Original synthetic study
Same feed two equations of state a reproducible comparison
This reproducible PR–SRK study uses one six-component feed and identical numerical state inputs. It reports model differences and balance diagnostics without declaring either EOS more accurate for an unmeasured fluid.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Specify the experiment completely
Both models use methane through n-hexane, the same feed fractions, the same pinned pure-component data and kij = 0. Pressure is fixed while recorded temperatures change.
Every row is a solved equilibrium state from the site's engines. The downloadable data distinguish PR and SRK outputs rather than combining them into one averaged prediction.
Compare amount and density separately
Vapor mole fraction is sensitive to phase equilibrium, while phase densities also reflect the EOS volume prediction. Agreement in one output need not imply agreement in the others.
The graph emphasizes vapor amount; the full recorded dataset retains the associated inputs and diagnostics for reproducibility.
Explain the evidence limit
An independent implementation can check equation consistency, and measured PVT data can assess fluid accuracy. This synthetic sweep does neither by itself merely because two models are plotted.
Use the accompanying method lesson for selection criteria. The study's distinct contribution is the original controlled dataset and its replay path.
Explore the example
Recorded using both supported compositional flash engines. Independent thermo reference fixtures are separately checked by the repository's compositional regression suite.
Select one of 5 recorded scenarios. Intermediate states are not interpolated.
Temperature (K) = 280. PR vapor mole fraction: 0.657564116; SRK vapor mole fraction: 0.658742945.
- PR vapor mole fraction
- SRK vapor mole fraction
Worked example
PR and SRK on an identical six-component feed
p = 2 MPa(a); methane/ethane/propane/n-butane/n-pentane/n-hexane mole fractions 0.50/0.15/0.15/0.10/0.05/0.05. CoolProp 8, kij = 0; only T changes.
Relation and unit basis
zi = (1 − β)xi + βyi; fi,liquid = fi,vapor
β is vapor mole fraction. Both models use the same pure-component constants and numerical state inputs.
1. Define the baseline
Temperature (K) = 280
p = 2 MPa(a); methane/ethane/propane/n-butane/n-pentane/n-hexane mole fractions 0.50/0.15/0.15/0.10/0.05/0.05. CoolProp 8, kij = 0; only T changes.
2. Select the relation
zi = (1 − β)xi + βyi; fi,liquid = fi,vapor
β is vapor mole fraction. Both models use the same pure-component constants and numerical state inputs.
3. Substitute the values
At 280 K and 2 MPa: PR β = 0.657564116; SRK β = 0.658742945; the complete component balances and fugacity diagnostics are saved with each solve.
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
PR vapor mole fraction = 0.657564116; SRK vapor mole fraction = 0.658742945
These are model differences, not measured errors or an accuracy ranking.
Result and interpretation
PR vapor mole fraction = 0.657564116; SRK vapor mole fraction = 0.658742945
These are model differences, not measured errors or an accuracy ranking.
The plotted difference is a model sensitivity under shared assumptions, with no experimental accuracy ranking.
Study data and reproduction
Recorded using both supported compositional flash engines. Independent thermo reference fixtures are separately checked by the repository's compositional regression suite.
| Temperature (K) | PR vapor mole fraction | SRK vapor mole fraction |
|---|---|---|
| 240 | 0.482854 | 0.4870871 |
| 260 | 0.5691658 | 0.5715311 |
| 280 | 0.6575641 | 0.6587429 |
| 300 | 0.7496529 | 0.749951 |
| 320 | 0.8434581 | 0.8429687 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Test your understanding
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. What additional evidence is needed to call PR or SRK more accurate for a sample?
Show the worked answer
Suitable independent PVT measurements at compatible states and a documented comparison of their residuals.
2. Reproduce the baseline PR vapor mole fraction without rounding intermediate values.
Show the worked answer
At 280 K and 2 MPa: PR β = 0.657564116; SRK β = 0.658742945; the complete component balances and fugacity diagnostics are saved with each solve.. PR vapor mole fraction = 0.657564116. These are model differences, not measured errors or an accuracy ranking.
3. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
Temperature (K) changes from 240 to 320. Other controls remain as stated in the premise. PR vapor mole fraction changes from 0.482854017 to 0.843458076.
4. What would be needed to apply this example to a different physical system?
Show the worked answer
Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. β is vapor mole fraction. Both models use the same pure-component constants and numerical state inputs. These are model differences, not measured errors or an accuracy ranking.
Before using the result
- Use identical feed and states.
- Record engine version and kij.
- Keep model difference distinct from measured error.
These are model differences, not measured errors or an accuracy ranking.
Continue learning
Start with the broader workflow guide
Sources and method
The explanation and synthetic examples are original PetroCalcHub teaching material. The references below support the definitions and model context. They do not supply field validation for the synthetic scenarios.