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Magnetocaloric Cooling

Johnny Pneumatic

Master Poster
J
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This is a few years old: http://www.er.doe.gov/Science_News/...ic_Refrigerator/New_Magnetic_Refrigerator.htm

But the point of my linking it is that I'm unsure if this has gotten it's science right: http://nobeliefs.com/death&timetravel.htm

I ask partially out of curiosity, and partly because I wrote a thing on magnetocaloric freezers than can put people in suspended animation by supercooling, where they can't freeze the normal, destructive way. In short, they can be brought back like in the linked writting above, that I'm questioning now, after having written the piece.

Does the writer of the, I don't want to say paper, because it's not a paper in a scientific journal, but, uh......, internet page have his science right, that things could be supercooled using magnetocaloric freezers?
In case you don't know what supercooling is: http://www.answers.com/supercool&r=67
 
I remember studying this in my thermodynamics course. My prof was doing research in the field, and there are a lot of papers out in solid state journals about the magnetocaloric effect. I asked if it was practical at the home or university level, and the short answer was no, it was far too big.
 
First you ask about steamers, now magnetocaloric freezers, should I be worried?
 
And next he'll ask about builidng his own cryogenic cooler...
 
eri said:
I remember studying this in my thermodynamics course. My prof was doing research in the field, and there are a lot of papers out in solid state journals about the magnetocaloric effect. I asked if it was practical at the home or university level, and the short answer was no, it was far too big.
Click to expand...

Yes, I know that. What I wrote is plausible, hopefully, SF fiction, and I want to know if it's plausible given enough advancement with magnets. Cellphones were once the size of, and weighed as much as, a large brick. My question simply is can a magnetocaloric freezer supercool something biological, or any other thing, so the liquid doesn't crystalize, destroying the cells? The size required to do so, currently, doesn't matter to me. In the fiction, room temp. superconducting magnets are used. You can pack a whole lotta Tesla into a superconducting magnet.
 
I came across a discussion some years ago about replacing water in body cells with sugars, which dehyrdated the cell without distortion. I'm not sure if the idea was then to freeze that, to avoid the expansion damage of water ice crystals, or whether the dehydration itself was enough for suspended animation. Never heard about it again.

When you gonna stop gathering ideas and actually write something???
 
SkepticJ said:
This is a few years old: http://www.er.doe.gov/Science_News/...ic_Refrigerator/New_Magnetic_Refrigerator.htm

But the point of my linking it is that I'm unsure if this has gotten it's science right: http://nobeliefs.com/death&timetravel.htm

I ask partially out of curiosity, and partly because I wrote a thing on magnetocaloric freezers than can put people in suspended animation by supercooling, where they can't freeze the normal, destructive way. In short, they can be brought back like in the linked writting above, that I'm questioning now, after having written the piece.
Click to expand...

The second link isn't so much wrong about magnetocaloric cooling as it is irrelevant. In terms of biological stability, magnetocaloric cooling is no different than other cooling techniques. The fact that it might take less energy to do is irrelevant, because it's not the energy costs that are the problem. The problem is, and always has been, to somehow avoid cellular damage during the freezing process, and to revive the entire organism successfully on thawing. Neither process is limited by cooling power, and magnetic cooling, while perhaps very efficient, doesn't even come CLOSE to the maximum cooling power available if you don't care about efficiency.

Does the writer of the, I don't want to say paper, because it's not a paper in a scientific journal, but, uh......, internet page have his science right, that things could be supercooled using magnetocaloric freezers?
In case you don't know what supercooling is: http://www.answers.com/supercool&r=67
Click to expand...

Yes, you can supercool using magnetocaloric cooling. But you can also supercool using a whole mess of other cooling techniques. There's nothing special about magnetocaloric cooling in this respect. It has much more to do with things like cooling rates, liquid purity, and various other tricks to prevent nucleation of solid phases, but none of that depends on exactly how the cooling is happening, only that it is happening.

His only real point is that, if interstellar space travel ever happens, efficiency will be important on a space ship, and so you'd want the most efficient technology available to do the freezing and unfreezing. And that's true enough. But we need to figure out how to safely freeze and unfreeze people first - until we can do that, it's really pointless to talk about how to do it more efficiently. And considering the astronomical (no pun intended) energy required to do the kind of space travel he's talking about, even the inefficiencies in cooling with conventional liquid/gas phase transition refrigerators is really going to be miniscule in comparison, so more efficient refrigeration technology isn't even among the many technological breakthroughs that would be necessary before we could travel among the stars.
 
Ziggurat said:
The problem is, and always has been, to somehow avoid cellular damage during the freezing process, and to revive the entire organism successfully on thawing.

Yes, you can supercool using magnetocaloric cooling. But you can also supercool using a whole mess of other cooling techniques. There's nothing special about magnetocaloric cooling in this respect. It has much more to do with things like cooling rates, liquid purity, and various other tricks to prevent nucleation of solid phases, but none of that depends on exactly how the cooling is happening, only that it is happening.

