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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2028