Compositional flash teaching cases with component balances
PetroCalcHub · Original synthetic teaching exercise · 2026-10-24

Practice equilibrium component balances, phase amount definitions and caloric specification choices using a recorded synthetic flash with explicit engine provenance.

Fixed PR case: 280 K, 2 MPa(a), total feed 100 mol, vapor mole fraction 0.657564115965. Component number selects methane through n-hexane.

1. For a fixed PT state, what happens to β if the total feed amount doubles?

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2. Reproduce the baseline Feed component (mol) without rounding intermediate values.

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3. Compare the first and last recorded scenarios. Which input changes?

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4. What would be needed to apply this example to a different physical system?

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5. A 100 mol feed has β = 0.6 and vapor methane fraction y = 0.8. Calculate vapor methane amount.

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6. Which outlet temperature is specified in a PH flash?

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ANSWER KEY

1. It remains unchanged under the same intensive equilibrium model; all phase and component amounts double.
2. Methane feed = 100 × 0.5 = 50 mol; liquid = 100 × (1 − 0.657564116) × 0.0971460404; vapor = 100 × 0.657564116 × 0.70979194; liquid + vapor = 50 mol. Feed component (mol) = 50. Phase composition and phase amount have different denominators. Every component must close independently.
3. Component number (C1 to nC6) changes from 1 to 6. Other controls remain as stated in the premise. Feed component (mol) changes from 50 to 5.
4. Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. Rows 1–6 are C1, C2, C3, nC4, nC5 and nC6. The equilibrium state does not change with component selection. Phase composition and phase amount have different denominators. Every component must close independently.
5. 100 × 0.6 × 0.8 = 48 mol. Vapor total is 60 mol; methane composition and phase fraction are different denominators.
6. It is solved, not specified. Outlet pressure and enthalpy constraint determine temperature and phase state under the selected model.

Method: Fixed snapshot from the site's CoolProp 8 PR engine, independently compared with the thermo reference fixture. Selecting a row does not run a new flash.
Sources:
CoolProp: cubic EOS and interaction-parameter assumptions: https://coolprop.org/coolprop/Cubics.html
CoolProp: mixture stability and equilibrium phase splitting: https://coolprop.org/fluid_properties/Mixtures.html
IDAES: flash material and energy balances: https://idaes-pse.readthedocs.io/en/stable/reference_guides/model_libraries/generic/unit_models/flash.html