Vacuum for heat insulation

By Eli Rejwan

April 25, 2001

The purpose of these comments is to draw attention to the many ways of making use of vacuum for heat insulation. It is efficient. Many possible applications. Commercially viable.

Vacuum for heat insulation

Vacuum can be used for heat insulation. It prevents the transfer of heat with the exception of transfer by radiation. It is not widely used because of the need for vacuum chamber walls that are strong enough to withstand the exterior atmospheric pressure. Two panels of glass sealed all around and all air in between removed would provide good window insulation, but would have to be either too small in size or unacceptably thick in order to withstand the atmospheric pressure on the outer sides of the panels.

One solution is to scatter coarse sand between the panels before sealing in order to support the panels and prevent them from collapsing inward. This allows thin glass to withstand the atmospheric pressure. In actual production, designed separators would be used instead of sand. The loss of heat by conduction through the separators is related to the contact area and would be small. This loss can be compensated by using multiple layers of glass.

A wide variety of materials can be used instead of glass: acrylic panels, tin, aluminum, and other metals. Their inner surfaces can be made reflective in order to minimize heat transfer by radiation. Multiple layers can be used to reduce heat leakage by radiation and by conduction through the supports. Only the outer panels have to withstand pressure.

If it is necessary to allow driving nails through the panels, as when used in building construction, the separators need to be in the form of edges of small squares. This limits the damage to only the affected squares.

The materials need not be rigid. Some materials can be rolled into cylinders for easy transportation. Good to take with you on your next trip to the south pole!

Cut a few pieces from a very fine-knit old vinyl curtain and get from your kitchen a few pieces of aluminum foil, slightly larger than the fabric. Arrange in alternate layers, make both outer layers aluminum. Fold the periphery and remove the air in between (easier said than done, but no problem if the equipment is available). You got excellent insulation to wrap around your cold beer bottle!

Most insulation materials presently in use produce toxic gas when exposed to heat. In case of fire, residential or commercial, these materials present more risks than fire itself. Metallic vacuum insulation would be safer. This is particularly true in aircrafts where air travellers may not have the possibility to escape the fumes.

Large scale production can make it economical to produce tiny vacuum chambers to incorporate in products such as clothing.

Costly energy and environmental considerations should make the adoption of vacuum for insulation an attractive proposition. Applications in industry can produce substantial savings.

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