The dynamics of head-on collision of unequal-size droplets were experimentally and theoretically investigated, with emphasis on identifying distinct collision outcomes and interpreting the size-ratio dependence. A unified regime diagram in terms of bouncing, permanent coalescence, and separation after coalescence was identified for hydrocarbon and water droplets in the parameter space of the size ratio and a collision Weber number. Experimental results show that the transition Weber number, Web-c, that separates the bouncing and permanent coalescence regimes, weakly depends on the size ratio, while the transition Weber number, Wec-s, that separates permanent coalescence and separation regimes, significantly increases with the size ratio. A theoretical model based on energy balance and scaling analysis was developed to explain the size-ratio dependence of Wec-s. The theoretical results show good agreement with the experimental data for tetradecane and decane droplets, with a moderate discrepancy for water droplets.
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Research Article| February 01 2012
Bouncing, coalescence, and separation in head-on collision of unequal-size droplets
Chenglong Tang, Peng Zhang, Chung K. Law; Bouncing, coalescence, and separation in head-on collision of unequal-size droplets. Physics of Fluids 1 February 2012; 24 (2): 022101. https://doi.org/10.1063/1.3679165
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