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Tunnel Exhaust Extractors
Name: Barbara
Status: other
Grade: other
Location: N/A
Country: N/A
Date: 4/2/2005
Question:
My question relates to the car exhaust extractors that
are used in traffic tunnels. When the exhaust fumes are discharged into
the atmosphere, do they rise or fall?
Replies:
The engineering part, my guess would be that they use fans with the blades
reversed. In winter, when one wants to keep the heat down, the
recommendation is to reverse the blades on the ceiling fan. Hence my guess
that is how the exhaust fan works, drawing the air out from the tunnel. The
winter analogy is to use the blades to draw the heat from the ceiling down to
the room.
Now once the tunnel air is excavated from the tunnel, it obviously has
particles suspended, but there are other properties, the heat from the
exhaust, the other emissions. Maybe the easier approach would be to ask the
question, "What could rise?" To a layman when it comes to molecules and
atoms, the guess is only gases lighter than air. The logical first thing
coming to mind would be helium, a gas that rises. But, a next question,
"How far?" Again the layman, there is the ozone "layer". So using this
reverse reasoning (often a good tool). There can be parts of the exhaust
that could rise, I doubt helium is produced, but there may be elements in the
fumes with potential. Everything else should fall to earth. One frustration
of vacations in Los Angeles is the smog, in the morning the smog, or murk
would hang
around, untill the locals would say ,"it burns off". My reasoning the sun
temperature causes the smog to disperse, some rising, as the ozone, but the
guess, more falling to earth.
James Przewoznik
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