Dimensionless quantity calculated as the ratio of momentum diffusivity (kinematic viscosity)
\nu to thermal diffusivity
a:
(1) | {\rm Pr} = \frac{\nu}{a} |
It is dynamic property of the substance at a given pressure and temperature: {\rm Pr} = {\rm Pr}(p, T)
For most gases over a wide range of temperature and pressure, Prandtl number is approximately constant at around
{\rm Pr} = 0.71.
For water in STP: {\rm Pr} = 7.56.