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Thread: Heat Reflective Ob Coating

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    The critical parameter is the emmissity of the paint and not it's color. Emissivity is a measure of how well a material radiates energy vs reflects it. You can have a black surface that stays cool if the emissivity is high. When you paint a surface you have to remember that there are two sides of the paint, one facing the outside and one that is facing the material it was applied to. So you want a paint that both reflects the in coming energy but also allows the energy on the inside of the observatory to also be released. If not once the inside becomes warm, the paint will hold the heat. Much like the atmosphere of Venus, it is highly reflective but has poor emissivity so it holds the heat.
    So these new speciality paints function in both manners and are engineered differently when a typical commerical white enamel.

    All the Best,
    - Dave

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    Art,
    I posted "Originally Posted by DAVEG
    You can have a black surface that stays cool if the emissivity is high. Dave
    and you replied
    "Really? Find me one!"

    Sure, the tiles on the space shuttle are black and only few seconds after they are heated to a many thousands of degrees you can hold them in your hands because of the emmissivity and thermal conductivity of the of the material.

    You stated "Finally, I dare you to find a single commercially made observatory dome for our community that is any other color than white."

    As for observatory domes, many of the modern ones are other colors then white because of the emissivity they have. Here is a link to Southern Gemini Observatory and the dome is silver Ariel View of Gemini South. Also here is a link to Ash Domes who makes domes from many of the domes from schools, university, private and public observatories. Their domes are pictured as silver as well. Ash-Dome: observatory domes and tracking instrument shelters Finally here is a link to ObservaDome which is another major manufactors of dome and they show pictures of their domes as silver and installed in places like goverment installation in desert locations were heat issues would be at their extremes.
    Observatory Dome Telescope Dome Structure Instrument Missile Tracking Laser Ranging Building Shelter
    I don't follow how the color of unmanned space crafts has anything to do with heat management. They simply could be white because that makes the spacecraft easier to track visually. If you look at the space shuttle external fuel tank, which is filled with super cooled liquid hydrogen at -454°F it is brown/orange in color. Again it is the thermal conductivity and the emissivity of the material that matters and not it's color.
    You can't completely prevent heat from getting into a building or observatory. The air itself is excellent an means of transport. At night the way that a structure losses it's heat is by black body radiation to the sky and the measure of which is emissivity. It is not the color that determines this but again the emissivity of the material.
    By the why, as you know I am a Dupont Research Chemist and Engineer and tomorrow I will have 26 years of experience in scientific research working for Dupont, including work on paint formulations which included Imron. So I have very good understanding of how theory is turned into practical results.

    All the Best,
    - Dave

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