Source: https://guthlabs.ai/docs/instruments/venturi-flow-meter-calculator/mechanism/

instrument mechanism / verified-clean

# Venturi Flow Meter Calculator mechanism

The inspectable method record for Venturi Flow Meter Calculator, kept separate from implementation and qualification.

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

## Model scope

NEEDS_REVIEW because the exact velocity definition and the definitions of beta and A2 are absent. The honest label is empty even though the instrument should disclose its incompressible-flow limitation and that gas/compressible-flow applications require a different model or correction.

- The stated flow formula is standard for steady, incompressible flow when beta=d2/d1 and A2 is the throat area, but beta and A2 are not defined in the specification.

- The specification promises a velocity output but provides no velocity formula or definition of which velocity is intended. Throat velocity would be v2=Q/A2; pipe inlet velocity would be v1=Q/A1, and these are different.

- The formula's applicability to compressible fluids, especially gases at substantial pressure differences, is not stated; the incompressible formula must not be presented as universally valid.

## Units and conventions

- Diameters are assumed to be in metres, producing A2 in m^2.

- Differential pressure DeltaP is assumed to be in pascals.

- Density rho is assumed to be in kg/m^3.

- The resulting volumetric flow Q is in m^3/s and throat velocity is in m/s.

- beta is assumed to be the dimensionless diameter ratio d2/d1, with d2 as throat diameter and d1 as upstream pipe diameter.

- Cd is dimensionless.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "pipe_diameter_d1_m": 0.1,
    "throat_diameter_d2_m": 0.05,
    "deltaP_Pa": 20000,
    "Cd": 0.97,
    "density_kg_m3": 998
  },
  "expected_outputs": {
    "Q_m3_s": 0.0124532,
    "throat_velocity_m_s": 6.34236
  },
  "working": "beta=d2/d1=0.05/0.1=0.5; beta^4=0.5^4=0.0625; 1-beta^4=0.9375. A2=pi*d2^2/4=pi*(0.05^2)/4=0.00196350 m^2. sqrt(2*DeltaP/(rho*(1-beta^4)))=sqrt(40000/(998*0.9375))=sqrt(40000/935.625)=sqrt(42.7522)=6.53851 m/s. Q=Cd*A2*sqrt(...)=0.97*0.00196350*6.53851=0.0124532 m^3/s. Throat velocity=Q/A2=0.0124532/0.00196350=6.34236 m/s."
}
````

## Failure boundary

- Division by zero or invalid results occur if density is zero or negative.

- The denominator factor 1-beta^4 must be positive; beta=1 causes division by zero and beta>1 makes the square-root argument negative.

- Negative DeltaP produces an invalid square root unless signed/reverse-flow handling is explicitly implemented.

- Diameters must be positive, and the throat diameter must be smaller than the pipe diameter.

- The velocity output is ambiguous unless the instrument specifies throat velocity versus upstream pipe velocity.

- Using this incompressible formula for gases or large pressure ratios can produce materially incorrect results.

- Cd must be constrained to a physically appropriate positive range and should not be silently assumed to be 0.95-0.98 for every venturi and Reynolds-number regime.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/venturi-flow-meter-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/venturi-flow-meter-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/venturi-flow-meter-calculator/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-tranche4/tranche4-results.json`