Now I have another question related to the same story. This one deals in cryonic preservation of a human head.
How much cooling could you achieve (in, say, a climate-controlled human-livable environment) with just equipment like an air conditioner – that is, a compressor using some kind of liquid coolant?
According to this page at Alcor, they have to replenish the liquid nitrogen that they use to store their patients[sup]1[/sup] every few weeks. Would it be possible to preserve somebody (in a comparable fashion) so that you only had to consume electrical power? Like if you had a body or head preserved in liquid nitrogen already, could you keep it at liquid nitrogen temperatures with some kind of air conditioner-type device without ever having to replenish the liquid nitrogen? It seems implausible to me, but I’m not sure. It sure would be handy for my story, but if it was possible, wouldn’t they be doing it at Alcor…?
Thanks for any information.
[sup]1[/sup]Don’t give me a hard time about that word, man!
You can use a Peltier element, which uses electrical current to create a temperature difference on two sides of a plate without any liquid coolant. It creates more heat on the hot side than it removes on the cold side (in accordance with thermodynamics) but if you had a nearly-unlimited supply of electrical power and a cold source like deep space to radiate to, you could avoid using convection altogether.
Place the head inside a hemisphere of Peltier elements and close it off from any airflow; make it dark inside. Hook the hemisphere up to the power supply. Now place a slightly larger hemisphere of Peltiers on top of it like a Russian nesting doll. Once you have a big enough temperature differential, build a white (?) heat sink out of something like gold or copper, with lots of surface area facing the black sky of space. If there’s an atmosphere, you can use electrical fans to blow ambient air across the heatsink fins and further reduce the temperature.
It’s probably vastly cheaper to use liquid nitrogen (which runs about $2/quart) than to attempt to maintain this temperature (77K) via space heating (or in this case, space cooling). In fact, I’m not sure you could make a conventional single closed-loop refrigeration cycle that would extract heat at this temperature. (Liquid nitrogen is manufactured by compressing air, cooling it down to liquifying temperature at that pressure state, and then undergoing fractional distillation to seperate nitrogen from the air.) You’d certainly have to have multiple cycles with different refrigerants seeing different temperature regimes in order to effectively extract the heat from a system with this low of a temperature to room temperature.
I don’t think any thermoelectric diode/solid state cooler is going to get you anywhere near this kind of temperature difference. They are used to cool spacecraft from Sun-facing radiation, but by dumping heat out the back to a the very cold 2.7K microwave background of ambient space. At normal Earth temperature ranges I think you’re going to have trouble getting more than a few tens of degrees temperature (Celcius) difference without resorting to a mechanical refrigeration cycle.
(Bolding mine)
I should probably clarify that when I said “using just electrical equipment,” I meant “using equipment that can be run using electricity,” not purely solid-state equipment like a Peltier cooler. A mechanical refrigeration cycle is what I was expecting would have to be used.
So the bold part above is what I’m interested in. Is it at all feasible to chill something (in this case, a person) down to cryonic temperatures using just refrigeration equipment rather than constantly having to replenish a consumable (like liquid nitrogen)?
Or, in the alternative, what about just having a machine that creates liquid nitrogen from the air (consuming nothing but air and electricity, essentially) and keeps the payload cold by doing that? Would it be feasible to pack that kind of equipment into a small space, like an 8’ by 8’ room, using current technology (as this part of the story takes place in the present)?
Cryo pumps are used to produce high vacuum, by reducing the temperature of an adsorbant to a few Kelvin. This is done strictly with mechanical refrigeration. They typically use a couple of stages of conventional evaporation/condensation followed by at least one stage of gas-only cycle. (Hydrogen IIRC)
Wrong on both counts, I’m afraid. To radiate efficiently, you want black, not white. Polished metal would be about the worst option. And if you’ve got a good black paint, then the standard high-surface-area heat sink shape won’t help you at all, since most of the energy radiated will just hit another fin of the heat-sink. It’s only the silhouette size which matters for a radiative heat sink. Fins are only effective for coupling to air or other convective fluid.
Since you specify current-day technology, there’s the question of resources. We can, for instance, launch a small payload out into the far reaches of the Solar System; it just costs a bunch. Are we talking a budget of thousands of dollars, here? Millions, or billions?
I have nothing to offer as an answer, but I think I can help with the question. I understand that what the OP wants is some way to keep a head alive without the help of other people coming to babysit the machine, is that it? I am also getting a feeling that this must happen in an otherwise regular looking building where other tenants are not necessarily aware of this, hence the size limitations. This might open up the field of possible solutions to this.
Precisely. It’s something that somebody is trying to do (present day) in secret. And to answer Chronos’s question about resources, he’s basically just a middle class guy with less than $100,000 in savings to work with.
ugh. I am afraid you have just messed up the whole scenario. That’s some skimpy budget you got there. Just the rent and power bill are going to eat through that fairly quickly, let alone the equipment.
Locations that use large quantities of liquid nitrogen can buy/lease equipment to run on site that liquifies nitrogen (done to cut down on liquid nitrogen transportation costs). As far as I know, this requires only electricity.
So, there’s your electricity-only method of cooling.
A small-scale inefficient system might be able to be bought/contstructed for less than $100,000. Leased equipment wouldn’t cost much upfront. I think the condensation/distillation part may require greater height than would fit in a bedroom, but again it could be done if even more inefficiencies are allowed and a sizeable electrical bill could be handled.
However, any mechanical system will require maintenance.
At the risk of spoiling the story, I recall from the other thread that chorpler already intended a sort of “free energy” device to exist in the universe of this story. I’m going to guess that the guy who invented it was present-day, and was looking for a way to use it to ensure his own immortality, hence the cryogenics. So the electricity wouldn’t actually cost him anything, beyond the cost of building the device in the first place (which, since we’ve no idea how it works, could be arbitrarily low or high).
Don’t know what it costs, but something like one of these should be enough to keep a cool head. They draw 900 watts and would fit in a (ventilated) closet. They require some routine maintenance, so you probably couldn’t keep it going for years unattended.