About particles injection

Hello everyone, I noticed something strange in my simulation results, so I want to share it in the forum and discuss the reasons with you. My case is a simple fluidized bed reactor that has a particle inlet. The particle’s velocity and the fluid’s velocity are 0.05m/s. The mass inlet start time is 0.5s.
When the simulation started for a while, I found some questions:

  1. Particles were injected at 0.57s instead of 0.5s.
  2. The initially injected particles have a large velocity, which looks like they are jetted into the reactor. However, subsequent particle injection is normal.
    What are the reasons for these phenomena? Is it because of the fluid time step (DT) and the solids time step (DTSOLIDS) setting?
    Details can be found in the following picture and video:

    particles have large inject velocity and normal velocity


boiler2-combustion_2023-03-31T215014.094832.zip (71.8 MB)

Please attach your project files if you want help. Main menu, "Submit bug report’, attach zip file.

Thanks for your suggestion, I have attached my project files.

The bed was initialized hot, and as the first particle being injected, it was heated quickly, and the drying happened with water vapor being released in the cell, which generated larger gas flow/velocity in the cell, and that caused the particle to move fast. After more particles being injected, more water was released, the bed was cooled down in the upper region due to the endothermic drying reaction, so it becomes more realistic. So it is just an initial stage caused by your initial condition. Let us know if it makes sense to you.


Hello Yupeng, thanks for your answer. Actually, the same phenomenon occurred in the case with no chemical reactions, so I don’t think it is caused by the drying process. And reactions or initial conditions can’t explain the delayed injection of particles.

The delayed injection is due to the need for particles to travel from the ghost layer to the first fluid cell and particles are visualized by default when their center is inside the fluid region. This is not a concern. Regarding the initial high velocity, it could be due to the difference in temperature between IC and BC.

Thank you jeff, I got it! :smile: