X-Message-Number: 1791
Date: 21 Feb 93 22:38:13 EST
From: Mike Darwin <>
Subject: CRYONICS Re: Remarks on Ettinger's Proposal

From: Mike Darwin
Re: Ettinger Proposal Comments
To: All
Date: 21 February, 1993

     Richard Schropel speculates that the temperature of liquid nitrogen 
vapor is the same as that of the liquid and asks for clarification.  
Having considerable first-hand experience with this I can readily back up 
Bob Ettinger.  The temperature even a few millimeters (indeed even a 
millimeter) above the liquid nitrogen is greatly higher.  Physics tells us 
why this should be so, but rather than try to explain thermodynamics 
(which is by no means my forte) it is perhaps sufficient to point out that 
if the nitrogen vapor were the same temperature as the liquid nitrogen it 
would also be liquid nitrogen instead of a gas...  The degree and 
stability of temperature stratification in a cryogenic dewar refrigerated 
by liquid nitrogen is truly astounding.  

     I conducted several experiments during my last few years at Alcor 
using a Linde LR-310A.  The LR-310A is a large diameter, relatively 
shallow dewar with a fiberglass interior which probably models  Ettinger's 
storage system reasonably closely.  What I found was that the temperature 
a centimeter or so above the liquid (with 3 inches of liquid in the bottom 
of the dewar) was -168*C and the temperature inside the lid was -138*C.  
Thermocouples placed at 2 cm intervals between the liquid and lid recorded 
different temperatures.  I do not have the original data from this 
experiment and I recall only the two most extreme  numbers.  But I do 
recall that even in the two feet or so of depth between neckplug and 
liquid there were quite a few strata and that they were very stable 
unless the system was invaded by opening the lid or adding liquid.

     It is notable that when liquid was added it was through a submerged 
fill pipe and there was still great disturbance of the temperature 
stratification and a marked lowering of the overall vapor temperatures.  I 
think that if this phenomenon were to be avoided in a system such as 
Ettinger proposes it would be necessary to use a phase separator on the 
liquid addition line and perhaps to use nonpressurized liquid to fill the 
dewar.  One of the things I repeatedly noted when filling the Alcor A-2452 
neuropatient dewar with liquid nitrogen from pressurized lS-160s is that 
the temperature would uniformly rise 1xC after each fill*.  Also, since 
the LN2 was being stored slightly "supercritical" (because it is 
pressurized to 25 psi to allow for dispensing) there was a tremendous 
amount of gas generated upon dispensing as some of the liquid quickly 
boiled away to lower the temperature (carry off heat) to the boiling point 
of LN2 at 1-atmosphere.  Thus, it may be necessary to pump the liquid from 
a reservoir at 1-atmosphere rather than using pressurized sources in order 
to avoid this rapid boil-off and resulting "roiling" or "turbulence" 
phenomenon.

     In response to Charles Platt's remarks: Yes, many materials become 
brittle at -196xC but this is not a serious engineering challenge.  After 
all, Bob has achieved a great deal and proven himself vis a vis materials 
since he has engineered whole dewars out of polymer.  While I still 
question the economics of his approach, I would not for a minute question 
his expertise in this area.  Additionally, I have cooled small specimens 
for years by floating them on a slab of expanded polystyrene (EPS) on 
liquid nitrogen.  The EPS got a little "soggy" after awhile, but it never 
sank.  I could think of many materials to make pontoons out of, including 
Ettinger's epoxy, aluminum, polypropylene, etc.

     Bob has obviously thought about this problem and has put forth a 
solution which incorporates elements that other minds wrestling with the 
same problem have come up with.  This is a good sign and may mean that we 
are on the right track.

     Finally, an issue which has not been raised and which probably needs 
to be:  The optimum way to handle this system would be to engineer it big 
-- the bigger the better.  In order to do that you need to be able to fill 
it as rapidly as possible.  The ideal way to achieve this end would be to 
store patients collectively.  If technology, location, and standards could 
be agreed upon this would make a great deal of sense.  One argument that 
was raised against my proposals for vapor storage of patients was that 
they were uneconomical because existing patients would still need to be 
stored "as is" and only new patients would benefit...and it would be a 
long while before there were enough new patients.  A community effort 
would solve this problem.  And since Alcor needs to move its storage 
facilities anyway this might be the perfect opportunity.

* Can anyone tell me why this should be so?  I would have thought that any 
LN2 in an open-topped container at 1-atmosphere would be at -196xC so 
quickly that a temperature rise would not occur.  Also, this phenomenon 
was observed with the old Bedford dewar when it was filled and is recorded 
in years of log entries.  I often wondered what effects these frequent and 
rapid 1xC or 2xC swings in temperature had on patients.  Has any other 
cryonics society observed this effect?

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