Thermal performance enhancement in a circular tube with louvered V-winglet inserts: effect of louver angle and opening area

This paper presents an evaluation of the thermal performance of a circular tube with louvered V-winglet inserts (LVWs) under turbulent flow conditions. The LVW parameters are fixed with an attack angle (α) of 45°, a pitch ratio (P R ) of 0.5, and a blockage ratio (B R ) of 0.3. The effects of varying the hole diameter ratio (d R ) from 0.4 to 0.8 and the louver angle (β) from 5° to 30° are investigated. The results show that the LVWs generate a main vortex flow and a secondary flow in the flow direction, as well as a pair of counter-rotating flows in the transverse plane. These enhance fluid mixing and improve heat transfer. The LVWs significantly reduce frictional loss (which helps to lower pumping/blowing energy losses) while only slightly reducing heat transfer, thereby improving overall thermal performance compared to that of solid V-winglets (SVWs). Increasing the d R and β values results in decreased heat transfer and frictional loss. Within the studied range, the LVWs achieved Nu/Nu 0 , f/f 0 , and TEF values of approximately 5.01–9.93, 65.46–208.13, and 1.025–2.055, respectively. The highest TEF, 2.055, was obtained at d R = 0.8, β = 10°, and Re = 3000.