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[GoblinCookie]

And how might the amount of time the smoke spends in the room impact the efficiency of material use?

Provided the dwarves are inhaling from the smoke column, not much. 

Is our goal to maximize the amount of smoke going up the chimney, or is it to minimize the amount of excess smoke?

Did you account for the fact that putting out a greater volume means you still get more soot everywhere? Do you know how quickly the smoke is going to cool when it comes in contact with the cold sides of the upper chimney? Do you know where gravity sends clumps of soot when they can no longer stick to the chimney? Did you consider the difficulty of keeping that chimney clean?

The goals are both served by the same ends.  We want to get rid of the smoke, the dwarves breathing it in does not get rid of the smoke since they breathe it out again.  The only way to get rid of the smoke aside from it falling to the ground as soot is for it is go through the chimney, the best way to make it go through the chimney is to ensure it is a single hot mass rather than lots of little masses. 

There is going to be some soot problems in any case, it is question of the amount. 

But more importantly: Did you forget that combustion turns O2 into CO2? Did you know that CO2 is of greater or equal density compared to O2? Did you account for the fact that turning solid material into smoke further increases the air pressure of the room? Did you figure out how you're going to get O2 from the surface against that pressure gradient? Do you know what combustion produces if it doesn't get enough O2? Do you know what happens to dwarves if they don't get enough O2, or if they inhale CO?

Combustion produces deadly carbon monoxide if it can't get enough O2?

The relative density of C02 against O2 is largely irrelevant here.  That is because they are both gasses and gasses are prone to equalise themselves, this is a far more powerful force than their relative density is.  That means O2 will come from the surface and C02 will leave through the chimney, the relative density is not a problem.  The relative density of the soot particles is not irrelevant by contrast, because these are solids not gasses. 

What is potentially a problem is that the fire will use up the O2 in the room and the air flow of hot air through the chimney will keep the O2 from equalising.  This is not a problem if we only use the smoking room for a short time every day, so that there is a lot of down time for the air to equalise itself.  If we want to have the smoking room used all the time however, then all we have to do is add a second chimney/ventilation shaft that is not above the fire. 

This second shaft is not blocked by the hot air rising, so the gasses (including carbon monoxide) can equalise unobstructed.   

The solution involves a fan or surface wind to get O2 into the room, regardless of getting rid of the smoke. (Ideally, the O2 enters near the floor of the room.) We maximize breathability using the least amount of combustion possible, which means not building a bonfire or brazier in the room. We use tiny fires in smoking pipes, ensure the overwhelming majority of it ends up in the lungs, and then let it out in small puffs to be carried away by the air current.

That would work but it is far more complex to engineer than my idea.  It also depends upon their actually being a wind, or it involves a ton of energy to turn those fans.  Also what happens when it rains and the rain decides to flow down your wind tunnels, which have to be at an angle to catch the wind?

aaaand now we're back into airflow debates, guys you all know this never ends well

To be fair that is the main issue with dwarves smoking. 

[betaking]

aaaand now we're back into airflow debates, guys you all know this never ends well

To be fair that is the main issue with dwarves smoking.

not really, I've mostly been thinking "smoking in pipes" as far as "personal pipe smoking" and simply ignore stuff like 2ndhand smoke or like "smoking rooms" and the proposed efficiency they might bring the same way underground furnace, kiln, etc. smoke is ignored. At most a "light cloud" forming on the tile every time a dwarf takes a hit/drag, but which dissipates fairly quickly.

The main benefits to smoking as a dwarf activity would be:
-Giving me something that would be believable to produce in the quantities my craftsdwarfs produce things in (pipes, hookahs, etc.)
more stuff to grow/farm and more stuff for hospitals/doctors to use (Opium poppy).

[Bumber]

And how might the amount of time the smoke spends in the room impact the efficiency of material use?

Provided the dwarves are inhaling from the smoke column, not much. 

And how many dwarves crowding that smoke column does it take for your expected economy of scales to kick in?

