Investigation of turbulent heat transfer and fluid flow in longitudinal rectangular-fin arrays of different geometries and shrouded fin array

Abstract

The effects of the fin arrays geometries and also the fin tip-to-shroud clearance on the heat transfer, the fluid flow and the pressure drop characteristics of longitudinal rectangular-fin arrays have been investigated. During the experiments, different geometrical parameters were varied such as the fin height ( H), the fin thickness ( t), the inter-fin space ( W), the fins number and the fin tip-to-shroud clearance ( C) was varied parametrically; starting with the no-clearance case. Two shroud types were used (one plain and the other is equipped with wires coil as modified shroud). The heat transfer coefficient corresponding to the presence and absence of clearance were compared under the condition of equal airflow rate. Air is the working fluid, the flow regime is turbulent, and the flow pattern around the tested models was visualized. It was found that the axial pressure drop along the tested model is increased as the flow travels in the inter-fin region deeply in the stream-wise ( X) direction, with increasing the fin height, the Reynolds number, and with decreasing the inter-fin space and the fin thickness. The tested model-mean Nusselt number ( Nu m) increases with increasing the Reynolds number, the inter-fin space, and the fin thickness and with decreasing the fin height. Increasing the clearance between the fin tip-to-shroud decreases the tested model-mean Nusselt number and at certain clearance to fin height ratio ( C/ H)=1.25, the effect of the fin tips plain shroud goes off. It was also found that the tested model with the modified shroud (equipped with wire coil) gives higher mean Nusselt number than that with the plain shroud, and at certain clearance to fin height ratio ( C/ H)=1, the effect of the wire coil goes off. Eleven empirical equations are derived to correlate the mean Nusselt number as a function of the Reynolds number and other experimental variable parameters individual, fin thickness, fin height, inter-fin space and shroud clearance to fin height ratio. Finally the present work general empirical formula is given in the form Nu m =5.734146(Re L) 0.42422 W L 0.214171 H W −0.36263 t W 0.15250885 where 24,649⩽ Re L ⩽189,462, 3 mm⩽t⩽9 mm, 23 mm⩽H⩽92 mm, 10 mm⩽W⩽42 mm and L=150 mm.