Heat transfer and pressure performance of a plain fin with radiantly arranged winglets around each tube in fin-and-tube heat transfer surface

A radiantly arranged LVGs enhanced fin-and-tube structure is numerically investigated in this paper to enhance air side heat transfer. The arrangement of LVGs is totally different from existing publications. In the proposed structure there exist 12 winglets around each tube. The attack angles are 50, 50, 50, 50, 70 and 110°, respectively. The height ends of the winglets are further away from the tube, while the closed point ends of winglets are close to the tube wall. Heat transfer and pressure drop performance is compared with other three structures: an arc-shaped wavy fin-and-tube surface, a common-flow-down LVGs enhanced fin-and-tube surface and a plain plate fin-and-tube surface. The simulation results show that the 12 winglets form five local passages which can guide the moving fluid from the main flow to the tube wall, leading to some impinging effect or reducing the wake region behind the tube. The performance evaluation of the four structures is conducted by using the newly proposed ln (Nue/Nuo) vs. ln (fe/fo) plot based on energy saving. It is found that the proposed radiantly arranged LVGs enhanced fin-and-tube surface is the best. The field synergy principle is adopted to analyze the four structures and it is found that the domain averaged synergy angle of the proposed radiantly arranged LVGs enhanced structure is significantly less than that of other three cases. Finally characteristics of the proposed fin-and-tube surface with five tubes are investigated at five fin pitches and compared with the wavy structure of six tubes at the same other conditions. It is found that the proposed structure of five tubes can replace the wavy structure of six tubes.