His only real point is that, if interstellar space travel ever happens, efficiency will be important on a space ship, and so you'd want the most efficient technology available to do the freezing and unfreezing. And that's true enough. But we need to figure out how to safely freeze and unfreeze people first - until we can do that, it's really pointless to talk about how to do it more efficiently. And considering the astronomical (no pun intended) energy required to do the kind of space travel he's talking about, even the inefficiencies in cooling with conventional liquid/gas phase transition refrigerators is really going to be miniscule in comparison, so more efficient refrigeration technology isn't even among the many technological breakthroughs that would be necessary before we could travel among the stars.
Click to expand...

If you supercool liquid though it doesn't go through a phase change, it just gets colder. Without the phase change, there's no cell damage from the microscopic ice crystals from the freezing water shredding the cells like tiny daggers. If there's no cell damage, it'd be easy to bring them back. There are frogs that freeze solid(They have a built in anti-freeze within their cells that prevents the damage from the ice) in the Winter, then come back to life when Spring's warmth comes.

I thought the point was the body wouldn't cool from the outside in, but would cool all at once the whole way through. If it's done the outside-inside way, then the outside may be supercooled, but the tissue just inside it would get cold due to the physical law that heat moves to a colder area(the colder area being the supercooled outside of the body) and freeze into ice instead of supercooling to a cold liquid just above 0K. So your outsides are preserved for all time, but your guts and brain are frostbitten. Frostbite on the brain means you're screwed; your "soul"(nerve connections) is destroyed. Or if you're preserving food this way, it's going to taste awful. Ever had frozen watermelon? No? Good, don't, it's nasty. Freezer burned meat? Don't try it.
 
SkepticJ said:
I thought the point was the body wouldn't cool from the outside in, but would cool all at once the whole way through.
Click to expand...
That wasn't my impression, though I admit I skipped the stuff where he talked about supercooling. But if that WAS the idea, then he really does have the science horribly wrong. Magnetocaloric cooling only works with magnetic materials. Our bodies are not magnetic (or more precisely, so weakly magnetic that there's no chance in hell we could ever experience a significant magnetocaloric effect). The way the refrigerator in the first link works is by cooling a permanent magnet with the magnetocaloric effect, then using the now-cold magnet to remove heat from whatever you want to freeze. The particular permanent magnet they use is an important part of the whole process, you can't cool arbitrary objects by applying and removing a magnetic field (in fact, not every magnetic material is good for this either). And you certainly can't do it to a human body. Which means using a magnetocaloric refrigerator to freeze a human body is still going to freeze from the outside in, just like every other method we have.
 
Ziggurat said:
That wasn't my impression, though I admit I skipped the stuff where he talked about supercooling. But if that WAS the idea, then he really does have the science horribly wrong.
Click to expand...

Maybe you could read that part? I re-read it and can't quite figure out what he means. I'll e-mail him if all else failes and ask him what he means.
 
SkepticJ said:
Maybe you could read that part? I re-read it and can't quite figure out what he means. I'll e-mail him if all else failes and ask him what he means.
Click to expand...

Don't bother. I read a little more extensively - not all of it, but enough to tell that he doesn't know what he's talking about.

I had initially only read the first paragraph under "Magnetic time suspension", where he mentions magnetic refrigerators. That paragraph was OK, though irrelevant. But I doubt he really understood it either. In your refrigerator, the freon gets cycled in temperature: it cools when evaporated, thereby cooling your refrigerator inside, then gets heated when it's compressed back into a liquid, dumping the heat out the backside of your refrigerator. It's that cycling which provides cooling power. The same sort of cycling happens with a magnetic refrigerator too: the magnetic material heats up (dumping energy) when exposed to a strong magnetic field, then cools down (sucking up energy) when removed from that field (the energy required to run it comes from the fact that after the magnetic material has dumped heat in the magnetic field, it is magnetized and it takes work to move it out of the field - no violations of thermodynamics occur, just as with a freon refrigerator). In other words, simply applying a magnetic field, regardless of how big it is, can never KEEP something cold directly. You only get the cooling power by cycling something in and out of the field, which means its temperature cycles too.

In the following paragraph where he talks about an atom trap, it becomes quite clear that he's really confused. It's not the magnetic field which cools the atoms, it's the lasers. The lasers are slightly detuned from the absorption spectra of the atoms, so that the atoms don't absorb very well when sitting still. If they're moving towards one of the lasers, however, the doppler shift increases the absorption, so that the atom gets pushed back and slowed down. The laser light thus discourages the atoms from moving, hence the cooling. The purpose of the magnetic field is not to cool the atoms, but to trap them spatially by tuning the absorption frequency of atoms (the orbits of the electrons shift energy in the presence of a magnetic field). By arranging the magnets in a particular way, you create a spot of zero magnetic field in the center, and increasing field as you move away from center. So what happens is that atoms which drift away from the center are more likely to absorb light, and hence get pushed back towards the center (there's also some dependence on the polarization to ensure that it's the light pushing back towards center and not away from the center which gets absorbed, but that's not important now). In other words, magnetic fields do NOT do the cooling, they're only there to help confine the atoms so that they don't all slowly drift down to the bottom of your chamber under the force of gravity.

