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I was thinking about creating an ice dragon for my world, but I didn't want the dragon to be magical or technological but biologically correct, so I went looking for cryogenic substances and found some very interesting ones, they are liquid hydrogen, liquid nitrogen and liquid oxygen.

Hydrogen struck me as a good candidate, -253º C temperature, it's not toxic... But it's flammable, the dragon will be used as a war beast by a rider, so if an ally is too close to fire and that dragon attacks an enemy equally close, the ally may be injured or die as the fire will expand.

Liquid nitrogen also seems like a good candidate, it's not flammable, it's not toxic, it has a temperature of -196º C, it has an abundance in the atmosphere...

I also thought about liquid oxygen, it's also not toxic, it's also not flammable, it's also abundant in the atmosphere, it has a temperature of -183º C... However, despite not being flammable, it encourages burning.

So I chose liquid nitrogen. The dragon will have a cryogenics system. The stages of this system are: third nostril, with it the dragon can take part of the air to start the nitrogen production process; liquefaction chamber, this is where the process of liquefying nitrogen will begin, I still don't know how this will be done, I need to research more about how it's done to try to find a more biological alternative; collecting water, the dragon can open a second "throat" (I don't know what the correct term would be) which it will use to drink water and store it; release, the dragon has two tubes in its mouth, one on each side, one releases liquid nitrogen and the other releases water, this will freeze the water that can be used for attack and defense, the dragon can choose which of the two substances to release and also the amount, for example releasing much more water than nitrogen. I also don't have a way to make the dragon not freeze with something at -196°C inside it.

Well, having said that I would like to ask: what do I need to change in my dragon for this to be plausible? There is no need to use hypotheses involving theory of evolution, that would limit the creature's plausibility too much(more than it already limits). If you want, you can use hypotheses involving the theory of creation or genetic mutations alà InGen. What's important is that the dragon's cryonics system doesn't rely on magic or technology.

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  • $\begingroup$ What's a biologically correct dragon? (We'd need to know to say how it would need to be changed). $\endgroup$ Commented Nov 20, 2021 at 8:08
  • $\begingroup$ A dragon that doesn't depend on magic or technology. $\endgroup$ Commented Nov 20, 2021 at 8:11
  • $\begingroup$ Then to the question "what do I need to change in my dragon" the answer is going to be "use magic or technology". $\endgroup$ Commented Nov 20, 2021 at 8:23
  • $\begingroup$ If I wanted my dragon to use magic or thecnology, I just didn't do the research and post the question. $\endgroup$ Commented Nov 20, 2021 at 8:40
  • $\begingroup$ That's why the question is tagged "science-based". $\endgroup$ Commented Nov 20, 2021 at 8:44

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Liquefying air is a complex process, it's not enough to simply cool it down.

The liquefaction of gases is a complicated process that uses various compressions and expansions to achieve high pressures and very low temperatures, using, for example, turboexpanders.

Industrially it is done with two different processes

Linde's process: Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid.

Claude's process: Air can also be liquefied by Claude's process in which the gas is allowed to expand isoentropically twice in two chambers. While expanding, the gas has to do work as it is led through an expansion turbine. The gas is not yet liquid, since that would destroy the turbine. Commercial air liquefication plants bypass this problem by expanding the air at supercritical pressures. Final liquefaction takes place by isoenthalpic expansion in a thermal expansion valve.

If you want your dragon to liquefy nitrogen from air, it needs to be somehow able to follow one of those two processes to first liquefy air and then extract the fraction you are interested in.

