The turbulent Prandtl number (Pr) is a non-dimensional term defined as the ratio between the momentum eddy diffusivity and the heat transfer eddy diffusivity.  It is useful for solving the heat transfer problem of turbulent boundary layer flows.  The simplest model for Pr is the Reynolds analogy, which yields a turbulent Prandtl number of 1.  From experimental data, Pr has an average value of 0.85, but ranges from 0.7 to 0.9 depending on the Prandtl number of the fluid in question.