Analysis on enhanced turbulent heat transfer and flow characteristic in a twisted and dimpled oval tube

Abstract

This work reveals the heat transfer and flow characteristic in a twisted and oval tube under turbulent flow and constant heat flux conditions. Numerical analyses were carried out on several twisted and oval tube configurations. In order to clearly reveal the effect of dimples in the swirl flow, the twisted oval tubes with and without dimples are considered. In order to enhance the convective heat transfer, the dimples were placed in the narrowing region of the twisted tube where the heat transfer was inefficient. The results indicate that the dimples on the twisted tube significantly increase the heat transfer, although they cause to slightly increase pressure drop penalty. While the decrease in the pitch length induced to enhance the heat transfer, it significantly and negatively affected the hydraulic performance of the tube. Furthermore, while the dimples on the twisted oval tube induce the average Nusselt number to increase by 14.8%, they cause to the friction factor increase by 18.0%. The best configuration that is the case of dimpled twisted oval tube having pitch length of 200 mm at Reynolds number of 10,000, yields thermo-hydraulic performance criteria of 1.428.