Experimental design for flowfield studies of louvered fins

Abstract

The dominant thermal resistance for most compact heat exchangers occurs on the gas side and as such an understanding of the gas side flowfield is needed before improving current designs. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. Detailed measurements can be accomplished with large-scale models of these louvered fins to gain a better understanding of the flowfield. This paper describes a methodology used for designing an experimental model of a two-dimensional louvered fin geometry, scaled up by a factor of 20, that allows for flowfield measurements. The particular louver geometry studied for these experiments had a louver angle of 27° and a ratio of fin pitch to louver pitch of 0.76. Simulations using computational fluid dynamics (CFD) both aided in designing the large-scale louver model, resulting in a total number of 19 louver rows, and identified the region where the flowfield could be considered as periodic. This paper also presents two component velocity measurements taken in the scaled up model at Reynolds numbers of Re=230, 450, and 1016. For all three Reynolds numbers the flow was louver directed rather than duct directed. The results indicated that significant differences between the three Reynolds numbers occurred. While the flow entering the louver passage at Re=1016 still had remnants of the louver wake convected from two louvers upstream, the Re=230 case did not. Time-resolved velocity measurements were also made in the wake region of a fully developed louver for a range of Reynolds numbers. For 1000 < Re < 1900, there was an identifiable peak frequency for the velocity fluctuations giving a constant Strouhal number of St=0.17.