So I have been doing some thinking and I now am trying to design some aliens who can exhale very cold gasses or cool the atmosphere around them as a side effect of their metabolism and also survive in an environment around room temperature, so does anyone know what kind of metabolism would do this to either refrigerate air or release cold air, effectively giving a creature limited freezing powers?
What we're looking for is a cold-blooded creature that uses a phase change material (PCM) to line the throat and lungs that absorbs heat with the passage of air.
An example of a phase change material is ice. Ice retains its temperature until it has completely melted. Pick up a partially melted piece of ice and it's the same temperature. Better still, pass warm air over it and you get cold air on the other side until the ice is completely melted.
Now, here's where I'm going to employ some handwaving, because I'm not an organic chemistry major. What we're looking for is the the skin equivalent of ice. Rather than melting, the skin equivalent is passing the thermal energy into the blood stream. Remember, the creature is cold blooded, and this highly evolved process would allow it to withstand cooler temperatures than a normal cold-blooded creature could. Remember, this PCM skin would line the throat and lungs.
And it would have the side effect of exhaling cooler air than it inhaled. How much cooler? That's a function of the efficiency of the system. But, please note the following:
The colder the outdoor temperature the less efficient the conversion. Our new creature may be capable of surviving sub-freezing temperatures, but its movements would be much more sluggish and its exhales only a degree or two colder than the ambient air. There's simply less energy to draw from the air as it gets cooler.
In a similar manner, in very hot temperatures the creature would likely obtain satisfactory heat through body absorption, leading to lower efficiency. Since it doesn't require to extract as much heat from ambient air via the throat and lungs (the blood being already warmed), the exhaled breath would be only be a few degrees cooler than the ambient air.
But, at its most efficient, which I arbitrarily delcare for exemplative purposes to be 70℉, then the efficiency is quite great and the exhaled air could be near or just below freezing.
How much would this really affect surroundings? Not that much unless the creature was gigantic. Think about how much your own breath affects surroundings. Even with the worst breath in the world, your impact is less than a 10' radius and that's only an odor. Your heated breath in cold weather can't be felt (or, if you really exhale, could only barely be felt) by someone standing in front of you, much less someone standing behind you. Our creature would have a very similar effect. It could, perhaps, cool someone's drink or, in hand-to-hand combat cause mild frostbite, but that is likely the extent of the effect. There's simply not enough breath involved.
P.S., there is a non-organic way to do this, too
Thermoelectric cooling uses solid state materials to generate electricity from ambient temperature. Basically, it's a thermoelectric heat pump. This is mega cool tech, but because it's non-organic, the materials involved cannot be directly used.
However, it is done in nature with ice and synthetically with thermoelectric coolers. Really, that means you only need a cool name to describe a biological PCM and you have something that meets the standards of suspending disbelief. Cheers.
In his comments, David Culp is essentially correct. Cold is the absence of heat, therefore your aliens could use the ability to generate extremely endothermic reactions as a weapon.
The most common endothermic reaction in nature is photosynthesis. It uses sunlight to convert water and CO2 into O2 and carbohydrates. Water and CO2 are the lower energy chemical configurations, so to use O2 and carbs for energy release, both plants and animals rely on something storing energy in that form, and that is what photosynthesis really is; storing energy captured from sunlight in chemical form.
So; your aliens have an extreme form of that process that allows them to capture massive amounts of heat energy from their environments and convert a large amount of CO2 and water (or other low energy chemicals) into more useful O2 and carbohydrates (or other high energy chemicals).
The limitations to this is that you would need to store water inside you for this process, not to mention find some way of storing CO2 that can't be reabsorbed into your 'bloodstream'. It could probably only be used once every given period (you'd need to replenish the water and CO2 levels) and it also means that your aliens probably only eat for nutrition, not energy. That means in effect that they may absorb proteins and trace minerals from soil, plants or animals to maintain their health, and use this freezing capability to 'feed'.
If your aliens came from a very hot planet (say, 70 degrees C) then this might be a survival response, which would also describe how it evolves.
That would not make them any less dangerous to humans. On the contrary, they could use the freezing (really heat absorption) process to stun or immobilise their animal prey, then absorb their nutrients at their leisure.
There is no eay to do this, unless:
- The creature has been designed by magical means;
- The creature has been developed by a civilization with a technology so advanced that it is practically magical to us;
- DC/Marvel style super powers.
The presence of reality check and science based tags makes this creature somewhat hard to design.
There is no living creature that cools the air (or water) around itself. Not even plants, which depend on photosynthesis - an endothermic process!
Your creature could maybe have ammonium chloride stored in a gland, in the form of microcrystals and protected by fat. It could secrete this substance along with sweat, and the dissolution of the crystals in water would be endothermic - i.e.: it would feel cold. The problem with this approach is that it would take too much mass to make this creature able to work even as a half-broken air conditioner for a very small room. Simply not feasible.
But since you also put in a sci-fi tag... If the creature has some endothermic metabolic processes, and can somehow take energy from our perceived three dimensions to use that energy in body parts that exist in four or more dimensions, then it could do what you want it to do. In Joe Haldeman's Marsbound trilogy, there is a creature that feeds on "energy" from its surroundings. The being, called Spy, describes his metabolism thus:
“I know it takes a lot of energy, or something like energy, to put me here and keep me here. I ‘absorb’ the kinetic energy of bullets and the chemical energy of food and the radiant energy from sunlight, and it all helps keep me here.”
