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Material Properties Flashcards

7 cards from real ASHRAE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Material Properties flashcards as text

  1. Which value is closest to the thermal conductivity of pure copper at room temperature?

    Answer: About 400 W/m·K

    Pure copper conducts about 400 W/m·K, roughly twice as well as aluminum (~205), which is why it is used for heat exchanger tubing.

  2. A radiant barrier works mainly because its surface has which property?

    Answer: Low emissivity, around 0.05

    Polished aluminum foil has an emissivity of about 0.03-0.05, so it gives off very little radiant heat across an air space.

  3. What is the approximate specific heat of liquid water in I-P units?

    Answer: 1.0 Btu/lb·°F

    The Btu was originally defined from water, so water's specific heat is about 1.0 Btu/lb·°F.

  4. What is the approximate density of water at 60°F?

    Answer: 62.4 lb/ft³

    Water at 60°F weighs about 62.4 lb/ft³, which is the same as about 8.34 lb/gal.

  5. Under the International Codes, what is the maximum vapor permeance of a Class I vapor retarder?

    Answer: 0.1 perm or less

    Class I vapor retarders, such as polyethylene sheet, are rated at 0.1 perm or less.

  6. Thermal diffusivity of a material is defined as which ratio?

    Answer: k / (ρ·cp)

    Thermal diffusivity α = k/(ρ·cp) tells you how quickly a temperature change spreads through a material.

  7. Which insulation typically gives the highest R-value per inch?

    Answer: Foil-faced polyisocyanurate board

    Polyiso is rated at about R-6 to R-6.5 per inch, compared with roughly R-3.1 to R-4 for the other three.