Numerical Analysis on Laminar Forced Convective Heat Transfer in Thermal Entrance Region of Circular Tube with Internal Longitudinal Fins

摘要

The laminar forced convective heat transfer is numerically analyzed in a circular tube with internal longitudinal fins, where the effect of the finite conductivity of the finned tube was taken into account in order to investigate the application of carbon steel tubes in heat exchangers. It is assnmed that the velocity profiles are fu1ly-develped at the inlet of the tube and that the heat flux at the outer wall is set to be uniform. Owing to the axial symmetry, the cross sectional area to be solved is limited to the circular sector which consists of two parts, fluid and finned tube regions. The governing equation for energy was analyzed by the implicit marching finite difference method after the velocity profiles were numerically obtained. First the numerical solutions in the thermal developing region obtained by the current method were compared with the numerical results based on the fully developed energy and momentum equations and good agreement between the former results far from the inlet and the latter was confirmed. For the wide range of geometrical parameters as well as the conductivity ratio of finned tube to fluid, the numerical calculations were carried out. It is found that the augmentation of the heat transfer is induced by a flow peak between the fins facing each other and that the optimal fin number at the thermal develping region in most cases agrees to that of the fully-developed case.