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 convection in large rectangular packed ducts is presented. The horizontally oriented ducts have the length-to-separation distance ratio of L/H = 16 with two aspect ratios of W/H = 8 and 4. A constant heat flux is supplied to the top wall, while the bottom and side walls are insulated. Packing of hard polyvinyl chloride Raschig rings with outside diameters of 48 and 34 mm, and expanded 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 flux, axial and transverse temperature profiles of air flow inside the ducts are measured at the steady state. Similar experiments have also been carried out with empty ducts. Numerical predictions of two-dimensional quasi-homogeneous model are found to be in agreement with the experimental results of the packed ducts. The correlation equations for the Nusselt number are obtained. It is found that the introduction of packing into the air flow passage yields about a three times increase in the wall-to-air heat-transfer rate compared with that of the empty duct. (C) 1999 Elsevier Science Ltd. All rights reserved.