The relative density of C02 against O2 is largely irrelevant here.  That is because they are both gasses and gasses are prone to equalise themselves, this is a far more powerful force than their relative density is.  That means O2 will come from the surface and C02 will leave through the chimney, the relative density is not a problem.  The relative density of the soot particles is not irrelevant by contrast, because these are solids not gasses.

What is potentially a problem is that the fire will use up the O2 in the room and the air flow of hot air through the chimney will keep the O2 from equalising.  This is not a problem if we only use the smoking room for a short time every day, so that there is a lot of down time for the air to equalise itself.  If we want to have the smoking room used all the time however, then all we have to do is add a second chimney/ventilation shaft that is not above the fire.

This second shaft is not blocked by the hot air rising, so the gasses (including carbon monoxide) can equalise unobstructed.

Diffusion and updraft are not going to be sufficient to clean the air underground.

Humans lose consciousness with an O2 content of less than 10%. A CO2 concentration of 7%-10% can cause suffocation even with sufficient O2, with unconsciousness setting in from a few minutes to an hour. Both dwarves and fire are constantly converting O2 into CO2. For carbon monoxide, 0.16% is lethal in 2 hours and 0.32% is lethal in 30 minutes. A carbon monoxide content of 1.28% is lethal after 2-3 breaths, so you won't have any warning of dizziness or headache. Even setting lethality aside, the room is not going to be a pleasant experience for anyone in it.

That would work but it is far more complex to engineer than my idea.  It also depends upon their actually being a wind, or it involves a ton of energy to turn those fans.  Also what happens when it rains and the rain decides to flow down your wind tunnels, which have to be at an angle to catch the wind?

The engineering is unavoidable if you're trying to supply air to an underground fort of 80+ dwarves (unless you have access to magic.) You can divert the rain water elsewhere because liquids behave differently.

[GoblinCookie]

And how many dwarves crowding that smoke column does it take for your expected economy of scales to kick in?

It depends upon how much fuel is being burned in their individual pipes against how much fuel is in the brazier.  Both of these are variable.  The stronger the 'hit' the dwarves want, the greater the values will be in both cases.

Diffusion and updraft are not going to be sufficient to clean the air underground.

Humans lose consciousness with an O2 content of less than 10%. A CO2 concentration of 7%-10% can cause suffocation even with sufficient O2, with unconsciousness setting in from a few minutes to an hour. Both dwarves and fire are constantly converting O2 into CO2. For carbon monoxide, 0.16% is lethal in 2 hours and 0.32% is lethal in 30 minutes. A carbon monoxide content of 1.28% is lethal after 2-3 breaths, so you won't have any warning of dizziness or headache. Even setting lethality aside, the room is not going to be a pleasant experience for anyone in it.

The same problems would apply to any forge or smelter underground.  I think the greater the difference between the CO2 underground and on the surface, the faster the gas will redistribute itself.  The real danger though is making sure there is always enough oxygen to keep the fire from poisoning everyone with carbon monoxide. 

Basically dwarves smoking is a problem because fire in general is a problem underground. 

The engineering is unavoidable if you're trying to supply air to an underground fort of 80+ dwarves (unless you have access to magic.) You can divert the rain water elsewhere because liquids behave differently.

Correct, clever engineering is always going to be needed to allow any amount of fire to burn safely underground.  A lot of what I am saying however is that having a single large central fire in a controlled locations more easily engineered for than a large number of little fires at indeterminate distances from the outflow vent. 

It might be possible for dwarves to make individual smoking work with an awful lot of highly expensive and complex engineering, but that in itself in an inefficiency which points towards the "sitting around a central fire breathing in the smoke" option for dwarves.

[Bumber]

I think the greater the difference between the CO2 underground and on the surface, the faster the gas will redistribute itself.

Not via diffusion. Since CO2 and O2 have similar densities, they're essentially treated as the same gas, which means the distribution is completely random.
Pressure difference will cause excess CO2 to move to the surface, but O2 isn't going to head down against the gradient without something pushing it.

