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In my world some people can control wind, including its temperature.

  • Would it be possible to freeze stuff solid immediately (I’m most interested in freezing people, but animals and inanimate objects also count) or at least very quickly (few seconds)?

  • If it’s possible, how cold would the air need to be?

  • Is it possible with today’s Earth technology? If yes, how about the energy expenditure of it?

  • Would the person being completely wet make it easier (or possible if it’s currently impossible)?

Why and how the people controls the wind is irrelevant. I searched the QA for an answer to this but could not find it. Feel free to mark as duplicate. Thank you!

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    $\begingroup$ Relevant but not an answer $\endgroup$ – Joe Bloggs Feb 9 '17 at 19:08
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    $\begingroup$ You can kill someone in seconds from exposure to very low temperatures. Do you mean that or do you mean actually turn the entire body to a solid ( i.e. freeze blood and other fluids throughout the body ) ? $\endgroup$ – StephenG Feb 9 '17 at 19:15
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    $\begingroup$ things yes, look up advection frost, people not unless the air is already unearthly cold. $\endgroup$ – John Feb 9 '17 at 19:17
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    $\begingroup$ @SRM I disagree. Overlap between sites is not necessarily a bad thing, and Worldbuilding is already a heavy mix of arts, sciences, and other ideas that each have their own sites. Physics may be able to answer the question more thoroughly or professionally but that doesn't mean it doesn't work in the context of building a fictional world. $\endgroup$ – Zxyrra Feb 9 '17 at 21:28
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    $\begingroup$ Worldbuilding biology is not the same as biology. $\endgroup$ – SRM Feb 10 '17 at 3:16
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It's not possible to quickly freeze thick things in seconds, due to thermodynamics.

Let's take an extreme example of a wind that is at -200 degrees C (close enough to absolute zero, but easy to use numbers) trying to cool down something that is at 23 C (room temperature), to 0 C (freezing). Let's assume the thing is mostly water (such as a human), with a heat capacity of roughly 4kJ/kg-C. Air has a heat capacity of roughly 1kJ/kg-C. This means that if you put 1kg of material in a room with 4kg of air (roughly 4 cubic meters of air), this ultra-cold air and this room temperature body will equalize at roughly freezing. A 100kg human would need 46 cubic meters of such air (roughly the size of a 20ft. cargo shipping container!). Now mind you, this air is colder than anything natural on Earth. The coldest temperature recorded is merely -89C. At that temperature, you'd need roughly twice as much cold air.

That's a large volume of air engaging in a perfect heat transfer, in terribly idealized conditions. In practice, you're going to have to do a lot more than that. The big limitation is insulation. As you freeze the outer surfaces of the object, that layer starts acting like a layer of insulation, slowing down the heat transfer. This is the reverse of the process which explains why you can't thaw a frozen steak simply by throwing it in hot water for a few seconds. It takes quite a long time for the inner center of the object to change temperature, and moving more wind past the outside of the object isn't going to help that much.

Adding water won't help much either. There will be some evaporative cooling, but the colder the wind is, the less that will matter. In fact, if they were wet, that would permit forming a layer of ice outside of their skin, making it even harder to freeze them to the core!

How would I freeze something quickly, if I had to? I'd break them into little bits! It could be a messy process, but it would ensure everything freezes fast enough. This was demonstrated in Norway a few years back, although for some reason they chose to atomize a cup of boiling water rather than a human being... can't imagine why!

