Investigation of transient heat transfer in a rectangular packed duct with asymmetric heating.
Habib H. A-Ali , Yasar Demirel, محمد شبر القلاف
كلية الهندسة-جامعة الملك فهد للبترول والمعادن · السعودية
The study investigated the transient convection heat transfer in a rectangular packed duct with asymmetric heating. The study involved both experimental and theoretical works. The experiments have been conducted in a rectangular packed duct with aspect ratio W/H of 4. Two different types of packing material have been used in the experiments, three sizes of expanded polystyrene spheres and two sizes of polyvinyl chloride Rashing Ring. The experimental runs for the different packing were conducted with heat flux in the range 20 to 243 W/m² and Reynolds number in the range of 300 to 1550. The theoretical analysis of the problem was based on solving the one phase pseudo-homogeneous mathematical model. The model was solved numerically using the method of orthogonal collection. The predicted air temperature trends were compared with those measured experimentally and they have shown a good agreement. The effect of shape, size of packing and Reynolds number on transient heat transfer was studied. It was found that the shape of packing has neither effect on heat transfer nor the time required to reach steady state. The size of packing has no effect on the time needed to reach steady state, however, the air temperature has shown a slight improvemetn when small particles wer used. As Reynolds number decreases, the time required to reach steady state increases. The study also investigated the significance of axial dispersion on the transient heat transfer process in a packed rectangular duct with heated top wall by a uniform heat flux and insulated bottom wall. It was concluded that the axial dispersion is significant in the early time and the degree of significance decreases as steady state is reached. It was found also that the significance of axial dispersion decreases as Reynolds number decreases.