A semi-empirical equation used for heat transfer in turbulent flow with Reynolds numbers ranging from 5,000 to 200,000 inside long tubes and defined as:

and is equal to $0.023{\text{Re}}^{-0.2}$. It applies over a range of Prandtl numbers from 0.6 to 120, but should not be used for Reynolds numbers below 6,000 or for molten metals that have unusually low Prandtl numbers.