Steam Tables Iapws

IAPWS Steam Tables

Overview

Water / steam properties via the IAPWS-95 utilities exposed through chemicals.iapws:

• Single-phase state (T, P): density, enthalpy, entropy, internal

energy, Cp, Cv, speed of sound, Joule-Thomson coefficient.

• Saturation: Psat(T) and Tsat(P).

Prerequisites

1. uv available.
2. On first use, the script writes LICENSE_NOTIFICATION.txt listing

the IAPWS terms.

When to Use

• Sizing a steam turbine, condenser, or reboiler.
• BFW or condensate stream property work at known temperature and pressure.
• Saturation pressure from temperature, or saturation temperature from pressure.

Don't use for

• Hydrocarbon systems — use vle-flash-calculations.
• Water + hydrocarbon two-phase systems — neither IAPWS nor plain cubic

EOS handles them well in isolation.

• Supercritical CO2 — use a CO2 EOS (Span-Wagner).

Utility Scripts

• uv run scripts/steam_props.py --temperature-k 773 --pressure-pa 1e7 --output /tmp/steam.json
• uv run scripts/steam_props.py --saturation --temperature-k 423 --output /tmp/sat.json

Procedure

1. Identify the state (T and P) or the saturation calculation (T or P).
2. Call the appropriate subcommand.
3. Inspect the returned properties; if any value seems unphysical,

recheck T and P bounds against the IAPWS validity range.

Pitfalls

• Confusing IAPWS-95 (scientific, full phase diagram, accurate near

critical point) with IAPWS-IF97 (industrial, faster, small region discontinuities). For simulation use IF97; for high accuracy near critical, use IAPWS-95.

• Treating the IAPWS Psat at the saturation curve as exact; the

formulation is accurate, but the calling code must be careful with rounding near saturation.

• Using IAPWS for sea water or brackish water — salt is not in the

formulation.

• Using cubic EOS for water/steam utility work — IAPWS is the industry

reference.

• Mixing kJ/kg (common in steam tables) with J/kg (the IAPWS native);

the script reports both bases.

• Reporting steam quality in a flash with a non-water hydrocarbon trace

contamination; IAPWS is pure-water only.

Fallback Strategies

• If chemicals.iapws is unavailable, surface to the user that no

fallback is available; do not attempt to substitute a cubic EOS.

Verification

• Run the listed script with representative inputs and an --output file when a deterministic calculation is available.
• Confirm the JSON result contains ok: true, expected units, and no unhandled warnings.
• Check result magnitudes against the stated assumptions, references, and a hand calculation or known operating range before reporting them.

References

• references/iapws_notes.md — region boundaries and validity ranges.
• IAPWS releases: https://iapws.org/
• chemicals.iapws docs: https://chemicals.readthedocs.io/chemicals.iapws.html

Anti-Patterns

• Using IAPWS for any non-water system.
• Quoting steam properties to four decimal places without naming the

underlying formulation.

• Mixing multiple water-property formulations within the same calculation

without naming the switch.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: jskherman
• Source: jskherman/engg-skills
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.