Contents - Index



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


The specific internal energy of incompressible substances is a function of only temperature.  Temperature must be the only argument, 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), enthalpy (H), relative humidity (R), humidity ratio (W), wetbulb (B), or dewpoint (D).  Note also that for substance AirH2O (psychrometrics), the specific internal energy returned by this function is the internal energy of the air and water vapor mixture per unit mass of dry air.


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




$UnitSystem SI C kPa mass

u_air=intEnergy(Air,T=25 [C])

u_stm=intEnergy(Steam,T=100 [C],P=50 [kPa])

u_sat=intEnergy(Steam,T=100 [C],x=1)




u_air=213 [kJ/kg]

u_copper=79.32 [kJ/kg]

u_sat=2,506 [kJ/kg]

u_stm=2,511 [kJ/kg]



Thermophysical functions