On Sun, 18 Feb 2007 01:26:56 +0000 (UTC),
(Michael Moroney) wrote:

mm writes:

What about air?

If you have a heated building and open an overhead door 12 to 16 feet
high, for trucks, how fast will the cold air outside pour into the
building, and how fast will the hot air nearer the ceiling be forced
out.

I was recently at such a building, when it was below freezing out, and
I was close to the door and every time the door was opened, I'd feel a
bit of cold air, but not as much as I expected, and when the door was
shut, the building seemed back to normal very quickly. If it had been
full of water, in a twentieth of the time it took a car to drive in or
out, all the water would have run out. Does air not flow even at
1/20th the speed of water? What am I missing?

How about this: I know of a grocery store that had a somewhat larger
opening, as its main entrance, that was open maybe 14 hours a day (during
normal open hours). Or was it open 24 hours? I forget. The difference
between this entrance and a simple opening is there was a substantial
downward blast of air as you entered or left through it. The air blast
somehow kept warm inside air and cold outside air separated. (How?)

I have seen that arrangement too. I was never sure if it was meant to
work like you say, or only to give people a warm feeling when they
walked in.

It like you say, I don't know how either.

And since this was in a suburb of Buffalo NY, the outside air could get
rather cold (and windy!)

Maybe there is a force field like Captain Wonder would have, if he had
his own comic book.