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).
My suspicion is that the best insulation performance for this application would be aerogel in a rough vacuum. This article states:
Vacuum insulations are commonplace in various products (such as Thermos bottles). These systems generally require a high vacuum to be maintained indefinitely to achieve the desired performance. In the case of aerogels, however, it is only necessary to reduce the pressure enough to lengthen the mean free path of the gas relative to the mean pore diameter. This occurs for most aerogels at a pressure of about 50 Torr. This is a very modest vacuum that can be easily obtained and maintained (by sealing the aerogel in a light plastic bag).
I suspect that with a vacuum of 1 Torr you could get down to 0.001W/m-K or even below.
So perlite powder apparently has a thermal conductivity of 0.02W/m-K
Thanks for your comment. I worked with superconducting magnets and ultra-low temp systems, so yes, you are clearly more in the know about these kinds of sizes and temperatures.
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
Could it be lowered by a further factor of 8 or so?
What is the thermal conductivity of pearlite powder? Is there something that isn’t a vacuum that is just one order of magnitude more insulating?
What about filling with a mix of aerogel and pearlite?
Seriously, if we can get a boiloff time of > 80 years for a cost of < 20 million we might have a serious chance of this being implemented.
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? ;)
I think that you can do much, much better than this by using a rough vacuum filled with powder or aerogel granules. I actually think that you can make a tank of diameter only 10 meters that would last for centuries. Such a small tank would probably only cost $200,000 or so to build, yes? The main issue would be maintaining the vacuum, but it would only need to be a rough vacuum (1/100 atmospheres).
I’m actually seriously considering pitching this idea to Ben Best when he comes to the UK in 15 days.
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.
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).
My suspicion is that the best insulation performance for this application would be aerogel in a rough vacuum. This article states:
I suspect that with a vacuum of 1 Torr you could get down to 0.001W/m-K or even below.
So perlite powder apparently has a thermal conductivity of 0.02W/m-K
Thanks for your comment. I worked with superconducting magnets and ultra-low temp systems, so yes, you are clearly more in the know about these kinds of sizes and temperatures.
Could it be lowered by a further factor of 8 or so?
What is the thermal conductivity of pearlite powder? Is there something that isn’t a vacuum that is just one order of magnitude more insulating?
What about filling with a mix of aerogel and pearlite?
Seriously, if we can get a boiloff time of > 80 years for a cost of < 20 million we might have a serious chance of this being implemented.
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? ;)
See A proposal for a cryogenic grave for cryonics
I think that you can do much, much better than this by using a rough vacuum filled with powder or aerogel granules. I actually think that you can make a tank of diameter only 10 meters that would last for centuries. Such a small tank would probably only cost $200,000 or so to build, yes? The main issue would be maintaining the vacuum, but it would only need to be a rough vacuum (1/100 atmospheres).
I’m actually seriously considering pitching this idea to Ben Best when he comes to the UK in 15 days.
So perlite powder apparently has a thermal conductivity of 0.02W/m-K
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.