Heat transfer in a rectangular duct with perforated blockages and dimpled side walls

Heat transfer and pressure drop in a duct with three serial perforated blockages equipped with staggered jets were experimentally investigated. Eight types of jet holes and three types of side walls, including dimpled walls, were tested. For heat transfer measurements, the transient liquid crystal technique was used. Reynolds numbers based on the hydraulic diameter of the duct and inlet velocity ranged from about 10,000-30,000. Experimental results showed that the Nusselt number ratios decreased as the Reynolds number increased, and the friction factor ratios increased as the Reynolds number increased. The heat transfer coefficient and the pressure loss were strongly affected by the number and the configuration of jets. Compared to the smooth side wall case, the cases with dimpled side walls showed large increases in heat transfer with slight increments in pressure loss. Therefore, it was determined that the thermal performance factor could be enhanced by up to 25% by using a dimpled side wall in the duct with perforated blockages. (C) 2016 Elsevier Ltd. All rights reserved.