Civil Engineering Reference
In-Depth Information
Thermal conductivity for granular aerogel Lumira
(adapted from Cabot
2012
)
Fig. 3
Commercially available aerogels for building purposes (translucent granular
aerogels) have a thermal conductivity between 0.013 and 0.018 W/m K at ambient
temperature; moreover, the value is nearly constant up to a temperature of 100 C
(Aspen, Cabot
2012
, Fig.
3
).
3.2 Optical Properties
The optical transmission and the scattering properties of silica aerogels are widely
investigated in the literature (Baetens et al.
2011
; Jensen et al.
2004
; Reim et al.
2004
,
2005
; Buratti
2003
, 2004; Buratti and Moretti
2011
,
b
,
2012
,
b
). The attitude
to diffuse natural light indoors is described by the light transmittance (s
v
), very
important since the natural light concurs to save electric energy in daytime and
affects general health of human beings.
Monolithic aerogels show very interesting optical properties for building
applications: the transmittance in the visible range is high, and it is similar to the
one of a 6-mm-thick clear float glass (Fig.
4
). Solar transmittance (s
e
) equal to
0.88 was found for an aerogel pane of 10 mm thickness; absorption bands in the
NIR transmission spectrum are shown. Furthermore, a part of the radiation is
scattered when transmitted through the material, according to the Rayleigh scat-
tering theory. It causes reddening of the transmitted light, the bluish appearance of
Fig. 4 Transmission
properties of monolithic silica
aerogels
