hpmer
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Posts: 240
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Post by hpmer on Aug 16, 2008 6:56:16 GMT -8
Since the best insulating material is generally considered to be that with many air pockets because of air's poor heat conductivity, wouldn't the best insulative material be a simple "dead air" chamber surrounding the combustion unit, or is there some advantage to having it interspaced with some material?
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Post by canyon on Aug 16, 2008 10:13:54 GMT -8
You've got it right about "air pockets" being the good insulator. Free air in a "dead air" chamber can then set up convection and greatly improve the heat exchange and therefore lessen the insulation value. By locking air into tiny pockets with some kind of low mass material you break up the convection and get good insulation. Vacuum is another matter. There isn't much air in a vacuum and hence convective currents can't establish. If a vacuum chamber could be kept around the heat riser despite the repeated thermal cycles that would be ideal!  p.s. it's easy to become a member (you are more than a guest!) |
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hpmer
Full Member
Posts: 240
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Post by hpmer on Aug 19, 2008 9:52:43 GMT -8
That makes perfect sense. Thank you.
And I assume coating the insulation (perlite etc.) in a thin layer of clay is to prolong the life of the material?
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Post by canyon on Aug 20, 2008 7:45:40 GMT -8
And I assume coating the insulation (perlite etc.) in a thin layer of clay is to prolong the life of the material? The clay binds it together and limits the mentioned convection currents etc as well as settling. Check out some of Donkey's sawdust/clay cast refractory experiments elsewhere on this site. Pretty cool idea that might give you more insight. |
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