Neqsim Two Phase Flow Regime Screening

Two-Phase Flow Regime Screening

Use this skill for public, educational two-phase flow-regime screening. It classifies a horizontal gas-liquid flow pattern from the superficial gas and liquid velocities using a simplified Mandhane-style decision tree and flags slug risk so an agent can decide whether to invoke validated NeqSim multiphase pipe-flow modelling.

When to Use

• When a user asks what flow regime a horizontal line is likely in.
• When an agent needs a quick slug-risk flag before slug or vibration work.
• When examples must run without confidential pipeline models or field data.

Inputs

Provide either the superficial velocities directly, or enough data to compute them:

• superficial_gas_velocity: gas superficial velocity Vsg in m/s.
• superficial_liquid_velocity: liquid superficial velocity Vsl in m/s.

or

• pipe_inner_diameter: pipe inner diameter in m.
• gas_mass_flow: gas mass flow in kg/s.
• liquid_mass_flow: liquid mass flow in kg/s.
• gas_density: gas density in kg/m3.
• liquid_density: liquid density in kg/m3.

Outputs

• superficial_gas_velocity_m_s: gas superficial velocity used.
• superficial_liquid_velocity_m_s: liquid superficial velocity used.
• mixture_velocity_m_s: Vsg + Vsl.
• flow_regime: stratified-smooth, stratified-wavy, elongated-bubble, slug, dispersed-bubble, or annular-mist.
• slug_risk: true when the regime is slug or elongated-bubble.
• regime_warning: ok, slug-risk, or high-velocity.
• assumptions: public assumptions used by the placeholder model.

Engineering Method

The Python class TwoPhaseRegimeModel uses a simplified public Mandhane-style classifier for horizontal flow:

• superficial velocities use Vs = (mdot / rho) / (pi/4 * D^2) when computed from flows.
• the regime is selected from public approximate boundaries: annular-mist above Vsg = 10 m/s, dispersed-bubble above Vsl = 2 m/s, stratified below Vsl = 0.1 m/s, elongated-bubble for low gas velocity, otherwise slug.
• slug_risk is flagged for the slug and elongated-bubble regimes.

This is educational and screening-only logic. The boundaries are public approximations, not the digitized Mandhane chart or a mechanistic model. It ignores pipe inclination, surface tension, viscosity, entrainment, and transient slugging. It is not a replacement for validated multiphase flow modelling and qualified flow assurance review.

Python Usage Pattern

from two_phase_flow_regime_screening import TwoPhaseRegimeModel

model = TwoPhaseRegimeModel()
result = model.evaluate(
    superficial_gas_velocity=3.0,
    superficial_liquid_velocity=0.5,
)

print(result.flow_regime)
print(result.slug_risk)
print(result.regime_warning)

Related NeqSim Functionality

For validated multiphase flow behaviour, redirect to existing NeqSim classes:

• neqsim.process.equipment.pipeline.PipeBeggsAndBrills — Beggs and Brills multiphase pressure drop and holdup with internal regime determination.
• neqsim.process.equipment.pipeline.TwoFluidPipe — two-fluid transient pipe flow.
• neqsim.process.equipment.pipeline.AdiabaticTwoPhasePipe — adiabatic two-phase line modelling.

This skill is a public flow-regime triage layer that decides when to invoke those validated pipe-flow classes.

When the regime is transient rather than steady — terrain slugging, ramp-up surge, shut-in and restart — escalate instead to the neqsim-olga-multiphase-simulator skill (or the olga-simulation-agent), which runs an OLGA transient case and reads its trend and profile results.

Validation Checklist

• Either superficial velocities or full flow/density/diameter data are supplied.
• Velocities are non-negative and finite.
• The regime and slug-risk flag are reported as screening indicators.
• Tests cover stratified, slug, annular, computed velocities, and invalid input.
• Real regime analysis is redirected to validated NeqSim pipe-flow classes and qualified review.

Common Mistakes

Limitations

• Horizontal flow only; no inclination or terrain slugging.
• Public approximate boundaries, not the digitized Mandhane chart.
• No surface-tension, viscosity, or entrainment effects.

References

• NeqSim repository: https://github.com/equinor/neqsim
• NeqSim Skills Guide: https://github.com/equinor/neqsim/blob/master/docs/integration/skills_guide.md