Density based solver with cnst density!
 

Hello,
I am really confused about how density based solver can work with constant density! How is it possible when density is a variable itself?!!
On the other hand, what does it mean when we are gonna use pressure based solver with say "ideal gas model"?
Are those cases possible?
I personally used density based model with constant density, and it yields good results! I am totally destroyed with my CFD knowledge!! Please help!