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Transcript of Thermal Considerations 01/17/2008 tmurphy/phys121/lectures/04_thermal.pdf · PDF file...

  • Thermal Considerations 01/17/2008

    Lecture 4 1

    Winter 2012

    UCSD: Physics 121; 2012

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    Material κ (W m-1 K-1) comments

    Silver 422 room T metals feel cold

    Copper 391 great for pulling away heat

    Gold 295

    Aluminum 205

    Stainless Steel 10–25 why cookware uses S.S.

    Glass, Concrete,Wood 0.5–3 buildings

    Many Plastics ~0.4 room T plastics feel warm

    G-10 fiberglass 0.29 strongest insulator choice

    Stagnant Air 0.024 but usually moving…

    Styrofoam 0.01–0.03 can be better than air!

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    •  Note that these examples use the non-SI definition and are per inch. Vacuum insulated panel has the highest R-value of (approximately 45 in English units) for flat, Aerogel has the next highest R-value 10, followed by isocyanurate and phenolic foam insulations with, 8.3 and 7, respectively. They are followed closely by polyurethane and polystyrene insulation at roughly R– 6 and R–5. Loose cellulose, fiberglass both blown and in batts, and rock wool both blown and in batts all possess an R-value of roughly 3. Straw bales perform at about R–1.45. Snow is roughly R–1.

    •  Absolutely still air has an R-value of about 5 but this has little practical use: Spaces of one centimeter or greater will allow air to circulate, convecting heat and greatly reducing the insulating value to roughly R–1

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