Hydrocarbon Bubble and Dew Pressure Band Calculator

Calculation sequence

1. Choose an increasing temperature interval no wider than 100 K and the C1-C6 feed. Software pressure bounds still apply to both endpoints at every temperature, so a broad band can fail even when a familiar PT flash is valid. Start with a narrow interval away from criticality.
2. At fifteen temperatures, independently request bubble and dew equilibrium from the proven flash engine. Check fugacity equality, PR pressure, incipient-phase compositions and feed allocation. Zero phase allocation at a saturation endpoint is deliberate; it is not a failed ordinary split with a hidden clipped fraction.
3. Require separated roots, bubble pressure greater than dew pressure and no missing points. This conservative band excludes retrograde or ambiguous branches. The plot joins sampled endpoint values for inspection, not for assigning a phase or tracing an uncomputed critical region.
4. At every returned state independently re-evaluate classical PR pressure, log fugacity and residual enthalpy/entropy. Require component balance <=2e-7, log-fugacity mismatch <=2e-5 and relative pressure residual <=2e-6. Reject vanishing phase fractions below 1e-6 and density separation below 1.1 for ordinary splits. These are numerical checks, not measured-PVT validation.
5. Calculations run locally in a dedicated WebAssembly worker. The advanced Python/scientific engine is a roughly 33 MB first download, separate from ordinary calculators; it is self-hosted and version pinned. No composition or measurements are sent to a calculation server. Save and file backups retain canonical inputs, while CSV/PDF include returned tables and source notes. The worker is released after idle time and failures never return partial results.

Worked check

At the low end of the synthetic 280-290 K band, the 280 K PR bubble pressure is about 9.242807 MPa and dew pressure is 0.126019 MPa. These widely separated endpoints are for the same overall feed. Temperatures below this band can put the dew pressure below the tool's 0.1 MPa lower limit; the tool reports that failure rather than omitting it.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

• Six components C1-C6, normal C4-C6, classical PR and all kij=0. No water, isomers, sour gas, heavy fractions, reactions, solids or volume translation. Use the expanded-mixture tools for their explicitly supported alternatives, not by inserting a new species in these fixed feed slots.
• Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation.
• Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range.
• A bubble/dew band only, not full phase-envelope continuation, critical-point location, cricondenbar/cricondentherm or retrograde tracing. If either saturation endpoint lies outside the pressure envelope, the complete calculation fails rather than plotting an incomplete curve. No extrapolation between disconnected branches.

Sources and maintenance

Published by PetroCalcHub Team. Implementation and source checks: 2026-10-22. This does not claim independent expert review.

• Thermo: FlashVL/FlashVLN stability and phase splitting (runtime pinned to 0.6.0)
• CoolProp v8.0.0: pinned cubic pure-component parameters
• CoolProp: Michelsen PT stability/phase-split method and Wilson initialization

Related tools and references