Thermo-hydraulic Performance Investigation of Twisted Tapes Having Teardrop-Shaped Dimple-Protrusion Patterns

Abstract

The teardrop pattern observed to be more efficient in straight tubes was examined for the first time in a twisted tape wall. The thermo-hydraulic performances of twisted tapes having periodically teardrop-shaped dimple-protrusion patterned walls are numerically investigated. The new designs have two different densities (N=30, and 45), three alternative types of layouts (composed of only protrusions, only dimples, and a combination of dimples and protrusions) align in two different flow directions. Designs have a constant twist ratio (TR) of 3, and calculations are conducted for Reynolds numbers (Re) between 3000 and 27000 by Ansys Fluent under a constant heat flux of 50000 W/m2. All cases have higher Nusselt number (Nu) values than traditional twisted tape (TT) in the tested Re region. Besides, all arrangements except the teardrop protruded twisted tape have higher thermal performance factors than the TT in the Re range from 3000 to 5500. All dense versions of the teardrop patterned twisted tapes have higher Nu and friction factor (f) than sparse versions of them. The dense teardrop dimpled-protruded (D-TDP) case reaches TPF of 1.517, the highest value among the tested twisted tapes, at Re = 3000.