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PT flash on pure component stream gives a wrong value

Python Scripting
Charan
2018-06-14
2018-06-15

  • Charan

    Charan - 2018-06-14

    Hi All,
    When i perform a PT flash on a pure water stream , all the values on the output material stream are incorrect.
    However if i perform a PH flash for the same stream the values are correct. I have attached my code below where i have just transferred values from one stream to another.
    The code was written inside the python scripting unit operation tool and water was the only component used

    from DWSIM.Thermodynamics import *

feed1 = ims1
P_1 = feed1.GetProp("pressure", "Overall", None, "", "")
massflow_1 = feed1.GetProp("totalFlow" ,"Overall", None, "", "mass")
molfrac_1 = feed1.GetProp("fraction", "Overall", None, "", "mole")
molflow_1 = feed1.GetProp("totalFlow" ,"Overall", None, "", "mole")
enthalpy_1 = feed1.GetProp("enthalpy" ,"Overall", None, "Mixture", "mass")
T_1 = feed1.GetProp("temperature","Overall",None,"","")

out = oms1
out.Clear()
out.SetProp("temperature","Overall",None,"","",T_1)
out.SetProp("pressure", "Overall", None, "", "", P_1)
out.SetProp("fraction", "Overall", None, "", "mole", molfrac_1)
out.SetProp("totalFlow", "Overall", None, "", "mass", massflow_1)
#out.SetProp("enthalpy", "Overall", None, "", "mass",enthalpy_1)
#out.PropertyPackage.DW_CalcEquilibrium(PropertyPackages.FlashSpec.P, PropertyPackages.FlashSpec.H)
     

  • Daniel Medeiros

    Daniel Medeiros - 2018-06-14

    Please define what are the correct and incorrect values...

     

  • Charan

    Charan - 2018-06-15

    This is output value i get when i use the code above. By incorrect values i mean that the input and output values are not same.I used the same property values for both material streams and therfore should get identical values. I get identical values only when i use PH flash

     
    Thumbnail
    Pure component.JPG

  • Daniel Medeiros

    Daniel Medeiros - 2018-06-15

    When a single-compound stream is connected to the outlet of an unit operation, a PH flash is forced. In this case, you must specify the enthalpy of the outlet stream so it can be calculated correctly. This is because you can't specify a partial vaporization (if required) with T and P only.

    See the debug output for more details:

    Calculation spec: Temperature_and_Pressure

Input variables: T = 373.132345797454 K, P = 101325 Pa

Checking mixture composition. Sum must be higher than zero. Sum = 1

Checking flow definition. Mass flow specified, will calculate molar and volumetric flow.

Property Package: Peng-Robinson (PR)

Flash Algorithm: NestedLoops

Calculating phase equilibria...

**Stream is single-compound and attached to the outlet of an unit operation. PH flash equilibrium calculation forced.**

Phase equilibria calculated succesfully.

Calculating phase properties...

Phase properties calculated successfully.

Material Stream calculated successfully.