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    $\begingroup$ You might want to point out that -200°C (73 K) is in the range where both oxygen and nitrogen are liquids rather than gases (oxygen's melting point is about 54 K, boiling point about 90 K; for nitrogen, melting point is about 63 K and boiling point about 77 K). So at -200°C, you wouldn't really have air; you'd have a fluid, likely a slush, consisting of nitrogen, oxygen and some contaminants that I didn't bother to look up whether they'd be gaseous or liquid, or even frozen. $\endgroup$ – a CVn Feb 9 '17 at 21:15
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    $\begingroup$ I have a question about the quantity of -200 degrees C air vs. the volume of a person, figuring in their heat capacity. It sounds as though you're saying that the air and the person would reach an temperature equilibrium somewhere between their starting temperatures. But in the OP's magic question, the air would be able to stay at -200 degrees C, as though being actively refrigerated. Does that change the answer? (Your point about insulation is still compelling.) $\endgroup$ – BrettFromLA Feb 9 '17 at 21:53
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    $\begingroup$ @BrettFromLA That would definitely affect the quantity of air required. You would be able to freeze something with a thimble full of air if you just kept it at -200C for a sufficiently long period of time (in theory). However, it wont affect the issues that arise from the insulating effects of the body. $\endgroup$ – Cort Ammon Feb 9 '17 at 21:56
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    $\begingroup$ @msb No, because the time it takes to freeze a body is dependent on too many factors which are not under the control of the caster. For example, if the body being frozen is that of a polar bear it may take a tremendously long amount of time due to its large mass and fur that has evolved specifically to prevent freezing winds from affecting the bear. Regardless however, any reasonable animal will absolutely take more than seconds to freeze, no matter how cold the wind is. Even freezing a Chihuahua this way would take longer than a few seconds. $\endgroup$ – Cort Ammon Feb 9 '17 at 23:10
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    $\begingroup$ @Catgut I'm amazed I got this many upvotes with such a blatant math error! I'll have to edit that correction in! As for the phase change, you're right that I could pull off a cop-out and claim that I was accounting for the phase change, but that'd be cheating. I was trying to generalize to any object, not just objects with water in them! $\endgroup$ – Cort Ammon Feb 10 '17 at 16:10
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Heat transfer coefficient of dry air with forced convection is up to 1kW per square meter per 1K temperature difference. Let's assume two square meters and 100kg human. Reasonable for a warrior and easy to calculate. Lowest natural temperature recorded on Earth was −89.2 °C. Let's be generous and assume 200K difference.*

Seems that best you can do is 400kW in perfect conditions. Perfect as in strong, really cold wind,virtually unlimited amount of air, and nude victim. But you need 3.5kJ to change temperature of 1kg of human flesh by 1 K. So for our example subject it takes 350kJ per 1K. With your wind, you would change his temperature by a bit over one degree during one second. Not instantly, by no means.

Truth to be told, it would be even worse. First, skin would cool down first, decreasing difference, and thus cooling speed, rapidly. Victim would curl, halving exposed area. Things like that.

You could hurt them. But it would take a while. Not even close to instant freeze.


References:


* I know that 200K difference is a lot. Indeed, it would put air near or over the gas / solid border on the phase diagram. On the other hand, we are talking about moving air and that changes quite a lot, and I'm overestimating to point out how impossible it is, even if conditions are more favorable than what's actually feasible.

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    $\begingroup$ I think this answer better than the more voted one. People always just go right to "the heat capacity of air" when the important factor is realizable convection coefficients. $\endgroup$ – JMac Feb 10 '17 at 12:17
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The lowest natural temperature:

The lowest natural temperature ever directly recorded at ground level on Earth is −89.2 °C (−128.6 °F; 184.0 K), which was at the Soviet Vostok Station in Antarctica, on July 21, 1983.

Lower temperatures have been recording using laboratory equipment. To separate the gases in the air, it is cooled until in a fully liquid state, and then as it warms each gas will evaporate at it's boiling temperature. The method of fractional distillation of air is described here:

Air is filtered to remove dust, and then cooled in stages until it reaches –200°C. At this temperature it is a liquid. We say that the air has been liquefied.

Here's what happens as the air liquefies:

-water vapour condenses, and is removed using absorbent filters

-carbon dioxide freezes at –79ºC, and is removed

-oxygen liquefies at –183ºC

-nitrogen liquefies at –196ºC

-The liquid nitrogen and oxygen are then separated by fractional distillation.

