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sajeesh May 6, 2013 04:53

DPM mass flow rate

During iteration it is showing
Injecting 1 particles with mass 2.72272e-12
this is not mass flow rate
I given mass flow rate as 2.72272 e -9 kg/sec as mass flow rate
In the summery result it is showing number as 3.33468 e-1 what is that..some body in DPM field pls help me

thanking You

RodriguezFatz May 7, 2013 03:25

Let me guess, your time-step is 1.0e-3, right?

sajeesh May 7, 2013 03:49

really thank you for the reply

I was stuck in this problem

I had given a time step of 0.001 seconds.and number of time step as 1 and start and stop injection i given is 0.001 and 300 sec respectively to ensure the presence of particle

Exactly i want to find out the extra hydraulic resistance produced by the presence of one particle in the measuring the pressure drop difference with particle and without one p[article

Thank you sir pls help me

RodriguezFatz May 7, 2013 04:07

You insert 1 particle of mass 2.72272e-12 kg per time step. Your time step is 1.0e-3 s. That gives you a mass flow rate of "2.72272e-12 kg / 1.0e-3 s = 2.72272e-9 kg/s". That's what you want. What is the problem?

sajeesh May 7, 2013 04:35

mass of one particle is volume of particle x density of particle
Diamter of particle is 25 micron
Volume 4/3 pi r^3
density is 998 kg/m3
so the mass i calculated for one particle is 8.181e-15 kg

Then after that
my channel is 2000 um length
Then to cover this distance with flow rate of continous phase 50 ul/min ( oil denisty 840 kg/m3) take nearly 0.003 seconds

Then mass flow rate i calculated as mass of one particle *number of partcicle(1) /0.003 kg/sec

AS you said this makes me wrong

Sir can i know what is meant by number of particle in parcel.A method to set the mass flow rate

I want to further discuss with you can i get your email id

Any way thanks for your replies

RodriguezFatz May 7, 2013 04:42

Maybe your confusion comes from the difference of particles and parcels.
Fluent Help ( says:

For typical applications, the computational cost of tracking all of the particles individually is prohibitive. Instead, the approach for the discrete element method is similar to that of the DPM, in that like particles are divided into parcels, and then the position of each parcel is determined by tracking a single representative particle. The DEM approach differs from the DPM in the following ways:
The mass used in the DEM calculations of the collisions is that of the entire parcel, not just that of the single representative particle.
The radius of the DEM parcel is that of a sphere whose volume is the mass of the entire parcel divided by the particle density.

Also: The mass flow rate of your inlet DPM phase has nothing to do with the size of your domain. It is just "injected mass per time step / time step size".

sajeesh May 7, 2013 05:46


Its very helpful for me.
During iteration it is showing

I particle tracked 1 particle escaped

at Some time 3 particle tracked 1 escaped ( ie is it mean two particle remain in the domain) Can i say it as a two particle of my specified diameter 25 micron or parcel. If it is parcel please explain me.

some time

At the end of iteration it is showing 1 particle tracked and 1 escaped.So it mean that no particle in the domain.

Sir one more help how can i animate these particle tracking.Movement of partcle with time
In workbench CFD post it is taking only trk files.But how can i get trk file in FLUENT...

Thank you.With out your help i may proceed the mass flow rate calculation with domain time


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