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-   -   about group injection of DPM model (http://www.cfd-online.com/Forums/fluent/33331-about-group-injection-dpm-model.html)

zwdi March 27, 2004 23:41

about group injection of DPM model
 
Hello everyone, I am using group injection type in DPM model. The total mass flow rate for the particle is 10g/s. I set the number of particle stream is 1,000. And the number of tries is 10. Now I am confused about how much value I should set for mass flow rate of each particle stream in the following point properties.(i.e. mass flow rate for the first point and mass flow rate for the last point)Is it 10g/s devided by 10 or 10g/s devided by 10000? And another question: If I want to set the particle uniform diameter about 1e-06m, could I choose the diameter distribution as linear and then for the first point and the last point, I set the same value(1e-06)? Does anybody have clear conception on these knowledge and give me a help? Thanks in advance for sharing idea with me. Best regards, Zwdi

David March 30, 2004 08:45

Re: about group injection of DPM model
 
hello,

concerning the particle uniform diameter, you are right, you should use a linear distribution with first and last point same value.

if you set the number of particle stream to 1,000 then you can divide your mass flow rate by 1,000 as it will allocate the mass flow rate for each particle stream.

i hope this helps

David

zwdi March 30, 2004 12:20

Re: about group injection of DPM model
 
Thank you very much, David.

In your response, you didn't mention what is the number of tries for. I just want to make sure if the flow rate for first point and last point is the total mass flow rate divided by 1000(number of particle stream), without relaitonship with number of tries(such as 10). Please give me response if I understand your answer correctly.

Thanks again

Zwdi

David March 30, 2004 12:29

Re: about group injection of DPM model
 
Hi,

you're welcome for the response.

This is the Fluent definition for the Number Of Tries:

"Specify the number of tries.

An input of zero tells FLUENT to compute the particle trajectory based on the mean continuous phase velocity field (Equation 19.2-1), ignoring the effects of turbulence on the particle trajectories.

An input of 1 or greater tells FLUENT to include turbulent velocity fluctuations in the particle force balance. The trajectory is computed more than once if your input exceeds 1: two trajectory calculations are performed if you input 2, three trajectory calculations are performed if you input 3, etc. Each trajectory calculation includes a new stochastic representation of the turbulent contributions to the trajectory equation. When a sufficient number of tries is requested, the trajectories computed will include a statistical representation of the spread of the particle stream due to turbulence. "

Is it cleared to you now?

so you dont need to include the number of tries in your calculation so you divide by 1,000 only.

i hope this helps

regards

David

zwdi April 2, 2004 13:18

Re: about group injection of DPM model
 
Hello David, Sorry for responsing so late. Thank you very much. Have a good weekend. Zwdi

David April 12, 2004 19:31

Re: about group injection of DPM model
 
Hi Zwdi,

please read this:

When multiple stochastic trajectory calculations are performed, the momentum and mass defined for the injection are divided evenly among the multiple particle/droplet tracks, and are thus spread out in terms of the interphase momentum, heat, and mass transfer calculations. Including turbulent dispersion in your model can thus have a significant impact on the effect of the particles on the continuous phase when coupled calculations are performed.

so i hope it clarifies it all

regards

David


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