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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

FORMATION OF LIQUID SHEETS BY DEPOSITION OF MONO-DISPERSE SPRAYS ON A FLAT SURFACE

DOI: 10.1615/TFESC1.iam.012557
pages 1499-1509

Alireza Dalili
Center for Advanced Coating Technologies, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada, M5S 3G8

Sanjeev Chandra
Center for Advanced Coating Technologies, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada, M5S 3G8

Javad Mostaghimi
Center for Advanced Coating Technologies, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada, M5S 3G8


KEY WORDS: Droplet deposition, Droplet coalescence, Overlap, Drawback, Liquid film formation

Abstract

A pneumatic droplet generator was used to deposit multiple droplets of highly viscous liquid (87 wt% glycerin-in-water solution with viscosity of 124 centipoise) onto a flat, transparent Plexiglass substrate. Liquid was dispensed through a nozzle plate consisting of a 5 cm × 5 cm stainless steel sheet with 49 holes, each 400 pm in diameter, arranged in a square pattern of 7 holes in 7 rows with equal spacing of 5 mm between holes. The nozzle to substrate spacing was kept constant at 14 cm. Uniform sized droplets, 2.5 mm in diameter, impacted the substrate, spread and coalesced to create a liquid sheet. Using a high-speed camera placed underneath the transparent substrate droplet impact was recorded. When overlapping droplets were deposited, surface tension forces pulled impacting droplets towards those already on the surface, a phenomena known as drawback, agglomerating liquid on the surface. The area covered by liquid was measured from photographs using image analysis software. Experimental data yielded an equation correlating the increase of wetted area with time. The overlap ratio between the droplets during film formation was calculated for each time step using the wetted surface area measurement and the number of droplets deposited. Continuous liquid films formed once the overlap ratio surpassed the critical value of λ=0.293.

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