Global Definitions — Parameters and Thermodynamics
Start by importing a set of global parameters defining the process conditions for the distillation column, including the operational conditions, feed flow rate and separation specifications.
Parameters
1
Click to select the Parameters  node under Global Definitions .
2
In the Settings window under Parameters, click the Load from File button .
3
Browse to the file distillation_column_parameters.txt in the following application library folder on your computer, Chemical_Reaction_Engineering_Module\Thermodynamics. Double-click to add or click Open.
Note: The location of a file is based on the installation. For example, if the installation is on your hard drive, the file path might be similar to C:\Program Files\COMSOL\COMSOL64\Multiphysics\applications\.
The parameters defined in the file are added to the Parameters table.
Now define a thermodynamic system including the available chemical species.
Thermodynamics
1
On the Reaction Engineering toolbar, click Thermodynamics  and choose Thermodynamic System . Alternatively, in the Model Builder window, right-click Global Definitions  and choose Thermodynamic System  under Thermodynamics.
This starts the Thermodynamic System Wizard. In the first step you specify the available phase or phases. You can choose among the following systems:
Gas
Liquid
Vapor–liquid
Vapor–liquid–liquid
Liquid–liquid
2
Choose Vapor–liquid from the list.
3
Click Next  to proceed to the next step, adding species.
4
In the Settings window for Select Species, select ethanol (64-17-5, C2H6O) in the Species list.
You can use the Species filter field to search among the available species in the database by either Name, CAS number or Formula.
5
Click Add Selected .
6
In the Species list, select water (7732-18-5, H2O).
7
Click Add Selected .
8
Click Next .
This takes you to the final step of the Thermodynamic System Wizard, selecting the models used to compute for thermodynamic and transport properties. For more information on how to choose the thermodynamic model see Selecting the Right Thermodynamic Model in the Chemical Reaction Engineering Module User’s Guide.
9
In this model the NRTL model is applied for the liquid phase, while the ideal gas law, is used for the gas phase. Choose NRTL from the Liquid phase model list, and Ideal gas from the Gas phase model list.
Select the Advanced options checkbox for detailed control of all models for thermodynamic and transport properties.
10
Click Finish  to create the Thermodynamic System and end the wizard.
The Settings window now displays the package details. The NRTL model requires three sets of binary interaction parameters as well as randomness parameters. Expand the Binary Interaction Parameters section in order to inspect or edit the interaction parameters needed.
Now add an Equilibrium Calculation node to generate an xy diagram for the ethanol–water system at 1 atm pressure.
Note that a thermodynamic system node has been added under Thermodynamics. It is named Vapor–Liquid System 1 reflecting the phases included.
Vapor–Liquid System 1 (pp1)
1
In the Model Builder window, right-click the Vapor–Liquid 1 (pp1)  node under Thermodynamics , and choose Equilibrium Calculation .
This starts the Equilibrium Calculation Wizard.
2
In the Select Species window, Click Add All .
3
Click Next .
4
In the Equilibrium Specifications window, choose mol from the Amount base unit list.
Specify the equilibrium conditions. It is possible to create different equilibrium diagrams such as T-x, h-x, P-x, x-y, and so on using two equilibrium conditions. These available conditions are: Temperature, Pressure, Phase fraction, Enthalpy, Entropy, Energy, Density, and Volume.
5
From the First condition list, choose Pressure.
6
From the Second condition list, choose Phase fraction.
7
Click Next  to go to the Equilibrium Function Overview.
8
Click Finish  to finalize the Equilibrium Function.
The Equilibrium Calculation Settings window now displays the set of functions included in the feature. Scroll down in the list and click to select Flash1_1_PhaseComposition_Vapor_ethanol in the Functions list. The name of the function is seen in the Name field. Copy (Ctrl+C) the entire function name to use it below.
Use an Analytic  function to change the composition arguments from moles to mole fractions.
Analytic 1 (an1)
1
In the Home toolbar, click Functions  and choose Analytic  under Global .
2
In the Settings window for Analytic , type x_y in the Function name text field.
3
Locate the Definition section. In the Expression text field, type Flash1_1_PhaseComposition_Vapor_ethanol(p,n,x1,x2).
4
In the Arguments text field, type p,n,x1,x2.
Remember to use the same order of the argument as defined in the Equilibrium Calculation node.
5
Locate the Units section.
In the Function text field, type mol/mol. Enter the following into the Arguments table:
Pa, 1, mol/mol, mol/mol.