Open godisreal opened 4 years ago
I also doubt if hot smoke cools down in FDS when it travel and mix with the cold air, especialy in a large-scale space like buildings.
When I run your example like simple_test.fds, it looks very good as smoke spread from ceiling to floor. But when I ran some other examples for a large-scale space, the smoke still spread very fast even if it is far away from the burner, and the simulation result looks a little strange and unrealistic.
Now I understand the problem. The key issue is you assume that soot and gas are the same in motion equation. This may be a good approximation if soot and gas are close enough to the burner. The hot gas carries small soot particle and they move together. However, if the gas has moved far from burner and has cooled down, such approximation is problematic. If soot particles follow Netwonian dynamics, is there any easy method to reduce the soot speed so that it spreads slower than gas?
If there is no burner or heat source, I suppose that soot movement should follow elementary diffusion equation. Comments are much welcome.
https://en.wikipedia.org/wiki/Diffusion_equation https://cn.bing.com/search?q=diffusion+equation&go=Submit&qs=n&form=QBLH&sp=-1&pq=fortran+90+basics+charles+anthony&sc=0-33&sk=&cvid=246F068B4B6F4352883D3A66A7D043D8
https://www.life.illinois.edu/crofts/bioph354/diffusion1.html (Useful Tips) Diffusion – useful equations Diffusion coefficient, D D = (1/f)kT f - frictional coefficient k, T, - Boltzman constant, absolute temperature f = 6p h r h - viscosity r - radius of sphere The value for f calculated for a sphere is a minimal value; asymmetric shape of molecule or non-elastic interaction with solvent (e.g. hydration) will increase f. Diffusion coefficient depends on size and shape of molecule, interaction with solvent and viscosity of solvent.
Diffusion over a distance The relationship below is generally valid:
Excuse me. I run an example as below. However, the smoke does not enter the small room top right. I also run another example where soot reaches the wall and reflects back like air flow. So may I ask what problem it is?