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file injection.: continuity fail; volume injection.: wrong total mass

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Old   April 6, 2018, 05:50
Default file injection.: continuity fail; volume injection.: wrong total mass
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Mario B.
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Dear all,
I am quite new to the forum and to Fluent.

I am trying to simulate a fluzidized bed with DEM as well as with KTGF (NETL SSCP I Challenge) for my Master Thesis. Now I am facing some troubles with the needed injections for the DDPM. I would very appreciate if someone can help me with my problems, please. (I am using Fluent 17, Euler -DDPM, realizeable ke)

a. Volume Injection
first I was using the beta feature "volume injection" (Like recommended by some tutorials for fluidized beds) - where I define my Particles and Parcels. However I observed that fluent is injecting the parcels at random places in the specified zone. My problem now is that a lot of parcels are partly outside of my defined volume - they are like randomly "cut away". So at Post-Processing -> Volume integrals my total solid mass is always different (but correct mass is "injected" regarding to the injection Summary) - And the mass is also always different for the same Case-Files. Also I observed that issue just for KTGF-Model. As soon as I activate DEM-Model my Particles are getting automatically staggered and the mass is always the same. I also tried to define the stagger radius for the KTGF but it seems to have no effect at all...
So my question are.: how can I make sure that my injected mass in my domain is always the same with KTGF-Model and volume injection,
or how to/can I activate the "automated DEM staggering" for KTGF
or how to use the "Stagger Radius" for Volume Injection?.

b. File Injection
After the troubles with Volume injection I used the File Injection like described in your threads.:

Using file to define injection distribution!!(DPM)

Does any know how to use "file" as the input of the particles in DPM?

When using the File Injection everything works fine as long as I have one Particle in one Parcel. Because I also want to do more complex and detailled calculations with more particles and finer meshes, I want to use the Parcel option. For that I estimate my parcel count for my cell size and create a file with x Lines to get x Parcels and use my Particle Diameter in every line; and I am calculating the mass flow by multiplying the amount of particles in Parcel with my denisty and particle volume and also considering the specified injection time. So that I will get my estimated total Mass and my estimated Particle Amount.
So in fluent after injecting/one timestep everything is fine. My Injection Summary shows me around my estimated mass and Particle Count, also Volume Integral is giving me the same values.
But after the 1st timestep my continuity residual is nearly immediately failing. I played around a bit with less particles but I am just not able to get the calculation starting...
Maybe someone have an idea what I am doing wrong or have some experience with Parcel-Particle File Injection - and knows where to be cautious?

Injection Summary and File Format.:
((3.110002e-03 3.110002e-03 3.110002e-03 0.000000 0.000000 0.000000 0.003256 293.000000 1.353232e+04) injection:0)
Total number of parcels : 14040
Total number of particles : 9.294477e+04
Total mass : 1.899938e+00 (kg)
Injection Time : 1e-08 (s)

Also when using File injection it just works with "standard Parcel" Method, whenever I choose another option nothing is injected at all - is it just not possible-or does it need some special settings?

c. Recommondations
Maybe someone have some better ideas/recommondations how I can initialize my bed? (I tried direct patching but it seems to make no sense for DDPM with DEM/KTGF?)

Sorry for the Long thread but I wanted to describe my problems in Detail ..
Thank you and best regards
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Old   April 8, 2018, 11:32
Default (Like recommended by some tutorials for fluidized beds)
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Rahul Dev
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I am doing Same Sir.Can You please send me some recommended tutorial for fluidised bed.

Thank You
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Old   April 9, 2018, 02:45
Default re tutorial
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Hello, there is a tutorial in the Ansys fluent Tutorial Guide (in Release 18 it is Chapter.: 21). Besides the standard fluent Tutorial Guide you can get some tutorials at the Ansys Customer Homepage, especially in the additional information slides about "Multiphase Modeling using
ANSYS Fluent".
Also there are some easy tutorials on youtube (e.g.: https://www.youtube.com/watch?v=nVrDczEjQpI - but that one is more for modelling a riser, but for learning the basic steps its fine).

Also you should definitly read the regarding chapters in Ansys Theory Guide and in the Ansys Fluent User Guide. For understanding the basic models this guides helped me a lot. But for injections i haven't found much helpful information at the official Ansys HP. CFD-Online forum was much more help for defining my injections.
I hope that information can help you. best regards
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Old   July 3, 2018, 08:13
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Ok I solved now some of my problems, Maybe this is a help for some others... took me some time to find out



first of all volume Injections is working far better with Ansys 19. Mass is not fluctuating that strong as in Fluent 17.



Also Volume Injection seems not to work properly with Mass-Flow-Inlet for the continuos Phase. (Actual Mass in Domain when using Volume Integral was always far too low when Injection Summary still showed the correct Mass - Was not happening when using Velocity Inlet)


Also when using Rosin Rammler Distribution in combination with Volume Injection.: The Total Parcel Count which can be defined in Injection Pane is just the amount for one Diameter Size. So the name is a bit confusing.


For the Parcel Release Method standard is almost everytime working, had sometimes troubles using the other ones
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Old   July 5, 2018, 15:16
Default Problem with fluidized bed
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Emerson
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Hello Mario.
I'm doing a fluidized bed for my master's too and I'm facing some problems. I need to simulate a cavity formation for particles diameter of 30 mm with a gas flow to "push them". The problem's basically this figure attached. If I wanted the particles to move with the gas, but the particles are there initially, is this a case of packed bed or fluidized bed? or none of them?
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File Type: png cfdforum.png (152.4 KB, 13 views)
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Old   July 16, 2018, 04:41
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Hello souza,


sry for late reply but I was on holiday last week..., dont know if I got you correctly... But I would say it depends on the velocity of your gas flow. If the velocity is higher than the minimum fluidization velocity it is a fluidized bed (Minimum fluidization velocity.: pressure drop is not increasing anymore ("relatively constant") with higher gas velocity.
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Old   October 2, 2018, 05:34
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Looks like that the problem with mass flow inlet is not because of the volume injection. Also getting the errors for file injection (for case files I already calculated in Fluent 17). Looks like there is generally an issue in Fluent 19 for DDPM injection with mass flow inlets....As soon as I change to velocity inlet everything was fine again....
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