Hagen number
Encyclopedia
The Hagen number is a dimensionless number used in forced flow calculations. It is the forced flow equivalent of the Grashof number and was named after the German hydraulic engineer G. H. L. Hagen
.
It is defined as:
Gotthilf Heinrich Ludwig Hagen
Gotthilf Heinrich Ludwig Hagen was a German physicist and hydraulic engineer.Hagen was born in Königsberg, East Prussia . He studied mathematics, architecture, and civil engineering at the University of Königsberg...
.
It is defined as:
-
where:
is the pressure gradient- L is a characteristic length
is the fluid densityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
is the kinematic viscosity
For natural convection
and so the Hagen number then coincides with the Grashof number.