Civil Engineering Reference
In-Depth Information
Table 9.2
Summary of advantages and disadvantages for vacuum insulation
panels and aerogel insulation
Advantages
Disadvantages
Aerogel
insulation
•
Relative low thermal
conductivity
•
Uncertain long-term physical
properties
•
Possible transparency
•
•
Energy-extensive and expensive
production process
On-site use similar to
traditional materials
•
Uncertain health risks
Vacuum
insulation
panels
•
Very low pristine
thermal conductivity
•
Aging and resulting increase of
thermal conductivity
•
Limited robustness
•
No adaptation on-site
•
Thermal bridging at panel edges
moisture requiring a hydrophobic material, and its resistance to mechanical
impact. The third requirement of importance is the possible ease of instal-
lation and its economic feasibility.
9.4.1 Nanoporous thermal insulators
The areas of application for aerogel insulation are strongly linked to their
physical properties, and so these will be discussed fi rst.
Properties
The main benefi t of aerogel insulation is its low thermal conductivity at
ambient conditions, while the material also shows exceptional properties
concerning optical transmittance, sound absorption, and fi re retardation.
Aerogel insulators have an overall thermal conductivity at ambient pres-
sure down to 0.012 W/(mK) at ambient pressure and to 0.004 W/(mK) at a
pressure of 50 mbar or less, whereas commercial aerogel thermal insulators
for building purposes have a thermal conductivity of around 0.014 W/(mK)
at ambient temperature and are very little affected up to a temperature of
200°C.
Silica aerogels have a high transmittance of radiation within the range of
visible light, i.e., radiation with a wavelength between 380 and 780 nm.
Monolith translucent silica aerogel in a 10 mm thick packed bed has a solar
transmittance
T
sol
of 0.88 and a possible high transparency in the infrared
spectrum
T
ir
of 0.85. Light refl ected by silica aerogels appears bluish and
transmitted light appears slightly reddened. This light scattering can be
explained by
λ
−4
-type Rayleigh scattering caused by the interaction with
inhomogeneities, and becomes more effective when the size of the particles
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