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     

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