Source: https://guthlabs.ai/docs/instruments/natural-convection-rayleigh-grashof-calculator/implementation/

instrument implementation / implementation-contract

# Natural Convection (Rayleigh/Grashof) Calculator implementation

A source-bound implementation contract for Natural Convection (Rayleigh/Grashof) 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**: t7-062

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification does not define invalid-input handling for zero viscosity, and the signed-temperature convention can produce a negative Rayleigh number that is invalid for fractional-power correlations unless an absolute-value convention is explicitly applied. The piecewise branch assumption also creates a discontinuous Nu result at Ra=10^9.

## 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": {
    "geometry": "vertical isothermal plate",
    "correlation": "all-range Churchill-Chu",
    "fluid": "water",
    "delta_T_K": 0,
    "L_m": 1,
    "g_m_per_s2": 9.80665,
    "beta_per_K": 0.000207,
    "nu_m2_per_s": 0.000001004,
    "Pr": 7.02,
    "k_W_per_mK": 0.598
  },
  "expected_outputs": {
    "Gr": 0,
    "Ra": 0,
    "Nu": 0.68,
    "h_W_per_m2K": 0.40664
  },
  "reference_data": {
    "g_m_per_s2": 9.80665,
    "g_source_convention": "CODATA standard gravity",
    "water_beta_per_K_at_20C": 0.000207,
    "water_beta_source_convention": "widely tabulated standard value",
    "water_kinematic_viscosity_m2_per_s_at_20C": 0.000001004,
    "water_kinematic_viscosity_source_convention": "widely tabulated standard value",
    "water_Pr_at_20C": 7.02,
    "water_Pr_source_convention": "widely tabulated standard value",
    "water_k_W_per_mK_at_20C": 0.598,
    "water_k_source_convention": "widely tabulated standard value"
  },
  "working": "Gr = (9.80665 × 0.000207 × 0 × 1.0^3)/(1.004×10^-6)^2 = 0. Ra = 0 × 7.02 = 0. Churchill–Chu: Nu = [0.825 + 0.387×0^(1/6)/(1 + (0.492/7.02)^(9/16))^(8/27)]^2 = 0.825^2 = 0.680625, reported as 0.68. h = Nu×k/L = 0.68×0.598/1.0 = 0.40664 W/(m^2·K). This is an edge case: the correlation returns a finite conduction-like Nu at Ra = 0, although there is no buoyancy-driven convection."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/natural-convection-rayleigh-grashof-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/natural-convection-rayleigh-grashof-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/natural-convection-rayleigh-grashof-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-tranche7/tranche7-results.json`