The ISE function block calculates the final enthalpy for isentropic expansion of steam to a given pressure for given entropy. If the entropy-pressure point is in the two-phase region, the combined enthalpy of steam and water for constant entropy is provided. Steam quality (percent moisture) and steam temperature are also calculated. The ISE function block is valid for the following pressure range: P > -14.696 psig (0 MPa), P <= 14489 psig (100 MPa).
The block calculations are based on The International Association for the Properties of Water and Steam (IAPWS) Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam.
If the input pressure value is out of the specified IF97 range, the value used for calculations is limited to the IF97 boundary value and the block status is set to Bad. If the combination of input pressure and entropy produce a temperature out of the IF97 range (greater than 800°C or 1472°F) the entropy is limited to the boundary value for the calculation. The block limits are set accordingly and the block status is set to Bad.
The following figure shows the internal components of the ISE function block:
