Extrapolation of IAPWS-IF97 data: The saturation pressure of H2O in the critical region

• Main Authors: Ustyuzhanin, E E, Ochkov, V F, Shishakov, V V, Rykov, A V
• Format: Conference Proceeding
• Language: English
• Subjects: Mathematical models; Physics; Thermophysical properties; Vapor pressure; Websites
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/653/1/012109

Some literature sources and web sites are analyzed in this report. These sources contain an information about thermophysical properties of H2O including the vapor pressure Ps. (Ps,T)-data have a form of the international standard tables named as "IAPWS-IF97 data". Our analysis shows that traditional databases represent (Ps,T)-data at t > 0.002, here t = (Tc − T) Tc is a reduced temperature. It is an interesting task to extrapolate IAPWS-IF97 data in to the critical region and to get (Ps,T)-data at t < 0.002. We have considered some equations Ps(t) and estimated that previous models do not follow to the degree laws of the scaling theory (ST). A combined model (CM) is chosen as a form, F(t,D,B), to express a function ln(Ps Pc) in the critical region including t < 0.002, here D = (α, Pc,Tc,...) are critical characteristics, B are adjustable coefficients. CM has a combined structure with scaling and regular parts. The degree laws of ST are taken into account to elaborate F(t, D, B). Adjustable coefficients (B) are determined by fitting CM to input (Ps,T)-points those belong to IAPWS-IF97 data. Application results are got with a help of CM in the critical region including values of the first and the second derivatives for Ps(T). Some models Ps(T) are compared with CM.