Naively, the colder something is, the faster it could freeze a person. However I’m told that liquid nitrogen for example forms a vapor barrier which actually slows heat transfer. And then there’s the specific heat of the coolant, which can vary a lot. Liquid helium is very cold but has a poor specific heat.
I presume then that the fastest freezing would occur when immersed in the coldest possible liquid that doesn’t boil at body heat. I did some research on this awhile back and came up with N-ethyl-N-methylethanamine, which at standard pressure boils at 60C and requires an astonishing -196C to freeze.
At that point it would be a question of heat conduction through a body: how fast heat could escape the body core; that I haven’t a clue about.
Thats interesting. As for preserving a human body frozen that fast I am not so sure it would not chrystalize the cells. Sushi is flash frozen as a means of sterilization, it supposedly kills everything.
The Leidenfrost effect (in which hot surfaces are insulated from cold liquids by a thin vapor film) only lasts until the very surface of the body cools down to somewhere close to the boiling point of the liquid. After that, you’ve got continuous liquid contact, and you can draw heat out of the body as fast as the body can conduct it to the surface. Which can take a good bit of time; thin sections like fingers, toes and ears would freeze pretty fast, but it will be a while before the trunk and heat freeze solid through.
If you can use the circulatory system to assist in the process, this speeds things up quite a bit:
tap into a major vein in two places a few inches apart.
At the downstream tap, begin pumping in your coolant at a temp just above freezing. This starts the cooling process, but the main purpose at this point is to flush out the blood, which would freeze at too high a temp and block the pipes.
At the upstreap tap, begin pumping out blood. Monitor the concentration of blood and coolant at this location.
When your upstream tap is extracting mostly coolant (and very little blood), the body is mostly devoid of blood and you can begin delivering -196C coolant at the downstream tap.
I’d imagine the fastest way to freeze someone is to place them in an extremely deep vacuum. That way, the freezing time is a function of the vacuum pump’s ability to remove vapor (maintain vacuum), rather than the circulation of a cold liquid within the nooks and crannies of our innards.
Actually, it’s mostly about heating the mass by compression under its own gravity.
For cooling, you would want to do the reverse: start with the body under ginormous pressure at ambient temperature, and rapidly de-pressurize it. This would make it instantly freeze, and also instantly explode into a zillion particles.
My point was that Randal mentions in passing that the vacuum won’t work very well as a heat sink; it’ll take a very long time to eventually cool. Which was the opposite of iceiso’s contention: that vacuums are good heat sinks.
Randall wasn’t exactly on point (for once). But it was too cool (heh!) a story to not share. Sorry to confuse.
Pulling a vacuum would remove energy from the system; as pressure decreases, water will boil off (reducing the temperature of the body) as the water tries to remain at equilibrium between liquid and vapor phases. Pulling vacuum to ~6.1 mbara and establishing equilibrium, the water should be at 32F and liquid. Quickly releasing vacuum and re-establishing atmospheric pressure will cause the water to turn to ice. This wouldn’t rely on conduction or convection, therefore, vacuum being an insulator wouldn’t be relevant.
This might all be a moot point. While the above method would work for a fluid like water, it may not on a structured body like a human. I’m reading about methods of dying in space, and it appears that our skin and other membranes are strong enough to withstand full vacuum (without exploding), therefore, the very liquid we are trying to cool might take a long time before ever being subject to the required 6.1 mbara.
Couldn’t you nullify the vapor barrier by simply agitating the liquid? Say, a gigantic not-so-lazy-river of liquid nitrogen and a person trapped up against some kind of a titanium grate? That would also ensure that any body heat transferred to the nitrogen would be quickly whisked away to maintain maximum heat transfer.
Liquid helium, being a superfluid at cold enough temperatures, can flow through extremely small openings, like the pores in (apparently) solid ceramic.
I believe that you could thread a body with thousands (maybe millions) of narrow tubes without too much irreversible structural damage, and then flow liquid helium through these. The tubes could be finer than acupuncture needles, and if you were careful enough, you could probably make it so that no part of the body is more than a few millimeters from one.
Liquid helium may have a poor specific heat, but its zero viscosity means you can pump it through the channels rapidly. Thread the body first, then turn on the pumps and freeze the body almost instantly.
True; although since the chemical I cited can still be liquid near the boiling point of liquid nitrogen (I still have a hard time believing that’s an accurate cite), liquid nitrogen wouldn’t gain you much unless it’s been chilled down to just above its freezing point.