Source: https://guthlabs.ai/docs/instruments/van-der-waals-real-gas-eos-solver/implementation/

instrument implementation / implementation-contract

# Van der Waals Real-Gas EOS Solver implementation

A source-bound implementation contract for Van der Waals Real-Gas EOS Solver; 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**: t8-003

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification leaves phase selection under the subcritical three-root regime unspecified, so a cubic/Newton solver may return an arbitrary liquid, unstable, or gas root. Exact singular inputs also require explicit rejection, and temperature-unit ambiguity can change the computed pressure from 2.243 MPa to a negative value.

## 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": {
    "gas": "CO2",
    "n_mol": 1,
    "T_K": 300,
    "V_L": 10,
    "a_Pa_m6_per_mol2": 0.364,
    "b_m3_per_mol": 0.0000427,
    "R_J_per_mol_K": 8.314462618
  },
  "expected_outputs": {
    "pressure_Pa": 246863.5286,
    "ideal_pressure_Pa": 249433.8785,
    "deviation_percent": -1.0304734
  },
  "reference_data": {
    "method": "P = nRT/(V-nb) - a n^2/V^2",
    "V_m3": 0.01
  },
  "working": "Convert volume: V = 10 L * 0.001 m^3/L = 0.01000000000 m^3. Compute nb = 1.0 * 0.0000427 = 0.0000427 m^3. Compute nRT = 1.0 * 8.314462618 * 300.0 = 2494.3387854 Pa m^3. Compute nRT/(V-nb) = 2494.3387854/(0.0100000000 - 0.0000427) = 2494.3387854/0.0099573 = 250503.5286 Pa. Compute a n^2/V^2 = 0.364/(0.0100000000^2) = 3640.0000 Pa. Therefore P = 250503.5286 - 3640.0000 = 246863.5286 Pa. Ideal pressure is P_ideal = nRT/V = 2494.3387854/0.0100000000 = 249433.8785 Pa. Deviation = 100*(246863.5286 - 249433.8785)/249433.8785 = -1.0304734%."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/van-der-waals-real-gas-eos-solver/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/van-der-waals-real-gas-eos-solver/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/van-der-waals-real-gas-eos-solver/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-tranche8/tranche8-results.json`