[CeesH]

Hello all,

I'm currently tracking particles (DPM) in an Euler-Euler simulation. The particles are in the continuous liquid phase, and are massless (i.e. they directly take the liquid phase velocity everywhere). Setup is transient, and I start with 100k particles at t=0.

What I observe is that, even at very small timesteps, some particles 'overshoot' into regions where the gas fraction is 100% (the trailing vortices behind impellers, and the headspace of the vessel). Once they get there, they get stuck because the liquid phase velocity is non-existent. So, my tracks are not reliable.

Did anyone experience this problem before? And more importantly, any solution?

Best,
Cees

[`e`]

Is it not reasonable and/or physically plausible for particles to leave the liquid phase and enter the gas phase? Why are you trying to limit the particles to the liquid phase?

[Amna]

hi everyone

i m working on gas-solid fluidized bed.Geometry is a simple 2D cylindrical column.During simulation as first step , i kept gas velocity equal to zero & selected surface injections in DDPM to inject solids from bottom of column i.e from gas inlet.

i have to inject 800 particles which will give 0.25 m static bed height (as per literature). but in my case static bed height i just get 0.125 m upon injection. Kindly let me know how could i get the required 0.25 m static bed height?

secondly, just to see the phenomena at 0.125 m static bed height , i gave 1.4 m/s gas velocity, i didn't get a proper fluidized bed rather some random solid fraction from inlet-outlet obtained, which isn't matching to any of fluidization stage.

Kindly tell me how could i get a proper fluidized bed by using this euler-Lagrangian approach?

Hope to get a prompt reply ......

[CeesH]

I use the particles to read a concentration vs timeseries of a certain component in the liquid phase. Physically, they represent organisms living inside the liquid phase broth of a fermentor. So in reality they are confined to the liquid phase. However, in FLUENT, I did not even have to specify their whereabouts - I believe by default tracking responds to the continuous phase velocity only in Euler-Euler. Hence the problem, once they get up in the headspace, they don't get down. They don't even move in the headspace - they are completely frozen in position.

[`e`]

I'm not sure how DPM operates with multiple phases, but it seems strange that the particles would stall/freeze in the gas phase. It'd be expected if the liquid phase was moving and the gas phase was still. Is gravity enabled, and should these organisms be floating on the surface instead?

If you're after monitoring the concentration over time you could look into using monitor points or interpolating values at a specific point and writing this data to a file.

[CeesH]

Organisms are massless particles (stokes < 0.01) so they should just follow the streamlines of the flow, + a turbulent kick from the discrete random walk model. What I reckon is that the latter is the cause of this issue, with turbulence being significant near the free surface.

Monitor points won't do, I want to track concentration vs. time from the reference frame of the organism reference frame, not from the lab frame.

[`e`]

A couple of non-ideal solutions could be: (1) remove the DRW model; and (2) reflect the particles when they reach the free surface (probably would require a scalar update at each step to check location; similar to my code I suggested for recycling particles).