Heat transfer enhancement in a tube by variable cross section twisted tape

In this thesis, a numerical study is conducted to investigate the influence of spherical-shaped and teardrop-shaped patterned walls of twisted tapes on thermo-hydraulic performance enhancement. All patterned twisted tapes were investigated by using Ansys Fluent under a constant heat flux of 5 W/cm2 for Reynolds numbers (Re) within the range of 3000 – 27000. Besides, they have different pattern numbers (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. Furthermore, the configurations of teardrop patterned twisted tapes align in two different flow directions. The results show that the dense spherical dimpled-protruded twisted tape (D-DPT) and the dense teardrop dimpled-protruded twisted tape (D-TDP) reach the highest thermal performance factor (TPF) values of 1.508 and 1.517, respectively at Re=3000. All patterned twisted tapes have higher Nusselt number (Nu) values than traditional twisted tape (TT) in the tested Re region. Moreover, all dense versions of them have higher Nu and friction factor (f) than those of their sparse versions.