Structure of the Formulation IF–97

Formulation consist of set of formulation for different areas, for next values of parameters:

273.15 ≤ T ≤ 1073.15 with p ≤ 100 MPa

1073.15 ≤ T ≤ 2273.15 with p ≤ 10 MPa

The layout of these areas in p-T diagram showed at pic. 1. Areas 1, 2, 5 based on fundamental equation for Gibbs's energy g(p, T), area 3 – fundamental equation for HelmHoltz's free energy f(ρ, T), and the saturation line represented by formulas Ps(Ts) and Ts(Ps). These five equations are make up the group of main equations of the Formulation IF-97. Except these equations there are some additional formulas in IF-97, which allow to don't use iterative calculations. Description of them given in [3].

Pic. 1. Areas of usage the Formulation IF-97

Borders of areas are clear from pic. 1, except border between areas 2 and 3. This border represent with next formula:

P = n1 + n2·T + n3·T2           (1)

or

T = n4 + ((P - n5)/n3)(1/2)     (2)

Formulations (1) and (2) are real for temperature from 623,15 K with pressure 16,5292 MPa to 863,15 K with pressure 100 MPa.