[srinidhi4u]

Hello,

I am using Particle Transport Fluid option to inject water at 2 Gallons/min water flow rate. The Air flow is around 3800 CFM. I am little confused whether I should consider the volumetric flow ratio of two phases to decide whether I should be DPM or is it the volume ratio of the particle and geometry? If I consider the volumetric flow ratio it would be much much lesser than 12% limit for considering DPM for calculation.

What about the number of particles? I have no data of number particles for injection. If I assume 5000 particles to represent 2 Gallons/min for instance, is that correct? I am using 2 way coupled solver for particles and air phase. Is that right? The size of the droplet is 15 microns.

I would appreciate your help in this regard.

Thank you in advance.

Shri

[ghorrocks]

Are you sure a lagrangian particle model is appropriate? I suspect you will have zillions of water particles which form a mist. IN these conditions often a eularian multiphase model is more appropriate.

Can you describe what you are doing and what you are try to model? We better check your choice of basic model (lagrangian versus eularian) is correct before we think about the details of the model.

[srinidhi4u]

Thanks for the reply ghorrocks.

I need to inject water along with the air (from compressor) at the inlet of a pipe which branches itself out into 6 pipes. I need to find out what is the distribution of air/water through each pipe. Later on I will add some separator aiming to separate water from 3 alternate pipes out of 6.

The water flow rate is 2 Gallons/min and air flow rate is 3800 CFM. I use steady state simulation with particle transport fluid and specify diameter of the droplets and mass flow rate of the droplets from the inlet. Do you think Eulerian model is more appropriate compared to the Lagrangian? approximating to Lagrangian model are we not making the system work here here or how much we lose out by shifting to Lagrangian instead of using Eulerian? I have approximated and used around 10000 particles to represent the droplet flow.

I appreciate your help in this regard.

Thank you.

Shri

[ghorrocks]

The Eularian model is more appropriate as the volume fraction of the disperse phase starts to get significant. It handles vast numbers of particles better and has better models for droplet interactions and maximum packing and things like that. Lagrangian particle tracking is good for low volume fractions and where a history of each particle bundle is required.

If you are doing Lagrangian particle tracking you need to show that you have enough particles to model the discrete phase. You will need to run with 10x the particles and see if it makes a difference.

From what you have described so far the model can probably be done either Eularian or Lagrangian. Eularian is easier so I would try that approach first and only move to Lagrangian if you need to do something you cannot do in a Eularian model.

[srinidhi4u]

Thanks a ton Glenn.

I have tried 10x particles for Lagrangian approach and separation efficiency has not changed much. Lagrangian approach is working well, but I want to try Eulerian approach too.

When we calculate volume fraction of each phase for Eulerian model it is volumetric flow rate of each phase/sum of volumetric flow of both the phases right?

Or is it

Volume fraction of a phase = Volume of the phase in a domain/Volume of a domain? Can you please help me to understand this part?

Thanks again

Shri

[ghorrocks]

Volume fraction is simply the volume taken up by the phase divided by the total volume - hence the name volume fraction. Volume fraction is not calculated on flow rates.

[srinidhi4u]

Thanks again for the clarification Glenn.

I end up with 1.6% volume fraction for my case which tells that DPM should be fine enough with sufficiently large number of particles representing the actual mass flow of the water being used. I am anyway trying Eulerian approach to cross check if I get the same numbers there too.

Thank you for the timely help.

Best regards,

Shri