X-Message-Number: 6064
Date: Thu, 11 Apr 1996 23:32:03 -0400
From: "Keith F. Lynch" <>
Subject: SCI.CRYONICS Re: Should cryostats be turned into pressure cookers?

In #6041, Doug Skrecky <> wrote:
> At -195.8 F the boiling point of liquid nitrogen is actually lower
> than it needs to be for cryopreservation.

Since nobody else has responded...

It's -195.8 C (-320 F), not -195.8 F, but you're right.

> If the boiling point could be increased boiloff would be reduced

True.

> and storage costs lowered.

Not necessarily.

> If the flowrate for the gas produced by boiling is limited
> sufficiently the pressure inside a cryostat will increase till
> the flowrate increases to match the boiloff.

Liquid nitrogen is cheap.  High-pressure dewars are expensive.
Especially when you must *guarantee* that there will *never* be a
sudden pressure loss.  If there was a sudden pressure loss, the change
of pressure and the change of temperature would probably shatter the
patient into small pieces.  Especially when the liquid nitrogen in the
patient's sinuses instantly and explosively flashes into vapor.

And how would you design the valve to allow refills?  It must let
liquid nitrogen flow against the pressure gradient, it must operate
at *both* liquid nitrogen temperatures (interior high pressure and
exterior low pressure), and it must *never* leak significantly or
become jammed, even after a century of use.  Good luck.
--
Keith Lynch, 
http://www.access.digex.net/~kfl/


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