Source: https://guthlabs.ai/docs/instruments/choked-flow-nozzle-mass-flow-calculator/mechanism/

instrument mechanism / verified-with-binding-errata

# Choked Flow / Nozzle Mass Flow Calculator mechanism

The inspectable method record for Choked Flow / Nozzle Mass Flow Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**

## Model scope

NEEDS_REVIEW because the general formula and the required R input are unspecified, and the exit-Mach calculation is geometry-dependent. The choked mass-flow equation itself is correct under the stated unit and ideal-flow assumptions. The honest label should disclose ideal-gas, constant-gamma, isentropic-flow, stagnation-property, converging-nozzle, and empirical-Cd assumptions; it should not imply validity for arbitrary nozzle geometries or real-gas flow.

- The choked-flow formula is standard for an ideal gas with constant gamma, adiabatic and isentropic flow, and stagnation inputs P0 and T0; those assumptions are not stated in the specification.

- The general isentropic nozzle-flow formula is not provided, so its correctness cannot be verified.

- For a converging nozzle in the unchoked regime, exit Mach can be obtained from back pressure only if the exit plane is the throat and the exit pressure equals back pressure; this geometry and assumption are unspecified.

- R is required by the formula but is absent from the listed user inputs and is only mentioned vaguely under data_needs.

- Cd is applied to the mass-flow formula, but the specification does not state whether it is an empirical mass-flow discharge coefficient or how it affects the reported exit Mach.

## Units and conventions

- P0 and back pressure are absolute pressures in Pa, not gauge pressures.

- T0 is absolute temperature in K.

- Throat area is in m^2.

- R is the specific gas constant in J/(kg·K) for the selected gas.

- gamma is dimensionless and constant, with gamma greater than 1.

- The choked criterion is back_pressure/P0 <= (2/(gamma+1))^(gamma/(gamma-1)); for gamma=1.4 this critical pressure ratio is approximately 0.578704.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "throat_area": 0.001,
    "P0": 300000,
    "T0": 300,
    "back_pressure": 100000,
    "Cd": 0.98,
    "gamma": 1.4,
    "R": 287
  },
  "expected_outputs": {
    "mass_flow_rate_kg_s": 0.6861,
    "choked": true,
    "exit_mach": 1
  },
  "working": "Critical ratio = (2/(1.4+1))^(1.4/(1.4-1)) = (2/2.4)^3.5 = 0.5283. Since 100000/300000 = 0.3333 <= 0.5283, the flow is choked. Choked mass flow = 0.98(0.001)(300000)sqrt(1.4/(287*300))(2/2.4)^3. 0.98(0.001)(300000) = 294. sqrt(1.4/86100) = 0.0040324. (2/2.4)^3 = 0.5787037. mdot = 294(0.0040324)(0.5787037) = 0.6861 kg/s. Choked exit Mach = 1."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The specification admits invalid zero-temperature inputs that produce an undefined or divergent mass-flow expression, and it does not define the equality convention at the critical-pressure boundary or whether pressures are absolute or gauge. A gauge interpretation can also make the back pressure exceed stagnation pressure and drive the general formula outside the square-root domain.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/choked-flow-nozzle-mass-flow-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/choked-flow-nozzle-mass-flow-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/choked-flow-nozzle-mass-flow-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-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`