How fluid is air, or what is the right question?
 

Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

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 fluid is air, or what is the right question?
 

On Feb 17, 5:00 pm, mm wrote:
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

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?


What you're missing is the density of the air just inside the door
opening is only a little less dense (because it's warm), than the
outside air that's on the other side. If the room were full of water,
there would be a huge density difference and gravity would cause it to
pour out.

Or create a water example, where you had a pool with a vertical
divider, seperating warmer water from cooler water. If you pull up
the divider for a minute, the water will begin to mix, but the warm
water won't just rush over in a minute.

How fluid is air, or what is the right question?
 

"mm" wrote in message
...
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

So does air, the pressure across the earth varies by 10% max.

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

What about air?

It is spread out evenly (more or less), see above.

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.

With just one opening, the cold air has to get in and the arm air get out.
A nice circulatory arrangement may occur, but it's better if there are two
openings, especially if they are arranged in the right places. Check out
solar chimneys

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?

Air can flow at 100 m/s or so on earth, in jet streams, can you find water
moving at anywhere near that speed?

How fluid is air, or what is the right question?
 

"mm" wrote in message 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?

You need something to move the air. When you open the door, there is
already air on both sides so there is little exchange. If there is a
breeze, or temperature differences, there will be some air movement, but it
is not like spilling water onto a table. To prove this, put a divider in a
container of water. Color the water on one side,let it stand and be very
still, then pull up the divider. It will eventually mix, but not very fast.
Just as some cocktails are poured in layers.

On a windy day, open the door and you will feel more air, but if you have
openings at the other end of the building, no matter how large, you will get
a draft through the building. At one of our buildings on a breezy day, I
can tell when a big door is opened as far as 1000 feet away. On a calm day,
you don't feel anything even 50 feet away.

How fluid is air, or what is the right question?
 

mm wrote:

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.

cfm = 16.6Avsqrt(HdT), for 2 Av ft^2 vents with an H' height diff and
dT (F) temp diff.

Nick

How fluid is air, or what is the right question?
 

"Russel Sprout" wrote in message
...

"mm" wrote in message
...
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

So does air, the pressure across the earth varies by 10% max.

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

What about air?

It is spread out evenly (more or less), see above.

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.

With just one opening, the cold air has to get in and the arm air get
out. A nice circulatory arrangement may occur, but it's better if there
are two openings, especially if they are arranged in the right places.
Check out solar chimneys

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?

Air can flow at 100 m/s or so on earth, in jet streams, can you find water
moving at anywhere near that speed?

Doesn't the tital waves move neat this speed ? I don't think in
meters/second but miles per hour. Thought the tital waves could hit several
humdred mph.

Air will expand to fill all the space, but cold and hot air are almost the
same density. Take a clear class and heat some water so it is about 150 deg
F and drop in a couple of drops of food coloring and see how slow the cold
fluid moves if you don't sitr it.

How fluid is air, or what is the right question?
 

In article , mm writes:
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

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 fast would water have run out of the building if you had water
outside, at same level as inside? The building is not surrounded by
vacuum.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

How fluid is air, or what is the right question?
 

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

How fluid is air, or what is the right question?
 

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.

How fluid is air, or what is the right question?
 

On Feb 17, 2:40 pm, "Ralph Mowery" wrote:
"Russel Sprout" wrote in message

...





"mm" wrote in message
.. .
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

So does air, the pressure across the earth varies by 10% max.

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

What about air?

It is spread out evenly (more or less), see above.

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.

With just one opening, the cold air has to get in and the arm air get
out. A nice circulatory arrangement may occur, but it's better if there
are two openings, especially if they are arranged in the right places.
Check out solar chimneys

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?

Air can flow at 100 m/s or so on earth, in jet streams, can you find water
moving at anywhere near that speed?

Doesn't the tital waves move neat this speed ? I don't think in
meters/second but miles per hour.

Time to get educated and join the rest of the world.

Thought the tital waves could hit several
humdred mph.

The wave moves, not the water. In the middle of the ocean, the tsunami
does not consist of water moving fast like in river rapids. As it
comes on shore, that changes, of course, as all the video shots from
2005 demonstrate.

R.G. Vickson



Air will expand to fill all the space, but cold and hot air are almost the
same density. Take a clear class and heat some water so it is about 150 deg
F and drop in a couple of drops of food coloring and see how slow the cold
fluid moves if you don't sitr it.

