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Ohnesorge number

The Ohnesorge number, Oh , is a dimensionless number that relates the viscous and surface tension force.

It is defined as: Oh = \frac{ \mu}{ \sqrt{\rho \sigma L }}


  • μ is the liquid viscosity
  • ρ is the liquid density
  • σ is the surface tension
  • L is the characteristic length scale (typically- drop diameter)


The Ohnesorge number for a 3 mm diameter rain drop is typically ~0.002. Larger Ohnesorge numbers indicate a more influence of the viscosity .

This is often used to relate to free surface fluid dynamics such as dispersion of liquids in gases and in spray technology.[1] [2]


  1. ^ Lefebvre, Arthur Henry (1989), , New York and Washington, D.C.: Hemisphere Publishing Corp., ISBN 978-0-89116-603-0, OCLC 18560155
  2. ^ Ohnesorge, W (1936). "Formation of drops by nozzles and the breakup of liquid jets". Zeitschrift für Angewandte Mathematik und Mechanik (ZAMM) [Applied Mathematics and Mechanics] 16: 355-358. Berlin: Akademie Verlag.

See also

  • Laplace number - There is an inverse relationship, Oh = 1/\sqrt{La}, between the Laplace number and the Ohnesorge number. It is more historically correct to use the Ohnesorge number, but often mathematically neater to use the Laplace number.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ohnesorge_number". A list of authors is available in Wikipedia.
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