X-Message-Number: 862
Date: Thu, 28 May 92 19:52:12 EDT
From: 
Subject: CRYONICS

In reference to msg #860:

1) Does ethyl chloride contract enough as it freezes that a float valve in the
   ethyl chloride tank could control the liquid nitrogen valve?  The less that
   we depend on the reliability of the power supply the better I like it.

2) Alternatively:  There are a number of ways that one can make a passive
   thermal switch.  Consider, for instance, two metal rods separated by a small
   gap, surrounded by a gas that condenses at the desired temperature.  If one
   of the rods gets too cold, the gas liquifies and bridges the gap,
   substantially increasing thermal conductivity across it.  Suppose now that I
   have a patient or group of patients surrounded by a small dewar (or perhaps
   simpler insulation for a 75 degree temperature difference), in turn
   surrounded by liquid nitrogen.  I'd like to dribble in just enough heat to
   keep them at -125.  If I simply run an insulated metal bar through a thermal
   switch to room temperature the system will regulate itself.  If the patient
   gets too warm the conducting layer evaporates, thermal conductivity drops,
   and the heat leak to the surrounding liquid nitrogen cools us down.  If the
   patient gets too cool the conducting layer condenses, bridges the gap
   between the rods, improves the thermal contact to room temperature, and
   warms us up.

Comments?                                   -Jeffrey Soreff

Standard discaimer: I do not speak for my employer.

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