Recirculating laminar mixed convection in a horizontal parallel plate duct

Abstract

Numerical investigations are conducted into steady, two-dimensional (2-D), laminar combined convection flows bounded between two very long and wide horizontal parallel plates. At some location along the duct, one, or both, of the duct surfaces undergoes a temperature change. These temperature changes create three case studies; namely, the lower wall is heated, the upper wall is heated, and both walls are heated. Results are obtained for a fixed Prandtl number of 7.02 at low and moderate values of the Reynolds number over a wide range of values for the ratio of the Grashof number to the square of the Reynolds number. It is observed that when applying heat at the upper wall, a thermally stratified flow is generated, and when the fluid is heated from the lower wall, a transversely oriented recirculation is predicted that extends upstream of the wall temperature discontinuity for values of Gr/Re 2 > 17; the exact value is a function of Re. When applying heat on both walls simultaneously, the stratification and recirculation effects of the other two cases are combined and enhanced.