Overriding Density Does Not Update MassFlow

[ioncube]

Firstly I updated density of NaOH + H2O mixture using this code [https://dwsim.org/wiki/index.php?title=Overriding_Calculated_Properties]

densobj = matstr.GetPhase('OverallLiquid').Properties.density
if (densobj <> None):
    currval = densobj
    # get massFrac of NaOH
    m_fr = matstr.GetPhase('OverallLiquid').Compounds['Sodium Hydroxide'].MassFraction * 100
    # update
    if (m_fr > 0):
        # write current value to the flowsheet (kg/m3)
        flowsheet.WriteMessage('current liquid mixture density value (kg/m3): ' + str(currval))
        # get temperature in Kelvin
        m_temp = matstr.GetTemperature()
        # calculate caustic density  
        # Multiple regression via Excel Anaysis toolkit
        propval = 1239.652 + 9.722088*m_fr - 0.68301*m_temp
        #flowsheet.WriteMessage('T(K): ' + str(m_temp))
        flowsheet.WriteMessage('updated liquid mixture density value (kg/m3): ' + str(propval))
    else:
        propval = currval
else:
    propval = 0.0    

It worked however massflow was not updated & was using previous density? As a workaround I manually added a script to update massflow & binded it to feed flow material stream

stream = Flowsheet.GetFlowsheetSimulationObject('FNaOH')
densobj = stream.GetPhase('OverallLiquid').Properties.density
volobj = stream.GetVolumetricFlow() # value must be in m3/s
calcmass = densobj * volobj
stream.SetMassFlow(calcmass)
Flowsheet.WriteMessage('FNaOH mass flow updated ' + str(densobj))

Shouldn't it update massflow automatically or I suppose the sequence is different. After updatng massflow, molarflow however was OK

[Daniel Medeiros]

The call to your overriding routines is done after the mass flow is updated and equilibrium is calculated. https://github.com/DanWBR/dwsim/blob/windows/DWSIM.Thermodynamics/MaterialStream/MaterialStream.vb#L784

[ioncube]

Lets ditch Override & use scripts dialogue . SetProp is not working here, It should be straight word as per API

matstr = Flowsheet.GetFlowsheetSimulationObject('FNaOH')
densobj = matstr.GetPhase('OverallLiquid').Properties.density
Flowsheet.WriteMessage('Echo1 ' + str(densobj))
m_fr = matstr.GetPhase('OverallLiquid').Compounds['Sodium Hydroxide'].MassFraction * 100
m_temp = matstr.GetTemperature()
propval = 1239.652 + 9.722088*m_fr - 0.68301*m_temp
matstr.SetProp('density', 'OverallLiquid', '', '', '', propval)
densobj = matstr.GetPhase('OverallLiquid').Properties.density
Flowsheet.WriteMessage('Echo2 ' + str(densobj))

Attached to event of solver start...
Script throws no error but fails to accomplish density update

[Daniel Medeiros]

if you attach to solver start, it will be overriden by the actual calculation routine. The correct attachment would be to the material stream's calculation finished event.

[ioncube]

I did that but no success, there is a problem with this line

matstr.SetProp('density', 'OverallLiquid', '', '', '', propval)
or
matstr.SetProp('density', 'OverallLiquid', '', 'Mixture', '', propval)

[ioncube]

The density routine for mixtures use molar fractions for density calculations for mixtures. However I have found that mass fractions produce more proper results, close to reality. For instance ∑ [xi * ρi] leads to less values while ∑ [mi * ρi] produce much better result

0.16180186x2130+0.83819814 x958= 1147.63177992 [bad]
0.31x2130+0.69x958 = 1321.32 [ok]

These lines https://github.com/DanWBR/dwsim/blob/554110f200ea055a29a872f216879744385efa31/DWSIM.Thermodynamics/PropertyPackages/PropertyPackage.vb#L5327C1-L5332C23
Can be configured (option for user) to use mass fraction.

[Daniel Medeiros]

that is not the actual mixture density calculation routine, this is the one: https://github.com/DanWBR/dwsim/blob/554110f200ea055a29a872f216879744385efa31/DWSIM.Thermodynamics/PropertyPackages/PropertyPackage.vb#L7295

The Vx argument is the mass fractions vector.

[Daniel Medeiros]

Please give me a few days as I'm working on some personal stuff here.

Thanks
Daniel

[Daniel Medeiros]

Your script should be linked to the material stream's post-calc event and do something like this:

• If you have only one liquid phase, update the density for phaase 'Liquid1'. If you have two, update it for 'Liquid1' and 'Liquid2', then update it for 'OverallLiquid'. Some unit ops will see Liquid1 only and others will see OverallLiquid, it depends.

matstr.GetPhase('Liquid1').Properties.density = 800 # kg/m3
matstr.GetPhase('Liquid2').Properties.density = 1000 # kg/m3
matstr.GetPhase('OverallLiquid').Properties.density = 900 # kg/m3

Then you'll also need to update the Mixture density and volumetric flow accordingly, using the current value for mass flow.

mf = matstr.GetMassFlow() # kg/s

mixdens = 900 # kg/m3

matstr.GetPhase('Mixture').Properties.density = 900
matstr.SetVolumetricFlow(mf/mixdens) # m3/s

[ioncube]

SOLVED