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This aerogel has remarkable thermal insulative properties, having an extremely low thermal conductivity: from 0.003 W·m −1 ·K −1 [64] in atmospheric pressure down to 0.004 W·m −1 ·K −1 [59] in modest vacuum, which correspond to R-values of 14 to 105 (US customary) or 3.0 to 22.2 (metric) for 3.5 in (89 mm) thickness. For comparison ...
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. ... Silica aerogel: 2.54: 1 1.76: 10.3 [2] 69
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 ...
Values in parentheses are extrapolated, interpolated, or estimated. *It happens that the online record has the thermal conductivity at 30 Kelvins and ∥ {\displaystyle \parallel } to the c axis posted at 1.36 W⋅cm −1 K −1 and 78.0 Btu hr −1 ft −1 F −1 which is incorrect.
The construction industry makes use of measures such as the R-value (resistance) and the U-value (transmittance or conductance). Although related to the thermal conductivity of a material used in an insulation product or assembly, R- and U-values are measured per unit area, and depend on the specified thickness of the product or assembly. [note 2]
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.
R ∗ = 8.314 32 × 10 3 N⋅m⋅kmol −1 ⋅K −1 = 8.314 32 J⋅K −1 ⋅mol −1. Note the use of the kilomole, with the resulting factor of 1000 in the constant. The USSA1976 acknowledges that this value is not consistent with the cited values for the Avogadro constant and the Boltzmann constant. [13]
Aerographene or graphene aerogel is the least dense solid known to exist, at 160 g/m 3 (0.0100 lb/cu ft; 0.16 mg/cm 3; 4.3 oz/cu yd). [1] The material reportedly can be produced at the scale of cubic meters.