Campus Units

Mechanical Engineering, Chemical and Biological Engineering

Document Type


Publication Version

Accepted Manuscript

Publication Date


Journal or Book Title

International Journal of Multiphase Flow




Understanding the near-field region of a spray is integral to optimization and control efforts because this region is where liquid break-up and spray formation occurs, setting the conditions under which the spray dynamics evolve under the gas turbulence and droplet inertia. However, the high optical density of this region complicates measurements; thus, it is not yet well characterized. This paper is intended to compare four of the leading experimental techniques that are being used or developed to study the near-field region of a spray. These techniques are shadowgraphy, tube source X-ray radiography, high-speed synchrotron white-beam X-ray imaging, and synchrotron focused-beam X-ray radiography. Each of these methods is applied to a canonical spray, using the same nozzle, under identical flow conditions. Synchrotron focused-beam radiography shows that a time-averaged Gaussian liquid distribution is a valid approximation very near the nozzle, before the core has broken apart. The Gaussian behavior continues as the spray progresses further downstream, showing self-similarity. A spray angle can be defined from the linear spreading of the Gaussian intensity distribution with downstream distance. The spray angle found from shadowgraphy is validated with focused-beam testing. Additionally, a novel method of estimating the intact length of the spray from different X-ray techniques, that uses broadband illumination, is presented.


This is a manuscript of an article published as Bothell, Julie K., Nathanael Machicoane, Danyu Li, Timothy B. Morgan, Alberto Aliseda, Alan L. Kastengren, and Theodore J. Heindel. "Comparison of X-ray and optical measurements in the near-field of an optically dense coaxial air-assisted atomizer." International Journal of Multiphase Flow (2020): 103219. DOI: 10.1016/j.ijmultiphaseflow.2020.103219. Posted with permission.

Copyright Owner

Elsevier Ltd.



File Format


Available for download on Thursday, January 13, 2022

Published Version