X-Message-Number: 2222
Date: Sun, 9 May 93 12:48:46 CDT
From: Brian Wowk <>
Subject: CRYONICS Foam Deterioration

Tim Freeman:
 
> Brian Wowk <> says:
>> Over many years the foam efficiency would decline by about 30% due to
>> air infusion...
 
> Under what conditions would it be practical and possible to replace
> the foam around the cold room?  Is this something you want to design
> for from the beginning?  Have the computations so far assumed that the
> foam is new, or that the foam is in its stable state?
 
        Replacing the foam would not be practical for the same reason 
that air infusion is not really a problem: It is very difficult for 
air to diffuse through huge blocks of foam surrounded by concrete and 
aluminum on all sides.  The removable foam blocks above the room are 
an exception, but of course they are easily replacable.
 
        It is really very conservative of me to mention this "problem" 
at all.  Let me quote from the Dow Chemical Company sheets on Trymer 
foam:
 
        The k-factor of isocyanate-based, cellular plastics does 
        increase slowly when not protected by an impermeable membrane.  
        The major change to occur in unprotected material is air 
        infusion which dilutes the effectiveness of the original cell 
        gas, increasing the initial k-values to approximately 0.027 
        W/m/degC.  *However, if the cellular plastic material is 
        properly protected with proper membranes, no change in the 
        initial k-factor will be observed even after many years of 
        service.*
 
The emphasis on the last sentence is Dow's, not mine.  Consider also 
that Dow usually sells Trymer to people who use it in 1 inch sheets to 
insulate hot pipes, not people who use it in 1 meter blocks to 
insulate coldrooms.  The large thickness and low temperature both work 
in our favor to reduce air infusion.  Consequently I don't think that 
air infusion is going to be a problem, even for the air-exposed blocks 
above the room.
 
        The $15,000 annual operating cost during the initial 15 year 
amortization period assumes the foam performs as new.  My long term 
operating cost estimate (post amortization) of $8000 assumes the foam 
has completely deteriorated.
 
                                                --- Brian Wowk

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