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D_Alex comments on Cryonics Wants To Be Big - Less Wrong
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Roko... you must have been dealing with small scale cryonics. I am an engineer in the LNG industry, and we routinely design cryogenic storage tanks up to 200,000 m3 in volume. Vacuum is never used on this scale, in fact we use pearlite powder insulation and wood blocks to support the inner liner, and glass or polyurethane foam to insulate the shell. The PU foam is cheap and can be more or less as thick as you wish. Heat loss for LNG tanks is around 5 watts/sqm, for large tanks this represents a boil-off of around 1/50th of 1% per day. I'm sure this can be lowered. $100 million will buy a 140,000 m3 tank. If you want one, let me know :)
(AFAIK, powder is also used in vacuum flasks instead of multiple layers).
The boil-off can be lowered by increasing the insulation thickness, using better materials etc... the current designs are far from optimised for heat loss, since the gas companies do want to eventually sell the LNG in gaseous state. I think that a factor of 8 is doable with current techniques at abt 2x the overall price (this is a guesstimate not a quotation, OK? ;)
At 125 neuro patients per m3, we're talking room for 25 million patients in a single 200,000 m3 tank. Total boiloff would be 40 m3 per day, which would take 5000 days if the tank is full of cryogen, or 1250 days (~4y) if the patients take up 75% of the volume.
If we wanted to get it to the century range, I wonder how much thicker the insulation needs to be... a factor of 25? Number of watts would need to go down to 200 milliwatt/sqm.