X-Message-Number: 6610
From: 
Date: Thu, 25 Jul 1996 13:10:48 -0400
Subject: SCI. CRYONICS higher temp storage

Thomas Donaldson suggests that the problem of storage at cryogenic
temperatures above that of liquid nitrogen, for vitrification patients, might
be economically serious, although he remembers the extended discussion of
this a couple of years ago on CryoNet.

As I recall, several people contributed to a "cold room" proposal that
apparently would meet reasonable reliability and economy requirements, if a
scale of (a couple of hundred?) patients could be reached.

On a smaller scale, if necessary, I suggested a very simple, passive system
essentially as follows. Use four concentric cylinders, with appropriate
insulation between inner/second and between third/outer. The liquid nitrogen
goes inside the inner cylinder. The patients (vertical) go between two/three.
Temperature rises outward.

Now, depending on the type and thickness of insulation, and other dimensions,
the temperature in the (entire) annular patient space will be whatever is
desired (possibly - 135 C or thereabouts, with very small variations), and
will remain so as long as the nitrogen is kept replenished. (Here I pass over
details of how to assure minimal vertical gradients.) 

An advantage of this type of arrangement is that, even though the patient
storage temperature is considerably higher than the boiling point of
nitrogen, still we get the full benefit of the heat of vaporization of
nitrogen. With more complicated arrangements we might also get some benefit
from the heat capacity of gaseous nitrogen as it warms.

A disadvantage is that the setup occupies a relatively large volume, although
floor space might be saved by building high. The relatively large diameter
also contributes to a relatively large heat leak and reduced efficiency.
However, larger numbers of patients would allow larger units which would
minimize this problem.

One of the CI research projects--although not with a high priority--is to
build and test such a unit. (And we have no interest in patents, profits, or
in secrecy.)

Robert Ettinger
Cryonics Institute
Immortalist society 


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