Since air is 78% nitrogen, let's assume that below -196 degrees the air is mostly water and no longer a gas. Now, the effects of a temperature of -196 degrees on a human being's exterior:

Sudden changes of temperature can have health problems even in everyday scenarios:

"It dries off your skin, the mucus membrane and the eyes. We see patients who say they went to the malls or their offices and it was extremely cold. Eye infections, respiratory infections and muscular spasms are caused by this change in temperature,"

Assuming you have unlimited air constantly hitting the skin at -196 degrees (this is not possible with current techology, but maybe within your world it is), it is safe to say that the exterior of the body would cool rapidly. This would cause water in the skin cells to freeze and expand, rupturing the cells. This would kill all cells exposed to the blast. The longer you freeze, the more deeply this will go into the body. There would be no bleeding, since cells would freeze together, however the expanding of the water may be enough to crush parts such as capillaries. If a major vein or artery close to the skin's surface were to block due to freezing, blood flow would be severely restricted, removing most of the oxygen supply to the body; the effects of this are severe. Stopping blood flow will likely result in a heart attack, and if the heart stops altogether, this results in sudden cardiac arrest:

Sudden Cardiac Arrest (SCA): also known as sudden cardiac death, this is when the heart suddenly and unexpectedly stops beating and blood stops flowing to the brain and other vital organs. SCA usually causes death if not treated in minutes.

In short, freezing will leave the victim unable to move or resist, and dying. With most of the external parts destroyed by freezing and a case of sudden cardiac arrest, the victim will die within minutes.

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Many answers address the heat transfer rates of air and of people's bodies. I'd like to point out that people will freeze much more quickly if the magicians can also make the air in their victims' lungs drop to absolute zero, not just the air around their victims.

Freezing flatuses in the intestines would speed things up too, but that would just be gross.

What about freezing the oxygen carried by the hemoglobin in the victims' blood? That would reduce the freezing time significantly! I don't think it's gaseous air at that point, so you'd need to decide whether that would be too much of a stretch to your characters' magical powers -- or whether you'll just save that trick for the final boss-battle of your story!

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To add to the answers above, the problem is that there's a limit to how fast you can get heat out of any object. That rate depends mainly on the thickness and material of the object, the heat capacities of the surrounding air/fluid and the object, the presence of any surface effects hindering heat flow (surface ice, clothing, air layers, fur/hair and ease of heat transfer across the object's boundary..), and the difference in temperature between the object and the air/fluid. The problem is that most living beings we know are thick enough to hinder heat transfer out, air has a limited and smallish heat capacity, and there is a limit to how much colder it can get outside. Basically "no". Not possible.

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  • Yes, it is possible to freeze someone/something solid within 30 seconds or so. I am talking about skinny people and kids here. If you want to freeze an elephant or rhino, it will take many long minutes, no matter how cold you make them. There is a lot of trapped heat inside larger creatures, and the cold penetrates very slowly, slowly freezing from the outside.

  • This depends on the temperature difference between the target object and the environment, but for the sake of generalizing, I would say that the air would need to be so cold that gets to liquid state. That is, at least -212 °C (-464 °F)

  • Yes it is possible with today's technology. Just spill a couple of drums of liquid nitrogen at someone and watch the fun! I cannot tell you about the energy expenditure right now, but you should be easily able to calculate that.

  • No. If the person is wet, it will make it harder to freeze them. Now you have water to freeze, before beginning to freeze the person. And water takes a LOT of heat (and cold/removal of heat) to change temperature.

All in all, if the person controlling the temperature is very very efficient at his skill, I would suggest freezing 2-3 drums volume of air to liquid and spilling it on the target one drum after another, slowly, without any haste.

