Ohnesorge number

The Ohnesorge number (symbol: Oh) is a dimensionless parameter of physics. It describes the impact toughness in the deformation of drops and bubbles.

Basically six forces acting on a falling drops:

  • Inertia of the liquid and the gas
  • Viscosity of the liquid and gas
  • Gravity and surface strength of the liquid

The two most important, the surface force and the inertial force is recognized when the Weber number ( We), the viscosity of the liquid with the Ohnesorge number.

  • Dynamic viscosity (in SI units Pas )
  • Density of the liquid of the droplet ( in SI units kg/m3)
  • Surface tension ( in SI units N / m)
  • Characteristic length (such as the bubble diameter ) ( in SI units m)
  • Reynolds number
  • Weber number

Importance of the ratio of Ohnesorge number to Reynolds number in the characterization of Fluidzerstäubung, a specialist field of process engineering. In the double logarithmic Ohnesorge diagram, the Ohnesorge number is plotted for the Reynolds number, so that the states " Rayleigh breakup ", " wavy sheet disintegration " and " sputtering " can be distinguished.