Archimedes number

From Chemepedia

The Archimedes number serves as a correlation between two hydrodynamic or thermal phenomena when determining factors include buoyant and viscous forces. (consider rain droplet falling in air)



  • Ar = Archimedes number [dimensionless quantity]
  • Dp = Diameter of particle [m]
  • g = gravity [m/s2]
  • ρair = density of air (or other dominant fluid) [kg/m3]
  • ρp = density of particle [kg/m3]

The characteristic velocity of the particle in a particular medium may be obtained from the square root of kinetic energy and mass forces of the particle such that


The Reynolds number can then be acquired from the correlation:


Once the Reynolds number is known, it may be used to estimate the terminal velocity of a particle from:


The Archimedes number has also been characterized as a ratio of lift forces to internal friction forces.

These correlations are not mine, in search of source to be posted**