Equilibrium Calculation
Now, use the thermodynamic system to define an equilibrium function. This will be used to visualize the phase envelope of the coolant mixture.
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In the Model Builder window, under  Global Definitions >  Thermodynamics right-click  Vapor-Liquid System 1 (pp1) and choose  Equilibrium Calculation.
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Go to the Select Species window.
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Click  Add All.
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Click  Next in the window toolbar.
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Go to the Equilibrium Specifications window.
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From the Amount base unit list, choose mol.
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.
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Find the Equilibrium conditions subsection. From the First condition list, choose Pressure.
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From the Second condition list, choose Phase fraction.
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Click  Next in the window toolbar.
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Go to the Equilibrium Function Overview window. The functions to be created and their arguments are now displayed. Note especially Flash1_1_Temperature. This equilibrium function will be used to plot the phase envelope
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Click  Finish in the window toolbar. This creates an Equilibrium Calculation node in the Model Builder window.
You can now create an  Analytic function to plot the phase envelope.