fluid dynamics, the Graetz number (Gz) is a dimensionless numberthat characterises laminar flow in a conduit. The number is defined as:
:"di" is the internal diameter in round tubes or hydraulic diameter in arbitrary cross-section ducts
:"L" is the length:"Re" is the
Reynolds numberand:"Pr" is the Prandtl number.
When used in connection with mass transfer the Prandtl number is replaced by the
Schmidt numberwhich expresses the ratio of the momentum diffusivity to the mass diffusivity.
The quantity is named after the physicist
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