Software for the Industrial Formulation IAPWSIF97 for Water and Steam
Information about the several Windows operating systems and Excel versions as well as about 64 Bit DLLs and .Net DLLs are given at the end of this software description.
1. Short information about IAPWSIF97
The Industrial Formulation IAPWSIF97 consists of a set of equations for different regions, which covers the following range of validity:
0 °C ≤ t ≤ 800 °C, p ≤ 1000 bar (100 MPa)
800 °C < t ≤ 2000 °C, p ≤ 500 bar (50 MPa)
The figure above shows the five regions into which the entire range of validity of IAPWSIF97 is divided. Regions 1 and 2 are both 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(ρ,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 five equations, shown in rectangular boxes in the figure, form the so called basic equations.
In addition to these basic equations, socalled backward equations are provided for regions 1 to 4. These backward equations were developed in the following combinations of variables: For regions 1 and 2 as equations of the form T(p,h), T(p,s), and p(h,s), for region 3 as equations of the form T(p,h), v(p,h), T(p,s), v(p,s), p(h,s) and v(p,T). The backward equation for the entire region 4 is a saturationtemperature equation T_{s}(p), and for the technically most important part of region 4 (s ≥ s’’ (623.15 K)), there is a saturationtemperature equation of the form T_{s}(h,s). In the figure above, in addition to the (framed) basic equations, all of these types of backward equations (marked in grey) are assigned to the corresponding region of IAPWSIF97.
With these backward equations, properties dependent on the input quantities (p,h), (p,s), (h,s), in region 3 also on the input quantities (p,T), are calculable without iterations, and thus very fast.
Further details of IAPWSIF97 see here.
Furthermore, the book
Wagner, W., Kretzschmar, H.J. International Steam Tables  Properties of Water and Steam Based on the Industrial Formulation IAPWSIF97. SpringerVerlag (Berlin), 2008
comprehensively describes IAPWSIF97. This book also contains the IAPWS equations for the most important transport properties and some other properties, and two wall charts, a Mollier h,s diagram and a T,s diagram. For more details (contents, sample pages, etc.) see here.
2. Software for IAPWSIF97
On the basis of IAPWSIF97, including all of the backward equations as well as the IAPWS equations for the transport properties and three further properties, there is a software package for the calculation of more than 25 properties. This software was especially established regarding an optimal programming to achieve short computing times.
When applying the software, it is not necessary to know which region of IAPWSIF97 the property to be calculated belongs to. Based on the given input quantities, the software automatically determines which equation of IAPWSIF97 has to be applied.
With our software package, the following thermodynamic properties, transport properties and three further properties of water and steam can be calculated:
2.1 Thermodynamic properties
Based on the corresponding equations of IAPWSIF97 the thermodynamic properties listed in Table 1 can be calculated with the software:
Table 1. Calculable thermodynamic properties
Symbol Property 
p 
Pressure 