Later on he says, "For the purpose of this thought experiment, imagine that the chamber uses magnetic field technology where superconducting magnets can literally halt the vibrations of every atom within its chamber." But this statement is nonsense. Magnetic fields do not halt the vibration of atoms. They cannot. There's only two things they can ever do: align magnetic moments, and (if there's a gradient to the field) exert a net force on those moments. But aligning magnetic moments in a field doesn't keep them cold, they will still return to the temperature of their surrounding environment, and being aligned doesn't prevent them from moving around. And you can't just apply a large force to the body to get the atoms to stop moving either, or you'll end up with a squished body which isn't moving because it's dead. It would be like trying to refrigerate something by putting it in a trash compactor, you're not going to get the results you're looking for. And there's no possibility of doing a laser trap (ala the supercooled atoms) with a human body either, since we're opaque and absorb broad spectra, not just specific frequencies. And in any case, the body isn't really magnetic (it's very weakly diamagnetic), which means that magnetic fields hardly do anything noticeable to your body. That's why you can sit comfortably in an MRI machine, but if anything magnetic gets brough near it serious problems occur.

In short: magnets can't do what he seems to think they can do, and they can't freeze a body from the inside out. If you want to cryogenically suspend someone, you've got to do it the hard way, from the outside in. The closest thing to freezing from the inside would be a cryogenic enema.
 
Actually, I thought of one way out which could work from a science fiction perspective but probably not in real life. Here's how it goes:

First, you need to ingest large amounts of some chemical which
a) doesn't mess with your metabolism
b) can be absorbed into individual cells
c) is strongly paramagnetic (has a large magnetic moment)

Once you're magnetized, you step into your big magnet, which start off at zero field (rather important or we're back to being squished when the magnet sucks us in at high speeds when we approach). Once inside we turn on the field SLOWLY (as in it might take a few days). As the field increases, the randomly oriented moments on our chemical will want to align with the field, but they can only do so by giving up heat. This means your body will warm up. This is why we do this stage slowly: it has to be done gradually enough that the body can safely dump the generated heat without causing damage (you'll die somewhere around 110 F). Once the field is sufficiently large, you decrease the field very rapidly. Now all those aligned magnetic moments are able to rotate again, but they'll only start rotating by sucking up thermal energy from their surroundings. So your whole body suddenly cools everywhere at once, and you get the desired result. Once you're frozen, though, your body needs be kept frozen by conventional refrigeration techniques. To thaw back out, ramp the field back up quickly (generating heat), then slowly lower it at a rate that the body can keep warm (ramping down is what cools).

So in a science fiction sense, yes, such a thing is conceivable. But it does rely on being able to make the body magnetic. Not only is there no way to do that right now, but I doubt anyone has any ideas about how to do it either.
 
Just to follow up on that previous post: in order to work, not only do you need to make the body magnetic, you need to make it VERY magnetic (as in probably a significant fraction of your body weight needs to be taken up by this hypothetical magnetic substance). There's an absolute limit to how much heat a single electron can absorb in such a process, and unlike a refrigerator (where cooling power in each pass doesn't need to be very high because you can cycle), you need to do this in one shot. My suspicion is that there's simply no way to introduce enough magnetic material into the body without getting killed, even if you found something completely non-toxic which the body wouldn't expell, just because of the problem of it getting in the way of normal biological processes. Maybe a genetically engineered organism which was designed specifically to incorporate large amounts of some paramagnetic substance could do it, though.
 
Ziggurat said:
Maybe a genetically engineered organism which was designed specifically to incorporate large amounts of some paramagnetic substance could do it, though.
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If you can do that though you could just engineer the organism to have those biological anti-freezes like those frogs that freeze solid and survive have. Then any old freezer that gets down to 1 Kelvin would do.
 
SkepticJ said:
What about the iron in blood? Sure, it's only weakly magnetic, but weak is enough in a strong enough field.
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No, unfortunately that's not the case. Once you've fully polarized your moments, increasing the field more won't increase the magnetization. Which means when you turn off that field, regardless of how high you went, you're always going to be limited in your cooling power by how many spins you have available to soak up that heat. So it is physically impossible to try to compensate for weak moments by simply using higher fields. There's simply no physical way that such a small number of iron atoms in the body can absorb enough heat from the rest of the body to make a large temperature change.
 
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