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mass flow rate in DPM single injection

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Old   August 24, 2015, 16:35
Default mass flow rate in DPM single injection
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Linwei
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hi all

i want to inject a single "combusting" coal particle (diameter 80um) in a flow when using DPM model. And the mass of one particle is about 3.75e-10 kg.

but in the 'Set Injection Properties' dialog box, it asks for the flow rate (kg/sec) and the start and end time... so how do i decide this flow rate...

Should it be just the mass of the 1 particle, like 3.75e-10 kg/s?

Could I choose the start and end time as 0s and 1s?

I am really confused about the two parameters. If anyone has any idea, please share...

Thanks a lot..
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Old   August 25, 2015, 10:48
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Eduardo Tola
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Hello Yezi

I am opinion, what you are trying to solve is an unsteady problem.
However, you are trying to solved as an steady problem. Steady problems are characterized for having a constant mass flow rate.

I haven't used Fluent for solving unsteady simulations, but I recommend you to check the unsteady model out.
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Old   August 25, 2015, 16:07
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Quote:
Originally Posted by edu_aero View Post
Hello Yezi

I am opinion, what you are trying to solve is an unsteady problem.
However, you are trying to solved as an steady problem. Steady problems are characterized for having a constant mass flow rate.

I haven't used Fluent for solving unsteady simulations, but I recommend you to check the unsteady model out.
Thanks a lot.

It's an unsteady problem. And I have to define the mass flow rate and time for one particle injection when setting 'Set Injection Properties' dialog box under DPM model.

I don't understand why I need to define and don't know how to define the mass flow rate if I want to inject only one particle...
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Old   August 26, 2015, 05:20
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Quote:
Originally Posted by Yezi View Post
Thanks a lot.

It's an unsteady problem. And I have to define the mass flow rate and time for one particle injection when setting 'Set Injection Properties' dialog box under DPM model.

I don't understand why I need to define and don't know how to define the mass flow rate if I want to inject only one particle...
But it doesn't seem like the configuration of an unsteady problem.
I mean, in an steady problem the flow rate should be a function of time, for example 'X' value for t=0s and 'Y' value for t=1s and between them according with a linear function.

I have never resolved this kind of problems, but for me it seems like the mass flow condiction that u are setting up is steady, because it does not change with time.
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Old   August 26, 2015, 08:39
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Particles are injected at each time step (within a specified range) for unsteady DPM cases. If you only want to track a single particle then set the start and stop times at 0 s. The mass flow rate is arbitrary (assuming one-way coupling); although I believe it's inversely related to the fluid time step (for example, dt = 0.1 s would need a mass flow rate 10 times the mass of a single particle to give one particle in the parcel).
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Old   August 31, 2015, 11:10
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Quote:
Originally Posted by `e` View Post
Particles are injected at each time step (within a specified range) for unsteady DPM cases. If you only want to track a single particle then set the start and stop times at 0 s. The mass flow rate is arbitrary (assuming one-way coupling); although I believe it's inversely related to the fluid time step (for example, dt = 0.1 s would need a mass flow rate 10 times the mass of a single particle to give one particle in the parcel).
Thanks a lot.

But if I set the start and stop time at 0 s, there was no particle injected...
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Old   August 31, 2015, 19:41
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Originally Posted by Yezi View Post
But if I set the start and stop time at 0 s, there was no particle injected...
Are you sure the simulation time is also at 0 s? Try initialising the solution and solving from t = 0 s.
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Old   September 1, 2015, 08:01
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Originally Posted by `e` View Post
Are you sure the simulation time is also at 0 s? Try initialising the solution and solving from t = 0 s.
Oh, the particle should be injected at 1200 s but I set the start/end time at 1200/0 s incorrectly. Now I set the start and end time at 1200 s and it works. Sincere thanks for your help.

I have other confusions about the single coal particle DPM model:
1. If I set the start and end time as the same, how about the mass flow rate of the particle?
2. I can get the temperature distribution of gas phase, is it possible to get the temperature of the coal particle?
3. The mass/mole fraction of gas species (e.g. O2/CO2/CO etc) along the axis wall or inlet or outlet can be obtained, is it possible to get the total mass fraction of CO2 in the reactor?
If you have any idea about these questions, could you please share with me? Thanks a lot...
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Old   September 1, 2015, 10:04
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Originally Posted by Yezi View Post
I have other confusions about the single coal particle DPM model:
1. If I set the start and end time as the same, how about the mass flow rate of the particle?
2. I can get the temperature distribution of gas phase, is it possible to get the temperature of the coal particle?
3. The mass/mole fraction of gas species (e.g. O2/CO2/CO etc) along the axis wall or inlet or outlet can be obtained, is it possible to get the total mass fraction of CO2 in the reactor?
1. I've answered this above.
2. Yes, either in contours/plots (same as other variables) or with the macro P_T (if the temperature is required within a UDF).
3. Could you apply the same method of finding this mass fraction on boundaries, to a cell zone? Alternatively, a long-winded approach would be to write a UDF and loop over all particles to calculate the total mass fraction.
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