X-ray Imaging Techniques to Quantify Spray Characteristics in the Near Field

Abstract

<p>Liquid sprays play a key role in many engineering processes, including, but not limited to, food processing, coating and painting, 3D printing, fire suppression, agricultural production, and combustion systems. Spray characteristics can easily be assessed in the mid- and far-field regions, well after liquid sheet breakup and droplet formation, using various optical and/or laser diagnostic techniques. The conditions in the near-field region influence mid- and far-field characteristics; however, near-field measurements are extremely challenging because the spray in this region is typically optically dense where optical and laser diagnostics are generally ineffective. This paper provides an overview of the various X-ray imaging techniques that can be used to characterize the near-field region of a spray. X-rays produced with tube sources as well as synchrotron sources will be discussed. Using tube-source X-rays, 2D radiographic videos are possible showing qualitative spray information. The 2D radiographs can also provide quantitative measurements of the optical depth (OD) in the near-field region. Tube sources can also provide X-ray computed tomography imaging that can produce time-average 3D density (mass distribution) maps of the spray. X-rays from synchrotron radiation provide a high-flux X-ray beam that can be used to provide high spatial and temporal resolution of the spray equivalent path length (EPL) as well as other characteristics, but it is more challenging to implement than using a common tube source. Various examples of these X-ray imaging techniques will be discussed.</p>