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ISSN Online: 2377-424X

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

Thermoacoustic and Buoyancy-driven Convection in Supercritical Fluids

Get access (open in a dialog) DOI: 10.1615/IHTC12.2040
6 pages

Résumé

We consider the problem of a flat Rayleigh-benard cell (i.e. heated from below), containing a supercritical fluid. Several specific features make this problem very different from the case of classical Boussinesq fluids (Chandrasekhar, 1961). First, the fluid under consideration is highly compressible so that it is initially stratified even in containers of small vertical extension. Then, when a heat flux or a temperature elevation is applied on the bottom of a horizontal cell filled with a supercritical fluid, a strong thermoacoustic convection ensues due to a fourth mode of heat transfer: the Piston Effect. As a consequence, the convective stability is not a competition between diffusion and convection but between the Piston Effect and convection. The techniques used are based on the association of asymptotic methods and traditional linear stability analysis. A first-order asymptotic approximation of the base flow is found analytically, and the dispersion equations of the problem are then established. They are finally solved numerically to find the instability threshold. Prediction of the shape of the unstable modes gives a qualitative indication of the morphology of the fluid flow appearing after the transition. Through this means, we identify four different scenarii describing the onset of convection in a bottom-heated supercitical fluid cell, the occurence of which depends both on the intensity of the heating and the initial proximity to the critical point.