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Drying of Multiphase Single Droplets in Ultrasonic Levitator

Al Zaitone, Belal (2009):
Drying of Multiphase Single Droplets in Ultrasonic Levitator.
Darmstadt, Technische Universität, TU Darmstadt, [Online-Edition: urn:nbn:de:tuda-tuprints-18926],
[Ph.D. Thesis]

Abstract

Spray drying is widely used in many industries, e.g. chemical, food and pharmaceutical processing, in which the spray generation is followed by solvent/liquid evaporation leading to a final powder product. As the liquid component evaporates, the droplet weight decreases. This evaporation process is accompanied by phase change of the volatile component. For a multiphase droplet, solid material is suspended or dissolved in the liquid phase. In such cases, it is important to have knowledge of transport phenomena for single droplets as it pertains to their evaporation and component distribution. The investigation of the evaporation of single droplets is particularly applicable to the study of spray drying and atomization. There are several different measurement techniques that can be used to analyze droplets of various components such as pure liquids, mixtures, solutions, and colloidal suspensions. The principle of ultrasonic levitation is unique in that it allows the isolation of a single droplet in space rather than a myriad of droplets. Having a multiphase droplet suspended in the acoustic field facilitates the study of the drying rate at different operational parameters, and tracking the morphological changes during the course of the drying process. The experiments conducted in this work were performed for a single droplet or separation of two single droplets. Single droplet analysis allows for characterization of the droplets drying rate. The multi-droplet analysis is pertinent to sound pressure level calibration. Understanding the sub-models for these processes is largely beneficial to the advance of modeling the overall spray drying process. In the present work, the drying of further example systems has been studied, and a characterization of the outer crust formed at the end of the first drying stage is presented. These are accompanied by "quasi" 2-D model formulations for the simulation of individual drop drying to describe the solid concentration profiles and the creation of the crust at the end of the constant rate period, when the solids concentration at the surface exceed the saturation concentration.

Item Type: Ph.D. Thesis
Erschienen: 2009
Creators: Al Zaitone, Belal
Title: Drying of Multiphase Single Droplets in Ultrasonic Levitator
Language: English
Abstract:

Spray drying is widely used in many industries, e.g. chemical, food and pharmaceutical processing, in which the spray generation is followed by solvent/liquid evaporation leading to a final powder product. As the liquid component evaporates, the droplet weight decreases. This evaporation process is accompanied by phase change of the volatile component. For a multiphase droplet, solid material is suspended or dissolved in the liquid phase. In such cases, it is important to have knowledge of transport phenomena for single droplets as it pertains to their evaporation and component distribution. The investigation of the evaporation of single droplets is particularly applicable to the study of spray drying and atomization. There are several different measurement techniques that can be used to analyze droplets of various components such as pure liquids, mixtures, solutions, and colloidal suspensions. The principle of ultrasonic levitation is unique in that it allows the isolation of a single droplet in space rather than a myriad of droplets. Having a multiphase droplet suspended in the acoustic field facilitates the study of the drying rate at different operational parameters, and tracking the morphological changes during the course of the drying process. The experiments conducted in this work were performed for a single droplet or separation of two single droplets. Single droplet analysis allows for characterization of the droplets drying rate. The multi-droplet analysis is pertinent to sound pressure level calibration. Understanding the sub-models for these processes is largely beneficial to the advance of modeling the overall spray drying process. In the present work, the drying of further example systems has been studied, and a characterization of the outer crust formed at the end of the first drying stage is presented. These are accompanied by "quasi" 2-D model formulations for the simulation of individual drop drying to describe the solid concentration profiles and the creation of the crust at the end of the constant rate period, when the solids concentration at the surface exceed the saturation concentration.

Place of Publication: Darmstadt
Publisher: Technische Universität
Uncontrolled Keywords: Evaporation, Drying kinetics, Multiphase single droplets, Crystallization, 2-D Drying model, Acoustic levitation
Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA)
Date Deposited: 08 Sep 2009 10:29
Official URL: urn:nbn:de:tuda-tuprints-18926
License: Creative Commons: Attribution-Noncommercial-No Derivative Works 3.0
Referees: Tropea, Prof. Dr.- Cameron and Stephan, Prof. Dr.- Peter
Refereed / Verteidigung / mdl. Prüfung: 20 May 2009
Alternative Abstract:
Alternative abstract Language
Schwerpunkte der vorliegenden Arbeit, die im Rahmen des Graduiertenkollegs GRK 1114 "Optische Messtechniken für die Charakterisierung von Transportprozessen an Grenzflächen" durchgeführt wurde, waren Untersuchungen über die Trocknung von mehrphasigen Tropfen, wie sie in der Sprühtrocknung vorkommen. Dabei wurden die Trocknungsrate und die Morphologie des getrockneten Pulvers im Detail untersucht. Die Arbeit beinhaltet sowohl experimentelle Untersuchungen wie auch eine mathematische Modellierungen der beobachteten Vorgänge. Technische Prozesse wie das Sprühtrocknen sind weit verbreitet in der Chemischen, Lebensmittel- oder Pharmazeutischen Industrie. Hierbei werden die Flüssigkeiten mit gelösten Feststoffen in das Gas gesprüht. Verdunstet die flüssige Komponente, verringert sich die Tropfenmasse. Dieser Verdunstungsprozess wird begleitet von einem Phasenwechsel der flüchtigen Komponente. Für einen Mehrphasentropfen wird festes Material in einer flüssigen Phase suspendiert. In diesen Fällen ist es wichtig, die Transportphänomene der einzelnen Tropfen zeitabhängig zu kennen, insbesondere die Verdunstung und Verteilung der Komponenten. Im Vordergrund der experimentellen Arbeiten stand daher das Trocknen einzelner Tropfen in einem akustischen Levitator, der eine berührungslose Fixierung des Tropfens ermöglicht. Aus Beobachtungen an einzelnen Tropfen könnten dann Sub-Modelle für die Verdunstung und Verteilung der Tropfenkomponenten mit der Zeit aufgestellt werden, nicht nur für reine Flüssigkeitstropfen sondern auch für komplexere Tropfen wie Suspensionen oder Emulsionen. In den Experimenten wurden auch zum Teil zwei getrennte Tropfen gleichzeitig im Levitator beobachtet. Somit konnte auch der veränderliche Schalldruck online gemessen und in der Auswertung berücksichtigt werden. In der vorliegenden Arbeit werd die Trocknung weiterer Beispielsysteme mit untersucht und die Charakterisierung der äußeren Kruste dargestellt. Hierfür wird ein "quasi" 2-D Trocknungs-Model formuliert, mit dem die Konzentrationsprofile und die Bildung der Kruste am Ende der konstanten Trocknungsperiode abgebildet werden konnten.German
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