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Old   November 18, 2005, 05:02
Default A question about solid surface reaction in FLUENT
  #1
RAO
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I did a case with DPM, and solid surface reaction , but the reaction didn't occur. can you give me some advise? Or can you provide me a case about this problem? thanks a lot! E-MAIL: rao_zh2000@hotmail.com
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Old   November 18, 2005, 05:29
Default Re: A question about solid surface reaction in FLU
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RAO
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Tdetails about my case: Reaction type is "particle surface", A particle is selected as solid species, and the injection properties is defined in DPM. Its particle type is "combusting" with "multiple-surface-model". The boundary conditions, Arrhenius Rate and other material properties are all set. But after run, the reaction rate always shows zero. why this happen ? pls help me , thank you!

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Old   November 18, 2005, 05:31
Default Re: A question about solid surface reaction in FLU
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RAO
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The details about my case: Reaction type is "particle surface", A particle is selected as solid species, and the injection properties is defined in DPM. Its particle type is "combusting" with "multiple-surface-model". The boundary conditions, Arrhenius Rate and other material properties are all set. But after run, the reaction rate always shows zero. why this happen ? pls help me , thank you!

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Old   November 18, 2005, 05:46
Default Re: A question about solid surface reaction in FLU
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RoM
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Reaction rates for multiple surface reactions are always displayed as zero, even if the reaction is running. Display dpm-burnout to see if your reaction is running and calculate an elemental mass balance for your case. This should give you an idea how much solid is converted.

RoM
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Old   November 19, 2005, 04:15
Default Re: A question about solid surface reaction in FLU
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nasser
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send me your case. explain your phisical model Nasser_rasooli@yahoo.com
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Old   November 23, 2005, 23:14
Default Re: A question about solid surface reaction in FLU
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RAO
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Thank you for your answer, which certainly answered some part of my question. But there is yet another question that puzzles me. The dpm-burnout value is displayed as zero also. I thought some B.C. or properties may not be set correctly, so I checked them carefully. But no incorrect setting was found. Or DPM model with Spcies model can not be used to solve my problem: Fe2O3 thermal decomposition reaction? pls help me, thanks a lot.

RAO.
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Old   November 24, 2005, 02:45
Default Re: A question about solid surface reaction in FLU
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RoM
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Praticel Reaction rates are calculated with equation 14.3-8 (Fluent 6.2 manual , chapter 14). The equation includes the bulk partial pressure of a gas phase reactant so it will evaluate zero if no reactant is specified. This is probably the case in your reaction. You can override the fluents reaction rate definition with a DEFINE_PR_RATE udf. I use this for gasification reactions and it works fine.

Hope it helps, RoM
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Old   November 24, 2005, 03:22
Default Re: A question about solid surface reaction in FLU
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RAO
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Hi, RoM. According to chapter 14 in Fluent 6.2 manual , equation 14.3-8 is used to calculate "the rate of the particle surface species depletion for reaction order Nr=1 ". And in my case, the order of the solid decomposition reaction is Nr=0. so the rate should be calculated by equation 14.3-9, and there isn't partial pressure of a gas phase reactant (pn)in it. I am not sure of it , can you answer me ? It is better for me to offer one of your successful case to me. You know, it has troubled me for several weeks. Thank you , thank you very meuch.

RAO
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Old   November 24, 2005, 03:45
Default Re: A question about solid surface reaction in FLU
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RoM
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I think reaction order is determined by the exponent of the gas phase reactant. There is no description in the manual what happens if no reactant is present. From your problems i would assume that the reaction rate is then set to zero. You can test is a gas phase reactant is really needed. Just add nitrogen to both sides of your reaction (1mol in and 1 mol out). This not really realistic but if the reaction starts you have found the cause of your problems.

Good Luck, RoM
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Old   November 25, 2005, 03:43
Default Re: A question about solid surface reaction in FLU
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RAO
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Hi, RoM

With your hints, my problem is solved and the reaction is running. I greatly appreciate your timely help. Thank you.

But, I also found the solution is hard to converge. The residuals of continuity as well as other parameters fluctuate repeatedly. What maybe cause this?

RAO
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Old   November 28, 2005, 02:24
Default Re: A question about solid surface reaction in FLU
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RoM
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You will get a peak in residuals every dpm iteration. If the solution start to converge those peaks will fall very fast. If you have convergence problems start with a very small dpm underrealxation. I usually start with 0,05 and increase it gradually up to 0,5. You should also monitor species concentration at the outlet to see if your solution is converging.

Good luck, RoM
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Old   August 12, 2012, 02:48
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leila
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hi rao
I know this is an old topic but I have the same problem as you. I want to model a particle surface reaction. I select Combusting particles in "set injection properties" and "multiple reaction" and define the reaction but no reaction happens. how you solved your case?
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