X-Message-Number: 1804 Date: Tue, 23 Feb 93 12:14:59 CST From: Brian Wowk <> Subject: CRYONICS temp rise Mike Darwin: > One of the things I repeatedly noted when filling the Alcor A-2452 > neuropatient dewar with liquid nitrogen from pressurized lS-160s is that > the temperature would uniformly rise 1xC after each fill*. My best guess: The pressurized LN2 enters the dewar through the submerged fill pipe at a temperature slightly higher than the 1 atm. boiling point of LN2. It is warmer while it is still in the IS-160 because it is boiling under pressure, and doesn't immediately cool to -196'C when it enters the dewar because the pressure *at depth* in the dewar is slightly greater than 1 atm. After filling stops, the warmer (and less dense) liquid will rise to the top and in a few minutes the -196'C uniform temperature will re- establish itself. I realize that the shallow depth of the old Bedford dewar is not consistent with this theory. Perhaps there was a pressure buildup in the dewar during filling because all the gas could not be vented fast enough? That would explain things quite nicely, and may be been a factor for the neuro dewar as well. --- Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=1804