In petroleum processing plants, it is often necessary to pump highly viscous liquids such as asphalt through pipes. In order to keep pumping costs within reason, the pipelines are electrically heated to reduce the viscosity of the asphalt. Consider a 15-cm-OD uninsulated pipe and an ambient temperature of 20°C. How much power per meter of pipe length is necessary to maintain the pipe at 50°C? If the pipe is insulated with 5 cm of fiberglass insulation, what is the power requirement?
GIVEN
An electrically heated pipe
Diameter (D) = 15 cm = 0.15 m
Pipe surface temperature (Tsp) = 50°C
ASSUMPTIONS
The pipe is horizontal and in quiescent air
Radiative heat transfer is negligible
No heat is transferred to the fluid in the pipe