iapws-if97

Industrial water and steam properties for Node.js and TypeScript.

Turn two known properties into a water or steam state using IAPWS-IF97. For steam tables, thermal-cycle calculations, and engineering tools.

API reference · References · Changelog

• Forward, backward, and saturation solvers for eight input pairs across IF97 Regions 1–5.
• Saturation results include liquid and vapor endpoints.
• Viscosity, thermal conductivity, surface tension, dielectric constant, and ionization constant where applicable.
• ESM with TypeScript declarations and no runtime dependencies.

Start calculating

Requires Node.js ≥20.19.0. Use ESM imports.

npm install iapws-if97

Save as example.mjs and run node example.mjs:

import { solvePT } from 'iapws-if97';

const steam = solvePT(3, 573.15); // 3 MPa, 300 °C

console.log(steam.enthalpy.toFixed(2)); // 2994.35 kJ/kg
console.log(steam.density.toFixed(3));  // 12.319 kg/m³

The result includes pressure, temperature, enthalpy, entropy, density, heat capacities, speed of sound, and applicable transport properties. All fields and units →

Use the properties you have

| Known properties | Solver | | --- | --- | | Pressure + temperature | solvePT(p, T) | | Pressure + enthalpy | solvePH(p, h) | | Pressure + entropy | solvePS(p, s) | | Enthalpy + entropy | solveHS(h, s) | | Temperature + enthalpy | solveTH(T, h) | | Temperature + entropy | solveTS(T, s) | | Pressure + vapor quality | solvePx(p, x) | | Temperature + vapor quality | solveTx(T, x) |

Use MPa, K, kJ/kg, and kJ/(kg·K) for pressure, temperature, enthalpy, and entropy. Vapor quality x is the vapor mass fraction, from 0 (saturated liquid) to 1 (saturated vapor).

Use solve() when the input pair is chosen at runtime:

import { solve } from 'iapws-if97';

const state = solve({ mode: 'PH', p: 3, h: 3000 });

Long field names such as pressure and enthalpy are also accepted. Use solveBasic() when you only need thermodynamics; it skips transport calculations and omits density.

Work with saturation

Specify quality to calculate saturated liquid, saturated vapor, or wet steam:

import { solvePx } from 'iapws-if97';

const wet = solvePx(1, 0.9); // 1 MPa, 90% vapor by mass

console.log(wet.temperature.toFixed(2)); // 453.04 K

if (wet.saturation) {
  const { liquid, vapor } = wet.saturation;
  const latentHeat = vapor.enthalpy - liquid.enthalpy;
  console.log(latentHeat.toFixed(2)); // 2014.44 kJ/kg
}

Every saturation result includes saturation.liquid and saturation.vapor for phase properties and latent-heat calculations. Use solveTx(T, x) when temperature is known instead of pressure.

Before integrating

• PT selects a single phase. Pressure and temperature alone do not determine wet-steam quality; use Px or Tx for a mixture.
• Single-phase quality is null. Mixtures return null for heat capacities, speed of sound, and most transport properties. Return-value details →
• TH and TS throw AmbiguousStateError with candidate states when multiple solutions exist. Use pressure or quality to resolve the state. Errors →
• The exact critical point is unsupported, and near-critical solves can fail. Transport correlations have separate validity ranges. Numerical limits → · Transport limits →

| Thermodynamic temperature range | Maximum pressure | | --- | --- | | 273.15–1073.15 K | 100 MPa | | Above 1073.15 K, up to 2273.15 K | 50 MPa |

Saturation solvers accept 273.16 ≤ T < 647.096 K or 0.000611657 ≤ p < 22.064 MPa. All numeric inputs must be finite; invalid or unresolved states throw typed errors.

Verification and development

Tests cover official IAPWS verification values, backward-solver round trips, region boundaries, and published ASME and GB/T steam tables. CI also checks TypeScript types, package exports, and coverage thresholds. Verification details and references →

npm ci
npm run typecheck
npm test
npm run test:package

For low-level region equations, saturation curves, transport correlations, or region detection, see advanced imports.

References

• IAPWS R7-97(2012), Industrial Formulation 1997.
• IAPWS supplementary releases for alternative input pairs, region boundaries, and Region 3 specific volume.
• R12-08, viscosity and R15-11, thermal conductivity.
• R1-76(2014), surface tension, R8-97, dielectric constant, and R11-24, ionization constant.

See the full reference list for release details.

Project origin

iapws-if97 began as the calculation engine behind the WeChat Mini Program "汽水计算器" (wxid: wx7201fd1713b524e5). Since its 2019 launch, it has served more than 20,000 users. AI-assisted review helped bring this open-source edition up to date with IAPWS R11-24 (2024). I am sharing the engine so it can reach engineers far beyond the original program.

License

MIT