X-Message-Number: 13844
Date: Mon, 05 Jun 2000 11:50:42 -0700
From: Jeff Davis <>
Subject: cryostats and economics of scale


In line with Dave Pizer's comments on the effects of suspension costs on
the growth and accessibility of cryonics, I would like to offer the
following, though it is by no means a new idea.  Part of the expense of
suspension stems from the cost per patient of their cryostat and of the
liquid nitrogen replenishment requirement arising from boil-off.

The leakage of heat into a cryostat, which causes the boil-off, passes
through the surface of the cryostat.  Because the ratio of surface to
interior volume decreases as the size of the cryostat increases, the
boil-off per patient, and the corresponding replenishment requirement,
decreases as well.  Thus, for a very simple example, with two cryostats,
one ten times as large as the other, the boil-off per patient--assuming
that the number of patients inside the larger cryostat is proportionately
larger: ten times as many--the cost per patient for liquid nitrogen
replenishment would be reduced by a factor of ten.

At the same time, because the material required per patient for the
cryostat is reduced by the same surface to volume ratio, the material cost
per patient is correspondingly reduced by a factor of ten when the cryostat
is ten times as large.  This particular factor is probably not that
important, because material costs are typically only a very small part of
the total cost of an item, but it is instructive.  The larger cost factor
would be the cost of taking those materials and fabricating them into the
actual cryostat in question.  The relative costs of fabrication of large vs
small do not obviously or so easily submit to analysis based on the
straitforward relationship of surface to volume.  Nevertheless, I am
willing to guess that the fabrication costs per patient also decrease
substantially, perhaps, based on careful design, even beyond the ten to one
advantage achieved for boil-off and simple materials. 

My background is in engineering.  From an engineering standpoint the goal
of any given design is functionality first and cost second.  Put simply,
first it has to work, then it has to work as cheaply as possible. A
cryostat need not be a high-tech item.  It's rather simple actually.  A
double walled tank with a vacuum in between.  A large cryostat could simply
be a large verticle concrete cylinder and end caps, as the outer wall.
This would be sheathed with a thin outer layer of corrosion-resistant metal
(stainless steel) to act as an vapor-impermeable barrier. Inside would be
essentially a metal tank--no need for expensive stainless here--smaller in
diameter than the inside diameter of the outer wall. With appropriate
forethought given to contraction and low-temperature brittleness, you have
yourself a big-ass cryostat, and more affordable cryonics.  It's not rocket

			Best, Jeff Davis

	   "Everything's hard till you know how to do it."
					Ray Charles				

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