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Atomization and Sprays

Impact factor: 1.235

ISSN Print: 1044-5110
ISSN Online: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.v20.i8.30
pages 697-720

VISCOELASTIC AIR-BLAST SPRAYS IN A CROSS-FLOW. PART 1: PENETRATION AND DISPERSION

Larry Li
Sheldon I. Green
Department of Mechanical Engineering, University of British Columbia, 3321−2260 West Mall, Vancouver, British Columbia, V6T1Z4, Canada
Martin H. Davy
Department of Mechanical Engineering, University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, British Columbia, V6T1Z4, Canada
Donald T. Eadie
Kelsan Technologies Corporation, 1140 West 15th Street, North Vancouver, British Columbia, V7P 1M9, Canada

ABSTRACT

Viscoelastic liquids, such as paints and coatings, are widely known to be more difficult to atomize than typical Newtonian liquids. What is not known, however, is how such a difference affects spray coating in field conditions. To address this, we have examined the effect of a cross-flow on two different air-blast sprays, one comprising water and the other an industrial coating. Using particle image velocimetry and raw Mie scattering, we measured the penetration and dispersion of both sprays over a wide range of spray:cross-flow momentum-flux ratios: 134 ≤ qab ≤ 1382. For both sprays, increasing the relative momentum-flux of the cross-flow led to reduced penetration but enhanced dispersion. The leeward boundary, meanwhile, consistently outspread the windward boundary, creating a bias for which we have proposed several plausible mechanisms. As for differences between the two sprays, the coating droplets outpenetrated the water droplets because they had lower drag-momentum ratios, due to their larger size. In response to this finding, we have proposed a new regression model for predicting the penetration of sprays differing in mean droplet size. The coating spray also spread later and more abruptly than did the water spray, particularly at low qab. To explain this behavior, we have suggested a physical mechanism based on the delayed breakup of the coating ligaments.