A lot of what I am saying however is that having a single large central fire in a controlled locations more easily engineered for than a large number of little fires at indeterminate distances from the outflow vent.

You just need a funnel at the top of the room, like a range hood above a stove. The smoke will be pulled along with the air current.

[GoblinCookie]

]Not via diffusion. Since CO2 and O2 have similar densities, they're essentially treated as the same gas, which means the distribution is completely random.
Pressure difference will cause excess CO2 to move to the surface, but O2 isn't going to head down against the gradient without something pushing it.

I was under the impression that gasses redistributed themselves so that the total distribution of the molecules of a given gas is equal everywhere.  So oxygen flows into a cave because there is less oxygen in the cave than there is on the surface, allowing cavern life to exist.  The same principle applies presumably to C02 and to carbon monoxide, fortunately. 

Oxygen I conceded is unlikely to go down if the air flow is in the other direction, which essentially means we need to have two vents, one for smoke and the other for oxygen since the smoke's updraft prevents oxygen from being replaced inside the chamber.  Having the fire (or smokers) directly beneath the chimney would presumably be necessary. 

You just need a funnel at the top of the room, like a range hood above a stove. The smoke will be pulled along with the air current.

There is still the issue of having to have a means of individual dwarves 'lighting up' and the potential this this creates for arson.  We can pretty much agree that an outbreak of fire in a dwarven fortress is pretty much the deadliest threat the dwarves could ever face. 

[Bumber]

I was under the impression that gasses redistributed themselves so that the total distribution of the molecules of a given gas is equal everywhere.  So oxygen flows into a cave because there is less oxygen in the cave than there is on the surface, allowing cavern life to exist.  The same principle applies presumably to C02 and to carbon monoxide, fortunately.

It's based on the random movement of particles:

A distinguishing feature of diffusion is that it depends on particle random walk, and results in mixing or mass transport without requiring directed bulk motion.

Spoiler: Picture (click to show/hide)

In other words, it's a mixing effect due to particles randomly bouncing off each other until the collisions eventually push them away from each other and they're evenly spread out. The oxygen molecules don't care if what they're colliding with is oxygen or not. That you eventually get an even distribution of oxygen is just statistics. The process is not going to accelerate just because there are less molecules of the same type. It collides with CO2 just as easily.

Oxygen flows into caves only with an air current (i.e., wind.) Otherwise it's down to random mixing, which is not going to be sufficient replenishment for high-consumption organisms, let alone fire. The fire's thermal updraft does create a bit of an air current, but that's completely undone by all the other stuff it's doing.

There is still the issue of having to have a means of individual dwarves 'lighting up' and the potential this this creates for arson.  We can pretty much agree that an outbreak of fire in a dwarven fortress is pretty much the deadliest threat the dwarves could ever face.

Good thing they tend to build using stone.

[GoblinCookie]

I was under the impression that gasses redistributed themselves so that the total distribution of the molecules of a given gas is equal everywhere.  So oxygen flows into a cave because there is less oxygen in the cave than there is on the surface, allowing cavern life to exist.  The same principle applies presumably to C02 and to carbon monoxide, fortunately.

It's based on the random movement of particles:

A distinguishing feature of diffusion is that it depends on particle random walk, and results in mixing or mass transport without requiring directed bulk motion.

Spoiler: Picture (click to show/hide)

In other words, it's a mixing effect due to particles randomly bouncing off each other until the collisions eventually push them away from each other and they're evenly spread out. The oxygen molecules don't care if what they're colliding with is oxygen or not. That you eventually get an even distribution of oxygen is just statistics. The process is not going to accelerate just because there are less molecules of the same type. It collides with CO2 just as easily.

Oxygen flows into caves only with an air current (i.e., wind.) Otherwise it's down to random mixing, which is not going to be sufficient replenishment for high-consumption organisms, let alone fire. The fire's thermal updraft does create a bit of an air current, but that's completely undone by all the other stuff it's doing.

