From: spike66 (spike66@attbi.com)
Date: Tue Jul 30 2002 - 23:15:07 MDT
While vacationing at Mount Rainier, I had an idea regarding
those in cryo-suspension. Perhaps this has already been
studied by the folks at Alcor.
Assume a dewar is filled with patients, so that none will
be coming or going in the immediately foreseeable. Now
imagine that as the nitrogen boils off, its volume is replaced
by spheres of dry ice, perhaps marble or golf ball sized.
These would sink the to bottom, being twice the density
of liquid nitrogen. It might help to pre-cool the dry ice to
-200C to prevent boiling nitrogen as the CO2 cools.
Eventually the dewar will be filled with CO2 spheres with
liquid nitrogen (and patients) in the interstices. The LN2
would continue to boil off as before and need regular replacment,
but this time the dewar would provide extra protection to the
patients in the event of a failure to replenish the LN2 for some
period. After the last of the LN2 boils off, the patients would
warm from -196C to about -78C, still cool enough to prevent
damage to the patients. They would stay at about -78C until all
the CO2 sublimes. CO2, being more dense than nitrogen, would
stay in the dewar better, so this would perhaps reduce one
of the mechanisms for introducing heat to the dewar.
I estimate that the CO2/LN2 mixure should last about
4 times as long as LN2 only. Reasoning: the latent heat
of vaporization of LN2 is about 160 Joules/ml whereas
CO2 is about 500 Joules/ml. Not only does the solid
CO2 have a much higher capacity to carry off heat
during vaporization, the heat load on the CO2 spheres
at the end of the LN2 boiling phase would drop significantly
as the contents of the dewar warmed from -196 C to -78 C.
When I asked why the patients were placed in the dewar
inverted, several suggested that it was to prolong the protection
in the event of a failure to refill the dewar with cryonic fluid
(for whatever reason.) The LN2/CO2 mixture idea would obviate
the need for suspending the patients upsidedown, a
practice which may cause surviving family members to be
squicked and attempt a lawsuit to recover the corpses
of their family member. I don't think we should ignore
this factor. Recall that the Apostle Peter humbled himself
below his master by requested to be crucified upsidedown,
which was considered a more dishonorable way to perish
than head-up. Ted William's daughter has demonstrated
that this head down business has its own drawbacks, even
if it adds a small theoretical safety advantage.
Has Alcor or equivalent looked into adding solid CO2 to
the dewars?
spike
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