# Setting mixture properties (density)

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 May 31, 2020, 16:18 Setting mixture properties (density) #1 Member   Anshuman Sinha Join Date: Oct 2018 Posts: 70 Rep Power: 7 Setting up the mixture template I'm having 2 species, oil = O2 + Kerosene . each with density 1.299 and 780 kg/m3 respectively. In the mixture density drop-down menu, I have selected the option of: ' Volume weighted mixing law'. For a 2D geometry ( Area ~= 0.1 cm2 ), I have set 'oil phase 'volume fraction as 1 and mass fraction as : O2 = 0.08 + Kerosene = 9.92. But the resultant density which I see in the results is coming out to be: 15.9 kg/m3, why am I getting such a result with the mixture, as if I had set for only kerosene as a phase then I would have got density = 780 kg/m3? The mixture template is given below. Screenshot 2020-06-01 at 1.46.06 AM.jpg

 June 2, 2020, 11:25 Diesel-Air #2 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35 Diesel is liquid while air is gas. So, those should not be in a single phase. Anshs likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

June 2, 2020, 14:01
creating mixture template
#3
Member

Anshuman Sinha
Join Date: Oct 2018
Posts: 70
Rep Power: 7
Quote:
 Originally Posted by vinerm Diesel is liquid while air is gas. So, those should not be in a single phase.
1. Does the solver know this? I thought it will recognize both a being fluid.

2. Do I have to be careful while picking species for my mixture template, taking care of their miscibility and solution behavior?

3. If I want to create a mixture of things for example. a mixture of ( thymol + water )? Which I know exists in experimentations! Then how may I create this?

As far as I know, I have to select a mixture template and then add species water and thymol to this template. Since thymol isn't present in the material database. Then I need to select any material and then change the properties according to thymol and then subsequently rename it as well!

 June 2, 2020, 15:30 Materials #4 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35 No, Fluent doesn't know this. In Fluent, fluid is just fluid. However, a species mixture implies components mixed at molecular level while if the mixing is not at molecular level then the fluids should be considered separate phases. So, it is on the user to define the morphology. Its just that the available models and the results are based on this chosen morphology. User can create any material, either as a new one or by copying an existing one and then modifying it. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

June 2, 2020, 17:39
why mixture density is so low?
#5
Member

Anshuman Sinha
Join Date: Oct 2018
Posts: 70
Rep Power: 7
Quote:
 Originally Posted by vinerm No, Fluent doesn't know this. In Fluent, fluid is just fluid. However, a species mixture implies components mixed at molecular level while if the mixing is not at molecular level then the fluids should be considered separate phases. So, it is on the user to define the morphology. Its just that the available models and the results are based on this chosen morphology. User can create any material, either as a new one or by copying an existing one and then modifying it.
Okay, so if I say I have just taken 2 species named 'kerosene' and 'oxygen' (assuming these to be mixed) and both are perfectly mixed, each with density 1.299 and 780 kg/m3.

with mass fraction as : Oxygen = 0.08 + Kerosene = 9.92 but the density is coming as 15.9 kg/m3 .

For 2D geometry A~= 0.1cm2

Why is it so?

 June 3, 2020, 02:42 Mixture Density #6 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35 That's because you are using volume-weighted-mixing-law for a species mixture while mass fraction is specified by the user. Volume weighted law is good if density ratio is close to 1. You should use mass-weighted-law. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

June 3, 2020, 07:31
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#7
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Anshuman Sinha
Join Date: Oct 2018
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Quote:
 Originally Posted by vinerm That's because you are using volume-weighted-mixing-law for a species mixture while mass fraction is specified by the user. Volume weighted law is good if density ratio is close to 1. You should use mass-weighted-law.
Yes, I intended to use a mass-weighted average, but somehow it is not there in the drop-down menu.

 June 3, 2020, 07:43 Mixing Law #8 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35 Mass weighted law is unavailable for Species Transport. You have to write a UDF for that. Anshs likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 Tags fluent, material properties, mixture setting, species transport