Source: https://guthlabs.ai/docs/instruments/pipe-duct-reynolds-number-flow-regime/mechanism/

instrument mechanism / verified-clean

# Pipe/Duct Reynolds Number & Flow Regime mechanism

The inspectable method record for Pipe/Duct Reynolds Number & Flow Regime, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

NEEDS_REVIEW because the specification does not define the unit schema, the regime thresholds, whether D means circular-pipe diameter or duct hydraulic diameter, or the required input validation. The honest label should state that this is an internal-flow Reynolds-number estimator using mean velocity and conventional thresholds, not a universal flow-state determination.

- Re=ρVD/μ is the standard Reynolds-number formula for internal flow when ρ is density, V is mean flow speed, D is pipe diameter or duct hydraulic diameter, and μ is dynamic viscosity.

- The equivalent form Re=VD/ν is valid only when ν is kinematic viscosity and ν=μ/ρ.

- The flow-regime classification thresholds are unspecified. The test vectors assume laminar for Re<2300, transitional for 2300≤Re≤4000, and turbulent for Re>4000; conventions vary, especially for ducts and non-ideal flows.

- For noncircular ducts, the characteristic length must be hydraulic diameter D_h=4A/P_w; using an unspecified physical duct dimension would be incorrect.

## Units and conventions

- Use a mutually consistent unit system: ρ in kg/m³, V in m/s, D or D_h in m, and μ in Pa·s, yielding dimensionless Re.

- If the ν form is used, use V in m/s, D in m, and ν in m²/s.

- Velocity is treated as a nonnegative mean speed; a signed velocity should normally use its magnitude for Reynolds-number classification.

- The vectors use the conventional internal-flow thresholds laminar Re<2300, transitional 2300≤Re≤4000, and turbulent Re>4000.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "rho_kg_m3": 998,
    "V_m_s": 2,
    "D_m": 0.05,
    "mu_Pa_s": 0.001
  },
  "expected_outputs": {
    "Re": 99800,
    "flow_regime": "turbulent"
  },
  "working": "Re = ρVD/μ = (998 kg/m³ × 2 m/s × 0.05 m) / 0.001 Pa·s. First, 2 × 0.05 = 0.1. Then, 998 × 0.1 = 99.8. Finally, 99.8 / 0.001 = 99,800. Since 99,800 > 4,000, the regime is turbulent."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The zero-viscosity vector produces an undefined Reynolds number and requires rejection; accepting it and returning a finite value or a regime would be erroneous. The specification also leaves regime thresholds and signed-velocity convention unstated.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/pipe-duct-reynolds-number-flow-regime/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/pipe-duct-reynolds-number-flow-regime/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/pipe-duct-reynolds-number-flow-regime/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`