X-Message-Number: 7667
Date: Fri, 07 Feb 1997 20:12:17 -0800
From: Paul Wakfer <>
Subject: Technology Disclosure

The purpose of this message is to describe some technological
innovations made by myself and being implemented by CryoSpan, Inc. which
should considerably reduce the liquid nitrogen boiloff rate of patient
dewars. Although the main ideas are mine, I wish to thank Mark
Connaughton, Greg Fahy, Steve Harris, and Brian Wowk for valuable
discussions while the development of these ideas was proceeding.

Philosophy of Intellectual Property Ownership

     While patents may have been very helpful to the progress and
development of modern technology, it is also clear that they are not
optimal and have often done a great deal of harm. I believe that the
spontaneous order of a truly free society would not include patenting as
it is currently implemented. Therefore, I have decided to proceed
without the use of a patent. In making this technology disclosure, I am
declaring that the innovations herein described are my intellectual
property, and that by this publication, I am *not* giving away the right
to their use. I wish to make this information public so that others may
more easily use and/or extend these innovations. If this technology is
effective in reducing someone's costs of operation, then I expect and
require that some reasonable value: a percentage of that cost reduction,
a one time payment, or an appropriate technology exchange with CryoSpan
should be forthcoming from that party.

     Although I have known the innovations disclosed herein for over two
years, I have not disclosed them earlier because they have not yet been
fully implemented on CryoSpan's patient storage system and, therefore,
their full potential has not yet been demonstrated. However, the basic
idea and part of the potential have been proven for sometime, and it has
recently become clear to me that for various reasons (mainly the
extremely slow rate of CryoSpan's cryonics patient expansion), it will
still be some time before the dewar system will be completed to a stage
where the full potential of the boiloff reduction method will be known.

The Basic Idea - Analysis of dewar boiloff rate

     After procuring CryoSpan's first whole-body dewar (based on the
Alcor design) at the beginning of 1994, I proceeded to analyze the heat
flow into the dewar by means of theoretical calculations, studying
previous analyses by others, and by placing thermocouples at various
points about the dewar. From these analyses and measurements, I
concluded that the heat flow into such a high-vacuum, superinsulation-
wrapped dewar is approximately as follows:

1) 5% of the heat flow is through the sides and base
2) 10% of the heat flow is through the foam lid
3) 85% of the heat flow is down the metal inner wall of the dewar

Therefore, it was clear that while using high vacuum and superinsulation
to reduce heat flow through the largest part of the surface area is very
efficient, and even the thick foam top does a reasonable insulating job
(partly because it interfaces only with warmer vapor), the major source
of heat inflow and subsequent boiloff is the continuous metal path
between the LN2 and the room air effected by the inner stainless steel
dewar wall. (This is one of the reasons for Bob Ettinger's attraction to
CI's fiberglass and perlite/foam cryostats.) After many thoughts of
possible ways to reduce the heat flow through this path, I decided that
the only feasible method was to lengthen the path from LN2 to room air
and to keep the temperature gradient along this path as small and as
uniform as possible. This is being implemented in the following ways:

1) CryoSpan's new dewar is 10" taller than the original Alcor design

     This additional height was used because the sheets of stainless
steel from which the dewar was built allowed that amount if used uncut.
Any taller would have been much more expensive whereas the 10" extra
cost little more. (Actually, no more because the extra welding cost was
offset by not including the roller feet and the handles of the original
Alcor design which do not fit our silos and insulation wrapping.)

2) The thickness of foam in the dewar neck will be increased by 10" 