The following are the steps of the Linde's process:

The cooling cycle proceeds in several steps:

  1. The gas is compressed, which adds external energy into the gas, to give it what is needed for running through the cycle. Linde's US patent gives an example with the low side pressure of 25 standard atmospheres (370 psi; 25 bar) and high side pressure of 75 standard atmospheres (1,100 psi; 76 bar).
  2. The high pressure gas is then cooled by immersing the gas in a cooler environment; the gas loses some of its energy (heat). Linde's patent example gives an example of brine at 10°C.
  3. The high pressure gas is further cooled with a countercurrent heat exchanger; the cooler gas leaving the last stage cools the gas going to the last stage.
  4. The gas is further cooled by passing the gas through a Joule–Thomson orifice (expansion valve); the gas is now at the lower pressure. The low pressure gas is now at its coolest in the current cycle. Some of the gas condenses and becomes output product.
  5. The low pressure gas is directed back to the countercurrent heat exchanger to cool the warmer, incoming, high-pressure gas.
  6. After leaving the countercurrent heat exchanger, the gas is warmer than it was at its coldest, but cooler than it started out at step 1.
  7. The gas is sent back to the compressor, mixed with warm incoming makeup gas (to replace condensed product), and returned to the compressor to make another trip through the cycle (and become still colder).

In each cycle the net cooling is more than the heat added at the beginning of the cycle. As the gas passes more cycles and becomes cooler, reaching lower temperatures at the expansion valve becomes more difficult.

Hint: it's probably too complex to be worthwhile having it happen in a living organism.

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  • $\begingroup$ Linde's process seems easier compared to Claude's. $\endgroup$ Commented Nov 20, 2021 at 8:46
  • $\begingroup$ I just need to figure out how a living organism could cool something down to minus degrees. $\endgroup$ Commented Nov 20, 2021 at 8:51
  • $\begingroup$ @WizardKing, you should make up your mind: liquefying a gas and going to negative temperature are two deeply different things. Your question above is about the first. $\endgroup$
    – L.Dutch
    Commented Nov 20, 2021 at 8:56
  • $\begingroup$ I know, I just wanted to emphasize that. $\endgroup$ Commented Nov 20, 2021 at 8:59
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Thermoacoustic refrigeration

The dragon uses ultrasound to do its cooling. That means ordinary vocal cords can be used, to interact with a special chamber, which uses the sound waves like a compressor. See LANL's animation and textbook. I found a link to a home demonstration a grade school student could do the last time I had an ice dragon breath question, but I'm not sure where that went. Probably just as well - it sounded like a loud experiment, which is OK for an ice dragon, but perhaps not so fine for the upstairs bedroom.

Of course, you still have to evolve some implausible things like a biological Dewar, or at least, something ridiculously insulating. The evolution of this thing makes basically no sense (so say it was driven by sexual selection).

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  • $\begingroup$ There is no need to use hypotheses involving the theory of evolution, if you want you can use the theory of creation or some theory involving genetic mutation. $\endgroup$ Commented Nov 21, 2021 at 0:33
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Body temperature 150K ?

I wonder how any beast would produce the temperature gradients and pressures needed for known air liquifying processes described in L.Dutch answer.. what if the dragon would - for some reason, handwaived - be very cold inside ? say around 150K and very well isolated. Your dragon would inhale the air, which would condensate immediately, ready to spit out again as fluid.

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  • $\begingroup$ And can a beast live with such a body temperature? Remember that the bottom line is not using magic or technology, so you need to give an explanation for that as well. $\endgroup$ Commented Nov 20, 2021 at 13:50
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    $\begingroup$ @WizardKing simple life apparently can't properly exist below - 20 degrees Celsius, multicellular life struggles greatly to live in temperatures below - 70 degrees Celsius. 150K is the same as - 123 degrees Celsius or about -188F. It's colder than the coldest natural place on earth and lower than the lowest temperature naturally possible on the planet as far as we're aware. Chances are that for it to be able to exist at such temperatures without its body completely shutting down it'll need its internal chemistry to be unlike anything on earth, assuming different chemicals could somehow work. $\endgroup$ Commented Nov 20, 2021 at 14:08
  • $\begingroup$ Yeah seems difficult to design a liquid air spewing ice dragon based on scientific reasoning (lol) $\endgroup$
    – Goodies
    Commented Nov 20, 2021 at 15:15

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