In September 1997, the International Association for the Properties of Water and Steam (IAPWS) adopted a new formulation for the thermodynamic properties of water and steam for industrial use. This new industrial standard is called "IAPWS Industrial Formulation for the Thermodynamic Properties of Water and Steam" (IAPWSIF97). The formulation IAPWSIF97 replaces the previous industrial standard IFC67.
Based on this new formulation, a new steam table, titled "Properties of Water and Steam" by W. Wagner and A. Kruse, was published by the SpringerVerlag, Berlin  NewYork  Tokyo in April 1998. This steam table, ref. [1] is bilingual (English / German) and contains a complete description of the equations of IAPWSIF97. This reference is the authoritative source of information for this implementation. A mostly identical version has been published by the International Association for the Properties of Water and Steam (IAPWS) with permission granted to republish the information if credit is given to IAPWS. This document is distributed with this library as IF97.pdf. In addition, the equations published by IAPWS for the transport properties dynamic viscosity (standards document: visc.pdf) and thermal conductivity (standards document: thcond.pdf) and equations for the surface tension (standards document: surf.pdf) are also implemented in this library and included for reference.
The functions in BaseIF97.mo are low level functions which should only be used in those exceptions when the standard user level functions in Water.mo do not contain the wanted properties.
Based on IAPWSIF97, Modelica functions are available for calculating the most common thermophysical properties (thermodynamic and transport properties). The implementation requires part of the common medium property infrastructure of the Modelica.Thermal.Properties library in the file Common.mo. There are a few extensions from the version of IF97 as documented in IF97.pdf in order to improve performance for dynamic simulations. Input variables for calculating the properties are only implemented for a limited number of variable pairs which make sense as dynamic states: (p,h), (p,T), (p,s) and (d,T).
The IAPWS Industrial Formulation 1997 consists of a set of equations for different regions which cover the following range of validity:
273,15 K < T < 1073,15 K  p < 100 MPa 
1073,15 K < T < 2273,15 K  p < 10 MPa 
Figure 1 shows the 5 regions into which the entire range of validity of IAPWSIF97 is divided. The boundaries of the regions can be directly taken from Fig. 1 except for the boundary between regions 2 and 3; this boundary, which corresponds approximately to the isentropic line s = 5.047 kJ kg ^{1}K^{1}, is defined by a corresponding auxiliary equation. Both regions 1 and 2 are individually covered by a fundamental equation for the specific Gibbs free energy g( p,T ), region 3 by a fundamental equation for the specific Helmholtz free energy f ( r,T ), and the saturation curve, corresponding to region 4, by a saturationpressure equation p_{s}( T ). The hightemperature region 5 is also covered by a g( p,T ) equation. These 5 equations, shown in rectangular boxes in Fig. 1, form the socalled basic equations.
In addition to these basic equations, socalled backward equations are provided for regions 1, 2, and 4 in form of T( p,h ) and T( p,s ) for regions 1 and 2, and T_{s}( p ) for region 4. These backward equations, marked in grey in Fig. 1, were developed in such a way that they are numerically very consistent with the corresponding basic equation. Thus, properties as functions of p,h and of p,s for regions 1 and 2, and of p for region 4 can be calculated without any iteration. As a result of this special concept for the development of the new industrial standard IAPWSIF97, the most important properties can be calculated extremely quickly. All Modelica functions are optimized with regard to short computing times.
The complete description of the individual equations of the new industrial formulation IAPWSIF97 is given in IF97.pdf. Comprehensive information on IAPWSIF97 (requirements, concept, accuracy, consistency along region boundaries, and the increase of computing speed in comparison with IFC67, etc.) can be taken from IF97.pdf or [2].
[2] Wagner, W., Cooper, J. R., Dittmann, A., Kijima, J., Kretzschmar, H.J., Kruse, A., Mareš R., Oguchi, K., Sato, H., Stöcker, I., Šifner, O., Takaishi, Y., Tanishita, I., Trübenbach, J., and Willkommen, Th. The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam. ASME Journal of Engineering for Gas Turbines and Power 122 (2000), 150  182.
Common name 
Abbreviation 
Unit 

1 
Pressure  p 
Pa 
2 
Temperature  T 
K 
3 
Density  d 
kg/m^{3} 
4 
Specific volume  v 
m^{3}/kg 
5 
Specific enthalpy  h 
J/kg 
6 
Specific entropy  s 
J/(kg K) 
7 
Specific internal energy 
u 
J/kg 
8 
Specific isobaric heat capacity  c_{p} 
J/(kg K) 
9 
Specific isochoric heat capacity  c_{v} 
J/(kg K) 
10 
Isentropic exponent, kappa = (v/p) (dp/dv)_{s}  kappa (κ) 
1 
11 
Speed of sound 
a 
m/s 
12 
Dryness fraction 
x 
kg/kg 
13 
Specific Helmholtz free energy, f = u  Ts  f 
J/kg 
14 
Specific Gibbs free energy, g = h  Ts  g 
J/kg 
15 
Isenthalpic exponent, theta = (v/p) (dp/dv)_{h}  theta (θ) 
1 
16 
Isobaric volume expansion coefficient, alpha = v^{1} (dv/dT)_{p}  alpha (α) 
1/K 
17 
Isochoric pressure coefficient, beta = p^{1}(dp/dT)_{v}  beta (β) 
1/K 
18 
Isothermal compressibility, gamma = v^{1}(dv/dp)_{T}  gamma (γ) 
1/Pa 
19 
Dynamic viscosity  eta (η) 
Pa s 
20 
Kinematic viscosity  nu (ν) 
m^{2}/s 
21 
Thermal conductivity  lambda (λ) 
W/(m K) 
22 
Surface tension  sigma (σ) 
N/m 
The properties 111 are calculated by default with the functions for dynamic simulation, 2 of these variables are the dynamic states and are the inputs to calculate all other properties. In addition to these properties of general interest, the entries to the thermodynamic Jacobian matrix which render the mass and energy balances explicit in the input variables to the property calculation are also calculated. For an explanatory example using pressure and specific enthalpy as states, see the Examples subpackage.
The highlevel calls to steam properties are grouped into records comprising both the properties of general interest and the entries to the thermodynamic Jacobian. If additional properties are needed the low level functions in BaseIF97 provide more choice.
Name  Description 

IterationData  Constants for iterations internal to some functions 
data  Constant IF97 data and region limits 
getTstar  Get normalization temperature for region 1, 2 or 5 
getpstar  Get normalization pressure for region 1, 2 or 5 
critical  Critical point data 
triple  Triple point data 
Regions  Functions to find the current region for given pairs of input variables 
Basic  Base functions as described in IAWPS/IF97 
IceBoundaries  The melting line and sublimation line curves from IAPWS 
Transport  Transport properties for water according to IAPWS/IF97 
Isentropic  Functions for calculating the isentropic enthalpy from pressure p and specific entropy s 
Inverses  Efficient inverses for selected pairs of variables 
ByRegion  Simple explicit functions for one region only 
TwoPhase  Steam properties in the twophase region and on the phase boundaries 
extraDerivs_ph  Function to calculate some extra thermophysical properties in regions 1, 2, 3 and 5 as f(p,h) 
extraDerivs_pT  Function to calculate some extra thermophysical properties in regions 1, 2, 3 and 5 as f(p,T) 