# Particle injection DPM

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• Last Post 22 February 2019
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murarz posted this 21 February 2019

Hello!
Could someone explain me the difference between group injection ( with number of streams) vs surface injection? Will it influence the result? Does the number of streams matter? If I'm not mistaken one stream = one parcel. So is there a difference when I specify one stream with flow rate lets say 0.1 kg/s, and 1000 streams with the same flow rate ?

PS. I asked about the difference between group and surface injection, because Residuals behave differently with these both.

abenhadj posted this 21 February 2019

Group Injection: It will inject a group of stream where the properties are interpolated linearly from first to last point. If you use the same property for first and last point there no variation.

Surface Injection: you are ideally injecting particle parcels from each facet of the surface.

More details to be found in the manual.

Best regards,

Amine

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rwoolhou posted this 21 February 2019

The more parcels you have for a set injection mass the lower the mass each parcel will contain. This means each parcel will have a lower source term as things happen within the domain.  Given we're mimicking an injection with many thousand particles with a few hundred parcels the more parcels the better.

The difference between a surface & group will be down to what you've defined: there's not an answer to that one!

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murarz posted this 21 February 2019

The more parcels the better, so when I define surface injection, which has a rather coarse meshing ->hence not many parcels at the inlet, then would it be better in this case to model a group injection with much more (streams) parcels ??

What I meant by comparison of surface injection and group is that can I use them interchangeably? When I tried both, I had different scaled residuals, so don't know if it's just stability issues, or it just gives different results.

abenhadj posted this 21 February 2019

You can use the most appropriate injection for your case? How are the particles injected in the reality? Again a realistic distribution would always require more parcels which will smooth out the sources terms applied into the carrier phase but having the drawback of tracking more parcels.

Best regards,

Amine

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murarz posted this 21 February 2019

What does it mean how hard the particles fed ? I

abenhadj posted this 21 February 2019

How are the particles injected in reality ?

Best regards,

Amine

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murarz posted this 21 February 2019

It just says, that pulverized coal is injected with a primary gas stream . Inlet diameter = 1.3cm . So I suppose both group and surface injection could be used.

abenhadj posted this 22 February 2019

Yes both are okay.

Best regards,

Amine