Degree Type

Dissertation

Date of Award

2021

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Major

Mech anical Engineering

First Advisor

Theodore J Heindel

Abstract

Atomization is a significant process in many industries, such as pharmaceuticals, agriculture, combustion, and spray drying. Atomization performance affects the efficiency and quality of these processes. Thus, it is important to know how the spray is influenced by various factors. The complexity of the atomization process makes it hard to theoretically formalize the breakup process; therefore, the accumulation of a large amount of experimental data is needed to study spray mechanisms. Primary breakup is the process during which a continuous liquid jet breaks up into ligaments and droplets. It is the initial stage of the atomization process and happens in the near-field region of the spray. However, it is hard to probe experimentally using optical-based methods because of the optical density of the liquid. X-ray based techniques provide an alternative for a better view. In this research, X-ray based diagnostics as well as backlit imaging were performed on the near-field region of sprays. The nozzle used was a two-fluid coaxial atomizer, and has been designed to be an open-source canonical atomizer that can be reproduced in any laboratory experiment or numerical simulation. Distilled water and air were used to create the spray. For X-ray radiography, potassium iodide was added to the water to increase the image contrast. Besides high-speed backlit imaging, a range of X-ray diagnostics were also performed, including tube X-ray radiography and X-ray computed tomography (CT), performed in the tube source X-ray facility in the Experimental Multiphase Flow Laboratory at Iowa State University, and white beam radiography and focused beam measurements, performed on the 7-BM beamline at the Advanced Photon Source (APS) at Argonne National Laboratory. In the experiment, a liquid core was observed and droplet tracking was performed in the near-field region. It is found that the influence of the swirl ratio on the spray is nonmonotonic due to the trade-off between the co-flow air and swirl air while the total amount of total air is constant. The liquid fraction distribution of the spray was calculated both by an Abel inversion performed on 2D projections and by X-ray CT reconstructions and results show that the Abel inversion of the tube source X-ray radiography by using the intensifier camera recovers the spray properly with more accurate information and less computational effort.

DOI

https://doi.org/10.31274/etd-20210609-104

Copyright Owner

Danyu Li

Language

en

File Format

application/pdf

File Size

196 pages

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