Effect of Hydraulic Diameter and Surface Roughness on Additively-Manufactured Offset Strip Fin Heat Exchanger Performance

Compact heat exchangers with air-side offset strip fins are commonly used where liquid-to-air heat transfer is required. The fins provide increased surface area for the air-side heat transfer, and the liquid is pumped through channels that are transverse to the air-flow direction. Traditionallymanufactured offset strip fin (OSF) heat exchangers are typically made by stamping sheet metal to produce fins with a sinusoidal or near square-wave fashion. These stamped sheets are then brazed or welded to the liquid channels. A plethora of empirical data and correlations exists to predict the heat transfer and pressure drop on the air-side of traditionally manufactured offset strip fin heat exchangers. Recently, additively-manufactured (AM) offset strip fin heat exchangers have been shown to provide manufacturing benefits, such as the ability to remove complicated liquid manifold welds as well as enhanced fin and oil channel features. Furthermore, they provide a convenient reference point for comparing the heat exchanger performance to that of a traditionally-manufactured equivalent. The present investigation shows empirical data from six additively-manufactured offset strip fin coupons of varying fin spacing and fin height to produce two groups of hydraulic diameters: 2.6 mm and 4.1 mm. The surface roughness of these coupons is notably different than traditionally-manufactured offset strip fins. The heat transfer and pressure drop behavior are compared to the correlations for traditionally-manufactured heat exchangers as well as ones derived specifically for ones that were additively manufactured.