Thread: Moly cooling
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Old 08-05-2010, 05:56 PM
Edward Skeels Edward Skeels is offline
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Quote:
Originally Posted by David Patchen View Post
Isn't the question about which absorbs heat more readily after 8 inches--the air or more blanket?
the question is whatever you want it to be.

Thermal Conductivity
at 80F,
air is approx .174 BTU/Hr ft2 (F)/in
8# 2600f fiber blanket is listed at .29 BTU/Hr ft2 (F)/in

at 500F,

air is approx .275 BTU/Hr ft2 (F)/in
8# 2600f fiber blanket is listed at .51 BTU/Hr ft2 (F)/in

so it would appear that air is a better insulator

but,

with added thickness, additional fiber retains more heat than free air

assuming a hot face temperature of 2000f on a vertical wall:

with a material thickness of 3 inches kastolite 30 backed by 6 inches of 8# density 1" blanket,

307 BTU/Hr ft2 heat pass through

add 6 more inches of fiber and

162 BTU/Hr ft2 heat pass through

ceramic fiber is simply a low mass material that contains a lot of air. Lower mass is lower conductivity. Mizzou is above 150#/cu.ft and not much of an insulator. 8# blanket is, well, 8#/cu.ft. Fluffy material provides more air pockets. It's the air pockets that slow down the energy transfer. Sawdust or shredded newspaper insulates well, but kind of flammable.

resources:
Heatransfer application at hwr.com
http://www.matweb.com/tools/unitconverter.aspx
http://users.wpi.edu/~ierardi/PDF/air_k_plot.PDF
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