Source: https://guthlabs.ai/docs/instruments/lmtd-heat-exchanger-calculator/implementation/

instrument implementation / implementation-contract

# LMTD Heat Exchanger Calculator implementation

A source-bound implementation contract for LMTD Heat Exchanger Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## 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-clean

**Evidence ID**: t4-168

**Effect**: Computation or source lookup only

## Input and validation requirements

A plain arithmetic implementation can fail at the removable 0/0 equal-terminal-difference case, produce undefined results or divide by zero when a terminal temperature difference is zero, and return materially different results when flow-arrangement or temperature-unit conventions are not explicit.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

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

````
{
  "inputs": {
    "operation": "heat_duty",
    "arrangement": "counterflow",
    "hot_in_C": 150,
    "hot_out_C": 90,
    "cold_in_C": 30,
    "cold_out_C": 70,
    "U_W_m2K": 500,
    "area_m2": 10,
    "F": 1
  },
  "expected_outputs": {
    "deltaT1_K": 80,
    "deltaT2_K": 60,
    "deltaTlm_K": 69.5212,
    "q_W": 347605.95
  },
  "working": "Counterflow: ΔT1=Th,in−Tc,out=150−70=80 K; ΔT2=Th,out−Tc,in=90−30=60 K. ΔTlm=(80−60)/ln(80/60)=20/ln(4/3)=20/0.287682072=69.5212 K. q=U·A·ΔTlm·F=500·10·69.5212·1=347605.95 W."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/lmtd-heat-exchanger-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/lmtd-heat-exchanger-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/lmtd-heat-exchanger-calculator/qualification/>)

## 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`