Equation number 3 from:
The International Association for the Properties of Water and Steam
Gaithersburg, Maryland, USA
September 2001
Supplementary Release on Backward Equations for Pressure as a
Function of Enthalpy and Entropy p(h,s) to the IAPWS Industrial
Formulation 1997 for the Thermodynamic Properties of Water and Steam
function p2a_hs extends Modelica.Icons.Function; input Units.SI.SpecificEnthalpy h "specific enthalpy"; input Units.SI.SpecificEntropy s "specific entropy"; output Units.SI.Pressure p "Pressure"; constant Real[:] n = {-0.182575361923032e-1, -0.125229548799536, 0.592290437320145, 0.604769706185122e1, 0.238624965444474e3, -0.298639090222922e3, 0.512250813040750e-1, -0.437266515606486, 0.413336902999504, -0.516468254574773e1, -0.557014838445711e1, 0.128555037824478e2, 0.114144108953290e2, -0.119504225652714e3, -0.284777985961560e4, 0.431757846408006e4, 0.112894040802650e1, 0.197409186206319e4, 0.151612444706087e4, 0.141324451421235e-1, 0.585501282219601, -0.297258075863012e1, 0.594567314847319e1, -0.623656565798905e4, 0.965986235133332e4, 0.681500934948134e1, -0.633207286824489e4, -0.558919224465760e1, 0.400645798472063e-1}; constant Real[:] I = {0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 3, 4, 5, 5, 6, 7}; constant Real[:] J = {1, 3, 6, 16, 20, 22, 0, 1, 2, 3, 5, 6, 10, 16, 20, 22, 3, 16, 20, 0, 2, 3, 6, 16, 16, 3, 16, 3, 1}; constant Units.SI.SpecificEnthalpy hstar = 4200e3 "normalization enthalpy"; constant Units.SI.Pressure pstar = 4e6 "normalization pressure"; constant Units.SI.SpecificEntropy sstar = 12e3 "normalization entropy"; end p2a_hs;