Enhancement of Heat Transfer in a Circular Wavy-surfaced Tube with a Helical-tape Insert

Abstract

The purpose of the present study is to investigate experimentally the heat transfer and turbulent flow friction characteristics in a circular wavy-surfaced and constant heat-flux tube with a helical-tape insert. In the experiment, heat transfer augmentation is expected from both the turbulence of flow near the tube wall produced by the wavy surface and the swirling flow generated by the helical-tape. The experiments are based on Reynolds number at the tube inlet, ranging from 3000 to 9200. The experimental results obtained are compared with those from plain tubes in the literature. The results show that the heat transfer rate from using the wavy surface and helical tape insert is considerably higher than that from the plain tube. The Nusselt numbers and friction factors are found to be, respectively, 3.0 and 50 times over the plain tube for the tube with wavy- surfaced wall alone and to be 4.2 and about 110 times for the tube with combined wavy-surfaced wall and the helical-tape. The wavy-surfaced tube combined with the helical-tape provides higher heat transfer rate and friction factor than the wavy-surfaced tube alone around 57% and 125%, respectively. In addition, effect of insertion of the helical-tape with/without core-rod is also investigated.