Solutal-thermo-diffusion convection in a vibrating rectangular cavity

Diffusion-dominated experiments on-board the International Space Station and other free-flying platforms are affected by the convective flow due to the residual acceleration field and/or to the oscillatory accelerations (g-jitters) caused by several external sources. We are interested in investigating these effects on the solutal-thermo-diffusion for a binary fluid mixture. We considered a rectangular rigid cavity filled with methane (20%) and normal butane (80%), subject to a temperature difference on its lateral walls and radiation heat transfer on the horizontal walls. The full transient Navier-Stokes equations, accounting for a unique mode of oscillatory acceleration, coupled with the mass and heat transfer formulations and the equation of state of the fluid were solved numerically using the control volume technique. The species transport equation accounts for varying diffusion coefficients with the temperature and the fluid composition and their effect is analysed as compared to that of their average constant values. Results revealed that convection is enhanced and temperature and species profiles distortion from purely diffusive (zero-gravity) condition increases in a buoyancy-destabilizing configuration. The numerical study shows that by elimination both the residual gravity and the g-jitter levels are essential to achieve nearly purely diffusive conditions when their direction is orthogonal to that of the temperature gradient. For the configuration investigated, the g-jitter is found to reduce compositional variation. When quasi-steady state conditions are attained, thermal and compositional quantities fluctuate following a mode whose fundamental (primary) frequency is equal to that of the initially imposed vibration.