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. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=862