TURBULENT CONVECTION HEAT-TRANSFER IN LONGITUDINALLY CONDUCTING, EXTERNALLY FINNED PIPES

A numerical investigation is conducted of turbulent convection in a longitudinally conducting, externally finned pipe. Results reveal significant enhancement in heat transfer due to finning. The heat transfer rate to the fluid increases with increasing thermal conductivity of the pipe wall, with increasing values of the external heat transfer coefficient, and with decreasing interfin spacing. Heat transfer is underestimated by as much as 30 times in the developed region when the thermal conductivity of the pipe wall is not accounted for. The magnitude of this underestimation decreases with decreasing wall conductivity. Finning is found to be most effective at low values of wall conductivity, where a nearly 10-fold increase in heat transfer is noted. At high thermal conductivities in the wall, the Nusselt number and the pipe wall temperature vary monotonically in the axial direction, and this variation becomes increasingly nonmonotonic at lower thermal conductivities. A constant, spatially averaged, Biot number solution is found to give satisfactory results only for cases of high conductivity in the wall. The asymptotically developed Nusselt numbers compare well (within 7%) with the axially averaged values for the cases of conducting pipe wall.