I seem to recall something called “aspiration” where a fluid (i.e. air) passing over an opening can create suction. And supposedly, this is how a chimney should work. Anyone know more on this subject? - Jinx
I think your referring to Burnoulli’s Principle.
A region of high velocity creates a low pressure, thereby creating suction against a lower velocity/higher pressure area…like the aspirator on an old-style perfume sprayer.
This principle also creates ventilation for rodent tunnels whereby said critter will have entrances at different heights the take advantage of wind velocity differential, which cuases pressure drop and thusly airflow.
The chimney is mostly hot air rising (convection). A strong wind at the top can actually blow back down if the rim is a particular shape.
Heat goes up.
Heat goes up, leaving a “vacuum” which is replaced by air from the house, which gets warmed and goes up, etc.
If chimneys worked solely on the Bernoulli Principle, they could be horizontal. I don’t think a horizontal chimney would work well.
Actually, no, as the Bernoulli Effect would require the wind to blow at 90 deg to the chimney. Since the wind changes directions, sometimes it would be blowing straight into the chimney rather than across it.
There is a device (called an owl in some sections of the US) that you put on top of a stovepipe chimney that increases the draft in the chimney. It is an ell on a 360[sup]o[/sup] ball bearing base with a wind vane on top so that the open end always faces downwind.
Sometimes, due to location of an obstruction, a chimmy doesn’t work for some wind directions. The obstruction makes the wind blow straight down the chimney.
So they put a thing on the top looks about like an “H” with the chimmney connecting in the middle of the horizontal bar. With this, no matter what direction the wind blows, it is always producing some suction.