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The lowest-density silica nanofoam weighs 1,000 g/m 3, [59] which is the evacuated version of the record-aerogel of 1,900 g/m 3. [60] The density of air is 1,200 g/m 3 (at 20 °C and 1 atm). [61] The silica solidifies into three-dimensional, intertwined clusters that make up only 3% of the volume. Conduction through the solid is therefore very low.
The R-value is the building industry term [3] for thermal resistance "per unit area." [4] It is sometimes denoted RSI-value if the SI units are used. [5] An R-value can be given for a material (e.g., for polyethylene foam), or for an assembly of materials (e.g., a wall or a window). In the case of materials, it is often expressed in terms of R ...
Typical R-values are given for various materials and structures as approximations based on the average of available figures and are sorted by lowest value. R-value at 1 m gives R-values normalised to a 1 metre (3 ft 3 in) thickness and sorts by median value of the range.
Based on a typical k-value of 0.007 W/(m·K), the R-value of a typical 25-millimetre-thick (1 in) VIP would be 3.5 m 2 ·K/W (20 h·ft 2 ·°F/BTU). To provide the same R-value, 154 millimetres (6 in) of rockwool or 84 millimetres (3 in) of rigid polyurethane foam panel would be required.
For example, in the US the insulation standard for attics, is recommended to be at least R-38 US units, (equivalent to R-6.7 or a U value of 0.15 in SI units). [5] The equivalent standard in the UK are technically comparable, the approved document L would normally require an average U value over the roof area of 0.11 to 0.18 depending on the ...
Boron nitride aerogel is an aerogel made of highly porous boron nitride (BN). It typically consists of a mixture of deformed boron nitride nanotubes and nanosheets . It can have a density as low as 0.6 mg/cm 3 and a specific surface area as high as 1050 m 2 /g, and therefore has potential applications as an absorbent , catalyst support and gas ...
For this reason, it is more common to use the thermal conductivity value when comparing the effectiveness of pipe insulation, and R-values of pipe insulation are not covered by the US FTC R-value rule Archived 2007-12-31 at the Wayback Machine. The thermal resistance of each insulation layer is calculated using the following equation:
This limits the sound transmitted into the air: much of it is reflected back into the piezoelectric material itself. An aerogel layer between the transducer and air can greatly increase the intensity of transmitted sound. Aerogels have been measured to absorb sound, but only at high frequencies, e.g., 70 kHz to 2 MHz.