How to scale down the simulation size into microns without sacrificing spring constant k?

MFiX How to
#1

Hi Developers,
I was trying scaling solid spheres in my simulation from millimeters down to microns, currently the simulation works for particles with diameter as 20 um, but the spring constant is really small (3 N/m), I have three questions as follows:

  1. Even this spring spring constant is simply a parameter in CFD, I’m thinking in the original DEM mathematical model k should be derived from the normal collision (Hook’s law), so it is still hard to explain how scaling down the simulation size leads to the change of spring constant;
  2. I’m wondering if this small k is reasonable (compared with the default one as ~1000 N/m), even if my simulation works well now;
  3. Are there any other possible parameters (without changing spring constant) that I can modify to get an acceptable time step?
    (For your convenience, I also attached my mfx file, see below)
    Thank you.
    stage1.mfx (15.2 KB)