From: Keith Henson (hkhenson@rogers.com)
Date: Tue Dec 07 2004 - 18:20:34 MST
At 07:29 AM 07/12/04 -0800, you wrote:
>[Re: Cryonics storage in Antarctica]
> >
> > It just isn't cold enough. The numbers are here:
>http://www.alcor.org/Library/html/HowColdIsColdEnough.html
> >
> > >Right now, if your LN2 supply is
> > >disrupted, you will lose the patients when it
> > >evaporates. Down there, at least the frozen will
> > >remain frozen, so you will have longer to recover.
> > >
>
>Let me try to be clearer - I'm not suggesting the
>patients are stored at Antarctic temps. I'm
>suggesting
>the LN2 will last longer in Antarctica than Riverside,
>CA (where Alcor is now).
Ah ... I hate to tell you this, but Alcor moved out of Riverside over ten
years ago. They are in Scottsdale, Arizona and have been since early 1994.
>Vostok station has a wintertime air temperature of
>-65C. Since the sun never gets very high, you can
>erect a reflective fence to keep the sun off a
>patch of ground, then place heat pipes in the ground
>connected to radiators pointed at the sky to provide
>passive cooling.
This is called a thermal diode. You use a liquid that condenses and runs
back down the tube when it is colder above ground than below.
>This should get the ice down to
>-80 to -100C.
Heat loss is more or less delta T dependant. So the cut in LN2 use would
be (300-77) deg K -(200-77) deg K)/300-77 deg K, a saving of less than half
in LN2 consumption.
LN2 cost in the range of $0.50 a liter. You have to either transport fuel
and make it on the spot or transport it in. I don't have a number for the
cost of shipping to Vostok station, do you? Besides the LN2 or fuel, you
have to bring in supplies for the staff. This isn't the kind of operation
you can leave to take care of itself.
>Into this chilled patch of ice you
>install your insulated LN2 storage chamber. In
>designing cryogenic tanks for spacecraft, the best
>results are obtained using multi-layer insulation
>consisting of many layers of reflective foil
>separated by plastic netting, all in a vacuum.
This is exactly how it is done on with Alcor's dewars. Incidentally, when
Alcor's dewars were in un airconditioned space in Riverside you could see
the difference between winter and summer LN2 consumption, but it wasn't
very much, a few percent.
The heat leakage is so low that the only way to improve it is to make the
neck longer since that is the major heat leak.
>Aerogel might do better, but I haven't seen
>performance numbers for it.
Not nearly as good.
>So you build essentially
>a large insulated dewar flask underground.
>
>This type of storage should keep the LN2 for
>years, possibly longer.
The best dewars have boil off rates in the 1-2% per day range. Alcor keeps
the patient dewars topped up so they could go perhaps 6 weeks in an
emergency without being refilled.
The engineering of these things is *not* simple. They have to maintain a
hard vacuum for many years and the stress on the shells is substantial,
over a ton per square foot of surface due to air pressure. Above some size
measured in single digit feet, it becomes better to do it with blocks of
foam. This doesn't work well either because the performance of the foam
declines as it gets colder.
>The bigger you make it,
>the longer the storage time will be without
>replenishment - It's a surface to volume ratio
>relationship. Yes, doing anything in Antarctica
>is horribly expensive right now, so it probably
>makes more sense to stay in California for now,
>but if technology improves to the point of having
>replicating robot factories, such projects could
>be relatively affordable.
If we get a bit further to nanotechnology we won't need this stopgap
measure at all.
This is getting a bit far from friendly AI. It is applicable to those of
us who won't make it to the singularity without help though.
Keith Henson
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