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    Experiments on Drop-impact Splashing, Singular Jets and Coalescence in Emulsions

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    Name:
    PhD_Dissertation_Yuansi_Tian_Final0809.pdf
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    51.20Mb
    Format:
    PDF
    Description:
    Dissertation - Yuansi Tian
    Embargo End Date:
    2021-08-30
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    Type
    Dissertation
    Authors
    Tian, Yuansi cc
    Advisors
    Thoroddsen, Sigurdur T cc
    Committee members
    Samtaney, Ravi cc
    Sun, Shuyu cc
    Castrejon-Pita, Jose Rafael
    Program
    Mechanical Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2020-06
    Embargo End Date
    2021-08-30
    Permanent link to this record
    http://hdl.handle.net/10754/664909
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation will become available to the public after the expiration of the embargo on 2021-08-30.
    Abstract
    This dissertation describes experiments on drop dynamics. It is split into two main parts: The first investigates the breakup of liquid during the impact of a drop on a pool surface, with focus on the smallest and fastest splashed satellite droplets. The second part studies the much slower coalescence of two minute water droplets in oil inside a micro-channel, with applications to separation of water droplets from crude oil emulsions. First, we study drop-on-liquid impacts in high-speed experiments with extreme time and spatial resolutions using up to 5 million frames-per-second video imaging. This is used to identify and explain two primary mechanisms which produce the smallest and fastest splashed secondary droplets, i.e. ejecta sheets and singular jets. Using a novel 25-m-tall vacuum tube we generate very large impact velocities, to reach regimes in parameter-space never studied before. During the earliest stage of the impact a fast-moving horizontal ejecta sheet emerges from the neck between drop and pool. The breakup of this sheet forms a myriad of micron-size droplets. The ejecta bending is dominated by air resistance, which we investigate under reduced ambient pressures and successfully model based on Bernoulli suction which pulls down the ejecta to hit the pool surface. The ejecta can initially bend up or down depending on the relative viscosities of the drop and pool, bending up if the pool is less viscous. Singular jets are produced by the collapse of drop-impact craters for deep pools, when a dimple forms at the bottom of the crater focusing the energy into a micron-sized region, with jetting velocities over 100 m/s. We use Gerris to study the fine details, obscured in the experiments. In the second part, we study the coalescence of water droplets inside an oil emulsion, developing an empirical relation between the coalescence interaction time tc and the modified shear-rate. This is done by tracking 3-D drop trajectories inside a microchannel, with two perpendicular high-speed cameras. For droplets in crude oil, we implement near-infrared visualization in an innovative device to quantify demulsifier efficiency, using mono-disperse micro-droplets.
    Citation
    Tian, Y. (2020). Experiments on Drop-impact Splashing, Singular Jets and Coalescence in Emulsions. KAUST Research Repository. https://doi.org/10.25781/KAUST-7N1YP
    DOI
    10.25781/KAUST-7N1YP
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-7N1YP
    Scopus Count
    Collections
    Dissertations; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program

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