Wikipedia:Reference desk/Archives/Miscellaneous/2017 December 16

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December 16

Riding out −150°F

In The Day After Tomorrow, the temperature in Brooklyn fall to −150°F and people ran into the building for dear life and the interior of the building was freezing up and walls and windows and things getting covered in ice. If the temperature fell to −150°F outside for say one day, what would you do indoors in order to survive? Would the interior (like in a home) actually gets covered in ice as seen in The Day After Tomorrow even with all the outside doors and windows closed tightly as it would be so cold? PlanetStar 04:48, 16 December 2017 (UTC)

N.B. −150°F equals -101° Celsius for the rest of us. Alansplodge (talk) 15:45, 17 December 2017 (UTC)

In Minnesota, there's a saying: "At 40 below they're the same!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:20, 17 December 2017 (UTC)

I once had a temp assignment with a wholesaler of camping gear. A sales rep said, "A customer is on the line saying, 'My new sleeping bag is marked –40°F and –40°C, which is it?!'" My presence was lucky. —Tamfang (talk) 19:57, 17 December 2017 (UTC)

There is no where on Earth where it gets that cold, even briefly, so we have no recorded information on what happens at that temperature inside a building. McMurdo Station is about the coldest environment for a building to be in, and the coldest it's ever been is about 100 degrees warmer than that.--Jayron32 04:52, 16 December 2017 (UTC)

Not quite correct. Vostok Station has reached −128.6 °F (or possibly -132°F). And a coldest wind chill of −124 °C (−191 °F). Note that dry ice will form from the atmosphere below -109°F. Rmhermen (talk) 16:07, 16 December 2017 (UTC)

I'm sure it could be simulated pretty accurately, though, if anyone wanted to put in the effort. The Day After Tomorrow didn't strike me as a film where they would have bothered to do that. --Trovatore (talk) 09:31, 16 December 2017 (UTC)

See wind chill. 86.169.56.46 (talk) 12:09, 16 December 2017 (UTC)

I know it doesn't happen on Earth, but talking about the imagination. If the temperature drops to -150 outside, the interior of a building, especially a room with windows, would become so cold that a glass of water would freeze as heater couldn't keep up. To maximize the chance of survival inside the home, in my opinion, take cover in a small interior room with no windows, such as a closet or a bathroom with a vent in them, and get huddled in blankets. Anybody agree? PlanetStar 20:46, 16 December 2017 (UTC)

That's a forum-type question. Or maybe you could google the subject and see if experiments have been done somewhere. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:18, 17 December 2017 (UTC)

Don't need experiments. The basic principles are well understood, and we could give defensible answers to this if anyone wanted to put in the work. I don't, so I'll describe the character of the problem instead.

Basically heat transfer is described by the heat equation, and all you need to do is solve it, for the particular space you have in mind. That can get a bit hairy, and some qualitatively unexpected things can happen, but there are lots of expensive software packages that can help you out. Try Googling "thermal simulation software" if you're interested to see some of them.

I don't know whether they would help you out with things like possible chemical changes in the walls when the temperature drops. I can't think of any such changes offhand; just pointing out possible gotchas that would have to be addressed if you're interested in a truly reliable solution.

You could get a quick-and-dirty answer, that would probably still be pretty good, by just considering the R-values of the building. Figure out what temperature you want it to be inside, and subtract the temperature outside. That's the temperature difference. Divide the temperature difference by the R-value and multiply by the area of the walls (different spots on the walls may correspond to different R-values, so break them up into chunks). That's the heat you need to supply per unit time.

Add the heat per unit time to heat up incoming air, and that's what you need. Do your heaters plus bodies supply that? If so, you're good. --Trovatore (talk) 09:14, 17 December 2017 (UTC)

Yep. If the space is reasonably well-sealed (not airtight, just not badly leaky) that R-value calculation is effectively just the same assumptions underlying Newton's Law of Cooling. What that means is – to a first approximation – the rate of heat loss is proportional to the temperature difference between the building and the outside. Twice the temperature difference means twice the heating required to maintain the temperature. Suppose you're someplace chilly and the outdoor temperature is -40°F, and the heater inside keeps the temperatures at a comfortable +70°F. That's a difference of 110°F. If the outdoor temperature drops to -150°F, that's another 110-degree drop, so you'll need roughly twice the heating capacity. Depending on the building, there may actually be sufficient heating capacity already installed—the furnace will just have to run more often. Or plug in a portable electric heater to take the edge off in one (preferably interior) room. If it's a temporary dip in temperature, there's also the thermal reservoir of the ground and foundation—not all sides of the hypothetical building are going to be exposed to the full depth of chill. (Things get tricky if your fuel oil tank is outside and frozen solid, or the electricity and natural gas supply shut down....)

