Abstract
We study convective instabilities induced in a supercritical CO_2 experimentally. The system which we investigate is as follows: CO_2 near the critical point, the temperature of which is slightly higher than the critical temperature, is confined between two horizontal plates. The temperature of the bottom plate is raised but the top plate is not heated nor cooled. The mode of convection induced in the system is investigated by visualizing the temperature field by the Schlieren method. The following results were obtained through the experiment: (1) Thermal plumes are induced upwards from the bottom thermal boundary layer. (2) Plumes are also driven downwards from the top thermal boundary layer although the top surface is not cooled. (3) The delay in the onset of the downward plumes becomes longer as the system temperature deviates from the critical temperature, whereas there is no effect of the initial temperature on the onset of the upward plumes. Finally, we discuss the mechanism of the onset of thermal plumes and the flow characteristics.
