User Define Scalar and Periodic Boundary Condition

Hi
I am going to simulate a fluidized bed with periodic boundary condition, and also I need to define a scalar for seeing a phenomena. In this regard, after the first round of simulation my defined scalar is washed from the bed and I do not have it for other periods? I think this problem is related to that I just set an initial condition for this scalar and after the first iterates, I do not have the effects of them for the next periods. I would be thankful if you could guide me, thanks.

What are you trying to do with the scalar?

I am trying to model the mixing of solid particles