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Insulation materials - a literature study on what matters to us

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  • Insulation materials - a literature study on what matters to us

    Many of you ready know all this, I wrote it to give guidance for those who just started to learn about building their own wood fired oven. If it is in the wrong section, please move this thread.

    What is insulation?
    Here is a very short literature study:

    Insulation is a material whose purpose is to stop heat flux from one place to another. Heat is transported in three ways:
    1. Conduction, Heat transport in a solid material. Less density increases insulation capacity.
    2. Convection, Gas movement in the porosity within a material. Like air movement in a two-glass-window. Too wide and the window is non-insulating due to air movement between the glasses and too thin makes the insulating air gap not sufficient. About 16 mm distance was found optimum for windows.
    3. Radiation, At elevated temperature (above about 600 C) – the IR radiation within the porous material is significant. Smaller pores increase insulation capacity.
    In a WFO, the temperature is at most around 600 C and the dominating contribution to the insulation capacity is conduction. Being so, the type of material or pore size does not really make that much of a difference. The focus shall be on to get low density of your insulating material.

    Reverse engineering of fire bricks, foam-crete, insulating fire bricks, perlite, Vermiculite concrete, CaSi, AlSi, fiber mats and construction insulating materials like EPS, glass wool and natural straw are shown in the following figure. Blue dots are Room Temperature data. Orange is at 400 C. Red is V-crete.

    Click image for larger version  Name:	image_90480.jpg Views:	3 Size:	91.4 KB ID:	425056

    Below 400 kg / m3 – the scatter when thermal conductivity is plotted to density goes down. Why? Likely because the porosity in the materials are similar enough that the dominating contribution is conduction. See enlargement in next image:

    Click image for larger version  Name:	0-500 Density TC.PNG Views:	0 Size:	69.2 KB ID:	425055
    The dot at 150 kg / m3 with very low TC is aero gel. You can read up on it if it is of interest.

    Why is this important? Well, because it does not matter what insulating material you use if its density is low enough. The reason why CaSi insulates about twice as good as V-crete (vol. 5:1) is because V-crete has 50 % higher density.

    What you should focus on is to get a material that is refractory, strong enough for your needs and water resistant, so it does not collapse if it gets wet. If you feel like experimenting, measure the density of your insulating material! It will tell if it is useful or not and how thick it needs to be. At 400 kg / m3, the material is a good insulator. At 200 kg / m3, the material is very good and below 150 kg / m3 is really not necessary to go.

    Not all references are listed, but a lot of good reading is found here. l_investigation_of_expanded_perlite_based_heat_ins ulation_materials'_thermal_conductivity_values l_investigation_of_expanded_perlite_based_heat_ins ulation_materials'_thermal_conductivity_values ers_for_Super-Insulated_Long-Term_Storages_up_to_300_C +perlite+particle+size+mm+thermal+conductivity&sou rce=bl&ots=Z3R2aE6_FD&sig=ACfU3U31ijAOOBnSPmLtq-e2O92Eb_PnuQ&hl=sv&sa=X&ved=2ahUKEwjOucHTtfvoAhVGi qQKHViJAdgQ6AEwA3oECAcQAQ#v=onepage&q=Expanded%20p erlite%20particle%20size%20mm%20thermal%20conducti vity&f=false +insulation+pore+size&tbm=isch&source=univ&sa=X&ve d=2ahUKEwjAx-KLv_voAhWD5KQKHVFjAGsQsAR6BAgGEAE&biw=767&bih=744& dpr=1.25 ABB276E0A3529ECAD0788A0FDA07E07788AAE2012EBFB66BD3 9D69ABB29A52A888961F

    Happy mixing!
    Last edited by Petter; 06-30-2020, 05:34 AM.