X-Message-Number: 2028
Date: Thu, 25 Mar 93 14:30:23 CST
From: Brian Wowk <>
Subject: CRYONICS The Utimate Design

        Thanks to Steve Harris for the great idea and great graphics.  
Since we want to go in from the top of the Room, the exact design must 
be different, but the principle of moving heat through metal rather than 
air remains powerful.
 
        I currently envision dividing the 25 square meter room into 20 
one square meter patient storage cells, each holding six whole body 
patients (which Hugh Hixon at Alcor says he can easily manage).  The 
outer wall of the room is covered with thick aluminum.  (Pound for 
pound, the thermal conductivity of aluminum is ten times that of steel.)  
The cells are also isolated from each other by solid aluminum walls with 
only small air circulation vents near the top.
 
        Four or five square meters at the center of the room are set 
aside as the "utility cell."  The utility cell holds the heavily 
insulated LN2 reservoir.  The reservoir is a can within a can.  The 
inner can is just a plain cylindrical tank that can be easily lifted out 
and replaced if necessary.  The base of the outer metal can holds the 
thermopile that controls LN2 boiloff for fine temperature control.  (As 
Steve Harris says, thermopiles may not *spontaneously* move much heat 
across a small temperature difference.  However they will pump heat like 
crazy if you actively force a current through them in the right 
direction.  In this way they can even make heat flow uphill.  We will 
instead be augmenting a downhill slide if necessary.)   
 
        Because the air ciculation system will be turned off from time 
to time (or it may fail completely) you want the reservoir "coldness" to 
be moved away from the center of the room as fast as possible.  This is 
accomplished in two ways.  First, the -196'C boiloff vapor from the 
reservoir (which accounts for about 25% of the heat flow) is carried 
through insulated pipes to uninsulated pipes attached to the room outer 
wall.  Second, the heat of LN2 vaporization will be directed into 
carefully designed metal conductors that move heat directly from the LN2 
outer can to the aluminum cell dividers adjacent to the utility cell.  
These dividers will distribte cold amongst the other dividers in the 
room much faster than just letting a pile of cold gas accumulate around 
the base of a thinly insulated reservoir.  Note that the reservoir is 
now thickly insulated (as is the utility room itself) so that heat flow 
does not involve gas in the utility cell at all.
 
        In addition to this wonderful passive heat distribution system, 
we have an active air circulation system.  The top half meter of each 
cell (clear of the patients in the 3 meter high cells) will be open to 
two adjacent cells.  The pattern of openings is designed to create a 
distinct cell-to-cell air circulation path.  (This ensures there will be 
no cells with dead air.)  The circulation path begins and ends in the 
utility cell where the fans are located.  The fans are actually inside 
conduits passing through the utility cell, but not involving air in the 
cell itself.  As discussed below, this means a worker can work in the 
utility cell without even turning off the air circulation system.
 
        What about the cooling thermopile(s) that must move heat to the 
thermopile in the LN2 reservoir?  They are in the utility room too, 
underneath removable sections of room insulation, connected to the 
aluminun walls of adjacent cells.
 
        Thus everything you would ever want to service in the Cold Room 
is accessible from the utility cell.  And the utility cell air is 
insulated and isolated from the rest of the room!  This means you can 
warm the utility cell air up to a cozy -40'C with space heaters without 
affecting the rest of the room.  A warmly dressed worker with an oxygen 
mask can now work in this room even with the -130'C air circulation 
system running.  You would only turn it off if you were replacing a fan.  
Goodbye cryosuits!
 
        A word on the fans.  They will have to use electric motors rated 
for operation at -130'C.  (According to Hugh Hixon these motors are 
expensive, but available.)  You will want two or three fans with 
independent backup batteries (presumably external to the room) operating 
in parallel.  To circulate the 75 cubic meters of air completely through 
the room once per minute, you will have to move it through the 0.5 
square meter cell vents at 2.5 meters per second.  This would give the 
200 kg of air in the room a kinetic energy of 600 joules which would 
have to replaced every once every minute (worst case).  This corresponds 
to a fan power of about ten watts.  I suggest using three 10 watt fans 
in parallel.  This will increase LN2 bioloff by about 6% considering the 
500 watt heat flow out of the room.
 
                                                --- Brian Wowk    
      

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