X-Message-Number: 2067 Date: Tue, 6 Apr 93 14:07:49 CDT From: Brian Wowk <> Subject: CRYONICS New LN2 System While I recover from my thermoelectric embarrassment let's get on with the business of designing an LN2 Cold Room. One of the problems of Cold Room design is achieving a decent temperature distribution for the case of air circulation failure. My old design with a central LN2 reservoir connected to adjacent metal cell wells would create a terrible temperature gradient without air circulation. I now have a new design that definitively solves this problem. Returning to our prototypical 5m x 5m room with square meter cells 3m high, we distribute four insulated LN2 reservoirs in four cells as shown below. This leaves 21 cells for patients, giving a 21 x 6 =126 patient capacity. Allowing space for insulation, I estimate we can squeeze 1000 liters in each reservoir for 4000 liters total, giving 20 days worth of cooling when full. O-------O-------O-------O-------O------O | | | | | | | | | | | | O--------------------------------------O | | | | | | | | LN2 | | LN2 | | O--------------------------------------O | | | | | | | | | | | | O--------------------------------------O | | | | | | | | LN2 | | LN2 | | O--------------------------------------O | | | | | | | | | | | | O-------O-------O-------O-------O------O Now here comes the clever part. The "O"s along the outer wall are lightly insulated vertical pipes holding LN2. The pipes bend and pass underneath the floor of the room connecting to the bottom of the nearest LN2 reservoir. No pumps are required required to keep LN2 in the pipes; hydrostatic pressure automatically keeps the LN2 level in the pipes the same as in the connecting reservoir. There are many beautiful aspects to this design. Because the pipes and reservior walls are metal (with a high thermal conductivity) the temperature underneath the insulation remains at -196'C along the entire vertical length of each. (Rising -196'C vapor from boiling LN2 in the pipes also helps this happen.) This means that the temperature distribution in the room remains very stable independent of the LN2 level. Also, the temperature of the room can be "fine tuned" very easily. By designing insulation around the reservoirs and pipes in the form of removable rods you can remove and replace rods (like in a nuclear reactor :) ) to achieve whatever temperature or temperature distribution you want. This would be done during the first few weeks of room operation (with fans turned off) as part of the commissioning process. As a final touch you might want to add electronically controlled heating elements in the reservoirs for continuous super- fine temperature control. Since the reservoirs are permanent, purging accumulated LOX (if this is a real concern) is somewhat problematic in this design. The only way to do this would be to peroidically (every year?) allow a reservoir to boil dry, relying on the remaining three reservoirs and fan-driven air circulation to keep that quadrant cold for the few hours that the LN2 is very low. I think this design is definitely on the right track. I await your feedback. --- Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2067