Abo Bibliothek: Guest

ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Universality in convective instabilities induced in critical fluids

Get access (open in a dialog) DOI: 10.1615/IHTC12.100
6 pages

Abstrakt

We study convective instabilities induced in a supercritical CO2 experimentally and theoretically. The system which we investigate in this study is as follows; CO2 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 temperature of the top plate is kept at the initial system temperature. The mode of convection induced in the system is investigated by visualising the temperature field by the Schlieren method. We also investigate the temperature propagation mode based on the thermofluiddynamics equations of critical fluids. Through the experimental and theoretical analyses, the following results have been obtained; (1) Temperature propagates very quickly as acoustic waves in critical fluids. The system temperature rises quickly and thin thermal boundary layers are established near the bottom and top walls although the top wall is not cooled. (2) Thermal plumes are induced upwards from the bottom thermal boundary layer. Plumes are also driven downwards from the top thermal boundary layer although the top wall temperature is not externally lowered. (3) As the system temperature deviates from the critical temperature, the delay in the onset of the downward plumes becomes longer. A power law applies to the delay in the onset of the thermal plumes from the top surface with respect to the difference between the initial system temperature and the critical temperature. (4) The wavelength between the thermal plumes becomes shorter as the system temperature approaches the critical temperature. A power law also applies to the wavelength of the thermal plumes. Finally, we estimate the onset of thermal plumes theoretically based on both Schwarzchild's and Rayleigh-Bénard's criteria and we also discuss the instability mode based on Rayleigh-Taylor and Rayleigh-Bénard instabilities.