Measurements of Natural Convection Across Tilted Rectangular Enclosures of Aspect Ratio 0.1 and 0.2

Abstract

Laboratory experiments with water are reported for the range 108<RaH<5×109 where the enclosure tilt angle, φ, is varied from zero (sideways heating) to 90 deg (heating from below). Shadowgraph observations show that the flow regime studied extends from laminar at φ=0 and lower RaH, to turbulent at φ>0 and high RaH. At φ≲72 deg the convection consists of a peripheral boundary layer which closely follows the enclosure boundaries. At φ≳72 deg the flow axis rotates 90 deg. Convection consists of a single transverse roll with axis oriented upslope of the heated wall. While the average heat transfer is found to be maximum at 50 deg <φ<60 deg, its variation with φ is small. A single correlation equation may be used to predict the average Nusselt number over all angles. The correlation proposed predicts the average Nusselt number with an r.m.s. deviation of ± 10 percent.