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Post by Dan (Upstate NY, USA) on Jan 31, 2012 2:53:58 GMT -8
Vermiculite, loose fill 2.08
Perlite, loose fill 2.7
Rock wool, batts 3.66
Rock wool, blown loose fill 2.93
Perlite concrete 1:8 1.96 R per inch
Vermiculite conrcrete 1:8 1.6 R per Inch
Does anyone know the R value of fire brick for comparative analysis?
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Deleted
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Post by Deleted on Jan 31, 2012 9:37:09 GMT -8
R-value (insulation) en.wikipedia.org/wiki/R-value_%28insulation%29#Example_.28SI_units.29Reflectivity en.wikipedia.org/wiki/ReflectivityAlbedo en.wikipedia.org/wiki/AlbedoEmissivity en.wikipedia.org/wiki/EmissivityThe R-value depends on thermal conductivity, color and Reflectivity (albedo), emissivity, transparency, convection, direction of transfer and just as well on the amount of layers. Things will not stay white or a miror in a stove. Multible layers of different materials may result in a very high total R-value. " With multiple modes of heat transfer, the final surface temperature (and hence the observed energy flux and calculated R-value) will be dependent on the relative contributions of radiation, conduction, and convection, even though the total energy contribution remains the same." BTW: The usual standard for the R-Value is at a temperature gradient of 24 °C, at 50% humidity with no wind. The temperature gradient of a rocket stove may be up to 1000°C. The thermal resistance may be very different under such conditions. The relative contributions of radiation, conduction, and convection may be very different too. |
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Post by machinemaker on Jan 31, 2012 19:04:25 GMT -8
something that I have considered in respect to the heat raiser in a RMH. First a bit a personal background: I have been building and using foundry furnaces, large reverbatory furnaces, heat treat ovens and other high temperature refractory lined vessels for several decades. In my shop I have a crucible furnace that I melt bronze in for casting, it is lined with a 3" layer of dense hard refractory that is the inner surface of the furnace and is exposed to a 1.25 million BTU propane flame. behind that is another 3" layer of low density concrete and outside of this is a stee shell. The dense hard refractory is nearly the same as dense hard fire brick. It is not very insulative, but when in use the heat transfer through the 3" thickness is fairly slow. for example after running the furnace for a 6 hour day of casting the interior of the refractory will be yellow to white hot within 15 minutes of starting the furnace, but the exterior of the furnace shell is only about 140 f. after a six hour day of operation. I have always liked using the dense castable rather than the more insulative refractories due to their ability to hold up to years of high heat and cooling cycles. My furnace interior is still hard as a rock and the one or two cracks in it have been there since its first firing. I believe that the surface does heat up and that it reflects that heat back into the interior of the furnace. Just the same as the large reverbatory furnaces that I have worked with over the years. I would think that in the raiser of a RMH that by having the surface of the raiser yellow to white hot, 2-3000 f that this would aid in the complete combustion of the flue gases. That and I have to believe that this would last for the life of the stove and house. Hey, I could be full of crap, but this is just my thoughts. here is a photo of us pulling a crucible of bronze out of this furnace. the metal inside the crucible is 2300 f, the exterior of the crucible is a bit hotter and the refractory lining of the interior of the furnace is hotter yet. I hope to start on a RMH for our green house later this spring or summer and plan to use castable refractory for the stove.  kent |
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