X-Message-Number: 11019
Date: Sun, 3 Jan 1999 10:23:33 EST
Subject: higher temp cryostats

Thomas Donaldson has asked for renewed discussion of cryostats operating at
higher temperatures than that of liquid nitrogen; he is uneasy about systems
depending on mechanical refrigeration.

It might be possible to get mechanical refrigeration systems with sufficient
reliability or redundancy, and some have been discussed years ago. However,
Cryonics Institute has a tentative design for a passive cryostat, using liquid
nitrogen but nevertheless allowing the storage chamber to maintain any desired
higher temperature.

The design isn't secret, and I have outlined it before. (None of our work is
secret.) Basically it just uses four concentric cylinders instead of two. The
inmost cylinder holds the liquid nitrogen. The first annular space holds
insulation. The second annular space is the storage chamber, large enough for
several patients. The third  annular space again holds insulation. 

The storage chamber is lined with heat conducting material (maybe copper or
aluminum) , to maintain a reasonably constant temperature over the height of
the chamber. The thicknesses of the two insulation layers are adjusted to
maintain the desired temperature in the storage chamber and to minimize
nitrogen boiloff. 

Variations could use cold nitrogen vented from the liquid to recirculate
through part of the system, or around it.

Compared to the "cold room" discussed elsewhere, there would be both certain
obvious advantages and disadvantages. Capital cost would be greater than for
LN2 temperature storage, but nitrogen use would be reduced. The main
advantage, of course, would be the biological result, if the vitrification
work proves out.

Obviously, feasiblity/desirability will depend on the results of actual tests.
This project will be activated at CI at a time that seems appropriate to us.

Robert Ettinger
Cryonics Institute
Immortalist Society

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