CFDEM - Micro unit system & OpenFOAM timestep

Hi everyone

I am running simulations of a pressure driven suspension flow through a micro channel, investigating particles sized of 1 micron and below in diameter. Because of the size of the particles I am required to use the 'micro' unit system within LIGGGHTS.

In order to get the correct units within OpenFOAM I have adjusted both the units in the constant '0' folder and also added in the similar details from the "ErgunTestMPI_cgs" tutorial case to the controldict file but converted to match the LIGGGHTs micro scale.

Using this I am getting good results, obtaining the closely correlating effective viscosity to theory. However I am concerned about the timestep units being used by OpenFOAM compared to LIGGGHTS. It is my understanding that OpenFOAM is using seconds, whilst LIGGGHTs is using Microseconds, does this mean that there is a mismatch in the times being communicated between the solvers? Or is there some code in the background from CFDEM which reads the unit system in LIGGGHTS and corrects this?

I am a little bit confused as I am getting the right number of output files printed at the end of the simulation such that it matches the end CFD time, so now I am wondering if the CFD time is actually unitless?

If this is not the case do I need to modify OpenFOAM to use microseconds?

Thank you all for your help clarifying how the timesteps should match up, I have looked at other forum posts but was unable to see any discussion other than the below which seems to indicate that the timestep mismatch should be an issue

https://www.cfdem.com/forums/unit-dem-and-cfd