X-Message-Number: 2135
Date: Tue, 20 Apr 93 13:20:49 CDT
From: Brian Wowk <>
Subject: CRYONICS Ballast Stacking

Steve Harris:
 
> Ethanol/water mixes, as they freeze, will
> be expected to freeze as pure water ice crystals, with ethanol
> concentrated solutions between.  This will continue until the mix
> between the water ice crystals is the minimum-freezing 
> water/ethanol eutectic mix, which will likely be some simple
> molar ration of ethanol and water (just as it is for ethylene
> glycol and water).  Given the very high freezing point of ice, I
> would not expect such a eutectic mix of ethanol and water to
> freeze at too much below the freezing point of pure ethanol.
 
        Of course!  I had not considered that the water would slightly
depress the freezing point of ethanol.  This could well be a superbly 
elegant solution (pardon the pun) to all our problems.
 
        By the way, I contacted some industrial chemical suppliers 
today and was quoted was $1.30 (USD) per liter for 95% ethanol 
purchased in 200 liter drums.  This would run us $6500 for 5000 
liters, which is reasonable.
 
 
> A thought about ballast conformation:  Water is HEAVY.  I'm
> not happy about stacking a lot of 80 lb cans of water on top of
> each other like a pile of bricks without mortar.  It sounds
> difficult and not very safe unless there are no open spaces
> anywhere in the structure.
 
        Yes, further thought suggests that 5 or even 2 gallon cans 
might be better than 10 gallon cans.  But you don't wan't too many 
small cans, or filling them and stacking them will be too labor 
intensive.
 
        I am indeed advocating that there be no open spaces anywhere 
in the structure.  The whole room should be packed full with cans up 
to a height of about 2 meters (lower if we can get rectangular cans 
that pack more efficiently).  You only remove enough cans to allow the 
insertion of each new patient, with any loose space packed with 
fiberglass batting.  Cans cannot fall because there is no place for 
them to fall to.  They are packed solid, and the top level is below 
the top of the patients.  (Recall that the bottom half meter of cans 
(these consisting of ethanol/water) are left intact under the 
patients.)  
 
        If we build in an area with high seismic risk (which I hope we 
don't) I would advocate the additional precaution of removable walls 
that can be slid in and out at intervals along the corriders.  
Otherwise I think this is expensive and unnecessary.
 
> Even then, with the floor loading
> we're talking about, this room is going to have to be built like
> a swimming pool.  Very difficult to have relatively delicate foam
> slabs underneath such a thing!
 
        Weight is not a problem.  30,000 liters of ballast spread over 
about 20 square meters is 1500 kg per square meter, or 15 kPa 
pressure.  The compresive strength of Trymer CPR 9545 foam at room 
temperature is 235 kPa, and is even higher at low temps.  To put this 
is perspective, remember that you can walk on Dow Styrofoam (imposing 
a load of 100 kPa) without denting it.  It is also important to 
realize that even when the room is full of patients with only residual 
ballast underneath them, there will still be a load of 1000 kg per 
square meter.   
 
 
>   Well then: an alternative to having to stack carefully might
> involve smaller ballast shapes which are deliberately poor at
> filling space or packing efficiently, such as long hollow plastic
> cylinders with fins (we want lots of space through which to move
> circulating air).
 
        You don't want haphazardly-stacked ballast because it will 
make it difficult to excavate patient slots, and will be prone to 
shifting and putting pressure on patients.  Also you want to minimize 
air space between the cans (hence my suggestion we use rectangular 
cans if possible).  Any air space between cans will be dead air space 
because most air will pass over the top of the ballast and heads 
(actually feet) of patients.  Air between cans will only reduce 
thermal conductance through the ballast, which we do not want.
 
        To recap the heat transfer situation: It is not important that 
air pass through the ballast because air will already be passing over 
and it and under it (under the false floor).  Conductivity of the 
ballast itself will be adequate to keep temperature differences below 
1'C at the rate heat would flow during a cooling failure.  
 
        By the way, it occurs to me that those rectangular 1 gallon 
metal cans that solvents are sold in might work for us.  Unfortunately 
we would have to lay them on their side for stability, which would 
make hooking the handle difficult.  We might have to use Steve's 
electromagnetic grabber.  
 
 
Steve Jackson:
 
> You still get the best packing efficiency
> with six-sided cells - they just have to be lengthened on one
> direction.
 
        Yes, I see that that is true for single-patient cells.  
However single-patient cells are expensive and inefficient.  (Obese 
patients might not even fit in them.)  I am currently enamored with my 
ad-hoc cell concept.
 
 
> Re ballast material: What happens if you use brine rather than pure 
> water?
 
        Not much.  The maximum freezing point depression you can get 
with a saturated salt solution is -21'C.  I think Steve Harris has hit 
the nail on the head with his idea of a water/ethanol solution.
 
                                                --- Brian Wowk

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