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October 30, 2017, 10:16 |
R constant in Perfet Fluid
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#1 |
Member
Mehdi Aminyavari
Join Date: Feb 2016
Location: Milan
Posts: 35
Rep Power: 10 |
Hello everybody,
in many cases of openFoam, you can find equation Of State that is modeled as a perfect Fluid such as in: tutorials/multiphase/compressibleMultiphaseInterFoam/laminar/damBreak4phase/constant/thermophysicalProperties.mercury Code:
thermoType { type heRhoThermo; mixture pureMixture; transport const; thermo hConst; equationOfState perfectFluid; specie specie; energy sensibleInternalEnergy; } mixture { specie { nMoles 1; molWeight 200.59; } equationOfState { R 6818; rho0 13529; } thermodynamics { Cp 139; Hf 0; } transport { mu 1.522e-3; Pr 0.022; } } tutorials/multiphase/reactingTwoPhaseEulerFoam/laminar/bubbleColumn/constant/thermophysicalProperties.water Code:
thermoType { type heRhoThermo; mixture pureMixture; transport const; thermo hConst; equationOfState perfectFluid; specie specie; energy sensibleInternalEnergy; } mixture { specie { nMoles 1; molWeight 18; } equationOfState { R 3000; rho0 1027; } thermodynamics { Cp 4195; Hf 0; } transport { mu 3.645e-4; Pr 2.289; } } I can't figure out what is this value of R which is 3000 for water and 6818 for mercury and how to calculate it for ammonia for example. any Idea?
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February 7, 2018, 03:10 |
I don't know, either. Any one know the answer?
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#2 |
New Member
Join Date: Dec 2012
Posts: 11
Rep Power: 13 |
There is no documentation related above question...
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March 6, 2018, 00:45 |
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#3 | |
Senior Member
Jie
Join Date: Jan 2010
Location: Australia
Posts: 134
Rep Power: 16 |
Quote:
I am having the same problem. I could not figure out the R of 3000 for water in the twoPhaseEulerFoam tutorial. In particular with respect to rhom (after you run the case) RAS/bubbleCoumn, rhom is around 1027 in the region where alpha.air=0 (meaning water) but rhom is around 513 in the region where alpha.air=1 (meaning air). Shouldn't the rhom be around 1.225 (density of air) in the region where alpha=1? Thanks Jie |
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May 1, 2018, 09:58 |
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#4 |
New Member
krishnan
Join Date: Feb 2018
Posts: 16
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Im also having a difficulty in understanding this. What is rhom and why is it as much as 513 in the region representing air?
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June 6, 2018, 18:01 |
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#5 |
New Member
Anh
Join Date: Jan 2012
Posts: 2
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with being the molecular weight of gas/fluid.
For air, and . https://en.wikipedia.org/wiki/Ideal_gas_law |
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June 19, 2018, 05:55 |
I don't think so, because..
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#6 |
New Member
Join Date: Dec 2012
Posts: 11
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According to your solution,
For example, in case of water (H2O) the molar mass is about 0.018 kg/mol so the R = 8.314/0.018 ~ 461.9 J/kg K. This value is not same with '3000' in the above tutorial. (Actually, I still don't know why the value is 3000....) |
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February 1, 2019, 06:04 |
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#7 |
New Member
Arne
Join Date: Dec 2018
Posts: 19
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I believe that in OpenFOAM 1806, R = 7255 for water. However, I have no idea what it means...
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August 17, 2019, 09:24 |
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#8 |
Senior Member
Joachim Herb
Join Date: Sep 2010
Posts: 650
Rep Power: 21 |
Have you solved this?
I think if you use R for a liquid, it is just some kind of compressibility of it. Regarding rhom: It is calculated here: https://github.com/OpenFOAM/OpenFOAM...Epsilon.C#L403 and it involves the use of a virtual mass model. What are the corresponding settings in your case? |
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May 9, 2020, 00:22 |
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#9 | |
New Member
M Shaaban
Join Date: Jun 2019
Posts: 9
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Quote:
If anyone is still wondering: R is (RT)^(-1) For water, it should be calculated from psi, the compressiblity. psi = rho/bulk modulus, giving around 4.5e-7 s2/m2 (check here https://www.openfoam.com/documentati...x12-620003.3.1) then R = 7255. the use of 3000 is a mystery. |
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February 13, 2021, 15:56 |
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#10 | |
New Member
Xingchun Wang
Join Date: Dec 2016
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Quote:
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February 15, 2021, 05:04 |
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#11 |
Senior Member
Join Date: Apr 2020
Location: UK
Posts: 670
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psi is defined as drho/dp|_T, and so for an ideal gas psi = rho/p = 1/RT. This is referred to as the compressibility. R is the ideal gas constant over the molecular weight; it doesn't have any meaning for a liquid.
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February 20, 2021, 00:30 |
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#12 |
New Member
Xingchun Wang
Join Date: Dec 2016
Posts: 3
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