Noun
Prandtl number (plural Prandtl numbers)
A dimensionless number (symbol Pr) defined as the ratio of momentum diffusivity to thermal diffusivity.
Note that whereas the Reynolds number and Grashof number are subscripted with a length scale variable, the Prandtl number contains no such length scale in its definition and is dependent only on the fluid and the fluid state. Source: Internet
The Dittus-Boelter equation is: : where: : is the inside diameter of the circular duct : is the Prandtl number : for heating of the fluid, and for cooling of the fluid. Source: Internet