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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.

Note

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
Scientific Industrial Calculates Property
Saturated vapor, liquid and two-phase functions
STTSAT ASTTSAT at specified temperature and quality
STPSAT ASTPSAT at specified pressure and quality
Superheated or subcooled functions
STTP ASTTP at specified temperature and pressure (T-P)
STTV ASTTV at specified temperature and specific volume (T-V)
STTV ASTTV at specified temperature and enthalpy (T-H)
STTS ASTTS at specified temperature and entropy (T-S)
STTU ASTTU at specified temperature and internal energy (T-U)
STPV ASTPV at specified pressure and specific volume (P-V)
STPH ASTPH at specified pressure and enthalpy (P-H)
STPS ASTPS at specified pressure and entropy (P-S)
STPU ASTPU at specified pressure and internal energy (P-U)
Constant property functions
STMW ASTMW molecular weight
STTC ASTTC critical temperature
STPC ASTPC critical pressure
STVC ASTVC critical specific volume
STRC ASTRC critical specific density
STZC ASTZC critical compressibility factor
STTPT ASTTPT triple point temperature
STTPP ASTTPP triple 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
Temperature °C °F
Pressure bar psia
Volume m3/kg ft3/lb
Density kg/m3 lb/ft3
Compressibility factor dimensionless dimensionless
Helmoltz free energy kJ/kg Btu/lb
Entropy kJ/(kg.°C) Btu/(lb.°F)
Internal Energy kJ/kg Btu/lb
Enthalpy kJ/kg Btu/lb
Gibbs free energy kJ/kg Btu/lb
Heat capacity at constant volume kJ/(kg.°C) Btu/(lb.°F)
Heat Capacity at constant pressure kJ/(kg.°C) Btu/(lb.°F)
Speed of sound m/s ft/s
Coefficient of thermal expansion 1/°C 1/°F
Isothermal compressibility 1/bar 1/psia
Partial derivative of pressure with temperature bar/°C psia/°F
Partial derivative of volume with temperature m3/(kg.°C) ft3/(lb.°F)
Partial derivative of volume with pressure m3/(kg.bar) ft3/(lb.°F)
Viscosity (dynamic) micro-Pa.s lb/(ft.hr)
Thermal conductivity W/(m.°C) Btu/(hr.ft.°F)
Surface Tension N/m N/m
Prandtl number dimensionless dimensionless
Static dielectric constant dimensionless dimensionless
Isothermal Joule-Thomson coefficient kJ/(kg.bar) Btu/(lb.psia)
Joule-Thomson coefficient °C/bar °F/psia
Quality (vapor-fraction) fraction fraction
Isentropic expansion dimensionless dimensionless
Latent heat of vaporization kJ/kg Btu/lb