initial idea to improve the state-of-the-art design of rotary atomizers, this study tries to deliver an extensive insight into the underlying functional principle of rotary atomizers. Understanding and controlling the resultant droplet size distribution is crucial for the design process of spray dryers, since it is instrumental in determining the resultant powder size distribution.

In this thesis the internal flow inside a rotary atomizer, the mechanisms of primary atomization, the outer flow of the jets, rivulets and drops are studied experimentally and analyzed theoretically. The flow is observed using a high resolution video system, while the size, velocity vector and the number density of the drops in the spray are characterized using a phase Doppler measurement system.

Two main regions of the internal flow in the insert are identified: a thin film flow and a single rivulet flow. Correspondingly, the drops in the spray are formed as a result of the film and rivulet atomization processes.

Finally it is shown, that the average dimensionless drop diameter, scaled by the jet thickness, correlates very well with the dimensionless stretching parameter. A semi-empirical model for the average diameter of drops in the spray is developed.

Place of Publication: Darmstadt
Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA)
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA) > Dynamics of drops and sprays
Date Deposited: 03 Mar 2019 20:55
Official URL: https://tuprints.ulb.tu-darmstadt.de/7414
URN: urn:nbn:de:tuda-tuprints-74148
Referees: Tropea, Prof. Dr. Cameron and Roisman, Prof. Dr. Ilia V. and Walzel, Prof. Dr. Peter
Refereed / Verteidigung / mdl. Prüfung: 9 October 2018
Alternative Abstract:
Alternative abstract Language
Rotationszerstäuber sind die bevorzugte Technologie für die Trocknung von unterschiedlichsten Materialien wie Molkereiprodukte, Lebensmittel, Polymere, etc., weshalb sie häufig im Bereich der Sprühtrocknung in der Chemie- und Lebensmittelindustrie zum Einsatz kommen. Sie sind in der Lage komplexe, hoch-viskose, mehrkomponenten Flüssigkeiten zu zerstäuben. Rotationszerstäuber werden seit über 90 Jahren erfolgreich in der Sprühtrocknungsindustrie eingesetzt, jedoch führt ein größer werdendes ökologisches Bewusstsein zu dem Wunsch einer besseren Energieeffizienz. Basierend auf der anfänglichen Idee das dem Stand der Technik entsprechende Design von Rotationszerstäubern zu verbessern, liefert diese Arbeit tiefere Einblicke in das zugrunde liegende Funktionsprinzip. Das Verständnis und die Kontrolle der resultierenden Tropfengrößenverteilung ist ausschlaggebend für das Design des Sprühtrocknungsprozesses, da es maßgeblich an der Entstehung der Pulvergrößenverteilung beteiligt ist. In dieser Arbeit werden die Innenströmung eines Rotationszerstäubers, die Aufbruchmechanismen der primären Zerstäubung, die externe Strömung der Gerinne und Tropfen experimentell untersucht und theoretisch analysiert. Die Strömung wird mit Hilfe eines hochauflösenden Kamerasystems erfasst, wohingegen die Größe, Geschwindigkeit und Tropfengrößenverteilung des erzeugten Sprays mit einem Phasen Doppler Messgerät erfasst werden. Im Bereich der Innenströmung der radialen Öffnungen können zwei Hauptbereich identifiziert werden: Eine dünne Filmströmung und eine Gerinneströmung. Dementsprechend entstehen die Tropfen im Spray aus dem Zerstäubungsprozess von Film und Gerinne. Schlussendlich kann gezeigt werden, dass der dimensionslose Tropfendurchmesser, skaliert mit der Gerinnehöhe, sehr gut mit dem dimensionslosen Dehnparameter korreliert. Ein semi-empirisches Modell zur Bestimmung des mittleren Tropfendurchmessers wird entwickelt und präsentiert.German
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