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

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!

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!

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

send me your case. explain your phisical model Nasser_rasooli@yahoo.com

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.

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

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

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

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

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

[lili]

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?