Enhancement of Natural Convection Heat Transfer from Horizontal Rectangular Fin Arrays with Perforations in Fin Base

The horizontal rectangular fin arrays with natural convection are often used as the heat sinks for high power LEDs. For long fin arrays, the overall convection heat transfer coefficients are quite low because the inner surfaces are not well ventilated with cold surrounding air. In this study, we introduce perforations in the fin base to improve ventilation with cold air from below. Aluminum fin arrays with length of 380 mm, fin height of 38 mm, and fin spacing of 10 mm are analyzed numerically with a temperature difference of 55K between the fin base and the surrounding. To account for the unsteady flow in the long fin arrays, an unsteady model is adopted. In the analysis, we consider multiple equal-length, equally-spaced rectangular perforations which cover the full width of the fin spacing and have a total perforation length of a half of the fin length. The flow fields and the longitudinal distributions of the height-averaged local heat flux from fin surface are analyzed to describe the effects of fin-base perforations. Without perforations, the local heat transfer coefficients in the inner region are much lower than those near the fin ends. The perforations, especially locating in the inner region, improve ventilation and heat transfer performance significantly. The overall heat transfer coefficients with perforations are enhanced by a factor of 2.0 to 2.7. Under a fixed total perforation length, the conditions with more distributed shorter perforations exhibit higher improvements.