Enhancement of convection heat-transfer in a rectangular duct

Characteristics of wall-to-air heat transfer for a fully developed forced c onvection have been studied in a large rectangular packed duct with 160 cm heated length, 40 cm width, and for low bed equivalent diameter to particle diameter ratio. The separation distance between the top and bottom walls i s 10 cm. A uniform heat flux is supplied at the top wall, while the bottom wall is insulated. Raschig rings in two and spherical packing in three size s have been used in the air flow passage to investigate the enhancement of heat transfer due to packing. Temperature profiles for the steady and unste ady states have been measured. In modeling, the Ergun equation and energy e quations are solved to calculate the temperature profile for the steady-sta te only. It has been found that the introduction of the packing into the ai r flow passage increases the wall-to-fluid heat transfer approximately thre e times compared with that of empty bed. This finding can enhance the ratio nal use of energy from solar air heaters, chemical reactors, electronic coo ling and many other engineering applications. (C) 1999 Elsevier Science Ltd . All rights reserved.