X-Message-Number: 13832
Date: Sat, 3 Jun 2000 10:36:19 EDT
Subject: nitrogen boil-off

James Swayze asked why we need to keep adding liquid nitrogen from time to 
time in the cryostats.

Because it's cheaper than using a closed circuit and re-refirgerating the 

In an old-fashioned ice box, the ice gradually melts as heat leaks in, and 
must be replaced from time to time. Same principle--heat leak makes the 
nitrogen evaporate, and it is then vented. There do exist electric 
refrigerators operating at liquid nitrogen temperature, but their use would 
be much more expensive than the "ice box" style. Fred Chamberlain recently 
remarked that use of vitrification may require intermediate-temperature 
storage (higher than that of liquid nitrogen), employing mechanical 
refrigeration at higher cost, even though the heat leak is less at the higher 

Cryonics Institute also has on the boards a different approach to 
intermediate temperature storage, if and when that is indicated or an 
option--a passive system using liquid nitrogen but still holding the patient 
region at the desired temperature. Maintenance cost would not be higher, but 
capital cost would.

Robert Ettinger
Cryonics Institute
Immortalist Society

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