     Both theory and measurements showed that is it very important to
have the escaping nitrogen gas generated by the boiloff "hug" the dewar
walls and be warmed as much as possible by the inflowing heat. By doing
so the heat removed to warm the LN2 gas is carried away back to the
outside by the escaping gas. This effect is of major importance to the
overall efficiency of the dewar. The ideal arrangement, therefore, would
be some kind of neck plug which would expand downwards to fill all the
space about the LN2 surface as it falls due to the boiloff, and yet
would be solid in the center, only allowing the gas to escape up the
inner wall. Although I have some ideas, we have not yet developed a
practical design for such a neck plug.
     Even if the total thickness of foam in the neck remains constant,
it is important to split the convection volume between plug and LN2
surface into several small parts. This can be accomplished by splitting
the extra 10" thickness into several pieces each of which can only drop
so far as the LN2 surface falls.
     In addition, we have found that it is particularly beneficial to
have a thickness of foam (as a circle tight to the inner dewar wall,
which we call a "baffle") riding on the surface of the LN2. This last
appears to greatly reduce the convection cooling of the walls, and to
keep all escaping nitrogen vapor close to the walls.
     We have partly been able to effect this last innovation with our
original dewar even though it was the standard Alcor height, because the
patient containers which we inherited with our three whole-body patients
from Trans Time were shorter than our standard containers (again based
on the Alcor design). In addition, they did not have the vertical "ears"
of the Alcor designed pods which would greatly hinder the effect of a
floating baffle when the LN2 level is low. With a 12" thick foam lid, a
3.5" foam floating baffle, and perhaps some natural reduction in the
ambient silo temperature, we have been getting a boiloff rate of 11.5
liters per day from a dewar which boiled off 14 liters per day with the
standard 14" thick foam top. Unfortunately, it will not be possible to
say for some time what boiloff advantage has been obtained with our new
taller dewar because it is currently being used as a reservoir with only
neuros in the bottom and its level varies widely.

3) The escaping nitrogen gas flow will be directed down the outer wall
   of the dewar

     This is possibly my most innovative idea. Others had tried thicker
tops, evacuated tops, or even "mushroom" type caps partly extending down
the outer wall of the dewar, all with little success. However, the
thickness of the dewar's outer wall at 3/16" or 187.5 mils is over 5
times that of the inner wall (35 mils). Therefore, the heat conduction
of a given length of outer wall is over 5 times that of the inner wall.
Thus, to gain much by making the temperature gradient extend down the
outer wall by insulating it from the external ambient heat source, the
insulation must be extended down the full length of the outer walls. In
point of fact, I found out after I made this discovery, that the idea
(and the actual implementation) of inverting another, slightly larger,
dewar upside down over the top of a given dewar had been tried before.
Therefore, my final proposed design (already partly implemented) of the
containment of the dewar is as follows:

     The outer wall is surrounded by corrugated fiberglass roofing
material (Home Depot) with corrugation running vertically to allow space
next to the outer wall down which the escaping nitrogen gas can flow.
This is covered by 5" of 1/2" foam layers bent to fit the curvature,
with interleaved joints and sealed with plastic wrapping. A 6" foam
external top is planned which will be sealed down tight onto the top of
the side foam and corrugated fiberglass. Thus, the escaping nitrogen
gas, which warms as it escapes and carries much of the inward flowing
heat back to the outside, after creeping up the sides of the inner wall
will be directed down the outer wall of the dewar to its bottom.
Finally, the gas will flow up the outside of the foam wrapping the
dewar, next to the 5" thick concrete silo walls and earth insulation.
     Once this is complete (we still don't have our sealed tops because
our automated filling system is not yet in place), I expect that there
should be a considerable temperature gradient down the silo wall and up
the dewar outer wall. The effect of this should be that the ambient
temperature at the very top of the dewar inside wall (which is normally
at room temperature) will be well below freezing. Therefore, the
gradient up the inner wall and the consequent boiloff rate should also
be considerably reduced.
     An additional advantage of this design will be that the entire silo
will be filled with cold, slowly exhausting nitrogen gas. No water ice
should be able to form anywhere around the lid, and various types of
data media should be able to be safely stored around the dewar at the
bottom of the silo. Finally, the 5" of foam surrounding the dewar and
only 1" from the silo wall should provided a large cushioning effect
from any buffeting which the dewar might incur during an earthquake.
     My calculations and my expectations are that when the final system
is complete, the boiloff rate of a dewar which was originally 14 liters
per day will be reduced to, at most, 9 liters per day.

     I hope that this is understandable without the use of diagrams. If
anyone has any questions or suggestions, please fire away.

-- Paul --

CryoSpan, Inc: low cost, secure cryogenic storage of biological material
1313 N Market St. Suite 3410, Wilmington, DE 19801-1151
Email:  Voice/Fax:909-481-4433

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