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Study of Near-Cup Droplet Breakup of an Automotive Electrostatic Rotary Bell (ESRB) Atomizer Using High-Speed Shadowgraph Imaging

1
Mechanical Engineering, University of Kentucky, 151 Ralph G. Anderson Building, Lexington, KY 40506, USA
2
Ford Motor Company, 6200 Mercury Dr, Dearborn, MI 48126, USA
*
Author to whom correspondence should be addressed.
Coatings 2018, 8(5), 174; https://doi.org/10.3390/coatings8050174
Received: 9 March 2018 / Revised: 5 April 2018 / Accepted: 29 April 2018 / Published: 3 May 2018
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Abstract

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. View Full-Text
Keywords: rotary bells; atomization; droplets; shadowgraph; droplet size distributions rotary bells; atomization; droplets; shadowgraph; droplet size distributions
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Wilson, J.E.; Grib, S.W.; Darwish Ahmad, A.; Renfro, M.W.; Adams, S.A.; Salaimeh, A.A. Study of Near-Cup Droplet Breakup of an Automotive Electrostatic Rotary Bell (ESRB) Atomizer Using High-Speed Shadowgraph Imaging. Coatings 2018, 8, 174.

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