# Neqsim Two Phase Flow Regime Screening

> Educational two-phase flow-regime screening that classifies a horizontal gas-liquid flow pattern from superficial velocities using a simplified public Mandhane-style map and flags slug risk. USE WHEN: a task needs a public, screening-level flow-regime flag (stratified, slug, annular, bubble) and slug-risk triage to pair with slug-flow and flow-induced-vibration work.

- **Type:** Skill
- **Install:** `agentstack add skill-equinor-neqsim-community-skills-two-phase-flow-regime-screening`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [equinor](https://agentstack.voostack.com/s/equinor)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** Apache-2.0
- **Upstream author:** [equinor](https://github.com/equinor)
- **Source:** https://github.com/equinor/neqsim-community-skills/tree/main/skills/flow-assurance/two-phase-flow-regime-screening
- **Website:** https://equinor.github.io/neqsimhome/

## Install

```sh
agentstack add skill-equinor-neqsim-community-skills-two-phase-flow-regime-screening
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# 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

```python
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

| Symptom | Cause | Fix |
| --- | --- | --- |
| Regime looks wrong | Used vertical or inclined line | This map is for horizontal flow only |
| Velocities too high | Mass flow given in kg/h not kg/s | Use kg/s, or pass velocities directly |
| Slug missed | Operating near a public boundary | Use a mechanistic NeqSim model near boundaries |

## 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

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [equinor](https://github.com/equinor)
- **Source:** [equinor/neqsim-community-skills](https://github.com/equinor/neqsim-community-skills)
- **License:** Apache-2.0
- **Homepage:** https://equinor.github.io/neqsimhome/

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-equinor-neqsim-community-skills-two-phase-flow-regime-screening
- Seller: https://agentstack.voostack.com/s/equinor
- Browse the marketplace: https://agentstack.voostack.com/browse

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