Hello,
I am a new user to MFiX, i have been trying to model a fixed bed model with fluid flowing over it, i want to show an increase in particle diameter. I am working with DEM model.
I have no clue about how to code the user defined files, can anyone help me with this?
In the DEM model, two options are available.
-
If you want to model the particle diameter change with time (increase or decrease due to mass transfer/reaction), you just need to set the Density —> constant. The solver will automatically calculate the particle diameter.
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If you set the density—> variable, the variable density model (particle diameter remains constant) will be activated.
@gaoxi thank you for your response, but i need more help with this, how can i code the chemistry to show a mass transfer reaction?
If you haven’t, I suggest you to see some good tutorial cases about how to code mass transfer/reaction in the usr_rats_des.f:
mfix-19.3.0\legacy_tests\dem-tests\evaporation
mfix-19.3.0\legacy_tests\dem-tests\reactive-chemistry
mfix-19.3.0\tutorials\pic\silane_pyrolysis_3d
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I am also interested in this topic. Thank you for your suggestion about good tutorial cases. However, it occured 3 errors when i run one of the cases (mfix-19.3.0\legacy_tests\dem-tests\evaporation).
.can you give me some advise? （MFiX version: 19.2.0）thank you again!
I tested the case in MFIX 19.3.0 and did not find any errors (19.2.0 should be OK too), please check your installation, are you able to run any other tutorial case?
I am looking for right now is only a physical change in dimensions of DEM particles, is there a way i can write a UDF that could be like
if (time>1s)
Diameter = Diameter+1.
something like this.
I don’t want to show any chemical changes because for that i will have to add solid and fluid species and these are not of my requirement right now. If you or anyone could help me with my problem it would be helpful.
Hi, gaoxi
How can i invoke the variable of diameter of particle when the reaction rate is related to it or its function? Define it by myself first? or it has been defined in programm, just invoke it? I am confused that there are new variables defined in usr_rates.f, have they existed in program ? If not, how can these new defined variables be intergrated into the whole program. I mean, i doubt that any variables defiend by myself, may not be identified by program.
Thank you!
In the file to define the reaction rate, for diameter in DEM, you can use DES_RADIUS(NP).
Thank you, gaoxi. Where can i find it by myself? I search “DES_RADIUS” in keywords browser, but find nothing. If i can find them on my own, it is not necessary to bother you, developers again.
Hi, gaoxi
Now, there are two kinds of particles in my simulation. I want to invoke the radii of one kind of particle in the cell, What keywords can i use? It seems that “DES_RADIUS(NP)” cannot distinguish different particles in the same cell.
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For example, you have two sold phases, one is inert sands and one is reactive solid fuel particles. You need to specify that only the fuel particles have reactions. You need to code like this in the file usr_rats_des.f
If (DES_RADIUS(NP) .gt. 0.001) then
! reaction rates
Else
！nothing
Endif
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Thank you, gaoxi.
It seems that it’s necessary to use a judgement statement to make sure if it is that particle i want. For special cases, for example, particle size is not enough to distinguish different particles, i.e their particle size distribtuons are overlapped. So, are there other ways to select the target particles out? I think it is more general to judge particle’s alias directly. But i haven’t found it yet. It seems to be not defined in MFIX.
You can use other parameters to identify specific particles/phases,
like:
phase index: M = PIJK(NP,5)
density: RO_SOL(NP)
solid species: DES_X_S(NP,: )
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Great! Thank you for your help!