อัปเดต 2026-09-07

Steam Tables

IAPWS-IF97 industrial formulation, Regions 1/2/4

Water/steam property lookup (v, h, s, u, cp, ρ) at any (T,P) or on the saturation curve, plus wet-steam (two-phase) mixture properties by quality — implementing IAPWS-IF97 Region 1 (compressed liquid), Region 2 (superheated vapor) and Region 4 (saturation curve).

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Direct evaluation of the IF-97 dimensionless Gibbs free-energy polynomial expansions (34 terms Region 1; 9 ideal-gas + 43 residual terms Region 2) and their analytic derivatives — no iteration. Saturation T↔P is an explicit 10-coefficient Wagner backward equation. Region 3 (near-critical) and Region 5 (>1073 K) are out of scope and reported as out-of-range.

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IAPWS-IF97 reduced Gibbs free energy → properties

γ (π, τ) = i \sum n_{i} (7.1 - π)^{I_{i}} (τ - 1.222)^{J_{i}} \Rightarrow h = τ γ_{τ} R T, s = (τ γ_{τ} - γ) R, v = \frac{π γ _{π} R T}{p}

Region 1 (compressed liquid): π=P/16.53 MPa, τ=1386/T, 34 terms. Region 2 (superheated vapor) uses γ=γ°(ideal)+γʳ(residual) with π=P[MPa], τ=540/T (9+43 terms) — same derivative formulas. R=0.461526 kJ/(kg·K) (specific gas constant for water). Region 4 saturation curve Psat(T)/Tsat(P) is a separate 10-coefficient Wagner backward equation. Two-phase mixture at quality x: h=h_f+x·h_fg (and likewise for s, v, u).

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