X-Message-Number: 2000
Date: 20 Mar 93 19:39:13 EST
From: Mike Darwin <>
Subject: CRYONICS Cold Room

From: Mike Darwin
To: All
> Subject: Cold Room
Date: 19 March, 1993

     I read with interest Timothy Freeman's comments attributed to me -- 
boy! you make one error demonstrating your basic ignorance of physics and 
mathematics and folks just won't give you a break!  I guess Brian pointed 
out that the comments were from him.  Nevertheless, Brian's remarks and 
Mr. Freeman's reaction to them prompts me to put my oar into dangerous 
waters yet again with the following observation about dewars and soft 
vacuum.  Please correct me if I'm wrong about the theoretical parts, but I 
can vouch for the practical parts from experience.

     I have been told by several cryogenic engineers that when a high 
vacuum system is failing (somewhat slowly) there is actually a point at 
which low vacuum is MORE conductive than no vaccum at all (i.e., 1 
atmosphere).  The reason I was given is that at some point the decreased 
viscosity of the gas allows the atoms in the annulus to brouce back and 
forth between the inner and outer can very rapidly without coliding with 
each other.  The analogy I was given was that it is sort of like people 
ferrying buckets of oranges back and forth across a bridge.  When things 
get crowded their transit time drops since they they start bumping into 
each other.

     I have observed this phenomenon with the old Bedford dewar when it 
was in for major repairs/revac.  The boil off rate was higher just before 
the vacuum was completely released (as measured by a flowmeter) than 
afterwards.

     I would urge Brian to contact Bob Ettinger.  I seem to remember that 
he initiallly got very large numbers for foam thickness but found out that 
in reality the actual benefit drops off sharply past 1-ft. thickness.  Why 
this was I don't recall.  Again, as I've often said I'm no physicist or 
mathmetician.

     My thanks to Keith Henson for his suggestion.

     As to the flashes of blue light:  Yes I was aware of triboluminesence 
and yes, wintergreen lifesavers do give off such flashes.  However, I 
wonder if this is what is going on in vitreous solutions.  Steve Harris 
tells me that triboluminesence occurs as a result of the excitation of 
nitrogen atoms and does not occur if the sugar crystals are crushed under 
vacuum or in a helium atmosphere, etc.

     I found Brian's comments interesting: the Russians reportedly 
measured the temperature of the flashes (how, I don't know) and found it 
to be either 1700*C or 2000*C according to Greg Fahy I can't remember  
which temperature).

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