Pure Fluid Water

[Johannes Neumeyer]

I want to define Water as a pure Fluid and I take the following line:

gas1=ct.Water(backend='Reynolds')

but I have troube with the enthalpy, because it is negative and i think the value isnt correct too.

Can anyone help me?

[Steven DeCaluwe]

Hi Johannes,

Negative enthalpy is not really a problem - all energy values are relative, so each equation of state must pick a “reference” state which it considers to be zero.

Can you tell me why you think the values are incorrect?  Rather than focusing on specific values of enthalpy, a better test would be to look at the differences in enthalpy between two states.  For example, for water at two different temperatures that are one degree apart but at the same pressure, one would expect that the values differ by the specific heat of water, 4.18 kJ/kg.

As expected, the following code:

>>> water = ct.Water()

>>> h1 = water.enthalpy_mass

>>> water.TP = 301, None

>>> h2 = water.enthalpy_mass

Does provide a difference of 4180.4 J/kg:

>>> print(h2-h1)

4180.402694197372

As a side note, the `backend` keyword you use gives me an error.  

>>> water = ct.Water(backend='Reynolds')

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: Water() got an unexpected keyword argument 'backend'

>>> water = ct.Water('Reynolds')

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: Water() takes 0 positional arguments but 1 was given

Not exactly sure what that is about.

Anyway, if you have a specific issue with the enthalpy values given, please do share so we can look into it. Note that we do test the performance of this class, in `test_problems/pureFluidTest/testPureWater.cpp`

Best,

Steven

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[Johannes Neumeyer]

Thank you,

another question I have is can I define the point on the dew curve?

Regards

[Bryan Weber]

Hi,

I'm not sure what you meant - do you mean set the reference state to a particular point on the dew curve? Or set the actual state based on the dew point temperature?

Best,

Bryan