NUMERICAL SIMULATION OF CONVECTIVE HEAT TRANSFER AND PRESSURE DROP IN TWO TYPES OF LONGITUDINALLY AND INTERNALLY FINNED TUBES

With two kinds of methods of boundary condition treatment, three-dimensional turbulent flow and heat transfer problems in two types of internally finned tubes with a blocked core-tube have been studied numerically by the realizable k-epsilon model. The numerical simulation results obtained from two calculation models were compared with experimental data. It was found that the simulation results obtained from the turbulent flow model are closer to the experimental values than those obtained from the laminar flow model. Meanwhile, it has been found that the critical Reynolds number for the flow that develops in internally finned tubes from a laminar flow to a turbulent one is much less than the Reynolds number for traditional bare tubes. The calculation results also indicate that the periodical ridges inside the finned tubes change the distribution of the inner flow field and temperature profile. Unlike straight tubes, in internally finned tubes, a secondary vortex flow emerges that plays a definitely destructive role for the flow boundary layer and increases the turbulent kinetic energy of the flow field. With the field synergy principle, a contrasting analysis of the intensified heat exchange mechanism for internally finned tubes and a bare annular tube was performed quantitatively. The results show that the field synergy degree of longitudinally ridged and internally finned tubes is better than that of bare annular tubes, which enhance heat transfer.