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Upside Down Cooling

Heat rises, So does cold helium
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(+6, -1)
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When you absoultely have to cool down a building quickly. Liquid helium will rise cooling as it goes, cold air will then drop giving a double whammy of cold. Helium manages to get into everywhere allowing you to smother a fire from underneath and in between floors. Pump it into an elevator shaft to save the internal structure of a building.
sartep, Jul 03 2005

Some interesting comparisons of different systems that are commercially available http://www.pyrogen....ads/Pyroleaflet.pdf
[Ling, Jul 04 2005]

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       //Liquid helium will rise// It will? You mean capillary-wise through the pores in the concrete? I don't get it.

Plus, I suspect that rapidly chilling a large structure by about 300 degrees will cause some problems of its own. Steel will contract differently from concrete, which will contract differently from glass, which will contract differently from office workers, etc etc.
Basepair, Jul 03 2005

       Liquid helium will change form rather quickly at STP and yes will rise.   

       Doing anything to excess will have its problems. Is it possible you could give me a bit more credit here?
sartep, Jul 03 2005

       //Liquid helium will change form rather quickly at STP and yes will rise.// OK, so what you mean is that you pump liquid helium in, and it will then vapourize and rise. Fair enough. However, what will happen is this. The liquid helium will form a pool in the basement, where it will cool whatever it is in contact with. It will boil, absorbing a large amount of heat from its immediate surroundings (and, if present in sufficient amounts, cracking the concrete it's in contact with) and producing helium gas at a very low temperature. This gas will indeed rise up the building. However, the heat capacity of helium gas (or indeed any gas) is so ludicrously low that the rising gas will have very little cooling capacity, even though it is initially very cold. So, the "cold" aspect of the liquid helium is effectively irrelevant.

However, you do have the asphyxiant properties of the helium gas, which might well extingquish fires simply by displacing the oxygen, so it's not a completely wrong idea.
Liquid helium costs something like $1-2 per litre, by the way. So, credit as an interesting halfbaked idea, but not as a practical solution.
Basepair, Jul 03 2005

       What is the speed of rising helium, is it slower than a helium balloon? As for price it costs less than many of the non water fire supression systems. Earlier you said that it did have the capability to cool by a great degree and now you negate that? What if this were high pressure low temperature gas helium?   

       From your first argument one could argue against the usage of water under pressure, for property damage and damage to humans inside.   

       Impressive how one couldn't find a way that could make it work in ones mind but instead had to destruct it and stack it into ways it wouldn't work first.
sartep, Jul 03 2005

       Hmmm. OK, a quick back-of-envelope calculation suggests that you need only a few tens of thousands of dollars' worth of helium to displace all the air in a smallish building. So, cost-wise, it's on the edge. However, I suspect that the helium gas would vent through the roof and, once gone, would simply pull a very strong current of rising air up behind it, reigniting the fire in the still- hot building. So, not completely whacko, but I'd sooner you try it on your building first :-)
Basepair, Jul 03 2005

       Nitrogen would be much cheaper. I do not know if the point where air + more N2 disallows fire is still within people's ability to remain conscious though (and not asphyxiate).
Zimmy, Jul 03 2005

       Getting there, thank you Basepair.   

       Do you find it interesting that as you are doing out more calculations, the idea becomes less whacko? My idea, didn't change.   

       But remember it would be bringing cold air back with it from behind.   

       Zimmy, agreed that it would be cheaper but with helium, it would be there and gone much faster causing fewer asphyxiating qualities.
sartep, Jul 03 2005

       + I can't think why this should not be tested.
Zimmy, Jul 04 2005

       {Ling}, most impressive. I was looking up quite a few fire suppressants and never saw anything like that.
Zimmy, Jul 04 2005

       A pool of liquid nitrogen on the roof would be cheaper, faster and automatic. When the fire occurs below, the nitrogen could be released and would flow downwards, cooling all before it, turning into gas en route until it hit the fire. It would then rapidly expand into gas, choking the fire. If the fire were really bad and compromised the structural integrity of the nitrogen pool on the roof or the roof itself,the nitrogen would work the same way - the pool would go and the nitrogen would dump down into the fire.
bungston, Jul 04 2005

       I thought nitrogen was still barely lighter than air. I guess i was mistaken?
Zimmy, Jul 04 2005

       It's a very good conductor of heat, if that helps.
Ling, Jul 04 2005

       //What is the speed of rising helium, is it slower than a helium balloon? //
Free helium gas should rise faster than a balloon, though it will mix with air and hence become less bouyant, I imagine.

// Earlier you said that it did have the capability to cool by a great degree and now you negate that? //
It is very simple: liquid helium will have a large cooling effect, since the latent heat of vapourization is high (it absorbs a lot of energy in order to boil and form helium gas). The gas itself has negligible cooling effect: it takes very little energy to warm up helium gas from -269°C (the b.p. of liquid helium) to, say, +300°C. So, there is no inconsistency here: we are talking about the difference between a liquid and gas.

