Choked Flow / Nozzle Mass Flow Calculator implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-with-binding-errata

Evidence ID

t5-096

Effect

Computation or source lookup only

Input and validation requirements

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.

Required corrections

[
  {
    "vector": 3,
    "field": "choked/exit_mach/mass_flow",
    "wrong": "choked true, M 1.0, mdot 0.2334",
    "correct": "choked FALSE, M 0.9196, mdot ~0.2321",
    "cause": "vector designed at back/P0 = (2/2.4)^3 = 0.578704, but the true critical ratio is (2/2.4)^3.5 = 0.528282 — exponent γ/(γ−1) slipped to 3"
  }
]

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "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."
}

Other records

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
• tranche errata record