Overall Heat Transfer Coefficient (U) Calculator mechanism

Model scope

The written resistance equation has the correct convection and cylindrical-wall terms, but the fouling term and U area basis are insufficiently defined. The honest label should state whether fouling inputs are total K/W or area-specific m²·K/W, identify inside versus outside fouling surfaces, expose whether the result is Ui or Uo, and disclose the required positivity and unit constraints. The TEMA fouling table also requires a defined source, applicability range, and temperature/fluid assumptions.

• The formula is valid only when Rfouling is a total thermal resistance in K/W. Standard fouling factors are area-specific in m²·K/W and must appear as Rf,i/Ai and/or Rf,o/Ao; the specification does not define which surface or area basis applies.
• The specification says fouling factors (plural), but the formula provides only one undefined Rfouling term.
• The formula computes UA first, so the implementation must explicitly calculate Ui=(UA)/Ai and/or Uo=(UA)/Ao. The output statement does not specify the default area basis.

Units and conventions

• hi and ho are in W/(m²·K).
• k is in W/(m·K), ri and ro are in m, and L is in m; all geometric quantities must use a consistent length unit before calculation.
• Ai=2πriL and Ao=2πroL for a cylindrical tube.
• The test vectors interpret Rfouling as a total resistance in K/W solely to evaluate the written formula. Conventional area-specific fouling factors would require division by the applicable area.
• UA is in W/K; Ui and Uo are in W/(m²·K).
• A valid tube requires ro>ri>0 and L>0.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "hi": 1000,
    "ho": 50,
    "k": 16,
    "ri": 0.01,
    "ro": 0.012,
    "L": 1,
    "Rfouling": 0,
    "units": "hi,ho W/(m²·K); k W/(m·K); dimensions m; Rfouling K/W"
  },
  "expected_outputs": {
    "UA_W_per_K": 3.534,
    "Ui_W_per_m2K": 56.241,
    "Uo_W_per_m2K": 46.868
  },
  "working": "Ai=2π(0.01)(1)=0.0628319 m²; Ao=2π(0.012)(1)=0.0753982 m². Ri=1/(1000×0.0628319)=0.0159155 K/W. Rwall=ln(0.012/0.01)/(2π×16×1)=ln(1.2)/100.531=0.0018136 K/W. Ro=1/(50×0.0753982)=0.2652582 K/W. Rtotal=0.0159155+0+0.0018136+0.2652582=0.2829873 K/W. UA=1/0.2829873=3.5337 W/K. Ui=3.5337/0.0628319=56.241 W/(m²·K). Uo=3.5337/0.0753982=46.868 W/(m²·K)."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The calculator should reject k=0 because the wall-resistance term divides by zero. The convention probe also exposes a substantial unit and radius-versus-diameter interpretation hazard if geometry metadata are not enforced.

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-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json