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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2222