DOUBLE-DIFFUSIVE NATURAL-CONVECTION BETWEEN VERTICAL PARALLEL WALLS - EXPERIMENTAL-STUDY OF 2-LAYER CONVECTION

When a two-layer system consisting of water (upper layer) and an aqueous solution (lower layer) is heated from one side and cooled from the opposite side, convection begins in each layer and a sharp horizontal interface is formed by two flows circulating in opposite directions. The heat transfer soon appears to become approximately steady, but the mass transfer remains unsteady. When the concentration difference becomes small and the interface unstable, phenomena such as wavering of the interface and a large interface slope are observed. The fluid near the wall finally streams into the other layer and the two-layer system changes into a one-layer system. For a typical two-layer convection in the present study, the temperature was high at the top of a layer and low at the bottom of the layer. The concentration gradient was sharp at the interface. The concentration in a layer was almost uniform. The average concentration in the upper layer increased linearly with time.