# Grashof number

The Grashof number ( by: Franz Grashof 1826-1893 ) is a dimensionless number in fluid dynamics. It indicates the ratio of the buoyancy of a fluid to the force acting on the fluid force by viscosity. The Grashof number is suitable for the estimation of flow on thermal convection.

The Grashof number is defined as:

- Acceleration due to gravity ( SI unit: )
- Thermal expansion coefficient ( SI unit: 1 / K)
- Temperature ( SI units: K)
- Resting temperature ( SI unit: K)
- Characteristic length ( SI units: m )
- Kinematic viscosity ( SI unit: )

More: You are the ratio of the buoyancy force to the viscous force multiplied by the ratio of inertial force to viscous force in a fluid. This occurs in the equation to the viscosity in the square.

In the reformulation of the Navier -Stokes equations in the dimensionless form is given to the above definition equivalent form yields

- Density (eg, in SI units: kg / m³)
- Density in the undisturbed fluid

One can convert the Grashof number and a Reynolds number equivalent to then apply the formulas of the free convection in the forced can. The conversion is performed according to: