EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT IN A PLATE FIN HEAT EXCHANGER USING RECTANGULAR TYPE WINGLETS
Plate fin heat exchangers, because of their compactness, low weight and high performance, are used in either individually or as components of a large thermal system. The theoretical or numerical solutions often suffer from oversimplification of fin and winglet channel geometry and simplifying assumptions made. The vortex generators in the form of a rectangular winglets are used in present study. These winglets are mounted by punching on the fin surfaces. These winglets induce stream wise longitudinal vortices. These vortices disrupt the growth of the thermal boundary layer and serves to bring about heat transfer enhancement between the fluid and the fin surfaces. The geometrical configuration considered in this study is representative of a plate-fin heat exchanger. Air is taken as the working fluid. This research work gives a performance data for rectangular winglets in a plate-fin heat exchanger. In order to evaluate the overall heat transfer performance, the factor η = (Nu/Nuo)/(f/fo), is determined, where comparison between with and without winglets are taken into consideration. The heat transfer enhancement is observed with the use of winglets and concluded that the heat transfer increases with the increase in the angle of attack and Reynolds number. The experiments are performed varying the geometrical sizes and the angles of attack for winglets. Rectangular type winglets with aspect ratios (L/H) of = 2, 3 and 4 with longitudinal pitch (staggered) 20, 40 & 60 mm, are studied at angle of attacks 20°, 40° and 60° at constant surface temperature, 95°C. The results indicate that the stream wise vortices generated by a winglets show optimum performance at the angle of attack, 40° with aspect ratio (L/H), 4 for longitudinal pitch of 20 mm. The overall heat transfer performance observed approximately 27 % higher than traditional baseline fins (triangular plain fins) by this passive technique. The evaluation of heat transfer augmentation based on the overall heat transfer performance factor, η, shows contradictory results in case of plate fin heat exchanger to the widely held axiom that the effect induced by the winglets on the heat transfer augmentation diminishes in the turbulent flow regime.