Mixed convection in a shallow enclosure with a series of heat generating components

Abstract

The problem of mixed convection flow and heat transfer in a shallow enclosure with a series of block-like heat generating components is studied numerically for a range of Reynolds and Grashof numbers and block-to-fluid thermal conductivity ratios. The flow and temperature distributions are taken to be two-dimensional. Regions with the same velocity and temperature distributions can be identified assuming repeated placement of the blocks and fluid entry and exit openings at regular distances, neglecting end wall effects. One half of such a rectangular region is chosen as the computational domain taking into account the symmetry about the vertical centerline. On the basis of the assumption that mixed convection inlet velocity can be treated as the superposition of forced convection and natural convection velocities at the inlet and that mixed convection pressure drop across the enclosure is due to the forced flow contribution alone, the individual flow components are delineated. The Reynolds number is based on forced convection velocity, which can be determined in practice from the fan characteristics. This is believed to be more meaningful unlike the frequently used total velocity based Reynolds number, which does not vanish even in pure natural convection and which makes the fan selection difficult. The results show that higher Reynolds numbers tend to create a recirculation region of increasing strength at the core region and that the effect of buoyancy becomes insignificant beyond a Reynolds number of typically 600. Results are also presented for a number of quantities of interest such as the flow and temperature distributions, local and average Nusselt numbers and the maximum dimensionless temperature in the block.