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DPM parcel mass content and convergence

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Old   March 20, 2012, 07:18
Question DPM parcel mass content and convergence
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Hi,

I am using FLUENT DPM model for simulation of dilute gas-solid flow. Now, I am looking for an information about the optimal, if exists, (regarding the optimal convergence) mass of particles in a parcel (Definition is included in FLUENT manual). However, I could not reach any info.

So, does anybody has any recommendation on this topic?

Thanks.
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Old   March 20, 2012, 11:39
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hi

if i'm understanding well, you mean how much mass would be optimal a fluent particle (to be intended as cluster of particles) represents, correct?

if yes, i think it's very important to consider the particle dimension with respect to the mesh resolution, particularly at the inlet. one cluster would tend to represent one real particle (in terms of its mass) if the mesh is ideally refined to infinite, or it generally would represent a more realistic mass if the mesh is highly refined, particularly for finer particles.

this would help to a better convergence

regards
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Old   March 20, 2012, 16:13
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Hi doronzo

Yes, you are correct. That is exactly what I tried to point. Thank you for your explanations.

I am currently trying to optimize the number of parcels of several injections that have different particle diameters and mass flowrates for a specific gas-solid conveying problem. So, do you have any recommendation on improving the convergence and/or any solution strategy for this type of problem.

thanks.


Quote:
Originally Posted by doronzo View Post
hi

if i'm understanding well, you mean how much mass would be optimal a fluent particle (to be intended as cluster of particles) represents, correct?

if yes, i think it's very important to consider the particle dimension with respect to the mesh resolution, particularly at the inlet. one cluster would tend to represent one real particle (in terms of its mass) if the mesh is ideally refined to infinite, or it generally would represent a more realistic mass if the mesh is highly refined, particularly for finer particles.

this would help to a better convergence

regards
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Old   March 20, 2012, 18:58
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the mass represented by each cluster/injection will depend on the inlet mesh, which is more like a choice or design than a method, and i haven't any specific suggestion.

what i can guess is a relatively high momentum exchange between the poorly-sorted population of particles and the fluid, which in terms of convergence could be managed by using few iterations for the fluid/iteration for the solid, particularly when the mixture is relatively dense. also, the two-way turbulence coupling could physically help.

how big are the smallest particles? how concentrated is the most dilute injection?
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Old   March 21, 2012, 07:56
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Hi doronzo,

Thank you for your comments. Representative average diameters are as follows: The smallest particle is approx 50 micron while the largest one is 600 micron.
If you ask DPM concentration, the max volume fraction inside the comp domain is aprox. 3e-4.

regards.
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Old   March 21, 2012, 08:16
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my experience would say that if you are using an implicit discretization, along with a relatively big time step, then you could use one iteration for the fluid/iteration for the solid, particularly when the fluid is compressible, and the solid is multiparticle

regards
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