And then later on, when questioned about the effects a special kind of nuke would have on him:
“A constant blast of radiation? I’d love it! A banquet.” He looked up at the sky. “I can feel a little secondary warmth reflected off the atmosphere, from the one you flew over yesterday.”
The book does not elaborate further on this, but such an "energy-eating" being could probably lower the temperature of their surroundings merely by feeding.
Finally, in the indie videogame FTL, there is sentient species that quickly sucks up the oxygen of whichever room they are in, creating vacuums. In a small, sealed room this would lower air pressure, which also reduces temperature.
Would it be helpful if the freezing power weren't constant but on-demand? It could have an organ, which basically works like a freezer: stores super-dense gas and releases it quickly into an appendage, which is then cooled. Although then this freezing power would only work with touch and not in a "freeze ray" type of thing.
The "freezing power" would work like a snake's poison bite: it would have a limited charge, and the alien would need time to rebuild it. Rebuilding it would possibly take a long time or a lot of energy. It would need tissues capable of holding gas at very high pressure, and it would need tissues which resistant to sudden freezing and then thawing up.
A real gas expanding from a higher pressure to a lower one will cool if that gas is below its inversion temperature. The inversion temperatures for N$_2$ and O$_2$ are both above 600 K, so when you expand regular air from a compressed pocket, it is cooled.
For Joule-Thomson expansion, the rate of change of temperature with change in pressure is equal to the Joule-Thomson coefficient. A graph of temperature against pressure, called an inversion curve, can be generated from experimental data. An example for many gasses can be found in a NASA technical note here. From Figure 6a, following the isenthalpic line at enthalpy 400 J/g, we can see that nitrogen gas starting at 40 MPa and 280 K expanded to atmospheric pressure (about 0.1 MPa) will drop in temperature to about 240 K, well below freezing. Lets adjust the slightly, so that starting at body temperature will allow you to blow out a gas at 260 K; or about 8 F.
Lets say you want to blow an entire room full of cold air. A 4m x 4m x 3m room has a volume of 48 m$^3$ (lets just say 50). At a pressure of 40 MPa, your roomful of air will take up 0.125 m$^2$. That is still a lot of space for an alien to store internally, since that is about the volume of a human. But if you were able to store that much gas at that pressure in some internal organ, you could blow a room full of air well below freezing.
A few things to note. Higher pressure will not benefit you since 40 MPa is the maximum inversion pressure for nitrogen. Above this pressure, the expansion of a gas will cause heating, not cooling. Also, if you can get the gas to be colder in the first place, this will help you a lot because for nitrogen the cooling effect is more pronounced at lower temperatures. While starting at 300K you could get 40K of cooling; if you started at 250K you would see more like 60K of cooling.
That is to say, if you use an endothermic process from one of the other answers to drop the temperature of your compressed air organ to 250 K before expelling it, you could then blow out a roomful of air at about 190 K; colder than the coldest temperatures on Earth, cold enough to freeze carbon dioxide. This would be easily cold enough to cause frostbite on exposed fingers and ears in a minute or less.
Let's review a few methods.
We have a lot to work with when it comes to super cold things you can spray at people. You mentioned a gas. Cold air can be harmful, but when it comes to materials they're generally not affected too drastically. At the other end of the spectrum, solids are hard to spray at people and are somewhat unfeasible for a living creature. Liquids are our optimal "projectile", if you will.
METHOD ONE: Decompression (not very feasible but gets really cold)
To get familiar with refrigeration, let's look at.. well.. a refrigerator! How does it work? In layman's terms, it compresses a gas, then decompresses it. This decompression causes the gas to rapidly drop in temperature. The reason this happens is that the gas rapidly expands; this expansion is fast enough that the energy in the gas remains the same, but the volume increases, meaning that the energy per fixed unit of volume goes down overall. See this StackExchange physics answer on the exact mechanics behind this cooling.
With this knowledge we could start building a creature. It would need pipe-like structure for carrying gas/liquid, that is resistant of cold and can hold reasonably high pressure. It could store pre-liquefied gas in a sort of biological "dewar"; unfortunately, I'm not too sure how this may work), and when the time comes, it can spew cryogenic liquid through an orifice lined with material to shield the rest of the organism from the cryogenic material emerging from itself.
Issues with this method are that it's generally quite hard for an organism to store materials that cold or materials at such high pressure. We could try using a high melting point gas, but a Freon-shooting dragon doesn't have the same touch to it.
METHOD TWO: Endothermic reactions (more feasible, not as cold as fast)
In order to understand how this method works we will have to dive deeper into coldness. If something is cold then its energy is low. Endothermic reactions are reactions absorbing energy from the outside. Thus, we can take a material and use an endothermic reaction to absorb the heat energy in it, making that material "cooler". This is how ice packs work.
The creature could secrete chemicals it stores in separate chambers, which it then combines during a time of need to create a cold slush. It then expels this mixture towards its target. This is somewhat reminiscent of a reverse bombardier beetle (which sprays a hot mixture instead of a cold one).
Issues with this method are that it doesn't get nearly as cold as the previous method.