//What if this were high pressure low temperature gas helium?//If you try to fill a building with compressed helium, the building will simply go pop. And the helium gas *will* be at low temperature (initially -269°C) if it comes from the boiling of liquid helium, but this won't really make much difference, for the reasons noted above.

The reason I was so negative to your initial posting is that you had several wrong assumptions, including the statement that liquid helium would rise and that the coldness of the gas it produces would be helpful (it won't be). The idea of using helium gas (whether produced by pumping in a liquid or pumping in a gas - no matter) as a rising fire asphyxiant is OK, though I still think it will rise too fast and leak out of the top of the building, and simply drive a blast of air both before and behind it.
Basepair, Jul 04 2005

       [Basepair] from what I've read today, temp seems to play a factor in combustability- I wonder if [sartep] can make a case for extinguishment prior to asphyxiation. (Your point of replacement volume of gases seem quite valid. (using liquid He in my opinion would break each an every window though).
Zimmy, Jul 04 2005

       I'm sure that temperature plays some part in combustibility (if nothing else, cooling a hot object will reduce the production of combustible gases from plastics etc). But my argument is that using a very cold *gas* is not an efficient way to cool a building quickly. I can comfortably hold my hand in the vapour sitting above liquid nitrogen in a large Dewar (-196°C) more or less indefinitely. It's not the temperature, it's the heat capacity.
Basepair, Jul 04 2005

       Yes, but if you were to hold the cold nitrogen and close your hand, you would tell a different story about cooling.
sartep, Jul 04 2005

       //Yes, but if you were to hold the cold nitrogen and close your hand, you would tell a different story about cooling.//
Exactly! That is my damned point! Liquid nitrogen will freeze your hand quickly because of its high latent heat of vapourization, nitrogen vapour at the same temperature will not, because of its low specific heat. The same goes for helium.

So, in your scheme, you are relying on the cold helium *gas* rising up the building, and my point is that it won't cool anything worth a damn. Fill the building with *liquid* helium and of course it will be cooled very quickly, but that's not really an option. Filling an entire modest building with *liquid* helium would require something like 10 million litres (for a 30 x 30 x 10 metre building) of the stuff, which is going to cost you something like $10million.

Stick to the asphyxiant effect of helium - it's more plausible.
Basepair, Jul 04 2005

       As the article states, I said pump it into an elevator shaft. Or pump it into the floor just below the fire. This depends on the size of your building. If you have control of the building you could open the elevator doors to the floor below the fire. Once again, there are ways that this can or may work more efficiently but you feel that you must stack a situation in such a way that it can only fail. You have again twisted it to say I am filling up the whole building.
sartep, Jul 04 2005

       I'm thinking forget fires and think air-con.
wagster, Jul 04 2005

       //I'm thinking forget fires and think air-con// I read that as "fire-and-forget air-con" and thought this was some weapon of mass ventilation.
AbsintheWithoutLeave, Jul 04 2005

       [Sartep] Take it easy. Half the point of the HB is to examine ideas and find flaws, and hence find the way forward. If we all just say "great idea" with no critique, then what is the reason for posting here?

All I am saying is that if your scheme relies on cold helium gas (coming from liquid helium in the elevator shaft if you like) rising up the building, then there will be asphyxiant effect on the fire (great while it lasts) but no worthwhile cooling effect (which was the main thrust of your original post). Cool down.
Basepair, Jul 04 2005

       It is kind of a cool idea.
Zimmy, Jul 04 2005

       Again, you are trying to say I am angry for some benefit of your own. I see, I lost some sort of sapient social game, now you can tell me that I am angry in a check mate fashion. Extra credit using the idea (cool down) to express that.   

       I see you are doing a service but twisting what others say is wrong, it creates a devide between you and another one.   

       My end statement is that the elements are there to do the desired effect, and the logic you used in 2 places was the same logic that wouldn't allow water to be used either. Often times I try to be efficient, instead of posting 2 ideas, I will post one idea that does two desired effects.
sartep, Jul 04 2005

       Okey dokey :-)
Basepair, Jul 04 2005

       He would only displace oxygen, and probably diffuse away before cooling the fire. Bromine containing compounds work better, because they are free radical poisons, chemically interfering with the combustion process, and are heavier than air, so pool around the fire. Think Halons. Unfortunately, they are also greenhouse gases.

The cooling aspect of He would probably be less than water, since the latent heat of evaporation of He is so low, and it would boil away before getting to the fire, so would not cool the fire directly
ldischler, Jul 04 2005

       Agreed, will not work as well as halons. Further, you want to smother the fire at its base, not on top, so you ideally want a heavier gas to begin with. Try spraying with liquid nitrogen or ground dry ice.
DrCurry, Jul 04 2005

       Liquid N2 has been used to snuff oil well fires.
ldischler, Jul 04 2005

       ...and everyone would speak with silly voices...   

       definate plus
DenholmRicshaw, Jul 04 2005


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