Thanks for the science, I actually did not know how the diffusion worked only that it did.

Oxygen flows into caves not just because of the wind, but because of the flow of water into the caves.  Oxygen does not simply redistribute itself between different bodies of air, it also redistributes itself into and out of water. 

Air is mostly nitrogen, carbon dioxide and oxygen both make up a minority of it.  Apparently according to google oxygen is dissolved in nitrogen but C02 is not dissolved in oxygen but is lighter than nitrogen.  CO2 on the other hand is not dissolved in oxygen/nitrogen but is lighter than nitrogen, by a factor of 5.  Oxygen is also apparently the same weight (despite having more molecules?), but it is dissolved into the nitrogen. 

The CO2 rises above the nitrogen, in which the oxygen is dissolved.  That means it does not matter that oxygen and nitrogen are the same weight separately because the C02 will automatically float out of the fortress provided it is going upwards as the nitrogen is heavier than it.  C02 poisoning is basically only something you have to worry about only if you are ventilating something from below rather than above.  That solves something I was wondering about subterranean life in RL, why does the C02 not just accumulate, the answer is that the C02 simply floats out of the cave entrances. 

Good thing they tend to build using stone.

Anything flammable in the fortress can still burn and the dwarves will not find it easy to dispose of the poisonous gasses in the smoke.

[thompson]

Thanks for the science, I actually did not know how the diffusion worked only that it did.

Oxygen flows into caves not just because of the wind, but because of the flow of water into the caves.  Oxygen does not simply redistribute itself between different bodies of air, it also redistributes itself into and out of water. 

Air is mostly nitrogen, carbon dioxide and oxygen both make up a minority of it.  Apparently according to google oxygen is dissolved in nitrogen but C02 is not dissolved in oxygen but is lighter than nitrogen.  CO2 on the other hand is not dissolved in oxygen/nitrogen but is lighter than nitrogen, by a factor of 5.  Oxygen is also apparently the same weight (despite having more molecules?), but it is dissolved into the nitrogen. 

The CO2 rises above the nitrogen, in which the oxygen is dissolved.  That means it does not matter that oxygen and nitrogen are the same weight separately because the C02 will automatically float out of the fortress provided it is going upwards as the nitrogen is heavier than it.  C02 poisoning is basically only something you have to worry about only if you are ventilating something from below rather than above.  That solves something I was wondering about subterranean life in RL, why does the C02 not just accumulate, the answer is that the C02 simply floats out of the cave entrances. 

Anything flammable in the fortress can still burn and the dwarves will not find it easy to dispose of the poisonous gasses in the smoke.

You're confusing liquids with gasses here. Density of a gas is proportional to molecular number, so 32 for O2, 28 for N2 and 44 for CO2. Solubility is also a non-issue for gaseous mixing. CO2 is the most dense, but the densities are close enough that you still get thorough mixing.

If you want to understand diffusion I'd recommend googling Fick's law. It was formulated for solids but applies to gasses as well. Essentially, diffusion is driven by a concentration gradient, where you get net movement from high to low concentrations. The process is limited by diffusion rates and the distance things need to travel. For gasses you would need to consider cavern width as well. In real life, ventilation underground is a big issue. It's not such a problem for natural caverns because large animals typically live near the entrances.

[GoblinCookie]

You're confusing liquids with gasses here. Density of a gas is proportional to molecular number, so 32 for O2, 28 for N2 and 44 for CO2. Solubility is also a non-issue for gaseous mixing. CO2 is the most dense, but the densities are close enough that you still get thorough mixing.

If you want to understand diffusion I'd recommend googling Fick's law. It was formulated for solids but applies to gasses as well. Essentially, diffusion is driven by a concentration gradient, where you get net movement from high to low concentrations. The process is limited by diffusion rates and the distance things need to travel. For gasses you would need to consider cavern width as well. In real life, ventilation underground is a big issue. It's not such a problem for natural caverns because large animals typically live near the entrances.

