Volume fraction of dispersed phase to determine DPM, VOF, Mixture model
Hello
For using DPM model in fluent, volume fraction of disperesed phase should be below 10% to 12 %, otherwise you have to look for other models such as mixture and VOF models in fluent. For determining Volume fraction of a particle, the following formula is used: alpha=NpVp/Vc where alpha= volume fraction of solid phase Np=Number of particles Vp=Volume of particle Vc= Volume of the container or total volume of the cylinder or the whole control volume. If alpha comes out to be greater than 12% then "mixture" or "VOF model" would be considered for dense phase. Please comment if the above statements are correct/wrong. Thank you so much. Mohsin 
Hi,
The whole idea is right but some other points should be noted:  Actually this range is not very tight; it's just a rule of thumb, I believe that if Lagrangian modeling could be proper for a case we can use it.  Note that DPM modeling in FLUENT encounter many bugs in brownian motion and computing deposition, so in many cases in which diffusion term is dominant in dispersion; such as nanoparticles, we have to use eulerian modeling, i.e. solving a transport eq. to find particle concentration. Amir 
Well, Amir, thank you very much for the guidance. Added to ur reputation:)

Hi Amir,
I am simulating gassolid flow with two fluid approach with fluent and I am trying to have 20% mass loading of the particle at the inlet. as it is same inlet for both phases area is not important... my air density is 1.2 kg/m3, velocity is 9.3 m/s. solid density is 2500 kg/m3 , I think velocity must be calculated but I am not sure or I can use 9.3 for solid as well? how I can calculate the uniform volume fraction of the solid at inlet while assuming constant particle to gas velocity ratio? do you have any idea? thanks in advance! 
how to define volume fraction in dpm
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