Contents - Index

P_SAT

P_SAT [Pa, kPa, bar, MPa, psia, atm] returns the saturation vapor pressure of a specified pure substance at the specified temperature.  The units and return value of this function depend on the settings in the Unit System dialog.  This function accepts only one argument, in addition to the fluid name, and that is the temperature.  The T= must precede the value, variable, or expression providing the temperature. The temperature must be provided in the units specified in the Unit Information dialog.   The fluid may be a fluid name or a string variable.   

Examples:  

$UnitSystem SI C kPa mass

PS=P_sat(R134a, T=25 [C])

Pv=P_sat(DowTherm_A,T=25 [C])

{Solution:

PS=665.8 [kPa]

Pv=0.048 [kPa]

}

Note that the saturation vapor pressure can also be obtained for real fluids using the Pressure function with a supplied quality value, as in the following example

PS2=pressure(R134a,T=25 [C], x=0.5)

Any value of the quality between 0 and 1 will return the saturation vapor pressure, so PS2 and PS in the above examples will return the same value.

The vapor pressure of a blend, e.g., R410A, depends on both the temperature and quality and so it cannot be returned by the P_SAT function.  However, the Pressure function will return a value appropriate to the quality that is supplied.

Thermophysical Property Functions