My smoke falleth to the ground

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R

RockCastile

Member
Nov 9, 2015
89
Blue Ridge of Va.
On the sometimes phenomenon of smoke exiting the chimney and immediately falling straight to the ground like a sack of bricks...
I only grasp in theory why this happens and that there are many factors that affect it: an inversion layer, the whimsy of wind, the micro aerodynamics created by the roof/chimney formation, etc.

But what doesn't jive to me is how a virtual geyser of gas that's extremely hot relative to the frigid air it is shooting itself up into does not continue to rise at least 15-20ft feet or so (lets assume there's little or no wind at the moment) before its heat is dissipated and it begins falling back down. I think of a beach ball forced as deeply as one can press it beneath the surface of the swimming pool, let go of it and...whoosh, gittyup. How come it's not the same, in terms of a relatively super dense mass of frigid air with a super hot and far less dense current of gas flowing up into it?
 
Now think of that beach ball full of sand. Basically smoke is loaded with particulates and once forces that act on it over come the draft it will fall or just get trapped under the inversion. Smoke in a stack is not pushed up by heat rising it's pulled.
 
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RockCastile,

I'm not sure what stove you have, but when mine is burning there isn't any visible smoke at all, nor should there be with an EPA-approved stove.
 
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I'm watching mine do that now. A small reload into a small bed of coals at 250 degrees. 16 degrees, a bit of wind. I don't know the physics of it, but good question.
 
rwhite said:
Now think of that beach ball full of sand. Basically smoke is loaded with particulates and once forces that act on it over come the draft it will fall or just get trapped under the inversion. Smoke in a stack is not pushed up by heat rising it's pulled.
Click to expand...

This!
 
Alternate theory:.



Your smoke is broken. The only way to fix this is dry pine. You're going to have to burn a lot of it... quickly.




I imagine you have an inversion. Do you live in a valley?
 
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No expert on this but what comes to mind is;
Draft is a weak force. Standard 0.05 WC converts to 0.002 PSI.
After smoke leaves the confines of the chimney it expands rapidly. Expansion of a gas causes it to cool.
I understand that the air can be stratified and that the layers of air are pretty distinct.
 
RockCastile said:
On the sometimes phenomenon of smoke exiting the chimney and immediately falling straight to the ground like a sack of bricks...
I only grasp in theory why this happens and that there are many factors that affect it: an inversion layer, the whimsy of wind, the micro aerodynamics created by the roof/chimney formation, etc.

But what doesn't jive to me is how a virtual geyser of gas that's extremely hot relative to the frigid air it is shooting itself up into does not continue to rise at least 15-20ft feet or so (lets assume there's little or no wind at the moment) before its heat is dissipated and it begins falling back down. I think of a beach ball forced as deeply as one can press it beneath the surface of the swimming pool, let go of it and...whoosh, gittyup. How come it's not the same, in terms of a relatively super dense mass of frigid air with a super hot and far less dense current of gas flowing up into it?
Click to expand...

Maybe the gas does rise, leaving the biggest (visible) chunks of water and ash and other combustion byproducts behind.
 
Good replies, thanks, i think I get it. To the couple if questions from above....1) yes, I do live in a low spot, a little micro valley.
2) It's a Jotul 602, bought new last year, flue is straight up and out near(ish) the roof's highest point, 15 ft total height.
And the smoke is for the most part only for a few minutes at startup and reload, but could probably reduce that with drier wood next winter.

Sent from my SM-S820L using Tapatalk
 
Depending on the weather and pressure we get smoke sinking on a startup sometimes. Happened this morning with a low pressure system upon us and no wind.
 
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Its all about moisture. Thats it. The smoke is always going to be hotter than the air. When the relative humidity is high (saturated air) it cant hold the moisture in the smoke. Your smoke is now literally fog. A cloud of moisture that falls to the ground because the air is too saturated to hold it.
 
I suspect it's a mistake to imagine that temperature and draft in the chimney are uniform. Hot gas enters at the bottom and cools as it goes up. That means that the densest, heaviest smoke will be what's coming out the top.

And what is coming out may actually be denser than the surrounding air. Smoke has a lot of CO2 in it, which is known to be denser than air: https://www.reddit.com/r/askscience...2_is_heavier_than_air_why_doesnt_it_all_sink/

So if the gas coming out the top of the chimney isn't hot enough to offset its heavier molecules, it will in fact sink.
 
Let's try putting the theory into practical terms. A temperature inversion basically puts a lid that normally doesn't exist on colder air underneath, holding pollution & particulate closer to the ground.

The other factor at play is air stability and temperature inversions basically create more stable air, but the two don't always occur together. The more stable an air mass is, the less vertical mixing that occurs (e.g. smoke & gases ability to travel up). Typically what happens is an air mass is most stable in the morning hours, becomes less unstable during the day due to temperature changes from the sun, and then starts to re-stabilize as night sets in.
 
woodchiprookie said:
Its all about moisture. Thats it. The smoke is always going to be hotter than the air. When the relative humidity is high (saturated air) it cant hold the moisture in the smoke. Your smoke is now literally fog. A cloud of moisture that falls to the ground because the air is too saturated to hold it.
Click to expand...
Dry air is heavier than moist air. Think more hydrogen molecules.
(broken link removed)
 
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