# Graetz Number

Graetz number, abbreviated as Ga, is a dimensionless number that characterizes laminar flow with heat transfer in a conduit. This number is used to determine the thermal development on the entrance to ducts. A Graetz number of 1000 and below is usually where a flow is considered thermally developed.

\(\large{ Gz = \frac {D_h}{l} \; Re \;Pr }\) Where: \(\large{ Gz }\) = Graetz number \(\large{ D_h }\) = hydraulic diameter \(\large{ l }\) = length \(\large{ Re }\) = Reynolds number \(\large{ Pr }\) = Prandtl number |