Heat transfer augmentation using periodically spherical dimple-protrusion patterned walls of twisted tape

Abstract

The heat transfer performances of pipes with twisted tape inserts having periodically spherical dimple-protrusion patterned walls are numerically investigated by Ansys Fluent under a constant heat flux of 5 W/cm2. The inserts having three different densities (N = 0, 30, and 45) and three different kinds of arrangement (composed of only dimples, only protrusions, and a combination of dimples and protrusions) with a constant twist ratio of 3 were tested for Reynolds numbers (Re) within the range from 3000 to 27000. Comparing the turbulence models proposed the validated realizable k-ϵ model coupled with enhanced wall function to employ on the numerical simulations. While the highest Nusselt number (Nu) and friction factor (f) values for the presented study were found for the dense protruded twisted tape (D-PT) arrangement at Re values lower than 18000 and for dense dimpled-protruded twisted tape (D-DPT) arrangement for the Re greater than 18000, dimpled-protruded twisted tape (DPT) and dimpled twisted tape (DT) sequences reached the lowest f values of 0.365 and 0.322 at Re = 3000, respectively. D-DPT and D-PT sequences reached the highest thermal performance factor (TPF) values of 1.508 and 1.478 at Re = 3000, respectively. All patterned twisted tapes performed better Nu than conventional twisted tapes in the analyzing range and performed better TPF than typically twisted tapes in the Re region of less than 6000.