Learning Forum

[ntrippella]

Hi,

I was trying to simulate the effect of a permanent magnet (a mangetic candle) on small solid ferromagentic paerticle in a water solution. 

In particular, particles are supposed to rotate around the magnet (this is how the device works). 

I have designed a simple magnetic candle in Ansys Maxwell. I have imported its B field inside fluent. You can see it on this figure:

(the white rectangle is where the magnete is supposed to be placed) 

 

Then I have activated the DPM and the MHD module.

The simulation converges.

However, the particles seems not to be affected by the magentic field. I tried changing their diameters, from 1e-6 to 1e-4 but nothing changes.

Even though I amplify it in the MHD module by a factor of 10, it seems to have zero effects on the particles trajectories. 

What do you think? I am doing something wrong on the simulation or the magnet is too weak? The weired thing is that even with a 10 factor amplification, i obtain the same results. 

[Rob]

Did you turn on anything in Fluent to tell the DPM particles about the magnetic field?

[ntrippella]

Hi, Rob. Thank you for your prompt reply. 

This is what I have in the DPM panel:

The source and the body force are activated from the MHD module 

 

 

 

 

[Rob]

I assume the particles have a charge? Does anything change if you switch to transient particles? I'll need to check this side if we have anything we can share.  

[ntrippella]

I have not tried with transient simulation. Do you think something could change? 

Particles are ferromagnetic particles with zero electric charge. I have tried stressing their permeability to 100 but it does not worked.

I could share my .cas file, could you please give me your email and I will send to you with we transfer if you have time

 

[Rob]

We're not permitted to download or receive files due to the Forum being "public". Commercial users with paid support can also raise tickets to do what you propose. 

I was wondering if transient tracking was needed as there's no reason for a particle to move once it arrives at the high/low/neutral charge point. So transient might at least show movement, albeit, not necessarily where you wanted it. 

[ntrippella]

I could try with transient simulation. However, now I was trying simulating greater particles (D form 1e-6 to 1e-5), to see whetere there could be changes. 

[Rob]

Possibly. As particles become smaller the drag effects may outweigh other body forces. But you tried 1e-4m already?

[Ulrich]

Make sure that you have activated "Include Lorentz Force" and that you have set a Charge Density other than zero.

[ntrippella]

Yes, I have activated the Include Lorentz Forca option. 

However, I have set the charge value equal to 0. Why do you think I have to chnage it to -500?

The small particles are ferromagnetic particles. I think they are not electrically charged. They represent the small dirt that can be present inside water in water hydraulic systems.

[Ulrich]

"-500" was just an arbitrary number.

If you look at the equation for the Lorentz force acting on the particle (see eq. (21-27) in te R 2024 R2 Fluent Theory Guide) you see that the force is zero without a charge.

[ntrippella]

Yes. Indeed the force for the particle should be the magnetic force associated to their permability which is different from the lorentz force, i suppose.