Tests of Free Convection in a Partially Enclosed Space Between Two Heated Vertical Plates

Abstract

Abstract The free-convection heat-transfer coefficients were measured, as a function of spacing, for two parallel, electrically heated, vertical plates. The top of the rectangular space between the plates was left open, and during most of the tests the bottom and sides were closed. The heat input per unit area was substantially uniform, and the Grashof number, based on plate height, was of the order of 1010. The results demonstrate how the surface-temperature rise increases, or the local Nusselt number decreases, as either of the cross-section dimensions of the free-convection space is reduced. This decrease in Nusselt number is less rapid than was expected from purely two-dimensional flow considerations. This is ascribed to the effect of an asymmetrical flow pattern observed in the space. In some cases, a periodic reversal of this asymmetrical flow also was observed. When the space between plates was opened sufficiently at the bottom, the results were reasonably consistent with the correlation proposed by Jakob for a single vertical plate with a turbulent boundary layer; these results were almost independent of spacing between the heated surfaces down to the minimum spacing tested.