Choked Flow / Nozzle Mass Flow Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified with errata that must be applied at binding time.

Area

Thermodynamics, Fluids & Aero

Tranche

tranche-5

Evidence ID

t5-096

Ledger rows

1

No ledger note is attached.

Review findings

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.

Formula and scope findings

• 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.

Unit assumptions

• 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.

Boundary hardening

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.

Errata and corrections

Tranche errata

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "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."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

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

• VERIFIED_LEDGER.json · VERIFIED_WITH_ERRATA
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json