X-Message-Number: 2077
Subject: Re: cryonics: #2065-#2069 
Date: Wed, 07 Apr 1993 12:43:08 -0400
From: "Perry E. Metzger" <>


> From: Brian Wowk <>
> 
> Perry Metzger:
>  
> > Assuming one built one's units with dual mechanical cooling units,
> > had backup power, and had enough thermal balast to keep the units
> > safely at temperature for half a day during catastrophic failures,
> > you should be fine...
>  
>         Rather than half a day, I would prefer at least *one week*
> worth of thermal ballast.  One of my tenets in this discussion is
> that a -130'C system can be built that is at least as safe as
> our current system. 

Well, I was just handwaving. If you can keep enough ethyl chloride
slurry around in your vault to keep things fine for a week, who is to
naysay that? The point is, however, simply this: it doesn't seem that
there is anything really wrong with mechanical systems if properly
designed.

>         What about mechanical refrigeration?  Well today I spoke with 
> an engineer at a cryogenic refrigeration company, and was given specs 
> on a system that could pump 200 watts at -196'C for a 4.5 kW input.  
> Assuming the efficiency is doubled at -130'C gives a coefficient of 
> performance of about 10%, and an annual operating cost of $5000.  We 
> would need two of these units at a capital cost of $34,000 and major 
> maintenance (change of seals, etc.) is required every 10,000 hours.
>  
>         It now looks like LN2 is not so bad after all.  Bulk purchased 
> it would give an operating cost of $10,000 a year versus $5000 for a 
> mechanical system, and with none of the headaches or capital cost.  I 
> suggest that we go with LN2 and leave the mechanical problems for the 
> LN2 producers to deal with.

I'm not comfortable with much of the handwaving here. There are too
many estimates being made with the outcomes being, from my
perspective, very close in numbers. Given the magnitude of the
decisions being made here, and the fact that we are talking about
small price differences, it might be very worthwhile to get very solid
numbers and a much more solid idea of what sort of maintainance would
actually be required either way.

Also, I suspect that systems that operate at -196 and -130 have very
different maintainance requirements -- I know that bio lab freezers
can operate for years without maintainance, which would mean more like
30000 or 50000 hours. This is likely because mechanical seals do much
better at higher temperatures.

Finally, I must admit to feeling a lot more comfortable with things
bought commercially from going concerns over things rigged by
amateurs. Its not that I don't believe that the amateur solutions
can't work -- its that I tend to believe that the pros tend to know
how to do things cheaper since they've been doing things longer, and
that their equipment comes with things like factories that make spare
parts. If it turns out that all we have to do is ask some freezer
company to do some slight engineering modifications on existing units
and buy a couple of diesel generators for emergencies, it would mean
that our efforts could be directed towards stuff the professionals
don't know how to do (like more research) and that we could quit
worrying about problem.

Again, I don't want to be annoying here -- I am merely suggesting that
the "right thing" to do would be to get very precise numbers on this
whole thing. Brian has been around long enough that he deserves a
bunch more respect than I do. I just think these items deserve very
precise quantification. 


Perry

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