gas separation by weight not working
 

Hi all,
I am trying to simulate gas separation with species of different molecular weight. For starters, I am doing a 2D box with 2 species 50-50 (one heavier than the other).
I am using rhoReactiveBuoyantFoam with chemistry off.

I expect that after a few seconds the heavy gas will sink to the bottom but it doesn't. :confused:

I am attaching my case files, if you could please have a look and shed some light on the subject I will be very grateful.