X-Message-Number: 2135 Date: Tue, 20 Apr 93 13:20:49 CDT From: Brian Wowk <> Subject: CRYONICS Ballast Stacking Steve Harris: > Ethanol/water mixes, as they freeze, will > be expected to freeze as pure water ice crystals, with ethanol > concentrated solutions between. This will continue until the mix > between the water ice crystals is the minimum-freezing > water/ethanol eutectic mix, which will likely be some simple > molar ration of ethanol and water (just as it is for ethylene > glycol and water). Given the very high freezing point of ice, I > would not expect such a eutectic mix of ethanol and water to > freeze at too much below the freezing point of pure ethanol. Of course! I had not considered that the water would slightly depress the freezing point of ethanol. This could well be a superbly elegant solution (pardon the pun) to all our problems. By the way, I contacted some industrial chemical suppliers today and was quoted was $1.30 (USD) per liter for 95% ethanol purchased in 200 liter drums. This would run us $6500 for 5000 liters, which is reasonable. > A thought about ballast conformation: Water is HEAVY. I'm > not happy about stacking a lot of 80 lb cans of water on top of > each other like a pile of bricks without mortar. It sounds > difficult and not very safe unless there are no open spaces > anywhere in the structure. Yes, further thought suggests that 5 or even 2 gallon cans might be better than 10 gallon cans. But you don't wan't too many small cans, or filling them and stacking them will be too labor intensive. I am indeed advocating that there be no open spaces anywhere in the structure. The whole room should be packed full with cans up to a height of about 2 meters (lower if we can get rectangular cans that pack more efficiently). You only remove enough cans to allow the insertion of each new patient, with any loose space packed with fiberglass batting. Cans cannot fall because there is no place for them to fall to. They are packed solid, and the top level is below the top of the patients. (Recall that the bottom half meter of cans (these consisting of ethanol/water) are left intact under the patients.) If we build in an area with high seismic risk (which I hope we don't) I would advocate the additional precaution of removable walls that can be slid in and out at intervals along the corriders. Otherwise I think this is expensive and unnecessary. > Even then, with the floor loading > we're talking about, this room is going to have to be built like > a swimming pool. Very difficult to have relatively delicate foam > slabs underneath such a thing! Weight is not a problem. 30,000 liters of ballast spread over about 20 square meters is 1500 kg per square meter, or 15 kPa pressure. The compresive strength of Trymer CPR 9545 foam at room temperature is 235 kPa, and is even higher at low temps. To put this is perspective, remember that you can walk on Dow Styrofoam (imposing a load of 100 kPa) without denting it. It is also important to realize that even when the room is full of patients with only residual ballast underneath them, there will still be a load of 1000 kg per square meter. > Well then: an alternative to having to stack carefully might > involve smaller ballast shapes which are deliberately poor at > filling space or packing efficiently, such as long hollow plastic > cylinders with fins (we want lots of space through which to move > circulating air). You don't want haphazardly-stacked ballast because it will make it difficult to excavate patient slots, and will be prone to shifting and putting pressure on patients. Also you want to minimize air space between the cans (hence my suggestion we use rectangular cans if possible). Any air space between cans will be dead air space because most air will pass over the top of the ballast and heads (actually feet) of patients. Air between cans will only reduce thermal conductance through the ballast, which we do not want. To recap the heat transfer situation: It is not important that air pass through the ballast because air will already be passing over and it and under it (under the false floor). Conductivity of the ballast itself will be adequate to keep temperature differences below 1'C at the rate heat would flow during a cooling failure. By the way, it occurs to me that those rectangular 1 gallon metal cans that solvents are sold in might work for us. Unfortunately we would have to lay them on their side for stability, which would make hooking the handle difficult. We might have to use Steve's electromagnetic grabber. Steve Jackson: > You still get the best packing efficiency > with six-sided cells - they just have to be lengthened on one > direction. Yes, I see that that is true for single-patient cells. However single-patient cells are expensive and inefficient. (Obese patients might not even fit in them.) I am currently enamored with my ad-hoc cell concept. > Re ballast material: What happens if you use brine rather than pure > water? Not much. The maximum freezing point depression you can get with a saturated salt solution is -21'C. I think Steve Harris has hit the nail on the head with his idea of a water/ethanol solution. --- Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2135