Chimney Draft Vs Atmospheric Conditions

That's all too scientific for me. So, can't argue any facts. All I know is: if dryer air is heavier than moist air, it should sink lower than moist air, correct? Yet, moisture condensates in the atmosphere, forming clouds. Then falls to the ground in the form of rain. Now, when it falls to the ground, where does the dry air it displaces go? I'm assuming up. Wouldn't that make the dry air lighter? Or, are you talking lighter, as in less dense?

Nope, dry air is heavier than humid air. Lee posted the scientist's name who proved it long ago. You are on the right track though....since it's less heavy than dry air it rises. Or as you put it the dry air sinks

(Post re done below)

scalabro wrote:Nope, dry air is heavier than humid air. Lee posted the scientist's name who proved it long ago. You are on the right track though....since it's less heavy than dry air it rises. Or as you put it the dry air sinks

Here's a really, really long shot. Did anyone ever think the scientist could be wrong??? They've been wrong before . No?

scalabro wrote: Is the box airtight?

Yes the box is airtight but the house isn't. And for demonstrational purposes the fire has an unlimited supply of oxygen and the exhaust doesn't influence the atmosphere in the box...

oliver power wrote:All I know is: if dryer air is heavier than moist air, it should sink lower than moist air, correct?

Yes that's right and that's what weather systems do. The heavier dry air wedges in under the moist air pushing it upward. As the moist air is lifted it condenses into clouds where it's colder at higher elevation and eventually forms rain. Or so that's how I understand it.

The wind is also a factor .... maybe another thread for that....

The horsepower of internal combustion engines is affected by barometric pressure, altitude, humidity, and temperature. Here is a fun calculator to play with.

http://www.csgnetwork.com/relhumhpcalc.html

Thanks Larry, I found this particularly interesting,

The barometric pressure is the corrected to sea level atmospheric pressure that is typically reported on the local news or may be available from a local airport

I remember from when I would go flying with my uncle in his little Cessna, the highest we could go was around 11,000 feet. One factor was because the air is thinner and won't support as much weight at a given airspeed. The other factor is because the engine mixture would become too rich because of less available oxygen per volume of air since the air molecules are spread further apart (loss of horsepower).

I think what we can deduce from this is that a stove at higher altitudes would require a higher combustion air setting to produce the same amount of heat as the same stove at sea level.

I agree it is odd. I wonder why our local weather stations report barometric pressure corrected to sea level. I.E., false barometric pressure.

OK, lets talk about this dry air. Where does it come from? What separates the dry air from moist air? You say the dry air wedges under the moist air, pushing the moist air up. Maybe the air at ground level is dryer due to the earths internal heat? In other words, the dryer, warmer air rises, taking moisture with it. Then forming clouds as it reaches cooler heights. Kind of like the chimney effect. The hot dry air in a chimney rises.
However, isn't the chimney daft the result of cooler air in the atmosphere pushing down? If the cooler air is pushing down, forcing the warmer air up, wouldn't that make the cooler air heavier than the warm air? Or, are we talking two different things here? Moist air / dry air, and cool air / warm air. I don't know. Trying to wrap my brain around this. All in fun........

lsayre wrote:I agree it is odd. I wonder why our local weather stations report barometric pressure corrected to sea level. I.E., false barometric pressure.

It's the only way that weather men can compare apples to apples. Weather stations aren't at the same altitude. The difference between a weather station at sea level and a station at 2000 feet would be different by several millibars. Sea level is about 1000 mb where 2000 feet would be about 940 mb. If there was no correction for altitude it would be impossible to track high or low pressure areas.

Lightning wrote:Thanks Larry, I found this particularly interesting,

The barometric pressure is the corrected to sea level atmospheric pressure that is typically reported on the local news or may be available from a local airport

I remember from when I would go flying with my uncle in his little Cessna, the highest we could go was around 11,000 feet. One factor was because the air is thinner and won't support as much weight at a given airspeed. The other factor is because the engine mixture would become too rich because of less available oxygen per volume of air since the air molecules are spread further apart (loss of horsepower).

I think what we can deduce from this is that a stove at higher altitudes would require a higher combustion air setting to produce the same amount of heat as the same stove at sea level.

Lee,

You and your uncle only went to 11K because the engine at that altitude had lost a significant amount of horsepower because of the lower air density/pressure. He had to lean out (remove fuel) via the carburetor mixture control to prevent the Fuel /Air mixture becoming to rich to support proper combustion. Hence less air and fuel = less BANG! Lol! Plus, at 12K you two would have started to feel the effects of hypoxia unless you were both on breathing oxygen.

The aircraft could have easily climbed higher with a more powerful engine.

Yeah yer right, he had leaned it out as far as he could lol. Our top altitude was 10,800 feet. We didn't stay there very long. The nose was pointing quite high to maintain that altitude hahaha.

oliver power wrote:OK, lets talk about this dry air. Where does it come from? What separates the dry air from moist air? You say the dry air wedges under the moist air, pushing the moist air up. Maybe the air at ground level is dryer due to the earths internal heat? In other words, the dryer, warmer air rises, taking moisture with it. Then forming clouds as it reaches cooler heights. Kind of like the chimney effect. The hot dry air in a chimney rises.
However, isn't the chimney daft the result of cooler air in the atmosphere pushing down? If the cooler air is pushing down, forcing the warmer air up, wouldn't that make the cooler air heavier than the warm air? Or, are we talking two different things here? Moist air / dry air, and cool air / warm air. I don't know. Trying to wrap my brain around this. All in fun........

Yeah, this one can be a real head scratcher!

Removing moisture from the conversation for a minute. Warm air is lighter so cold air forces it up - like a boat floats on water. And just like a boat can't rise on it's own, warm air never rises, it is pushed up as colder air seeks the lowest points under the warm air forcing the warm air upward. If the air temp is the same throughout a room there is no air movement.

Now add back the moisture. What the gas law guy says is that in a gaseous state, water vapor molecules are lighter than just air molecules ( I never knew that before). As the water molecules displace heavier air molecules, each cubic foot of air so affected becomes lighter. Dry air being heavier sinks below moist air thus forcing the lighter moist air upward.

I think what really makes it confusing is that it's kinda hard to imagine that a water molecule is lighter than an air molecule.

Paul