The following calculation employs the heat transfer theory to calculate the pipe surface temperature by utilising the standard pipe size (ASME B36.10M) and the thermal conductivities of commercially available wrought steel and insulating materials. The results of calculation are the surface temperature of a bare pipe and those of an insulated pipe, thereby shows a contrast between the two different scenarios.
The basic equation of the overall heat transfer (per unit length) across an insulated pipe is:
With the of wind speed taken into consideration, the calculated surface temperature sees the combined effect of forced convection and natural convection around a pipe rather simply the natural convection in still air. The dimensionless Nusselt number (Nu) which is a function of Grashof number (Gr), Prandtl number (Pr) and Reynolds number (Re), provides a basis for calculating the heat transfer coefficient of forced convection and natural convection.
Holman (2010) presented the following equations the calculate Nusselt number of both forced and natural convections.
Forced Convection, Cross Flow Over Cylinders