[EvanHuang]

Hi
I am now dealing with DPM model in Ansys Fluent, and I set up the correct mass flow rate for my particles but the number of particles tracked which showed on the console has a big difference from what I have calculated. I want to ask why? and How to maintain the correct particle number in the flow domain?

injection type : surface injection
particle velocity : 6 m/s
particle diameter : 55 micron
continuous phase time step size : 3*10^-5 s
mass flow rate : 0.000508 kg/s

size of inlet surface : 0.006912 m^2
particle treatment : unsteady particle tracking & track with the fluid flow time step

according to my calculation, the particle number should be around 15000~18000, but after the simulation, the no.particles tracked showed around 2 million.
--------------------------------------------------------------------------------------
Updating solution at time level N... done.
Injecting 1653 particle parcels with mass 1.524e-10 at t = 0.70368

Advancing DPM injections ....
number tracked = 2925478, escaped = 1666, aborted = 0, trapped = 0, evaporated = 0, incomplete = 0, incomplete_parallel = 0, coalesced = 1
----------------------------------------------------------------------------------------
please help me to figure out this.

Thanks a lot!

[monali2015m]

did u figure out the cause because I have a similar problem !!!

[masi]

Hi,
I have the same problem and it seems the particles do not evaporate. Did u figure out this problem?

[Kummi]

Hello masi,
Unless you give some information, its hard to get help from here.
Try to post some screenshots of your evaporating species, boundary settings, and observe the DPM related quantities by contour plots for the mean values. Sometimes if diameter is quite higher (10^-4), then the evaporation will not be appropriate. So, go with Rosin-rammler diameter distribution and set: Max, mean and min dia as 10^-4,10^-5,10^-6 or calculate the diameter ranges using formula as described in user guide

Some other below links may help you.
https://forum.ansys.com/discussion/2...es-evaporation
https://www.youtube.com/watch?v=6CggFyAsDwI
https://www.researchgate.net/post/Sa..._DPM_in_Fluent
Thank you

[masi]

Hello Kummi,
Thank you for your help.
I modeled spray in the open air. DPM Model: nozzle: solid-cone / multi-component/ inlet velocity of nozzle 90 m/s / Rosin-rammler min: 1.2e-6 and max 50 e-6 / angle: 10 / radius : 0.165
boundary condition for open air : pressure-inlet 0 / pressure-outlet 0
boundary condition for nozzle : inlet velocity 90 m/s / trap in nozzle wall and escape other walls

[masi]

It seems when the geometry of the nozzle is changed evaporation happens 1.jpg. the correct GEO is Fig.2 2.jpg. but in this model with the same condition particles do not evaporate.

[Kummi]

Hi Masi, it looks like continuous phase is dominating the discrete phase. The reason why evaporation s not happening. It's just my guess.

Interaction with continuous phase is ON ?
Try to give conditions such that discrete phase should have enough residence time to react.
Inject particle time step ~ reduce it and check. With pressure inlet = 0, what is the velocity calculated at the inlet, if then the velocity at the main inlet is reasonable ? Boundary conditions is the key. And how about the mass flow rate of the injection. All your parameters need to be appropriate and if they are physically reasonable your case will work.

Use various trail and error methods. Check as many references. I'm sure u can find your way. Try giving high mass flow rate as a trail case, so there might be a chance for evaporation to happen.
Feel free to ask further.
Thank you

[widad]

Hello,
I used DPM model in fluent for particles injections, the problème that i have is the particle keep moving in solid phase ( cause i have 2 phases the first is liquid and the second is solid ( solidification active)), now i want to stop the particles when they arrive to the solid phase ( velocity = 0) by UDF but i don't know which function can do that ( read the liquide fraction depend on the particle posiiton, then if the fraction is 0 update the velocity to 0)
Please if someone have a solution could help me
Thanks