LAMINAR MIXED CONVECTION HEAT-TRANSFER IN EXTERNALLY FINNED PIPES

The influence of aiding and opposing buoyancy forces on forced convect ion heal transfer in vertically oriented, externally finned pipes is s tudied numerically. A periodically varying external heat transfer coef ficient is used to model the finned surface. Results are presented in terms of the streamwise variation of the fluid bulk temperature and tu be-side Nusselt number, axially-averaged and periodically fully develo ped Nusselt number values, and axial velocity and temperature profiles . Average Nusselt number correlations for both constant and periodical ly varying Blot numbers are also presented. Buoyancy induced effects a re observed to increase with higher levels of the external heat transf er coefficient (or fin effectiveness) and decrease with increasing int er-fin spacing. A constant spatially averaged Blot number approximatio n to the periodic variation is found to be satisfactory only in the pe riodically developed regions of the flow.