neqsim-phase-envelope

NeqSim PT Phase Envelopes

Overview

Use this skill to generate physically interpretable PT phase envelopes and to modify the Michelsen continuation solver safely. Prefer the structured segment API, verify branch identity from physics, and preserve the caller's thermodynamic system.

Route the Task

• Use @thermo-fluid for envelope generation, plotting, properties, and solver defects.
• Chain to neqsim-eos-regression or @pvt-simulation when matching lab data or tuning EOS parameters.
• Chain to neqsim-flow-assurance for operating-path, hydrate, wax, or pipeline assessments.
• Chain to neqsim-ccs-hydrogen for CO2/H2 impurity envelopes.
• Chain to neqsim-troubleshooting when continuation does not converge or output is incomplete.

Workflow

1. Verify the API and inputs

Read these sources before generating or changing code:

• ThermodynamicOperations.calcPTphaseEnvelope(...) and getEnvelopeSegments()
• PTPhaseEnvelopeMichelsen result getters and continuation settings
• EnvelopeSegment getters and PhaseType
• Neighboring tests in PTPhaseEnvelopeMichelsenTest, PTPhaseEnvelopeRobustnessTest, and PTPhaseEnvelopeSegmentsTest

Validate that temperature is in K, pressure is in bara, component amounts are finite and non-negative, and the mixing rule is set. Choose the EOS from the fluid chemistry, not from the desired plot shape.

2. Handle zero and trace components correctly

The Michelsen Jacobian contains terms divided by overall mole fraction $z_i$. Components with zero or numerically negligible $z_i$ can therefore make the Jacobian singular.

• Current PTPhaseEnvelopeMichelsen excludes components with $z_i < 10^{-12}$ from a private clone after composition initialization.
• Do not remove components from the caller's SystemInterface.
• Do not discard physically meaningful trace impurities at or above the threshold merely to obtain convergence. Their impact can be important for CO2 quality, water behavior, and H2S.
• When changing the threshold or filtering logic, add a regression proving both finite envelope output and unchanged caller composition.