Ohnesorge number - Alchetron, The Free Social Encyclopedia

The Ohnesorge number (Oh) is a dimensionless number that relates the viscous forces to inertial and surface tension forces. The number was defined by Wolfgang von Ohnesorge in his 1936 doctoral thesis.

It is defined as:

O h = μ ρ σ L = W e R e ∼ viscous forces inertia ⋅ surface tension

Where

μ is the liquid viscosity

ρ is the liquid density

σ is the surface tension

L is the characteristic length scale (typically drop diameter)

Re is the Reynolds number

We is the Weber number

Applications

The Ohnesorge number for a 3 mm diameter rain drop is typically ~0.002. Larger Ohnesorge numbers indicate a greater 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.

In inkjet printing, liquids whose Ohnesorge number is less than 1 and greater than 0.1 are jettable (1<Z<10 where Z is the reciprocal of the Ohnersorge number).

References

Ohnesorge number Wikipedia

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