Enthalpy balance violated mixing liquid and gaseous phases

[fwitte]

E.g. mixing two streams of water (one liquid and one gaseous), the enthalpy of the mixed stream is not equal to the sum of the enthalpy of the incoming streams. I checked within the method mix_from, the enthalpy value assigned to the mixed Stream seems to be correct at that point (https://github.com/BioSTEAMDevelopmentGroup/thermosteam/blob/master/thermosteam/_stream.py#L896).

Maybe there is something wrong in my code?

import thermosteam as tmo

chemicals = tmo.Chemicals(['Water', 'Ethanol'])
thermo = tmo.Thermo(chemicals)
tmo.settings.set_thermo(thermo)
s3 = tmo.Stream('s3', T=300, P=1e5, Water=10, units='kg/hr')
s4 = tmo.Stream('s4', phase='g', T=400, P=1e5, Water=10, units='kg/hr')
s_eq = tmo.Stream('s34_mixture')
s_eq.mix_from([s3, s4])

print('MultiStream with enthalpy added by mix_from')
s_eq.vle(H=s_eq.H, P=1e5)
s_eq.show(composition=True)
print('Absolute deviation in enthalpy:', s_eq.H - (s3.H + s4.H))

print('MultiStream with Enthalpy summed individually')
s_eq.vle(H=s3.H + s4.H, P=1e5)
s_eq.show(composition=True)

yields

MultiStream with enthalpy added by mix_from
MultiStream: s34_mixture
 phases: ('g', 'l'), T: 372.79 K, P: 100000 Pa
 composition: (g) Water  1
                  -----  0.538 kmol/hr
              (l) Water  1
                  -----  0.572 kmol/hr
Absolute deviation in enthalpy: 1802.331630182045
MultiStream with Enthalpy summed individually
MultiStream: s34_mixture
 phases: ('g', 'l'), T: 372.79 K, P: 100000 Pa
 composition: (g) Water  1
                  -----  0.497 kmol/hr
              (l) Water  1
                  -----  0.614 kmol/hr

[yoelcortes]

Thanks for the bug report! It's been taken care of. You should get the following using your code:

MultiStream with enthalpy added by mix_from
MultiStream: s34_mixture
 phases: ('g', 'l'), T: 372.79 K, P: 100000 Pa
 composition: (g) Water  1
                  -----  0.497 kmol/hr
              (l) Water  1
                  -----  0.614 kmol/hr
Absolute deviation in enthalpy: -2.382876118645072e-09
MultiStream with Enthalpy summed individually
MultiStream: s34_mixture
 phases: ('g', 'l'), T: 372.79 K, P: 100000 Pa
 composition: (g) Water  1
                  -----  0.497 kmol/hr
              (l) Water  1
                  -----  0.614 kmol/hr

Edit: You can "pip install thermosteam==0.21.6" for convenience or use the github repo