Dynamics of a binary mixture subjected to a temperature gradient and oscillatory forcing

We examine the dynamics of a binary mixture in a cubic cell subjected to a temperature differential and oscillatory forcing. The Soret effect, which is negative in the present study, provides a coupling mechanism by which a temperature gradient establishes a concentration gradient in a mixture. We present the results of experiments that were performed on the International Space Station (ISS) and compare the observations with the results of direct numerical simulations. The evolution of temperature and concentration fields is investigated by optical digital interferometry. One advantage of the experimental technique is the observation of the fields along two perpendicular directions of the cell, allowing us to restore the three-dimensional field. Experimental evidence disproves speculations that the ISS microgravity environment always affects diffusion-controlled processes. Furthermore, we demonstrate that imposed vibrations with constant frequency and amplitude create slow mean flows and that they do influence the diffusion kinetics. The perturbation of the diffusive fields scales as the square of the vibrational velocity. In addition to calculations of the full three-dimensional Navier–Stokes equations, a two-time-scale computational methodology is used for situations in which the forcing period is very small compared to the natural time scales of the problem. The simulations show excellent agreement with experimental observations.