Simulation of Ludwig–Soret effect of a water–ethanol mixture in a cavity filled with aluminum oxide powder under high pressure

Thermosolutal convection of a water–ethanol binary mixture, with a 50% mass fraction, at a high pressure of 750 bar, in a three-dimensional horizontal cavity, filled with an aluminum oxide (Al2O3) porous medium, is numerically investigated. Such investigation is examined in terms of the compositional separation versus the thermal conductivity and permeability of Al2O3 porous medium. The thermal diffusion, or Soret effect, is analyzed globally with a separation ratio and locally with the distributions of ethanol mole fraction on the horizontal and vertical lines in the center of the porous cavity. The Soret coefficient of ethanol at 30 °C was found to vary between −0.00699 and −0.00610 when pressure increases from 1 to 750 bar, leading to a ± 13.74 % relative variation around the mean value. On the other hand, the Soret coefficient of ethanol at 750 bar will vary from −0.00697 to −0.00534 when the temperature increases from 10 to 50 °C, leading to ± 26.48 % relative variation around the mean value. The details of the compositional separation at the steady state of thermosolutal convection are also applied to study the characteristics of Soret effect. When the value of permeability is less than 104 md, the compositional separation in the cavity is evident. However, when the value of permeability is larger than 104 md, the thermosolutal convection creates a mixing of the substances and the separation is diminished. Recommendations are made for the experimental design based on the results of numerical analysis.