X-Message-Number: 2127
Date: 19 Apr 93 05:12:30 EDT
From: "Steven B. Harris" <>
Subject: CRYONICS Ballast Stuff...

Dear Brian:

   It may indeed be that, even counting the heat of fusion, 
ethanol/water has less heat capacity over the temperature range
we're interested in than water ice.  The only reason to use
ethanol/water over water might be the heat of fusion temperature
"knee."  But that may be a good enough reason.

   It all depends on that knee: how sharp is it?  I dunno.  We'll
have to do some experiments to find out.  The whole thing can be
done well enough for our purposes by taking a cheap styrofoam ice
chest with some quart jugs in it full of various ethanol water
mixes (or jugs of the pure substances), pouring LN2 into it until
full at thermal equilibrium, putting the lid on and just doing a
strip chart from a thermocouple reading inside as it all warms to
room temp.  The "best" curve here, as judged by some combination
of total time to warm and slow temp increases in the critical
region, will tell us what ballast mix to use in our big project. 

   As for fire marshalls not being able to object to pure ethanol
canisters surrounded by ice, by the way, remember that 1) fire
marshalls are not rocket scientists, and 2) even savvy fire
marshalls sometimes work with statutes about safety standards for
given quantities of pure solvents that may leave them no room to
maneuver.  Nobody writing fire codes has thought of containers of
pure ethanol being protected from potential fires by being frozen
in blocks of water ice at -130 C, for instance, I guarantee you.

   It may not matter.  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.  Who
knows, it may freeze at about where 1-propanol does, and save us
a lot of trouble.  Anyway, the point is that fire marshals and
the law cannot be expected to take notice of the defacto micro
separation of ethanol and water which occurs when ethanol
solutions freeze.  So in this case, the fire codes will probably
permit us to do what we want.

   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.  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!  Under such circumstances, one
might end up using cans which were deliberately filled much less
than full. 
   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).  Perhaps the ubiquitous and surprisingly
durable polycarbonate 2-liter pop bottles would do.  To fill
space in a cold room you might simply drop the ballast units in
willy nilly to fill all available dead air space.  Add some iron
to each one, and you can pick them out with a fishing magnet (or
an electromagnet-- small load commercial ones, judging from the
prices in Edmund Scientific, are not too expensive).  For that
matter, once you decide that you don't want nearly maximum weight
for your space, you can do all kinds of strange things:  a first
idea that springs to mind is that you could make ballast out of
ethanol/water soaked sponges, packaged with a few nails in Tyvek
8" X 11" mailing envelopes.  You'd just shovel `em in.  You could
even superglue steel washers to a million ping pong balls and
inject each with a little vodka...

    I'd better stop while I'm ahead.

                                          Steve

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