NTU-Effectiveness Heat Exchanger 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

t4-180

Effect

Computation or source lookup only

Input and validation requirements

The raw counterflow formula is undefined at Cr=1 because it becomes 0/0, requiring the limiting expression epsilon=NTU/(1+NTU). A zero capacity rate makes NTU divide by zero and should be rejected. These are concrete failure points unless explicit boundary and input validation branches are implemented.

Required corrections

[
  {
    "vector": 1,
    "field": "q_W / T_hot_out / T_cold_out",
    "wrong": "q 132,891.81, Tho 116.42, Tco 59.74",
    "correct": "q 265,783.63, Tho 52.83, Tco 99.48",
    "cause": "q exactly halved; her epsilon 0.7948 is correct and outlets inherit the halving"
  }
]

Inspectable interface fixture

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

{
  "inputs": {
    "configuration": "counterflow",
    "U_W_m2K": 500,
    "A_m2": 10,
    "m_hot_kg_s": 0.5,
    "cp_hot_J_kgK": 4180,
    "m_cold_kg_s": 0.8,
    "cp_cold_J_kgK": 4180,
    "T_hot_in_C": 180,
    "T_cold_in_C": 20
  },
  "expected_outputs": {
    "epsilon": 0.7948075,
    "q_W": 132891.81,
    "T_hot_out_C": 116.4154,
    "T_cold_out_C": 59.7404
  },
  "working": "Ch=0.5·4180=2090 W/K; Cc=0.8·4180=3344 W/K; Cmin=2090; Cmax=3344; Cr=2090/3344=0.625. UA=500·10=5000 W/K. NTU=5000/2090=2.3923445. x=NTU·(1−Cr)=2.3923445·0.375=0.8971292. exp(−x)=exp(−0.8971292)=0.4077385. ε=(1−0.4077385)/(1−0.625·0.4077385)=0.5922615/0.7451634=0.7948075. ΔTin=180−20=160 K. q=0.7948075·2090·160=132891.81 W. Th,out=180−132891.81/2090=180−63.5846=116.4154 °C. Tc,out=20+132891.81/3344=20+39.7404=59.7404 °C."
}

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
• tranche errata record