Experimental determination and computational fluid dynamics predictions of pressure loss in close-coupled elbows (RP-1682)

An experimental program was implemented to study pressure losses in HVAC duct systems associated with 305mm (12 in.) diameter close-coupled round five-gore elbows. The goal of this program was to experimentally verify a computational fluid dynamics model to accurately predict pressure losses in order to design duct systems more effectively. The results of this study showed that the loss coefficient increased as a function of separation distance between the elbows in a Z-configuration and decreased in a U-configuration. For both 305mm (12 in.) and 203mm (8 in.) diameter elbows, power law expressions correlating the combination loss coefficient data as a function of intermediate length for close-coupled elbows arranged in a Z-configuration or a U-configuration were presented. Computational fluid dynamics modeling with enhanced wall treatment using the k-E method was generally able to correctly predict elbow loss coefficients with an error of less than 15%.