No solubility is very much an issue, just like with liquids gasses dissolve into each-other, they just don't behave quite the same way when they do so.  Nitrogen is the heaviest gas in the air, it is also makes up the largest quantity of it at the surface.  We don't suffocate because oxygen dissolves into the nitrogen we breathe, that means that even though it is lighter than the nitrogen the oxygen does not simply float away to form a layer in the upper atmosphere.  Also consider the amount of oxygen that can dissolve into the nitrogen is limited, if you go over that limit then we get free oxygen which will simply float away because it is lighter than the nitrogen it is mixed with. CO2 always floats away because it does not dissolve in nitrogen unlike oxygen, which is what causes global warming; the majority of the C02 forms a layer below the ozone but above the nitrogen which works like a blanket because it is so dense compared to what is above and below it. 

Here is the clever thing.  As we breathe air in a cave we make the nitrogen we are breathing less dense because we take oxygen out of it, while the C02 we breathe out floats away to cause global warming like good C02 should  .  Because of the diffusion of gasses this drags fresh nitrogen down with oxygen in tow because the nitrogen diffuses itself into the cavern in order to equalize the density in the cavern which is reduced by our breathing. 

A lot of creatures in caverns do not live near the entrances.  They live along or in underground rivers that flow deep underground, because rivers as bodies of flowing water dissolve oxygen from the air.  The funny thing is that dissolved gasses still defuse, the oxygen in the water redistributes itself into the nitrogen of the cavern air, because oxygen is soluble in both substances. 

[thompson]

You're confusing liquids with gasses here. Density of a gas is proportional to molecular number, so 32 for O2, 28 for N2 and 44 for CO2. Solubility is also a non-issue for gaseous mixing. CO2 is the most dense, but the densities are close enough that you still get thorough mixing.

If you want to understand diffusion I'd recommend googling Fick's law. It was formulated for solids but applies to gasses as well. Essentially, diffusion is driven by a concentration gradient, where you get net movement from high to low concentrations. The process is limited by diffusion rates and the distance things need to travel. For gasses you would need to consider cavern width as well. In real life, ventilation underground is a big issue. It's not such a problem for natural caverns because large animals typically live near the entrances.

No solubility is very much an issue, just like with liquids gasses dissolve into each-other, they just don't behave quite the same way when they do so.  Nitrogen is the heaviest gas in the air, it is also makes up the largest quantity of it at the surface.  We don't suffocate because oxygen dissolves into the nitrogen we breathe, that means that even though it is lighter than the nitrogen the oxygen does not simply float away to form a layer in the upper atmosphere.  Also consider the amount of oxygen that can dissolve into the nitrogen is limited, if you go over that limit then we get free oxygen which will simply float away because it is lighter than the nitrogen it is mixed with. CO2 always floats away because it does not dissolve in nitrogen unlike oxygen, which is what causes global warming; the majority of the C02 forms a layer below the ozone but above the nitrogen which works like a blanket because it is so dense compared to what is above and below it. 

Here is the clever thing.  As we breathe air in a cave we make the nitrogen we are breathing less dense because we take oxygen out of it, while the C02 we breathe out floats away to cause global warming like good C02 should  .  Because of the diffusion of gasses this drags fresh nitrogen down with oxygen in tow because the nitrogen diffuses itself into the cavern in order to equalize the density in the cavern which is reduced by our breathing. 

A lot of creatures in caverns do not live near the entrances.  They live along or in underground rivers that flow deep underground, because rivers as bodies of flowing water dissolve oxygen from the air.  The funny thing is that dissolved gasses still defuse, the oxygen in the water redistributes itself into the nitrogen of the cavern air, because oxygen is soluble in both substances.

No.

[Bumber]

Nitrogen is the heaviest gas in the air [...] so dense compared to what is above and below it.

Excuse me, what?!

[therahedwig]

And I think we're now getting a proper glimpse on why I stated on page 1 that I would totally discuss the topic of smoking dwarves with anyone but GC. I do not think they've ever seen smoke in real life to begin with. It might thus not be fruitful to continue this discussion.

