Fugacity coefficients of mixtures with phase not imposed

[Salvador Asensio]

Hi,

This may be a silly question, but I can't find an answer, sorry.

I am working with a mixture of R134a and R1234yf at different compositions and when I needed to calculate the fugacity coefficients of each component of the mixture I found out that when I do not impose the phase I get a result I do not understand, as it is neither the gas nor the liquid phase fugacity coefficient.

An example of this is below. With this code, the liquid phase fugacity coefficient is 0.873 and 0.909 for each compound, for the gas, the coefficients are 0.894 and 0.887, and the third case gives 0.798 and 0.787 as a result. What phase do these fugacity coefficients correspond to? Or what am I calculating instead of gas or liquid?

Thank you in advance.

Python code:

import CoolProp

AS = CoolProp.AbstractState('HEOS','R134a&R1234yf')

x = 0.517

T = 283.16               

P = .4498                

AS.set_mole_fractions([x,1-x])

AS.specify_phase(CoolProp.iphase_liquid)

AS.update(CoolProp.PT_INPUTS,P*1e6,T)

print(AS.fugacity_coefficient(0),AS.fugacity_coefficient(1))

print(' ')

print(' ')

AS2 = CoolProp.AbstractState('HEOS','R134a&R1234yf')           

AS2.set_mole_fractions([x,1-x])

AS2.specify_phase(CoolProp.iphase_gas)

AS2.update(CoolProp.PT_INPUTS,P*1e6,T)

print(AS2.fugacity_coefficient(0),AS2.fugacity_coefficient(1))

print(' ')

print(' ')

AS3 = CoolProp.AbstractState('HEOS','R134a&R1234yf')      

AS3.set_mole_fractions([x,1-x])

AS3.update(CoolProp.PT_INPUTS,P*1e6,T)

print(AS3.fugacity_coefficient(0),AS3.fugacity_coefficient(1))

[Ian Bell]

The question is what densities (and vapor qualities if two-phase) you are getting from these approaches.  If all are the same, then the fugacity coefficients should definitely all be the same.  

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[Salvador Asensio]

Hi again and thank you for the fast response.

Checking the vapor quality and density, I see that when I do not specify the phase, I get a two phase mixture.

Now, I have a new question. When I use AS.phase(), I get the outputs 0, 5 and 6 for the liquid, vapor, and two-phase mixture.

What do these numbers mean?

Thank you,

Python code:

import CoolProp

AS = CoolProp.AbstractState('HEOS','R134a&R1234yf')

x = 0.517

T = 283.16               

P = .4498                

AS.set_mole_fractions([x,1-x])

AS.specify_phase(CoolProp.iphase_liquid)

AS.update(CoolProp.PT_INPUTS,P*1e6,T)

print(AS.fugacity_coefficient(0),AS.fugacity_coefficient(1))

print(AS.rhomolar())

print(AS.get_mole_fractions())

print(AS.Q())

print(AS.phase())

print(' ')

AS2 = CoolProp.AbstractState('HEOS','R134a&R1234yf')           

AS2.set_mole_fractions([x,1-x])

AS2.specify_phase(CoolProp.iphase_gas)

AS2.update(CoolProp.PT_INPUTS,P*1e6,T)

print(AS2.fugacity_coefficient(0),AS2.fugacity_coefficient(1))

print(AS2.rhomolar())

print(AS2.get_mole_fractions())

print(AS2.Q())

print(AS2.phase())

print(' ')

AS3 = CoolProp.AbstractState('HEOS','R134a&R1234yf')      

AS3.set_mole_fractions([x,1-x])

AS3.update(CoolProp.PT_INPUTS,P*1e6,T)

print(AS3.fugacity_coefficient(0),AS3.fugacity_coefficient(1))

print(AS3.rhomolar())

print(AS3.get_mole_fractions())

print(AS3.mole_fractions_liquid())

print(AS3.mole_fractions_vapor())

print(AS3.Q())

print(AS3.phase())

[Ian Bell]

Docs for phase: http://www.coolprop.org/apidoc/CoolProp.AbstractState.html#CoolProp.AbstractState.phase

Returns one of these values: http://www.coolprop.org/_static/doxygen/html/namespace_cool_prop.html#a99d892f7b3bb9808265335ac1efb858f

Numerical values can be obtained programmatically (you should never hard-code, always query).  In Python:

>>> import CoolProp as CP
>>> CP.iphase_liquid
0

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[Salvador Asensio]

Alright, thank you very much.