EXPERIMENTAL-STUDY OF FREE-CONVECTIVE FLOW ON A VERTICAL PLATE WITH ACONSTANT HEAT-FLUX IN THE PRESENCE OF ONE OR MORE STEPS

Free-convective heat transfer on a vertical plate with a constant heat flux in the presence of one or more regular steps on a plate was stud ied experimentally. Temperature fields were investigated by a Mach-Zeh nder interferometer. The structure of free-convective flows on a plate was studied by the method of tracking visualization using a laser kni fe. A circulation free-convective flow, having the shape of two opposi tely rotating vortices, was observed directly behind a step. During th e experiment the Rayleigh number varied from zero to Ra = 2.8 x 10(3). The maximum Rayleigh number attained had a value Ra similar to 2 x 10 (4). The free-convective flow rate grew with Ra; however, qualitative changes in the structure of flow and of a temperature field were not o bserved in this case. The flow was visualized at different distances b etween the steps. As the width of the spacing between the steps increa sed, the vortices, arising in the separation zone, became more extende d downstream. With the ratio of the step height to the spacing width e qual to 1:3 and greater, a stagnation zone appeared near the first ups tream step. A vortex how between the steps enhanced heat transfer betw een the plate and environment.