air quality analysis

[RobLWI]

Hi, I am interested in using FDS for air quality analysis in rooms (no fire) and I would like to just get some ideas about any issues I should consider before I get started.

In one case I am looking at the concentrations of gases from Formic and Acetic acid in rooms. So that we can position sensors correctly. As I understand these gases disperse well in air, i.e. they do not sink or rise, or form layers. Does anyone have some initial ideas how I could go about this?

The second case is a underground car park with mould formation and adding fans to ensure that there are no zones of dead air in the garage. I think this is pretty straightforward tbh.

I assume that FDS can do this with LES, and that I just have to do some sensitivity analysis of mesh size to ensure that I am modelling eddies correctly. Or is it not suited for these purposes? or should I rather use DNS?

Thanks

[rmcdermo]

If you use SIMULATION_MODE='LES' on MISC, then FDS will include the molecular diffusivities in the transport calculation. These are usually small compared to turbulent diffusivities, but if you do not have a fire, the flow may be mild. You should read the guide discussions on specifying your own species. You will want to pay close attention to thermophysical properties, since these are not gases FDS has in its database---you will have to supply the data. For example, here is the NIST webbook link for acetic acid.

[mcgratta]

Also, FDS does not include any background motion at start-up. For IAQ applications, users typically add "people" in the form of obstructions that generate about 100 W of heat. That stirs up the air a bit.

[RobLWI]

Thanks. I was wondering how to include random air movement. I was considering having some vents that blow a puff of walking speed air at set intervals, to simulate people moving around. There could also be heating in the room which would also stir up the air, but in summer that will not be in operation, so can not rely on that. There may also be heat generating equipment which can be reliably considered.