Contents - Index



ENTHALPY [J/kg, J/kmol, kJ/kg, kJ/kmol, Btu/lbm Btu/lbmol] returns the specific enthalpy of a specified substance.  The value and units of the returned value depends on the Unit System setting.  The exact form of the enthalpy function depends on the substance and independent variable(s) selected.  Substances that obey the ideal gas law, such as air, require a single argument in addition to the substance name (temperature or internal energy) whereas real fluid substances, e.g., Steam and CarbonDioxide, will always require two independent variables.  


The specific enthalpy of incompressible substances is a function of only temperature and pressure since h=u+P v.  Both temperature and pressure  must be the provided as arguments, in addition to the substance name.


For AirH2O, three arguments are required.  One of these arguments must be total pressure (P).  The remaining two can be any of the following: temperature (T), internal energy (U), relative humidity (R),  humidity ratio (W), wetbulb (B), or dewpoint (D).   Note also that for substance AirH2O (psychrometrics), the specific enthalpy returned by this function is the enthalpy of the air and water vapor mixture per unit mass of dry air.


The reference state upon which the value of enthalpy is based varies with the substance.  However, all ideal gas substances (which have a chemical symbol name, e.g., N2, CO2, CH4) have enthalpy values corresponding to JANAF table references.  The JANAF table reference for enthalpy is based on the elements having an enthalpy value of 0 at 298 K (537 R).


The list of property identifiers needed in the calling arguments and instructions are available in the Thermophysical Function help.




$UnitSystem SI C kPa mass

h_air=enthalpy(Air,T=25 [C])

h_stm=enthalpy(Steam,T=100 [C],P=50 [kPa])

h_sat=enthalpy(Steam,T=100 [C],x=1)

h_copper=enthalpy(Copper,T=25,P=5000 [kPa])



h_air=298.6 [kJ/kg]

h_copper=79.88 [kJ/kg]

h_sat=2,676 [kJ/kg]

h_stm=2,682 [kJ/kg]



Thermophysical functions