Visualizing Near-Field Spray Characteristics With Broadband X-Rays

Liquid sprays play a key role in many engineering processes (e.g., food processing, coating and painting, 3D printing, fire suppression, agricultural production, combustion systems, etc.). Spray characteristics can easily be assessed in the mid- and far-field regions, well after liquid sheet breakup and droplet formation, using various optical/laser diagnostic techniques. The conditions in the near-field region, near the spray nozzle exit, can influence mid- and far-field characteristics; however, near-field measurements are extremely challenging because the spray in this region is typically optically dense and optical/laser diagnostics are ineffective in this region. This study presents the advantages and challenges of using broadband X-rays to characterize the near-field region of a spray. A generic spiral jet hollow cone spray nozzle is used to demonstrate near-field spray imaging for three different flow conditions. Radiographic movies of the spray show a very dynamic near-field region. X-ray computed tomography (CT) reconstructions of the spray display a 3D map of the time-average spray distribution. The two X-ray imaging modes provide qualitative information of the near-field spray region. A discussion of the quantitative measures that can be acquired from X-ray radiographs and CT images is provided.