Forming experiment of extruded tube with crossed ellipsoidal dimples and numerical investigation on heat transfer enhancement and flow characteristics

In this paper, an extruded tube with crossed ellipsoidal dimples was proposed to achieve heat transfer enhancement. This extruded tube was produced by mechanical extrusion, and an experiment was carried out to confirm the validity and rationality of the manufacture. The experimental results revealed that the error between geometric models built by mechanical simulation and actual manufacture was less than 15%. On this basis, the thermo-hydraulic characteristics were analyzed by numerical simulations. The CFD analysis indicated that the extruded tube improves thermo-hydraulic performance because the structure of dimples promotes mixing degree and boundary layer destruction. In addition, the dimensionless number Nu/Nu0, f/f0 and PEC were presented to illustrate the effects of geometry, such as dimple depth, pitch, the semi-major axis of rigid ellipsoidal blocks and dimple configuration. It was found that the maximum PEC = 2.4 was observed when D = 3 mm, P = 25 mm, a = 10 mm and the dimples configuration is cross. The range of Nu/Nu0, f/f0 and PEC for ETCED is 2.1-4.2, 1.75-7.24 and 1.7-2.4. Finally, the overall performance was compared among different enhanced tubes. The results showed that the extruded tube provided better overall performance than other enhanced tubes. The achievement of this paper can be extended to engineering applications in heat transfer enhancement.