local age of air in starccm+

Mike23

Hi

I am trying to evaluate the ventilation effectiveness in an enclosed car park with impulse fans in starccm+. (first time working with such kind of problem)

Right now i am trying to determine the age of air and I have seen in this forum an advice to use 1/density for the passive scalar value. But I am not seeing how can this produce a variable with units of time... What should be th field function definition? Do you know any place where I can get any information on this topic?

And, one other thing: what boundary condition do you use for air extraction ducts? Pressure outlets? I mean, in case of fire air inlets are shut down and air extractors work at full power and the manufacturer gives me the volumetric flow rate they can handle. But I am not being able to specify a BC that removes air from my domain...

any help appreciated!

tanks in advance