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Post by baronkev on Mar 13, 2012 11:04:27 GMT
what about vermicrete and steel.. can you add them to the list.
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Post by cannyfradock on Mar 13, 2012 16:09:28 GMT
Thank you Turkey and Calef for that information. The thermal values actually DO help a lot when choosing what to use and the list of materials with values creates a clear picture of what is good and what is not. More information please !!!! ;D Tom Quite right Tom....my remark earlier was flippent....sorry chaps Terry |
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Post by turkey on Mar 13, 2012 22:00:11 GMT
Not having any of either perlite or vermiculite to look at in detail, is perlite smaller? If it was then to make it solid with cement might require more cement resulting in a lower final U value, larger irregular shapes might be better?
But I do think there is something to it and construction in general uses vermiculite for insulated concrete or lightweight concrete. It still has decent compressive strength, so it's probably a tried and tested recipe the FB boys saw and have adopted.
u values of steel.. Well it would be high as it's such a good conductor, 1.2 I found on a quick google. No idea for vermicrete unfortunately, it's not a fixed item so would depend on ratio it's made to... If anyone finds anything I would love to know.
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Post by Calaf on Mar 14, 2012 8:17:53 GMT
Turkey, Perlite is a bit like Rice Crispies. Unlike Vermiculite it has tiny air pockets that I think must account for the better thermal value on paper. But I suspect this also makes the resulting "perlicrete" slightly porous. It's the same price as Vermiculite and readily available. In my little test I found the Vermiculite concrete had better tensile strength than Perlite concrete but were comparable in compression.
U-value is not the same thing as Thermal resistence/conductivity. The U-value of a material is its insulation value for a specified thickness. Thermal Conductivity is the intrinsic property of the material.
The Thermal conductivity of Steel, on the same scale as above, is 35-55 depending on tempering. But this is where eyes may glaze over... you have to think of the scale as logarithmic...
Steel -- 35-55
Copper -- 400
Gold -- 310
Diamond -- 2,000
Open a hot oven while wearing a Gold chain and you'll know the effect. Stings like buggery because it absorbs a lot of heat in a fraction of a second.
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Post by tonyb on Mar 14, 2012 11:18:45 GMT
Calaf, I'm pretty sure that all the references I've seen show vermiculite and perlite as having the same or similar thermal conductivity, though some variation depending on density ie how much entrained air. Can you remember the reference?
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Post by Calaf on Mar 14, 2012 12:58:30 GMT
Tony, an old colleague of mine is an academic working in Materials Science at a local U. He provided the data in SI units, W/(mK) but I don't know what Journal or database he uses. He did say that figures will vary wildly as its not easy to measure in a standardised method and to be aware US data are often quoted in BTUs. I noticed when trying to find the value for Celcon/Thermalite blocks figures quoted from 1.1 to 2.2, so it was good to get an impartial source. And it's important to remember convection and surface refraction etc. also play a part in real world applications. Edit: found this www.engineeringtoolbox.com/thermal-conductivity-d_429.htmlData has slight differences, but largely in agreement. |
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Post by turkey on Mar 14, 2012 13:33:05 GMT
[digression] we where talking about this recently, as I had seen some folks make their own CPU heat paste with some diamond powder and paste of some sort, and then bench-marked its results and it out performed some of the commercial silver premium products. very weird to think of diamonds as such superconductors but they are carbon after all. [/digression] |
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Post by Calaf on Mar 14, 2012 14:14:13 GMT
Wow! Extravagant. Arctic Silver, popular with overclockers, claim 8.89 in the leaflet it comes with.
My gran told me the way to tell a real diamond is to put it to your tongue. It will feel cold like ice (quickly conducts heat away).
Could probably make good Firebricks with diamond dust.
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Post by veauifru on Mar 14, 2012 17:07:55 GMT
It would be useful to have a list of common materials used in oven building with their thermal values. Would it be possible to make a table and post it in the construction forum?
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Post by baronkev on Mar 14, 2012 17:33:59 GMT
It would be useful to have a list of common materials used in oven building with their thermal values. Would it be possible to make a table and post it in the construction forum? Seconded!  Needs to be in an easily accessable part of the forum for easy referance. |
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Post by Terry Hardwood on Mar 15, 2012 17:14:38 GMT
I saw a list somewhere of refractory materials with their U-values or something. I'll see if I can find it again and post it for you. Certainly would come in handy.
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Needs to be in an easily accessable part of the forum for easy referance. 