Graetz Number

Graetz number, abbreviated as Ga, a dimensionless number, also known as the Graetz ratio or Graetz problem parameter, 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.  The Graetz number describes the relative significance of convective heat transfer and conductive heat transfer in the flow.  It indicates the extent to which the fluid flow influences the heat transfer process.  A high Graetz number indicates that convection dominates over conduction, while a low Graetz number suggests that conduction is more significant.

In practical applications, the Graetz number is commonly used to analyze and design heat exchangers, where heat is transferred between two fluids separated by a solid wall.  It helps engineers assess the efficiency and performance of the heat exchanger and determine the appropriate design parameters for optimal heat transfer.

 

Graetz number formula
\( Gz \;=\; ( D_h \;/\; l ) \; Re \;Pr \)     (Graetz Number) \( D_h \;=\; Gz \; l \;/\; Re \; Pr \)  \( l \;=\; D_h \; Re \; Pr \;/\; Gz \)  \( Re \;=\; Gz \; l \;/\; D_h \; Pr \)  \( Pr \;=\; Gz \; l  \;/\; D_h \; Re \)
Symbol	English	Metric
\( Gz \) = Graetz number	\(dimensionless\)	\( dimensionless \)
\( D_h \) = pipe hydraulic diameter	\(ft\)	\(m\)
\( l \) = pipe length	\(ft\)	\(m\)
\( Re \) = Reynolds number	\(dimensionless\)	\( dimensionless \)
\( Pr \) = Prandtl number	\(dimensionless\)	\( dimensionless \)