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Vaporisation temperature Tvap Effect

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Old   April 25, 2014, 06:26
Question Vaporisation temperature Tvap Effect
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Hi Everyone i am new in this forum and start working with OpenFoam and i have some questions.

I am working on Diesel Spray Injection Model. I am using "Liquid Evaporation model" and "SingleKineticRateDevolatilisation Model" and i am using OpenFoam 2.1.0(I also Used 2.3.0 Version and it crashes i write that problem with details in other thread later).
  • I just want to Know from where and how these two models uses the values of Tmin, Tvap Tbp and specially how it calculate Tvap as i read both the models in details but did not find anything related to its dependence , use , calculation etc.
  • And it calculate the value of Tvap for both Model in with same way or its different ??
Because when i run the simulation with only Liquid Evaporation model results and especially temperature drop at outlet is more and different as compared to using both the models


Please answer your help will be really appreciated. Thanks
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Old   April 28, 2014, 03:49
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Hello again,

I think that information i gave before i not enough so i gave you some more details maybe then you people can help me.

  • I am using Steady state Solver (The closest solver you will find to what i am using is LTSReactingParcelFoam link is down ) can anyone tell me how the max track time and calcFrequency in this file is calculated and how it effect the solution??
https://github.com/OpenFOAM/OpenFOAM...oud1Properties


  • I am taking dt time step (in Control Dict file ) and track time (In Reacting Cloud1 Properties) both equal to 10.
  • The values of Tmin, Tvap, Tbp that are defined in Reacting cloud 1 properties can any body tell me how they are calculated for both Models and where or from where they are call ??
  • I am using the same constant properties for liquid evaporation model as for the SingleKineticRateDevolatilisation Model which are

transient no;
calcFrequency 1;//
maxTrackTime 10;
maxCo 0.2;
coupled true;
cellValueSourceCorrection off;

sourceTerms
{
resetOnStartup false;
schemes
{
rho semiImplicit 1;
U semiImplicit 1;
Yi semiImplicit 1;
hs semiImplicit 1;
}
}

interpolationSchemes
{
rho cell;
U cellPoint;
mu cell;
T cell;
Cp cell;
p cell;
}

integrationSchemes
{
U Euler;
T analytical;
}
}

constantProperties
{
parcelTypeId 1;
rhoMin 1e-15;
TMin 200;
pMin 1000;
minParticleMass 1e-15;
rho0 1087;
T0 333.15;
Cp0 3395;
youngsModulus 1e9;
poissonsRatio 0.35;
epsilon0 1;
f0 0.5;
Tvap 273;
Tbp 378;
Pr 0.7;
LDevol 3086523;
hRetentionCoeff 0;
constantVolume false;
}

subModels
{
particleForces
{
sphereDrag;

}

injectionModel coneInjection;

dispersionModel stochasticDispersionRAS;

patchInteractionModel localInteraction;


heatTransferModel RanzMarshall;

compositionModel singleMixtureFraction;

phaseChangeModel liquidEvaporation;

devolatilisationModel none;//singleKineticRateDevolatilisation;

surfaceReactionModel none;

surfaceFilmModel none;

radiation off;

but the outlet average temperature in both cases is coming different. Anyone know why

Help me Now!!
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Old   April 29, 2014, 05:15
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Please read this carefully, it makes it much easier to read your posts!
http://www.cfd-online.com/Forums/ope...tml#post424508

About your actual problem, OF 2.1.0 has some bugs in the temperature calculation (mainly related to the critical temperature). They are all fixed in the latest 2.2.x and 2.3.0. You will not get any useful result with 2.1.0.

Also note that with the fixes and some further improvements in 2.3.0, the bogus "Tvap" and "Tbp" are removed from the cloud dictionary, this is now handled consistently in the liquid properties.
The corresponding temperature for devolatilisation would be called "TDevol", in case you are really using a devolatilisation model.
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Old   April 29, 2014, 09:03
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Thanks Armin,

I appreciate your concern and i read the link and i hope next time i try to write more clearly.

ok you said there is a temperature bug in OF 2.1.0. I agree and i used 2.3.0 where the Tvap and Tbp are taken automatically by the solver from Janab table but there is a problem with 2.3.0 that its only working in series when i try to run it in parallel it crashes and secondly it took long time and results are same no difference.

And second i am trying to write that OF 2.1.0 models in Analytical form and i did not find in the model .H and .C file where and how its calculate the Tvap and Tbp. Thats why i am really stuck to my work and need help if someone tell me from where these values are taken or calculated.
And yes you are right about TDevol and i am using devolatilisation model and when i used devolatilisation model and Evaporation model together the temperature is coming different that why i need to know how they are calculating in the model.

if you can help more i will be really happy

Regards,

Bilal
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Old   April 29, 2014, 09:51
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Quote:
Originally Posted by brbbhatti View Post
ok you said there is a temperature bug in OF 2.1.0. I agree and i used 2.3.0 where the Tvap and Tbp are taken automatically by the solver from Janab table but there is a problem with 2.3.0 that its only working in series when i try to run it in parallel it crashes and secondly it took long time and results are same no difference.
There were several things that went wrong in 2.1.0, cannot recall them right now off the top of my head.

However, neither Tvap nor Tbp are used in the evaporation routine (not in 2.1.0 or in 2.3.0). The boiling temperature is calculated from the vapor pressure relationship (look for the function pvInvert in liquidProperties). The function pvInvert checks also for critical and solid phase (triple point) conditions.
Just to mention, the JANAF/NASA tables are only used for gas phase properties (i.e. h/cp/s).

You find the code for the liquid properties here:
Code:
src/thermophysicalModels/properties/liquidProperties/liquidProperties/liquidProperties.H
Tvap was only used in the devolatilisation model, therefore it was also renamed to TDevol in 2.3.0.
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Old   May 7, 2014, 08:59
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Thanks Armin,

I check the link you mention it gave me some idea so thanks for your help .
And maybe you are right Tvap was used in the devolatilisation model, therefore it was also renamed to TDevol in 2.3.0. but not sure as it is also used in Liquid properties of Liquid Evaporation Model in OF 2.1.0.

Can you please also check my other thread and answer that post too.

Thanks
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Old   May 7, 2014, 09:25
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IIRC then Tvap was never used in the evaporation model. Anyway, if it was used there, then it's just wrong.

The quantity makes only sense in the devolatilisation model, therefore it was also renamed to TDevol in 2.3.0.

As I said, the lower temperature limit for evaporation is given by the triple point and should therefore be taken from the liquid mixture class. (Check the code in 2.3.0 and forget about 2.1.0)
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Old   May 7, 2014, 09:53
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Hi Armin,

Ok thanks. i had used the OF 2.3.0 and there is its written as you said TDevol. I am using both the Model Liquid Evaporation and Devolatilization together.

I worked on 2.3.0 but it crashes when i try to run in parallel it is only working in series and the output results are same even it took more time when i run the Swak Expression. I will post the error with details tomorrow then you can check that and let me know what is wrong . So thats why i shift back to 2.3.0.

My other thread was about devolatilization model so can you please have a look on that and answer me there my quires.

And one more question can you please tell me how DeltaT and TrackTime effects the temperature drop when i increase there values in these models because they decrease the Exhaust temperature drop but i am not sure how. Really appreciate your reply and time. thanks
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