Thermodiffusion in a Binary Fluid Mixture Subject to External Vibrations: Effect of Variable Physical Properties

Abstract

A microgravity environment is essential for studying the phenomenon of thermodiffusion in order to suppress the microscopic flows in the mixture. It is, however, noted that the residual micro accelerations (g-jitters) in the space laboratories is produced by several sources such as crew activities, mechanical systems, thrusters firing, spacecraft docking, etc. Such external forces lead to significant flows which can induce convection that may affect the accuracy of the experiment. Consequently, an appropriate interpretation of the space experimental results relies on theoretical and numerical studies of the g-jitter effect on the temperature and the concentration fields. In this paper, we have modeled the thermodiffusion experiment subjected to different levels of vibration when the steady gravity is assumed zero. A rectangular cavity that is subjected to a thermal gradient is filled with a binary mixture (water and isopropanol) and put under the influence of different levels of vibrations. The thermal gradient is applied perpendicular to the vibration. All physical properties including density, mass diffusion and thermodiffusion coefficients are assumed variable as function of temperature and concentration using PC-SAFT equation of state. It is found that using variable physical properties including density and diffusion coefficients make the results more realistic in comparison with the constant model especially in cases with higher Rayleigh vibrations.