X-Message-Number: 2160
Subject: CRYONICS Reliability
Date: Mon, 26 Apr 93 14:20:14 -0400
From: 


How many days can the present systems used for keeping patients cold
go without adding LN2 and without warming up the patients?

Mike Darwin says in cryomsg 2152:

>For instance, using a  mechanical  refrigerator  to 
>liquefy or keep liquid a large reservoir of nitrogen would be  acceptable.  
>If the refrigerator fails, you still have plenty of liquid nitrogen around 
>and  what  is more, the system can be run by just having  liquid  nitrogen 
>delivered.   I  am opposed to systems which rely  on  refrigeration  alone 
>(such as the Queue) or which rely on refrigeration and a passive heat sink 
>(such  as  lots of water ice) without the ability to plug in  a  delivered 
>refrigerant such as LN2 if the refrigerator goes down.

The system Wowk is proposing would be able to use delivered LN2 if
both coolers went down at once or the electricity and the diesel
generator both failed at once.  The idea is to pour it over the heat
exchanger coils, if I remember right.  (I wonder whether delivering
another cooler would be easier or harder than delivering the LN2.)
Being able to use delivered LN2 does not imply being able to
manufacture LN2 on site.  Using electricity to make LN2 is
inefficient, so it seems best not to routinely use electricity to keep
something at LN2 temperature on site.

>You never want to be under the gun to get the mechanical system up and
>running.

You are continuously under the gun to get LN2 delivered; I don't see
how mechanical systems are special.  With Wowk's scheme, a spare third
refrigerator sitting turned off in the closet is cheaper in the long
run than continuously using LN2, so potential problems with repairing
mechanical refrigerators shouldn't defeat his scheme.

I would feel better having my cryonics organization depend on
electrical power (assuming spare refrigerators and a backup diesel
generator and lots of ballast) than having it depend on an LN2
manufacturer who in turn depends on electrical power and working
delivery trucks and working roads and working delivery truck
drivers...

Tim

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