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SteamTab Duo Functions

The SteamTab Duo add-in package is based on a set of 19 core functions that together calculate over 30 thermodynamic and transport properties of steam. You can use these functions directly in your spreadsheet or you can use SteamTab Duo’s easy-to-use dialog boxes to automatically generate the appropriate function call with the correct arguments.

SteamTab Duo functions are divided into three categories:

  1. Functions for saturated vapor, liquid or two-phase properties (2 functions)
    These two functions calculate vapor, liquid and two-phase properties from the triple point up to the critical point. You can choose either temperature or pressure as the independent variable.
  2. Functions for superheated vapor or subcooled liquid properties (9 functions)
    The functions in this category provide you with a rich set of tools for conducting several constant-property processes. Depending on the choice of independent variables, you can model isentropic, isenthalpic, constant volume, or constant internal energy processes.
  3. Functions for constant steam properties (8 functions)
    The 8 functions in this category give you access to fundamental steam properties that are not functions of temperature or pressure, such as, molecular weight, critical properties, and triple point properties.


All SteamTab Duo functions based on the scientific formulation (IAPWS-95) begin with the prefix ST, and all of the SteamTab Duo functions based on the industrial formulation (IAPWS-IF97) begin with the prefix AST.

The following table gives a quick overview of these functions and their calling sequence.

Table 1: SteamTab Duo Functions
ScientificIndustrialCalculates Property
Saturated vapor, liquid and two-phase functions
STTSATASTTSATat specified temperature and quality
STPSATASTPSATat specified pressure and quality
Superheated or subcooled functions
STTPASTTPat specified temperature and pressure (T-P)
STTVASTTVat specified temperature and specific volume (T-V)
STTVASTTVat specified temperature and enthalpy (T-H)
STTSASTTSat specified temperature and entropy (T-S)
STTUASTTUat specified temperature and internal energy (T-U)
STPVASTPVat specified pressure and specific volume (P-V)
STPHASTPHat specified pressure and enthalpy (P-H)
STPSASTPSat specified pressure and entropy (P-S)
STPUASTPUat specified pressure and internal energy (P-U)
Constant property functions
STMWASTMWmolecular weight
STTCASTTCcritical temperature
STPCASTPCcritical pressure
STVCASTVCcritical specific volume
STRCASTRCcritical specific density
STZCASTZCcritical compressibility factor
STTPTASTTPTtriple point temperature
STTPPASTTPPtriple point pressure

The SteamTab Duo functions return the requested property in either Metric/SI or English units. The thermodynamic and transport properties of steam and the units in which they are available is shown in the following table.


Table 2: Thermodynamic and Transport Properties of Water and Steam
Property Metric/SI Units English Units
Compressibility factordimensionlessdimensionless
Helmoltz free energykJ/kgBtu/lb
Internal EnergykJ/kgBtu/lb
Gibbs free energykJ/kgBtu/lb
Heat capacity at constant volumekJ/(kg.°C)Btu/(lb.°F)
Heat Capacity at constant pressurekJ/(kg.°C)Btu/(lb.°F)
Speed of soundm/sft/s
Coefficient of thermal expansion1/°C1/°F
Isothermal compressibility1/bar1/psia
Partial derivative of pressure with temperaturebar/°Cpsia/°F
Partial derivative of volume with temperaturem3/(kg.°C)ft3/(lb.°F)
Partial derivative of volume with pressurem3/( ft3/(lb.°F)
Viscosity (dynamic)micro-Pa.slb/(
Thermal conductivityW/(m.°C)Btu/(hr.ft.°F)
Surface TensionN/mN/m
Prandtl numberdimensionlessdimensionless
Static dielectric constantdimensionlessdimensionless
Isothermal Joule-Thomson coefficientkJ/(
Joule-Thomson coefficient°C/bar°F/psia
Quality (vapor-fraction)fractionfraction
Isentropic expansiondimensionlessdimensionless
Latent heat of vaporizationkJ/kgBtu/lb