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Urgent help needed plz! No. of particles in surface injection

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Old   March 21, 2011, 14:21
Default Urgent help needed plz! No. of particles in surface injection
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Hi
I am trying to simulate two-phase jet flow. I use my inlet surface which is 0.1x0.1 to inject particles. Mass loading is 0.1, diameter of the particle is 7.69E-04m and the total mass flow rate of particles is 0.01225 kg/s. Using this data i calculated i need to inject 7.04E+04 particles to achieve the mass loading of 0.1. But in surface injection, the number of particles injected are equal to number of cell faces on that surface which in my mesh are 25.
I do know that i can increase the number of particles by creating a surface and samples on that surface which will be equal to number of particles, or/and and i can switch on the stochastic tracking in which case No. of tries are multiplied to the number of particles released by the surface.
my question is what is the significace of specifying mass flow rate in point properties tab of DPM, how does it effect the number of particles injected? As i increase or decrease the value of total mass flow rate of particles, the number of particles remain same= No of mesh faces. Soo why does fluent need the total mass flow rate of particles. Also if i switch on stochastic tracking and increase the number of tries just to increase the number of particles, what other implications will it have other than increasing the number of particles?
I will really appreciate if sumone culd help, i urgently need to clear this. Thanks
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Old   March 21, 2011, 17:00
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Hi,
the particle mass flow rate doesn't change the No. of particle streams but it implicitly affect particle numbers in the flow field. you can imagine each stream as a sequence of specified particles and you can change that by changing mass flow rate.
in finding particle trajectories, the mass flow rate doesn't play a role but in particle concentration concepts it's very important.
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Old   March 22, 2011, 09:21
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Quote:
Originally Posted by Amir View Post
Hi,
the particle mass flow rate doesn't change the No. of particle streams but it implicitly affect particle numbers in the flow field. you can imagine each stream as a sequence of specified particles and you can change that by changing mass flow rate.
in finding particle trajectories, the mass flow rate doesn't play a role but in particle concentration concepts it's very important.
Hi Amir thanks for your helpful reply. How do i determine the totall No. of particles being ejected? Am i right to understand that each particles stream represent No. of particles according to the totall mass flow rate specified in point properties? I have 25 mesh faces on the inlet surface so there are 25 particles streams being ejected. If i divide the total mass flow rate by 25 is it correct to say that i will get mass flow rate of each stream and then i can calculate No. of particles in each stream by
No of particles in each stream= mass flow rate of stream/mass of single particle

Also in my case the diameter of all particles is same and the distribution is uniform.
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Old   March 22, 2011, 09:43
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Hi,
If you divide the total mass flow rate by 25; you'll obtain mass flow rate of each stream.
so i correct your statement:
No of particles in each stream= (mass flow rate of stream/mass of single particle)*(the time of first particle tracking in each stream)

so it's dimension is also correct.
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Old   March 22, 2011, 12:32
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yes ofcoarse i meant number of particles in 1 second. Thank you very much amir, you have been very helpful
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