Thermal performance improvement of a circular tube-and-fin heat exchanger by ellipsoidal protrusions on fin surfaces

Abstract

A novel fin stamped out with ellipsoidal protrusions is proposed to improve the performance of a circular tube-and-fin heat exchanger in this paper. The ellipsoidal protrusions have a similar function as the traditional plane or curved vortex generators that can generate longitudinal vortices in the flow channel. The effect of different attack angles of the ellipsoidal protrusions on the thermal performance of a circular tube-and-fin heat exchanger is numerically analyzed. The turbulent flow and heat transfer properties were investigated by Standard k-ε turbulence model with finite volume method. The results illustrated that the ellipsoidal protrusions can substantially improve the intensity of secondary flow and enhance the heat transfer. The ellipsoidal protrusions exhibited better heat transfer than the traditional vortex generators. Nu of the fin with ellipsoidal protrusions increased up to 31.73 % and 19.95 % compared with the smooth fin and the fin with vortex generators, respectively. Both Nu and f of the fin with ellipsoidal protrusions increased with the increase in attack angle. An optimum attack angle of 20° of the ellipsoidal protrusion existed for the highest thermal performance factor of 1.165. Fitted equations for Nu, f, and JF were provided for facilitating application to engineering.