Incidentally, in reference to Rmhermen's comment about dry ice above, there's no risk that atmospheric carbon dioxide would freeze out at these temperatures. The vapor pressure of carbon dioxide is provided on our data page. At -100°C (about -150°F) the vapor pressure is roughly 100 mmHg, which is way above the partial pressure of CO2 in our atmosphere. TenOfAllTrades(talk) 14:02, 17 December 2017 (UTC)

Conversely, for those of us in Britain, 38°C is 101°F. 176.26.66.173 (talk) 19:15, 17 December 2017 (UTC)

Fritz Leiber's story A Pail of Air describes low tech survival in an even colder environment, although it is, of course, fiction. CodeTalker (talk) 03:48, 18 December 2017 (UTC)

Let's throw some quick and dirty maths at this. Looking at the readout from my fancy thermostat, with the heating off last night my house fell from about 20C to about 18C over 6 hours, with an external temperature around 0C. So for a 20 degree difference, we lose about one third of a degree of temperature in an hour. As noted above, the rate of heat loss is proportional to the temperature difference, so if the external temperature was -100C, we would expect about 6 times the heat loss - i.e. the temperature will fall about 6 times as fast, so about 2 degrees an hour. Meaning that even without the heating on, the temperature inside is falling to only about -52C. Now, when the heating comes back on in the morning at full blast, it rises those same 2 degrees in about 2 hours - i.e. about 1 degree an hour, or a net 1 1/3 degrees an hour (since it'll still be losing about 2/3 of a degree per hour to the outside). With an external temperature of -100C, the house will lose a net 2/3 of a degree per hour (the boiler is still pumping out enough heat for 1 1/3 degree an hour, but the house is losing enough heat for 2 degrees an hour), which will take the temperature to about 4C after 24h.

Of course, there are a ton of simplifications there (the house has essentially been treated as a solid lump of a single material, that large a temperature difference will probably do some nasty things to the insulation - e.g. breaking windows due to thermal gradients, and the external water pipes freezing would cut off the heating), but in principle a kinda-OKish-insulated terraced house in southern England could stand up to the cold while keeping the inside at temperatures which would be survivable in sufficient clothing. MChesterMC (talk) 11:04, 18 December 2017 (UTC)

Those who know that 10° C equals 50° F will easily remember this simple conversion formula:

Fahrenheit to Centigrade:

Add 40, multiply by 5, divide by 9, subtract 40

Centigrade to Fahrenheit:

Add 40, multiply by 9, divide by 5, subtract 40 — Preceding unsigned comment added by 92.5.85.128 (talk) 15:42, 18 December 2017 (UTC)

The above is the typical Belgian conversion. For those of us comfortable with the original American, the formulae are:

Fahrenheit to Celsius:

Subtract 32, divide by 9, multiply by 5

Celsius to Fahrenheit:

Multiply by 9, divide by 5, add 32

Note the horrible .55 imprecision of the Swedish system compared to the Pomeranian. μηδείς (talk) 00:18, 20 December 2017 (UTC)

3d printing living stuff

Has anyone ever 3d printed living algae? And mycelium? Other stuff that is alive? I know that people 3d print dead algae as a bioplastic. (((The Quixotic Potato))) (talk) 17:14, 16 December 2017 (UTC)

I don't think so. The dividing line between living and non-living is still something of a mystery. The best 3D printers have a resolution of about 16 microns which is probably insufficient to reproduce a living cell, even if the correct combination materials were used, but 3D printing using living cells has recently become possible. See 3D bioprinting. Dbfirs 18:30, 16 December 2017 (UTC)

Organ printing printing may interest you. It's not assembling a living thing from non-living molecules, but it's using living cells to build a structure out of living cells.

And here's an art project where someone rigged a 3d printer to print with living algae, and a medium for it to grow in. (Again, living cells were used as source material. It didn't actually build the algae cells.) 100.0.181.245 (talk) 04:49, 17 December 2017 (UTC)

Thanks Dbfirs and 100.0.181.245! I was thinking about doing something similar to that art project. Creating life Frankenstein-style and printing something that is already alive are both really interesting topics to me. (((The Quixotic Potato))) (talk) 09:50, 22 December 2017 (UTC)

Living organisms can be considered to be 3D printers that are constantly at work to make the parts they themselves consist of. Count Iblis (talk) 16:25, 22 December 2017 (UTC)