Modeling of Separation in a Binary Mixture with Negative Soret Effect in a Cylindrical Thermogravitational Column

A numerical simulation of convective instability of a binary fluid with negative Soret effect in a cylindrical thermogravitational column is performed. The general problem statement, including equations of motion and heat/mass transfer with boundary conditions, are written in cylindrical coordinates. This is implemented in order to take into account the impact of the column geometry on the separation process and stability of the convective flow. The calculations for two cylindrical columns are performed in Ansys Fluent 14.5. The used parameters and values of applied temperature differences between the walls correspond to the reported experimental data. The considered binary fluid is an ethanol-water mixture at a concentration ratio of 0.2204/0.7796. At such a composition the mixture exhibits a negative Soret effect (the lighter component, ethanol, is enriched in the cold region). The results of simulation show that the convective flow in the column with a smaller gap between the walls is unstable for all applied temperature differences, while it remains stable in the column with a larger gap.