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Physics of Fluids / Volume 24 / Issue 2 / ARTICLES / Interfacial Flows

Phys. Fluids 24, 022101 (2012); http://dx.doi.org/10.1063/1.3679165 (15 pages)

Bouncing, coalescence, and separation in head-on collision of unequal-size droplets

Chenglong Tang, Peng Zhang, and Chung K. Law

Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA

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(Received 10 April 2011; accepted 3 January 2012; published online 1 February 2012)

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.

© 2012 American Institute of Physics

Article Outline

  1. INTRODUCTION
  2. EXPERIMENTAL METHODOLOGY
  3. EXPERIMENTAL OBSERVATIONS
    1. Collision images and time sequences
    2. Regime diagram in Δ- We space
  4. CRITERION FOR COALESCENCE-SEPARATION TRANSITION
    1. Theoretical model
    2. Evaluation of viscous dissipation in Stages 1–3
    3. Model predictions and comparison with experiments
  5. CONCLUDING REMARKS

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KEYWORDS and PACS

Keywords

drops, flow separation, two-phase flow, water

PACS

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3679165

PUBLICATION DATA

ISSN

1070-6631 (print)  
1089-7666 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
    J. R. Adam, N. R. Lindblad, and C. D. Hendrick, “Collision coalescence and disruption of water droplets,” J. Appl. Phys. 39, 5173 (1968)JAPIAU000039000011005173000001.

    M. R. Nobari, Y. J. Jan, and G. Tryggvason, “Head-on collision of drops - A numerical investigation,” Phys. Fluids 8, 29 (1996)PHFLE6000008000001000029000001.


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