X-Message-Number: 1995
Date: Fri, 19 Mar 93 13:10:05 CST
From: Brian Wowk <>
Subject: CRYONICS K values

Steve Harris:
 
> I assumed one foot thick foam, but used a K of ~ 0.01 watt/m*K, which
> was the number I got for the best cryogenic foams used in insulating
> the non-Dewar tanks of liquid fuel cryogen rockets, like the
> space shuttle (NASA reprint #1002).
 
        I started from the room-temperature R value of Dow Styrofoam 
(quoted to me by a dealer), which is 5 per inch.  This corresponds to a 
room-temperature conductivity of 0.028 watt/m*K.  Considering that the 
thermal conductivity of a gas varies as the square root of the absolute 
temperature, this value scaled to a point midway between 20'C and -130'C 
comes out to be 0.024 watt/m*K.  Polyurethane foam, with R = 5.9, would 
be only 20% better.
 
        It would be useful to know what K value Hugh Hixon used to 
successfully predict the performance of the Trymer cool-down boxes.     
 
                                                --- Brian Wowk

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