Packing size and shape effects on forced convection in large rectangular packed ducts with asymmetric heating

An experimental and numerical investigation of fully developed forced conve ction in large rectangular packed ducts is presented. The horizontally orie nted ducts have the length-to-separation distance ratio of L/H = 16 with tw o aspect ratios of W/H = 8 and 4. A constant heat flux is supplied to the t op wall, while the bottom and side walls are insulated. Packing of hard pol yvinyl chloride Raschig rings with outside diameters of 48 and 34 mm, and e xpanded polystyrene spheres with diameters of 48, 38 and 29 mm are used in the air flow passage. The experiments are carried out for 200 < (Re-p = ud( p)/v(f)) < 1450, and 4.5 < d(e)/d(p), < 9.0. The pressure drop, the heat fl ux, axial and transverse temperature profiles of air flow inside the ducts are measured at the steady state. Similar experiments have also been carrie d out with empty ducts. Numerical predictions of two-dimensional quasi-homo geneous model are found to be in agreement with the experimental results of the packed ducts. The correlation equations for the Nusselt number are obt ained. It is found that the introduction of packing into the air flow passa ge yields about a three times increase in the wall-to-air heat-transfer rat e compared with that of the empty duct. (C) 1999 Elsevier Science Ltd. All rights reserved.