A dimensionless equation used in heat transfer for forced convection. For a fluid with turbulent flow in a pipe of circular cross section:

where the Nusselt number is given by:

Reynolds number by:

and Prandtl number by:

The exponent n has a value of 0.4 for the heating of a fluid and 0.33 for the cooling of a fluid. This shows that doubling the forced flow of the fluid does not double the heat transfer coefficient, but raises it by a factor of 1.75 times. Compare natural convection.