Thermodynamic characteristics of a novel combination of three-start twisted tube and oval dimples

In order to further improve the heat transfer performance inside tubes, a three-start twisted tube combined with oval dimples is proposed. The effects of dimple depths on the characteristics of fluid flow and heat transfer are numerically studied. The results indicate that the fluid mixing inside the tube is greatly improved by the longitudinal vortex generated behind the dimple compared with the corresponding three-start twisted tube without dimples. The maximum increases in Nusselt number and friction factor of the three-start twisted tube with dimples are 26.68% and 19.96% compared with the three-start twisted tube without dimples at Re = 2000, respectively. The maximum thermal performance factor of the three-start twisted tube with oval dimples is 1.19 compared with the three-start twisted tube without dimples. The thermal performance factor of the three-start twisted tube with oval dimples is up to 1.38 compared with the straight tube, which is larger than the reported twisted tubes, such as twisted tube, multi-start spirally corrugated tube, and twisted square duck reported in the open literature. The proposed three-start twisted tube with dimples provides a new choice for the heat transfer enhancement inside tubes.