X-Message-Number: 2156 Date: Mon, 26 Apr 93 09:58:13 CDT From: Brian Wowk <> Subject: CRYONICS Reply to Mike Darwin Mike Darwin: > If the Polycool system is as good as its manufacturers claim it > is, then it sounds like it should be vigorously pursued and > used to refrigerate a reservoir of LN2. What I think would be a > real mistake would be to use the refrigerator and a heat exchanger > with fans blowing over it such as is used in conventional > refrigerators -- even if you have a lot of heat sink material like > water ice lying around to buy you a week or two. You never want > to be under the gun to get the mechanical system up and running. > Redundancy, redundancy, redundancy is ever the name of the game. Mechanical refrigerators that pump heat from -130'C are much cheaper and more reliable than mechanical refrigerators that pump heat from a -196'C LN2 reservior. In fact refrigerating to -196'C ends up costing (not coincidentally) as much LN2 itself. I advocate a system wherein LN2 would be added to the room only when needed (if *both* refrigerators failed simultaneously). The LN2 backup would be simple and stable (a calibrated tank in a heat exchange cell), and there would be no rush to implement it since the room would warm at only 0.02'C per hour. > Re: Thermal Ballast. My ten cents worth is that you don't want > lots of small containers. They will cost you a lot in time and you > will have to have heavy lift capability anyway to move patients > around. Just use drum sized units that interlock and move them > around with your overhead "floor crane." Alternatively the > facility could be designed such that the ballast spaces are an > integral part of the construction and are flooded and sealed > during the building of the unit. You do not want to pour ballast into water/ethanol proof walls waiting for it to freeze. The constuction costs will be high, and the risk of ruining foam under the room with leaks is high. More importantly, the walls will split due to freezing expansion. Alternatively, you could just fill walls with small ballast containers. But then you might as well put them in the room anyway. Free standing, properly-stacked square ballast containers can support all manner of mechanical stresses, including compresion and shear. The only exception is tension, which wood resists very well anyway. I might point out that using stacked ice to resist compression and wood to resist tension is similar to the way civil engineers build bridges. In bridges, the concrete deck gives compressive strength, and thin steel reinforcing rods give tensile strength. I admit I am partial to the five gallon plastic cubes suggested by Steve Harris because I can buy them at Kmart. So far everthing we need to build the interior of the room can be bought at Kmart or Home Hardware, and I like that (although of course we will buy wholesale). I simply do not know where to get other larger square containers that will stack nicely, and they may not cost less if they are not mass-market items. --- Brian Wowk P.S. I will address the patient storage questions tomorrow. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2156