T 
Temperature 

v 
Specific volume 

ρ 
Density 

h 
Specific enthalpy 

s 
Specific entropy 

cp 
Specific isobaric heat capacity 

u 
Specific internal energy 

c_{v} 
Specific isochoric heat capacity 

x 
Vapour fraction 

w 
Speed of sound 

g 
Specific Gibbs free energy g = h − Ts 

f 
Specific Helmholtz free energy f = u − Ts 

z 
Compression factor 

f* 
Fugacity 

α_{v } 
Isobaric cubic expansion coefficient, α_{v } = v^{− }^{1} (∂v/∂T)_{p } 

α_{p} 
_{ } Relative pressure coefficient, α = v^{−1} (∂v/∂T)_{p} 

β_{p} 
Isothermal stress coefficient, β = p^{−1} (∂p/∂T)_{v} 

κ 
Isentropic exponent, κ = − (v/p) (∂p/ ∂v)_{s} 

κ_{T} 
Isothermal compressibility, κ_{T } = –v^{ }^{1} (∂v/∂p)_{T } 

µ 
Joule‑Thomson coefficient, µ = (∂T/∂p)_{h } 

(∂v/∂p)_{h} 
Partial derivative 

(∂ρ/∂p)_{h} 
Partial derivative 

(∂v/∂h)_{p} 
Partial derivative 

(∂ρ/∂h)_{p} 
Partial derivative 

(∂h/∂p)_{T} 
Partial derivative 

x 
Vapour fraction 

________________________________________________________ 
All these properties can be calculated in the entire range of validity of IAPWSIF97, see Sec. 1. Concerning region 4 (twophase region), the properties ν, ρ, h, s, u, f, g and x can also be calculated within the twophase region. The other properties can only be calculated on the phase boundaries (saturatedliquid line and saturatedvapour line) because they are not defined within the twophase region.
2.2 Transport properties and further properties
The software allows the calculation of transport properties, dielectric constant, refractive index, and surface tension listed in Table 2.
Table 2. Calculable transport and further properties
Symbol 
Property 
η 
Dynamic viscosity 
v 
Kinematic viscosity, v = η / ρ 
λ 
Thermal conductivity 
Pr 
Prandtl number, Pr = η c_{p}/ λ 
a 
Thermal diffusivity, a = λ /(ρc_{p}) 
ε 
Relative static dielectric constant 
n 
Refractive index 
σ 
Surface tension 
_____________________________________________________
The internationally agreed equations for calculating these properties, which do not belong to IAPWSIF97, are described in Ref. [165] and in the corresponding IAPWS Releases, see www.iapws.org. It should be noted that these equations are functions of temperature and density (not pressure). This fact has consequences for the necessity of iterations. The surface tension is a function of temperature only. Except for the dielectric constant ε, all the other properties can be calculated in the entire range of validity of IAPWSIF97, see Sec. 1.
The range of validity of the equation for ε is limited to 873.15 K, but the equation can be reasonably extrapolated up to 1073.15 K. The surface tension σ(T) refers only to the twophase region, region 4.
2.3 Combinations of input variables for calculating the several properties
2.3.1 Regions 15
For regions 13 and 5 (singlephase regions) and region 4 (twophase region), all properties listed in Tables 1 and 2 can be calculated as a function of the pairs of input variables shown in Table 3. For region 5, properties for input variables other than (p,T) are calculated via iterations only; there are no backward equations. Properties in region 4 cannot be calculated for the combination (p,T) as input variables, because p and T are not independent of each other in this region.
Table 3. Possible combinations of input variables for calculations in regions 1 to 5; for region 4, (p,T) cannot be used 
(p,T) 
(T,h) 
(ν,h) 
(h,s) 
(p,h) 
(T,s) 
(ν,s) 

(p,s) 
(T,ν) 


(p,ν) 
(T,ρ) 


The most important properties can directly be calculated from the functions in the software for the pairs of input variables listed in Table 3. The calculation of further properties as functions of all the pairs of input variables is possible by corresponding combinations of functions in the software.
2.3.2 Calculations for region 4 (twophase region) only
For region 4 [saturation pressure p_{sat} , saturation temperature T_{sat}, saturatedliquid line [('), x = 0, bubble line], saturatedvapour line [("), x = 1, dew line], twophase region (0 < x < 1)], the properties in the left column of Table 4 can be calculated from the functions given in the software for all listed input variables.
Table 4. Calculable properties for the entire region 4 (saturatedliquid line, saturatedvapour line and within the twophase region) from the corresponding functions listed in the software 
Calculable properties 
Input variables^{1} 
Explanations 
p_{sat} 
T, h, s, ρ, x 
^{1}In addition to the input variables given here, the properties can also be calculated using the corresponding input variables listed in Table 3 [except for 
T_{sat } 
p, h, s, ρ 

v, h, s 
(T,x), (p,x) 

ν, f, g 
(T,x), (p,x) 

x 
(p,h), (p,s), (p,v) 
Those properties listed in Tables 1 and 2 that are not given in the left column of Table 4 cannot be calculated within the twophase region (0 < x < 1) but only on the saturatedliquid and saturatedvapour line; these properties are not defined within the twophase region.
2.4 Dynamic Link Library for userspecific calculations
For the integration of IAPWSIF97 into user specific applications, the software contains a Dynamic Link Library (DLL). This DLL contains numerous functions thath enable the calculation of all properties listed above dependend on all combinations of input variables listed below. The user can choose between the calculation of properties with the backward equations of IAPWSIF97 or with iterations using only the basic equations. The calls of the functions of the DLL are made via simple names of functions that are based on the property to be calculated and the selected input variables. For example, the enthalpy h for given values of temperature T and pressure p is calculated from function HBPT.
The software allows the selection whether the backward equations should be used or only basic equations with iterations if iterations are necessary for the calculation of the corresponding property.
The software contains a .LIB file that allows the integration of the DLL into user specific Fortran programs, C programs, and Visual Basic.
In addition, the software contains an AddIn file that allows a simple integration of the DLL into Microsoft Excel. In this way, the considered properties can directly be calculated from within an Excel spreadsheet by calling the name of the corresponding function with the required input values.
As an example, the following screenshot shows the results of the calculation of all the properties for T = 300 K and p = 1 MPa. For T = 300 K, all properties on the saturatedliquid line and saturatedvapour line were calculated as well. For the vapour fraction x = 0.5, all properties that are defined within the twophase region are also calculated. All these properties were calculated at once. This Excel spreadsheet contains all the functions that are provided by the software. Of course, a userspecific Excel spreadsheet can be designed.
Example screenshot of calculations with the software package IAPWSIF97 from within a Microsoft Excel spreadsheet.
All functions that can be called from the DLL are specified in the file MANUAL.PDF that is also part of this software.
The DLL and the die Excelfiles .xla, .xlam, .xls, xlsm are configurated in such a way that they can be used under the several Windows operating systems [Windows 2000 to XP (32 Bit), Windows 7 and 8
(32 Bit/64 Bit)] and under the several Excel versions [2003 to 2013 (32 Bit)].
The IAPWSIF97 software is now available as a 64Bit version, which can be, under the 64Bit operating systems of Windows XP to Windows 2010 and the supplied 64bit Excel Addins, incorporated into the 64Bit versions of Excel 20102016. Using the supplied LIB file, the software can also be integrated into other 64Bit applications (e.g. Matlab).
.Net DLLs are also available.
The software is not free of charge.
Contact:
Prof. em. Dr.Ing. W. Wagner
Tel. +49 (0)234 3229033
Fax +49 (0)234 3214945
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