Separation Conditions
Now, you need to define the separation conditions for the column, such as feed, bottom, and distillate mass fractions for the more volatile species (ethanol).
In the Model Builder window, locate the Definitions  node under Component 2 .
Variables 1
1
Right-click Definitions  and choose Variables .
2
In the Settings window for Variables, locate the Variables section.
3
Click Load from File .
4
Browse to the model’s Application Libraries folder and double-click the file distillation_column_variables.txt.
Note that some of the Expression in the table are marked yellow. This is due to undefined variables such as the liquid mole fraction from the not yet available second Transport of Concentrated Species interface.
Add a second Transport of Concentrated Species  interface which will be used for the liquid phase.
Add Physics
1
In the Home toolbar, click Add Physics  to open the Add Physics window.
2
Go to the Add Physics window.
3
In the tree, select Transport of Concentrated Species  in the Chemical Species Transport  branch.
4
Click to expand the Dependent Variables section. In the Mass fractions table, type wEl for the liquid mass fraction of ethanol and wWl for the liquid mass fraction of water.
5
Click Add to Component 2  in the window toolbar.
In the Home toolbar, click Add Physics  to close the corresponding window.