Equation number 4 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 p2b_hs extends Modelica.Icons.Function; input SI.SpecificEnthalpy h "specific enthalpy"; input SI.SpecificEntropy s "specific entropy"; output SI.Pressure p "Pressure"; constant Real[:] n = {0.801496989929495e-1, -0.543862807146111, 0.337455597421283, 0.890555451157450e1, 0.313840736431485e3, 0.797367065977789, -0.121616973556240e1, 0.872803386937477e1, -0.169769781757602e2, -0.186552827328416e3, 0.951159274344237e5, -0.189168510120494e2, -0.433407037194840e4, 0.543212633012715e9, 0.144793408386013, 0.128024559637516e3, -0.672309534071268e5, 0.336972380095287e8, -0.586634196762720e3, -0.221403224769889e11, 0.171606668708389e4, -0.570817595806302e9, -0.312109693178482e4, -0.207841384633010e7, 0.305605946157786e13, 0.322157004314333e4, 0.326810259797295e12, -0.144104158934487e4, 0.410694867802691e3, 0.109077066873024e12, -0.247964654258893e14, 0.188801906865134e10, -0.123651009018773e15}; constant Real[:] I = {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4, 5, 5, 6, 6, 6, 7, 7, 8, 8, 8, 8, 12, 14}; constant Real[:] J = {0, 1, 2, 4, 8, 0, 1, 2, 3, 5, 12, 1, 6, 18, 0, 1, 7, 12, 1, 16, 1, 12, 1, 8, 18, 1, 16, 1, 3, 14, 18, 10, 16}; constant SI.SpecificEnthalpy hstar = 4100e3 "normalization enthalpy"; constant SI.Pressure pstar = 100e6 "normalization pressure"; constant SI.SpecificEntropy sstar = 7.9e3 "normalization entropy"; end p2b_hs;