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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2160