is a transparent thermal insulator with applications in energy efficient
windows. It consists of two sheets of glass separated by a narrow
evacuated space. The concept of vacuum glazing operates on the same
principles as the conventional Dewar flask - the vacuum eliminates
conductive and convective heat flow due to gas between the two glass
plates, and internal low emittance coating reduces radiative heat
transport to a low level.
insulating performance of windows is very important in the design
of energy efficient buildings. Since windows are considerably less
insulating than the other components of surrounding building structure,
they play an important role in energy consumption.
design and manufacture of vacuum glazing
consists of two flat sheets of glass hermetically sealed together
around the edges, and separated by a narrow (~0.15 mm) evacuated
space (see figure). Under the influence of atmospheric pressure,
the internal surfaces of the glass sheets are kept apart by an array
of small support pillars which are high strength material such as
metal (stainless steel or Inconel 718) or ceramic (alumina or zirconia).
The actual glazing
is made from two sheets of soda-lime glass. The glass sheets, typically
3 mm thick, are separated by a large number of small support pillars.
The edge seal around the glazing periphery is made from solder glass,
which is a low melting point glass with a coefficient of thermal
expansion matching that of the soda-lime glass. The sample is evacuated
through the small pumpout tube, which is sealed to the outer surface
of the upper glass sheet with solder glass. The internal space is
evacuated to a pressure of about 10-4 Torr. After completion of
the evacuation and outgassing process, the end of the pumpout tube
is melted and sealed.
emittance coatings on the internal surfaces of one or both of the
glass sheets are used to reduce radiative heat transport to a low
level. Both pyrolytically deposited coatings (based on tin oxide),
and sputtered coatings (multilayer stacks of silver and dielectric
materials) have been successfully incorporated into vacuum glazing.
on vacuum glazing
of Applied Physics in the University of Sydney was the first institution
in the world to produce thermally insulating samples of vacuum glazing.
This occurred in 1988. We have since made very substantial progress
on the science and technology of these devices.
Over the years,
research has been done on various aspects of vacuum glazing. Over
1000 samples of vacuum glazing, with dimensions up to 1 m x 1 m,
have been made at the University of Sydney using constructions similar
to that shown in the figure above. Research has focused on
- heat transport
- stress due
to atmospheric pressure and temperature differences
of the internal vacuum
of heat flow
technology and costs
of Sydney vacuum glazing is being developed commercially in Japan
under a licensing agreement. The technology has the potential to
achieve substantial energy savings in buildings.
information on vacuum glazing project, please contact Dr.
Nelson Ng, email@example.com