X-Message-Number: 2069
Date: Tue, 6 Apr 93 14:06:15 CDT
From: Brian Wowk <>
Subject: CRYONICS Thermoelectric Blues

        Yesterday I spoke with an engineer at Melcor, a major supplier 
of thermoelectric cooling modules.  I was told that single modules can 
indeed operate between a 70'C difference, and that modules can be 
cascaded to operate between even greater differences.  However the 
cascade scaling is not linear because each module must pump waste heat 
from all the ones beneath it.  The result?  Cooling between room temp 
and below -100'C would require a six stage system with a negligible 
coefficient of performance.  In other words thermoelectric cooling 
cannot maintain -140'C.  Cest la vie.
 
        As Robert Ettinger says, we will have to wait for the 
technology to improve.  It is still very, very far from the 
theoretical ideal.  Perhaps our 1000 patient storage system of 2005 
will use thermoelectricity.
 
        What about mechanical refrigeration?  Well today I spoke with 
an engineer at a cryogenic refrigeration company, and was given specs 
on a system that could pump 200 watts at -196'C for a 4.5 kW input.  
Assuming the efficiency is doubled at -130'C gives a coefficient of 
performance of about 10%, and an annual operating cost of $5000.  We 
would need two of these units at a capital cost of $34,000 and major 
maintenance (change of seals, etc.) is required every 10,000 hours.
 
        It now looks like LN2 is not so bad after all.  Bulk purchased 
it would give an operating cost of $10,000 a year versus $5000 for a 
mechanical system, and with none of the headaches or capital cost.  I 
suggest that we go with LN2 and leave the mechanical problems for the 
LN2 producers to deal with.
 
                                                --- Brian Wowk     

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2069