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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. Why does R-13 cavity insulation in a steel-stud wall deliver much less than R-13 overall?

    Answer: Steel conducts heat roughly 400 times better than wood and forms thermal bridges

    Steel (~50 W/m·K) conducts far better than wood (~0.12 W/m·K), so an R-13 cavity in 16-in. o.c. steel studs works out to only about R-6.

  2. What happens to the dynamic viscosity of liquid water as its temperature rises?

    Answer: It decreases

    Liquid water gets thinner as it warms, so friction losses in hot water piping are a bit lower.

  3. An assembly has a total thermal resistance, including air films, of R-20. What is its U-factor?

    Answer: 0.05 Btu/h·ft²·°F

    U = 1/R_total = 1/20 = 0.05 Btu/h·ft²·°F.

  4. About what thermal resistance does ASHRAE list for still air on the inside of a vertical surface with heat flowing horizontally?

    Answer: R-0.68

    ASHRAE lists still air on a vertical surface at about 0.68 h·ft²·°F/Btu, compared with about 0.17 for an outside surface in a 15 mph wind.

  5. What is the ozone depletion potential (ODP) of R-410A?

    Answer: 0

    R-410A is an HFC blend with no chlorine, so its ODP is zero, even though its GWP is high (~2,088).

  6. How does the thermal conductivity of austenitic stainless steel compare with carbon steel?

    Answer: It is much lower, about 16 vs 50 W/m·K

    Austenitic stainless steel has about one-third the conductivity of carbon steel, which reduces heat transfer in thin-wall exchangers.

  7. Which insulation is most commonly used on refrigerant suction lines to stop condensation?

    Answer: Flexible closed-cell elastomeric foam

    Closed-cell elastomeric foam has very low vapor permeance and needs no separate vapor jacket, so moisture does not get in on cold lines.