Study of near-cup droplet breakup of an automotive Electrostatic Rotary Bell (ESRB) atomizer using high-speed shadowgraph imaging

Jacob E. Wilson, Stephen W. Grib, Adnan Darwish Ahmad, Michael W. Renfro, Scott A. Adams, Ahmad A. Salaimeh

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Electrostatic Rotary bell (ESRB) atomizers are used as the dominant means of paint application by the automotive industry. They utilize the high rotational speed of a cup to induce primary atomization of a liquid along with shaping air to provide secondary atomization and transport. In order to better understand the fluid breakup mechanisms involved in this process, high-speed shadowgraph imaging was used to visualize the edge of a serrated rotary bell at speeds varying between 5000 and 12,000 RPM and with a water flow rate of 250 ccm. A multi-step image processing algorithm was developed to differentiate between ligaments and droplets during the primary atomization process. The results from this experiment showed that higher bell speeds resulted in a 26.8% reduction in ligament and 22.3% reduction in droplet Sauter Mean Diameters (SMD). Additionally, the ligament (ranging from 40 to 400 μm) diameters formed bimodal distributions, while the droplet (ranging from 40 to 300 μm) diameters formed a normal distribution. Velocities were also measured using particle tracking velocimetry, in which size-dependent velocities could then be computed. Droplet velocities were affected more by rotational speed than droplet SMD, while ligaments were affected by other factors than the rotational speed and ligament SMD.

Original languageEnglish
Article number174
Issue number5
StatePublished - May 1 2018

Bibliographical note

Funding Information:
Funding: This research was funded internally by the University of Kentucky Institute of Research for Technology Development (IR4TD).

Publisher Copyright:
© 2018 by the authors.


  • Atomization
  • Droplet size distributions
  • Droplets
  • Rotary bells
  • Shadowgraph

ASJC Scopus subject areas

  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry


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