[thompson]

GC has always been a bit of an enigma to me. He seems reasonable articulate, can grasp some esoteric philosophical concepts, and has a broad knowledge base, yet manages to get everything consistently wrong.

I suspect GC may be innumerate. He can discuss things on purely qualitative terms but is unable to determine the relative significance of different factors because he cannot make quantitative assessments of each. So, negligible factors (gravitational separation due to density, in this case) are given equal or greater weighting to significant ones (entropy). I'm surprised that he failed to instantly recognise that CO2 should be denser than O2 (by virtue of having an additional carbon worth of weight), but if you view the world in strictly qualitative terms I suppose Aristotle's classical elements may be a more intuitive way of viewing material properties.

Please don't take offence GC. Your way of thinking is very much reminiscent of that of classical philosophers and dominated human intuition for thousands of years. Unfortunately, there are very serious limitations to that approach of reasoning, and it has very much been superseded by other approaches that are rigorously grounded in mathematics rather than rhetoric.

[GoblinCookie]

Excuse me, what?!

Nitrogen has a greater mass than ozone, oxygen, C02 and the rest.  This is why close to the surface, nitrogen predominates and the air we breathe is hence mostly nitrogen; it sinks to the bottom of the atmosphere, which is where we are. 

GC has always been a bit of an enigma to me. He seems reasonable articulate, can grasp some esoteric philosophical concepts, and has a broad knowledge base, yet manages to get everything consistently wrong.

I suspect GC may be innumerate. He can discuss things on purely qualitative terms but is unable to determine the relative significance of different factors because he cannot make quantitative assessments of each. So, negligible factors (gravitational separation due to density, in this case) are given equal or greater weighting to significant ones (entropy). I'm surprised that he failed to instantly recognise that CO2 should be denser than O2 (by virtue of having an additional carbon worth of weight), but if you view the world in strictly qualitative terms I suppose Aristotle's classical elements may be a more intuitive way of viewing material properties.

Please don't take offence GC. Your way of thinking is very much reminiscent of that of classical philosophers and dominated human intuition for thousands of years. Unfortunately, there are very serious limitations to that approach of reasoning, and it has very much been superseded by other approaches that are rigorously grounded in mathematics rather than rhetoric.

I am seldom wrong, that is why I am an enigma to you because you are quite the opposite as are those you admire and follow.  You start from degenerate intellectual foundations, disparaging the true foundations of human knowledge as having 'very serious limitations'; but did Issac Newton not say we "stand on the shoulders of giants"?  I don't know what to do with a person who thinks that rationality is some form of technology; how are we to evaluate the relative merits of older and newer rationality without some kind of neutral rationality to do so?  I spy a certain Appeal to Novelty fallacy here. 

I started on the assumption that C02 was heavier than Oxygen, I thought Bumber informed me that actually C02 was the same mass as oxygen and I believed Bumber (did Bumber actually say density?).  I conceded the point so easily because it's *completely irrelevant* to what I was saying, since C02 is not competing directly with oxygen because the air is NOT MADE OF OXYGEN.  Thinking that the air is made of oxygen is like thinking the sea is made of salt, partly true but not very useful.

The air consists of nitrogen with oxygen dissolved into it, just like the sea behaves like water and not like a heap of salt, the oxygen in the air behaves like the nitrogen it is dissolved into.  That means that we don't suffocate, because the oxygen which would normally float above the level of nitrogen is dissolved into the nitrogen we breathe and our lungs extract the oxygen from the nitrogen because of the diffusion of dissolved substances. 

Even though oxygen is dissolved into the nitrogen, the oxygen in the nitrogen still diffuses itself, but only does so between and within substances in which it is soluble.  Oxygen is soluble in both water and nitrogen, that means that if there is a deficit of oxygen in the water of the blood, the oxygen will flow from the air into the blood.  Conversely if there is a surplus of C02 in the blood, it will flow into the nitrogen of the air in the lungs.