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    $\begingroup$ Liquid air (or nitrogen) is much, much denser than the atmosphere. We need not only to cool the air but somehow concentrate the resulting liquid. If we make a very cold air to blowing very, very fast, liquefied droplets would just shred the target apart rather than get it frozen. $\endgroup$ – Alexander Feb 9 '17 at 21:12
  • $\begingroup$ Your first point contradicts other answers. Do you have a reference or calculation? $\endgroup$ – JDługosz Feb 10 '17 at 9:41
  • $\begingroup$ @Alexander: yes of course that is correct. I never mentioned shooting the target with a hail of frozen air. I mentioned spilling drums of liquefied air upon them. $\endgroup$ – Youstay Igo Feb 10 '17 at 21:05
  • $\begingroup$ @JDługosz: I can include calculations to support my idea, but for the sake of brevity, lets say that the target would freeze solid at least from the exterior, within 30 seconds or so. While the interior will take longer than that, the target will still be frozen solid for the general use of the phrase. $\endgroup$ – Youstay Igo Feb 11 '17 at 14:46
  • $\begingroup$ The general meaning of frozen solid means all the way through, not unfrozen in tge center. $\endgroup$ – JDługosz Feb 11 '17 at 21:43
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I've seen a documentary where the naturalist was in Russia, at -40C°, he had a thermos with some boiling water inside, he just throwed the water outside and most of it just frozen instantly.

Due to thermodynamics if an object is small enough and is exposed to enough cold it will freeze instantly. Maybe bigger objects may take much more.

For instance the Earth is continuosly blowed by froozing winds but its internal core will require milions of years to cool down.

There is a limit to Cold, the temperature cannot drop below 0 Kelvin so you actually have a bound to cooling speed.

Also note that you also have a limit to temperature of your wind, because under a certain temperature air liquify.

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  • $\begingroup$ Name of documentary? $\endgroup$ – Wildcard Feb 11 '17 at 1:49
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    $\begingroup$ "the temperature cannot drop below 0 Kelvin" There's a funny concept in physics called negative temperature. I don't claim to understand it myself. $\endgroup$ – a CVn Feb 11 '17 at 20:40
  • $\begingroup$ Well I don't think we are actually in quantum mechanics, but nice to know! :) $\endgroup$ – GameDeveloper Feb 13 '17 at 8:55
  • $\begingroup$ @Wildcard It was a documentary by Alberto Angela, I don't remember the exact name. $\endgroup$ – GameDeveloper Feb 13 '17 at 8:57
  • $\begingroup$ @MichaelKjörling, interesting but hardly authoritative. I would say that the "in physics" should be qualified as speculative or theoretical physics. The whole page is mathematical and abstract in nature. $\endgroup$ – Wildcard Feb 13 '17 at 10:02
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I'm curious what the purpose of a solid freeze would actually be. If you want sudden lethality, there are better ways to use the cold. If your guy can control only air, or gasses and only from the outside the body or object, focus on freezing the openings for air into the body (mouth and nose) or directly blowing super cooled air into the lungs to stop the gas exchange. Of course if you have that level of control, high pressure air into the lungs in order to rupture them would be equally lethal, if not gruesome.

Frozen water spears, ala Avatar: The Last Airbender, are also something for flash-freeze killing.

Control of air can also be used to blow a hapless victim into a wall with enough force for a satisfying splat. Certainly enough to make a point to reluctant minions or cocksure heroes.

Air as the mechanism of freezing is kind of inefficient. Now a mage who could control the amount of energy inherent in a given amount of volume at a molecular vibration level, that might be interesting as well. Make all molecules in a given area vibrate at exactly the same, slow rate. There is your magical instant deep freeze.

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    $\begingroup$ nah actually it's the common fantasy "stun by freezing" where the caster could either kill the victim by shattering the ice or wait for it to thaw harmlessly. As the other guys stated that's not how it works (sadly for me). ): $\endgroup$ – rschpdr Feb 10 '17 at 18:49

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