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Compressible air entrapment in high-speed drop impacts on solid surfaces

Published online by Cambridge University Press:  28 January 2013

Yuan Liu
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China
Peng Tan
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China
Lei Xu*
Affiliation:
Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China
*
Email address for correspondence: [email protected]

Abstract

Using high-speed photography coupled with optical interference, we experimentally study the air entrapment during a liquid drop impacting a solid substrate. We observe the formation of a compressed air film before the liquid touches the substrate, with internal pressure considerably higher than the atmospheric value. The degree of compression highly depends on the impact velocity, as explained by balancing the liquid deceleration with the large pressure of the compressed air. After contact, the air film expands vertically at the edge, reducing its pressure within a few tens of microseconds and producing a thick rim on the perimeter. This thick-rimmed air film subsequently contracts into an air bubble, governed by the complex interaction between surface tension, inertia and viscous drag. Such a process is universally observed for impacts above a few centimetres high.

Type
Rapids
Copyright
©2013 Cambridge University Press

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