X-Message-Number: 5711
Date: Tue, 6 Feb 1996 22:29:58 -0500
From: "Keith F. Lynch" <>
Subject: Fast freeze

In #5704 "Richard Schroeppel" <> writes:
> f) Superconductors and LHe have interesting heat-conduction
> properties.  Can we use make use of them?

Many superconductors of electricity are known, but they are never
superconductors of heat, and they aren't even superconductors
of electricity until they are already close to liquid nitrogen
temperatures.

Liquid helium *is* sometimes a superconductor of heat.  But never
at even the lowest temperatures used in cryonics.  Liquid nitrogen
would itself freeze solid long before helium condenses into a liquid.
Liquid helium is only useful for conducting heat between things that
are already within a few degrees of absolute zero.

What are you trying to accomplish by freezing patients faster?  The
trend in cryonics appears to be toward freezing them more slowly.
If you are trying to prevent ice crystallization without using
cryoprotectant, this requires *enormous* cooling rates, which have
henceforth only been achieved in microscopic droplets.

If you could somehow cool a whole patient from normothermy to liquid
nitrogen in one thousandth of a second, this would:

* Be far too slow to prevent all the ice from crystallizing.

* Be so fast that the differential coefficients of expansion of
  different tissues would cause a shock wave sufficient to explode
  the patient like something from a Dave Barry humor column.
--
Keith Lynch, 
http://www.access.digex.net/~kfl/


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