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.

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