Microconvection in a Binary System

On the basis of an essentially subsonic-flow approximation, the effect of small density variations of the medium on the development of natural convection in a slightly nonisothermal binary mixture at very small Rayleigh numbers and a constant mean thermodynamic pressure (microconvection) is studied analytically and numerically. Microconvective flows are characterized by a nonsolenoidal velocity field. As compared with microconvection in pure fluid, the presence of an admixture and the thermodiffusion effect result in a number of new interesting opportunities. Attention is mainly focused on essentially unsteady processes (transition processes after two different media are brought into contact and convection in rapidly varying temperature fields), in which the medium volume expansion is very significant. The conditions of onset of monotonic modes of the Rayleigh-Bénard and Bénard-Marangoni long-wave instabilities are also considered.