# SteamTab *Quad* Functions

The SteamTab *Quad* 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 call out these functions directly in your spreadsheet or you can use SteamTab *Quad*’s easy-to-use dialog boxes to automatically generate the appropriate function call with the correct arguments.

SteamTab *Quad* functions are divided into three categories:

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

The SteamTab *Quad *functions for the older scientific formulation (NBS/NRC-85) begin with the prefix `OST` and the IFC-67 industrial formulation begin with the prefix `OAST`.

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

**Table 1: SteamTab Quad 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 |

**Note**: Append the letter `O` to the function names for the older Scientific (NBS/NRC-84) and the Industrial (IFC-67) Formulations. For example, use `OSTxx` for the NBS/NRC-84 formulation and `OASTxx` for the IFC-67 formulation.

The SteamTab *Quad* 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 |