Problem with Additional Variables
 

Hi,

I try to simulate a diffusion process through a thin sheet in a closed chamber. The aim is the Oxygen concentration depending on time in the chamber. For this transient simulation I used a Additional Variables type Volumetic and as Units [mol/m^3]. I've select Diffusive Transport Equation at both Domains and a different Kinematic Diffusivity.
My problem is that the time to the equilibrium state depends on the density of Fluid in the chamber. As far as I know is, that depends only on the diffusion constant. What did I do wrong?

Thank you in advance!