Jiri Lonsky on sat 28 feb 04
I just can't resist this one, it is so elementary: There is a gradient =
of pressure in the atmosphere. The chimney bridges this gradient, =
allowing a "shortcut" if you will, to the top. So, the taller the =
chimney, the greater gradient it spans, and the lower the atmospheric =
pressure at its top, therefore, the stronger the draft. (Since the =
chimney insulates the rising hot gas, it is not cooling off as much as =
it rises, and retains its low specific weight, and its buyoancy =
comparative to surrounding atmosphere).
Jiri Lonsky.
Ivor and Olive Lewis on sun 29 feb 04
Dear Jiri,
The proposition is that the higher the stack the greater the velocity
of gas through the kiln and up the stack..
Assume that at higher levels the atmosphere reduces in density.
Assume that the heated air maintains the same density.
Then it follows that eventually the density differential decreases to
zero. At which point flow up the stack should stop. no more draft ! !
This is contrary to expectations.
If what you suggest is true, then perpetual motion seems to be a
reality.
I must admit, I do not know the answer.
Best regards,
Bruce Girrell on sun 29 feb 04
> The proposition is that the higher the stack the greater the velocity
> of gas through the kiln and up the stack..
> Assume that at higher levels the atmosphere reduces in density.
Good so far.
> Assume that the heated air maintains the same density.
Oops! Can't assume that. Gravity gets in here again. Why does the atmosphere
reduce in density at higher altitudes? Less gravity. The same lower gravity
would also affect the gas within the chimney proportionally reducing its
density. Hence, this assumption is invalid.
Bruce "if that summer sun is getting to you, Ivor, send some this way"
Girrell
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