Hagen number

The Hagen number is a dimensionless number used in forced flow calculations. It is the forced flow equivalent of the Grashof number.

It is defined as:

: $mathit\{Hg\}\; =\; -frac\{1\}\{\; ho\}frac\{mathrm\{d\}\; p\}\{\; mathrm\{d\}\; x\}frac\{L^3\}\{\; u^2\}$

where:

*$frac\{mathrm\{d\}\; p\}\{mathrm\{d\}\; x\}$ is the pressure gradient
*"L" is a characteristic length
*"$ho$" is the fluid density
*"$u$" is the kinematic viscosity

For natural convection

:

and so the Hagen number then coincides with the Grashof number.

ee also