Grashof number

The Grashof Number is a dimensionless number which approximates the ratio of bouyancy force to the vicous force acting on a fluid.

Gr = ( g β (Ts - Tinf) L3 ) / ν^2

  g     gravity
  β     volumetric thermal expansion coefficient
  Ts    source temperature
  Tinf   quiescent temperature
  L     characteristic length
  ν     kinematic viscosity

See also Reynolds number, Fluid Mechanics, Bouyancy.