Enhancement of natural convection heat transfer from horizontal rectangular fin arrays with perforations in fin base

Abstract

The overall convection heat transfer coefficients for long horizontal rectangular fin arrays are low because the surfaces in the inner region are poorly ventilated. In this study, we introduce perforations through the fin base to improve ventilation with cold air from below the fin base. Aluminum fin arrays with length L = 380 mm or 104 mm, fin height H = 38 mm, fin thickness tf = 1 mm, and fin spacing S = 10 mm are analyzed numerically with a temperature difference of 55 K between the fin base and the surroundings. Since the flow associated with horizontal rectangular fin arrays longer than about 100 mm tends to be unsteady, an unsteady model is adopted. In the main part of the present study, we analyze a single channel with multiple equal-length, equally spaced rectangular perforations which cover the full width of the fin spacing and have a total perforation length of L/2 or L/4. In addition, a multi-channel analysis is conducted for a selected fin array configuration with the uniform heat applied on the bottom surface at the middle part and longitudinal perforations arranged on the fin base outside the heated region. The perforations, especially located in the inner region, improve ventilation and heat transfer performance significantly. The patterns with more distributed shorter perforations exhibit better improvements. The overall heat transfer coefficients can be more than twice as large as that without perforations for long fin arrays. 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.