Convection Coefficient (Nu Correlation) Estimator mechanism

Model scope

The supplied correlations are standard but the instrument is not fully specified for all advertised geometries. Verdict is NEEDS_REVIEW because local-versus-average flat-plate output, Dittus-Boelter heating/cooling exponent, property-reference temperature, and cylinder/sphere correlations are ambiguous or missing. The requested honest label of correlation-dependent accuracy of approximately plus or minus 10-25 percent is reasonable only within each correlation's applicability range; it should not imply validity outside those ranges.

• Nu=hL/k is the standard definition of the Nusselt number, provided L is the same characteristic length used by the selected correlation and k is evaluated at a stated reference temperature.
• Nu=0.664 Re_L^0.5 Pr^(1/3) is the standard local laminar flat-plate correlation for a smooth plate with constant properties and zero pressure gradient; the average-from-leading-edge laminar correlation is instead Nu_L=1.328 Re_L^0.5 Pr^(1/3). The instrument must state whether local or average h is intended.
• The flat-plate laminar correlation requires an applicable laminar Reynolds-number range, commonly Re_L less than approximately 5.0e5 for a smooth plate. Transition, roughness, pressure gradient, and leading-edge effects are not specified.
• Dittus-Boelter Nu=0.023 Re_D^0.8 Pr^n is an approximate correlation for fully developed turbulent flow in a smooth circular tube with approximately constant properties. It generally requires Re_D above about 1.0e4 and an appropriate Prandtl-number range.
• The Dittus-Boelter exponent n is not specified: n=0.4 is conventionally used for heating the fluid and n=0.3 for cooling the fluid. The heat-transfer direction must be an explicit input.
• The geometry picker lists cylinders and spheres, but no cylinder or sphere correlation is supplied. Those selections cannot produce a verified result from this specification.

Units and conventions

• Velocity is converted to m/s, characteristic length to m, k to W/(m*K), and kinematic viscosity nu to m^2/s.
• Re=VL/nu for the flat plate and Re=VD/nu for the circular pipe.
• Pr is dimensionless and supplied directly by the fluid-property table; equivalently Pr=nu/alpha when thermal diffusivity is available.
• For the flat plate, L is the distance from the leading edge and the reported value uses the local correlation Nu_x=0.664 Re_x^0.5 Pr^(1/3).
• For the pipe, D is the inside diameter and h is based on Nu_D=0.023 Re_D^0.8 Pr^0.4, assuming fluid heating.
• The tabulated properties are treated as exact inputs for these test calculations, although real-property uncertainty and interpolation uncertainty remain.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "geometry": "flat_plate",
    "fluid": "air",
    "temperature_C": 20,
    "velocity_m_per_s": 10,
    "characteristic_length_m": 0.5,
    "correlation": "local laminar flat plate",
    "property_reference_temperature": "20 C"
  },
  "expected_outputs": {
    "Re": 332005.31,
    "Pr": 0.707,
    "Nu": 340.84,
    "h_W_per_m2_K": 17.52
  },
  "reference_data": {
    "temperature_C": 20,
    "air_kinematic_viscosity_m2_per_s": 0.00001506,
    "air_thermal_conductivity_W_per_m_K": 0.0257,
    "air_Prandtl_number": 0.707,
    "source_convention": "widely tabulated standard value; Incropera heat-transfer textbook air-properties table"
  },
  "working": "Re=VL/nu=(10 m/s)(0.5 m)/(1.506e-5 m^2/s)=5/(1.506e-5)=332005.31. sqrt(Re)=sqrt(332005.31)=576.20. Pr^(1/3)=0.707^(1/3)=0.89085. Nu=0.664(576.20)(0.89085)=340.84. h=Nu*k/L=(340.84)(0.0257 W/(m*K))/(0.5 m)=17.52 W/(m^2*K)."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The zero-characteristic-length input produces h=0/0 and must be rejected. The signed-velocity probe also exposes an implementation hazard: directly raising negative Re to the fractional power 0.8 produces an undefined real-valued result, so velocity magnitude handling must be explicit.

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-tranche7/tranche7-results.json
• BOUNDARY_HAZARD_CATALOG.json