Brulin, Sebastian (2021)
Hydrodynamic Investigations of Rapidly Stretched Liquid Bridges.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00017537
Ph.D. Thesis, Primary publication, Publisher's Version
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Item Type: | Ph.D. Thesis | ||||
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Type of entry: | Primary publication | ||||
Title: | Hydrodynamic Investigations of Rapidly Stretched Liquid Bridges | ||||
Language: | English | ||||
Referees: | Roisman, Apl. Prof. Ilia V. ; Hussong, Prof. Jeanette ; Dörsam, Prof. Edgar | ||||
Date: | 2021 | ||||
Place of Publication: | Darmstadt | ||||
Collation: | viii, 145 Seiten | ||||
Date of oral examination: | 16 December 2020 | ||||
DOI: | 10.26083/tuprints-00017537 | ||||
Abstract: | Liquid bridges have become an integral part of many industrial processes relevant to consumer production. For example, the coating technology often includes dip-coating, printing, or spraying of liquid materials. Liquid bridge or liquid jet fast stretching is an essential element of such processes. Bridge stretching determines the outcome of liquid atomization and the agglomeration of wet particles. Moreover, liquid bridge stretching is used for the rheological characterization of complex liquids. This thesis deals with the investigation of fast stretched Newtonian fluid bridges. The unique feature of this study is the investigation of particularly high stretching rates for very small liquid bridge heights. A system consisting of two parallel substrates was developed. One substrate can be moved with a constant, controllable acceleration while the other substrate remains stationary. It allows performing parameter studies with accelerations of up to 180 m/s2 and initial bridge heights starting from 50 μm. Extensive experimental and theoretical studies were carried out to identify the most influencing parameters and, therefore, to understand the physical mechanisms of the observed phenomena better. The characterization includes a description of the kinematics of the liquid bridge stretching and different outcomes like liquid cavitation, finger formation during stretching, and bridge pinch-off. The evolution of the main geometrical properties of the stretching liquid bridge is characterized. These properties include the curvature and shape of the meniscus, length, and diameter of the liquid bridge. Two main regimes of a fast stretching are identified: viscous regime, determined by the Reynolds number, and capillary regime for low viscosity liquids, governed by the Weber number. The knowledge of the kinematics of the bridge allows us to determine the appropriate scales for a description of the stretching outcomes. The cavitation phenomena are described using the estimation of the distribution of the viscous pressure in the gap. This pressure determines the evolution of the cavity radius. A bubble growth model has been developed, which allows the prediction of the instant of the maximum bubble diameter as a function of the cavitation inception rather well. Next, the stability analysis of the bridge free interface is performed, which accounts for the viscous effects and inertia. The predicted condition for the appearance of the fingers and the number of these fingers agree well with the experimental data. Finally, the model for the pinch-off time of the stretching bridge is developed. The scales for the pinch-off time have been determined for viscous and for the capillary stretching regimes. The experimental and theoretical results can be potentially useful for optimizing the operational conditions during printing and modeling atomization, accretion, and agglomeration phenomena. |
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Status: | Publisher's Version | ||||
URN: | urn:nbn:de:tuda-tuprints-175375 | ||||
Classification DDC: | 600 Technology, medicine, applied sciences > 620 Engineering and machine engineering | ||||
Divisions: | 16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA) DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 1194: Interaction between Transport and Wetting Processes > Research Area A: Generic Experiments > A03: Investigation of Fast De-wetting from Substrates with Complex Surface Morphologies |
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Date Deposited: | 18 Mar 2021 12:41 | ||||
Last Modified: | 18 Mar 2021 12:41 | ||||
URI: | https://tuprints.ulb.tu-darmstadt.de/id/eprint/17537 | ||||
PPN: | 477787541 | ||||
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