Multicomponent Convection

Abstract

In two early reviews of this subject (Turner 1973, 1974), the phenomena described were adequately covered by the name double-diffusive convection. They were treated as generalizations of the process of thermal convection in a thin fluid layer, which arise when spatial variations of a second component with a different molecular diffusivity are added to the thermal gradients ; the term thermohaline convection was introduced to describe the heat-salt system. The experimental and theoretical results then available could be described in terms of the differential diffusion of two components acting so as to release potential energy from a component that is heavy at the top, even though the net density decreases upward. It was also shown that the form of the resulting motions depends on whether the driving energy comes from the component having the higher or lower diffusivity. Where one layer of fluid is placed above another (denser) layer having different properties, two basic types of convective instabilities arise, in the diffusive and finger configurations. These are illustrated in Figures 1 and 2, respectively. In both cases, the double-diffusive fluxes can be much larger than the vertical transport in a single-component fluid because of the coupling between and convective processes. The main development of these ideas since 1974 has occurred in the field of oceanography, with interactions between theoreticians, laboratory experimenters, and sea-going oceanographers playing a vital role. The field has also broadened considerably, with new applications becoming ap­ parent in addition to those outlined by Turner (1974). A rather personal historical review of the subject was presented by Huppert & Turner (198 1a), in which they emphasized the importance of transfer of information from