How fluid is air, or what is the right question?
 

"mm" wrote in message ...
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain,


Yes is will.

http://www.shiromi.com/gallery2/d/16...water3_std.jpg
http://static.flickr.com/21/24681862_be8d89ed03.jpg
http://www.corporate.basf.com/basfco...r_droplets.jpg

How fluid is air, or what is the right question?
 

On Feb 17, 11:00 pm, mm wrote:
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

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?

Actually, air and water are pretty much the same thing when you study
the dynamics of fluids and gasses. The physical properties of both are
a bit different, water is for instance much less compressible than
air, water is more dense and the specific heat differs. Yet, there
isn't really a lot of difference when the dynamics of fluids and
gasses are modeled, it is all Navier Stokes maybe in a slightly
different form. Maybe a good book is "Ocean Atmosphere Dynamics" by
Gill which treats both topics next to each other.

http://www.amazon.com/Atmosphere-Oce.../dp/0122835220

Your building example is not really fair, a building filled with water
in an air environment is something different than a building filled
with air in an air environment. Why not a building filled with warm
water in a cold water environment?

Ejo


Ejo

How fluid is air, or what is the right question?
 

In sci.physics, Androcles

wrote
on Sun, 18 Feb 2007 04:22:46 GMT
:

"mm" wrote in message ...
Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain,


Yes is will.

http://www.shiromi.com/gallery2/d/16...water3_std.jpg
http://static.flickr.com/21/24681862_be8d89ed03.jpg
http://www.corporate.basf.com/basfco...r_droplets.jpg

Androcles does have a point here; if the water doesn't
adhere to the tabletop (e.g., wax), it will bead up.
These are definitely "little mountains", although more in
the US Eastern sense, not the Sierra Nevada. :-)

Even if the water does adhere to the tabletop, it will
still bead up, although not as much.

To be sure, surface tension can only go so far; if one
pours a cubic meter (1 metric tonne) of water on a 1 m^2
wax-coated tabletop, it won't all fit as little beads.

However, neither will it all fall off the edges, either.
Most of it, yes -- but not all. The rest will have to
be wiped off with a towel or left to evaporate; if one is
working with impure water, one gets salt -- a fact noticed
by many after a rainfall on their car rooftops, windshields,
hoods, etc.

--
#191,
Useless C++ Programming Idea #8830129:
std::set... v; for(..:iterator i = v.begin(); i != v.end(); i++)
if(*i == thing) {...}

--
Posted via a free Usenet account from http://www.teranews.com

How fluid is air, or what is the right question?
 

On Sat, 17 Feb 2007 22:23:53 GMT, "Edwin Pawlowski"
wrote:


"mm" wrote in message 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?

You need something to move the air. When you open the door, there is
already air on both sides so there is little exchange. If there is a
breeze, or temperature differences, there will be some air movement, but it
is not like spilling water onto a table. To prove this, put a divider in a
container of water. Color the water on one side,let it stand and be very
still, then pull up the divider. It will eventually mix, but not very fast.
Just as some cocktails are poured in layers.

On a windy day, open the door and you will feel more air, but if you have
openings at the other end of the building, no matter how large, you will get
a draft through the building. At one of our buildings on a breezy day, I
can tell when a big door is opened as far as 1000 feet away. On a calm day,
you don't feel anything even 50 feet away.


Air movement in side a closed or semiclosed area is extremely complex.
Although air densitytemperature gradients play an important role, air
mixing is highly dependent on the existing HVAC and placement of
furniture or equipment in the room. Although I could not find the
report in a short imte, I have seen a Department of Energy study from
quite a few years ago that discussed the result of smoke tests in a
variety of room configuratoins. What amazed me is that in some parts
of rooms with what might be consdered good circulation, there were
dead air spots that persisted for very long periods.

How fluid is air, or what is the right question?
 

Gas behaves similar to liquid--both move faster with higher
temperatures. But there is one important difference: gas (air) is
spongy meaning that it easily expands and contracts in volume,
depending on temperature and pressure. Liquids (and solids) stay
about the same volume. Molecules are close together in solids, far
apart in gases. Water will move faster than a gas in an air
environment due to the differences in specific gravity. Also, nature
tends to dissipate substances.

On Sat, 17 Feb 2007 17:00:18 -0500, mm
wrote:

Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

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?