Vacuum flask
From Wikipedia, the free encyclopedia
- This article is about the vacuum-insulated flask. For the flask used in filtration under vacuum, see Büchner flask.
A vacuum flask is a vessel designed to provide thermal insulation. It was invented by Sir James Dewar, while working as a scientist at Oxford University in 1892. In form, a vacuum flask is a glass, metal, or plastic bottle, with a double-layer construction. It can also be considered to be two thin-walled bottles nested one inside the other, and sealed together at their necks. The narrow space between is evacuated almost entirely of air. The vacuum flask is also known as a Dewar flask after its inventor.
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[edit] Construction
Instead of only relying on a traditional thermal insulator to insulate the inside from the outside, the sealed container contains a near vacuum. A vacuum does not conduct heat at all by conduction or convection. The inner surfaces of the outer bottle, and the outer surface of the inner bottle, have a metallic or similar reflective coating to prevent heat from being transmitted via radiation, the other form of heat transfer. Dewar himself used silver for this purpose. This is so effective that what little heat transport does occur is almost entirely via the neck and stopper; insulating materials such as cork are often used for the stopper.
[edit] Performance
The construction provides excellent thermal insulation. For example when filled with a hot liquid, the vessel will not allow heat to easily escape, and the liquid will stay hot for far longer than in a typical container.
The first vacuum flasks for commercial use were made in 1904 when a German company, Thermos GmbH, was formed. "Thermos", their tradename for their flasks, remains a registered trademark in some countries but was declared a genericized trademark in the US in 1963 as it is colloquially synonymous with vacuum flasks in general.
[edit] Laboratory use
A very common use of the Vacuum flask in laboratories is the storage of liquid nitrogen; in this case, the leakage of heat into the extremely cold interior of the bottle results in a slow "boiling-off" of the liquid (a pressure relief valve is provided to prevent pressure from building up). The excellent insulation of the Dewar flask results in a very slow "boil" and thus the nitrogen lasts a long time without the need for expensive refrigeration equipment.
[edit] See also
[edit] External links
- Burger, R., U.S. Patent 872795, "Double walled vessel with a space for a vacuum between the walls", December 3, 1907.
- Thermos LLC Major manufacturer of Vacuum flasks for consumers
- Stanley Major manufacturer of Vacuum flasks for consumers
- The Gourmet Kitchen Major retailer of Vacuum flasks for consumers
