X-Message-Number: 7675
Date: Mon, 10 Feb 1997 14:34:13 -0500
From:  (Ken)
Subject: Re: Technology Disclosure

Paul, I just saw your idea for an improved Dewar vault, and I love it!
I particularly like the beautiful negative feedback mechanism built into
the design (i.e. increased ambient temperature->slightly increased boiloff
rate -> increaed cooling of the external surfaces -> resistance to further
increase in boiloff rate).

So. how to improve it?  One critical observation: you're reaching the
point where the major thermal conductors into the system are the air
and nitrogen vapors themselves.  Design accordingly- insulate the walls
and floor of your silo.  Hopefully you're not using bare concrete
for the floor; you should at least have a raised wooden platform
packed with foam to really take advantage of this design.  Or, if
you really want to do it 'right', consider doing for the air/nitrogen
gas what you're already doing for the metal Dewar walls: reduce the
thermal gradient by lengthening the path out of your system.  May
I suggest piping the escaping gas through something, e.g. a garden
hose packed in some insulation?  If 85% of your current losses are
through the metal inner dewar wall, I'd actually be surprised if you
didn't cut your LN2 boiloff in half with this overall approach.
(What will the economics of cryonics storage look like if boiloff
gets cut down to the 3 or 4 l/day neighborhood?)

Good luck!


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