Dewar flask


Dewar flask
Dewar flask.
(Deutsches Museum, Munich).

A Dewar flask is a vessel designed to provide very good thermal insulation. For instance, when filled with a hot liquid, the vessel will not allow the heat to easily escape, and the liquid will stay hot for far longer than in a typical container. The Dewar flask was named after its inventor, the Scottish physicist Sir James Dewar (18421923).

Cross section of a Dewar flask. The red area is a vacuum.

In form, a Dewar flask is a glass or metal bottle, with a double-layer construction; in fact, it can be considered to be two thin-walled bottles nested one inside the other, and sealed together at the neck. The narrow space between is evacuated almost entirely of air; the near vacuum minimizes conduction and convection of heat.

The inner surfaces of the outer bottle, and the outer surface of the inner bottle, have a metallic or similarly reflective coating to prevent heat from being transmitted via radiation. Dewar himself used silver for this purpose. The open end of the flask is reduced to a small diameter relative to the body of the flask, reducing the only opening by which heat loss can occur. The design of the Dewar flask 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 to further reduce heat loss.

A very common use of the Dewar 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.

A Thermos bottle (trademarked), or vacuum flask (generic) used to keep coffee or other beverages hot, is usually based on the design of a Dewar flask; since glass dewar flasks are fragile and somewhat expensive to fabricate, other constructions based on plastic or insulated metal are also popular.

See also

Patents

  • Burger, R., U.S. Patent 872,795, "Double walled vessel with a space for a vacuum between the walls", December 3, 1907.

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Look at other dictionaries:

  • Dewar flask — Dewar Dew ar (d[=u] [ e]r), Dewar vessel Dew ar ves sel, Dewar flask Dew ar flask [After Sir James Dewar, British physicist.] A double walled glass vessel for holding liquid air, liquid nitrogen, etc., having the space between the walls exhausted …   The Collaborative International Dictionary of English

  • Dewar (flask) — [do͞o′ər, dyo͞o′ər] n. 〚after Sir James Dewar (1848 1923), Scot chemist & physicist〛 a double walled flask with a vacuum between the walls, which are silvered on the inside, used esp. for storage of liquefied gases: also written dewar * * * …   Universalium

  • Dewar (flask) — [do͞o′ər, dyo͞o′ər] n. [after Sir James Dewar (1848 1923), Scot chemist & physicist] a double walled flask with a vacuum between the walls, which are silvered on the inside, used esp. for storage of liquefied gases: also written dewar …   English World dictionary

  • Dewar flask — noun vacuum flask that holds liquid air or helium for scientific experiments • Syn: ↑Dewar • Hypernyms: ↑vacuum flask, ↑vacuum bottle * * * noun see dewar * * * Dewar flask /dūˈər fläsk/ noun (sometimes without …   Useful english dictionary

  • Dewar flask — Diuaro indas statusas T sritis Standartizacija ir metrologija apibrėžtis Vakuuminis indas, kuriame ilgą laiką galima laikyti skysčius toje pačioje arba labai lėtai kintančioje temperatūroje. Diuaro inde galima laikyti skystą helį, azotą ar pan.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • Dewar flask — Diuaro indas statusas T sritis fizika atitikmenys: angl. Dewar flask; Dewar vacuum flask; vacuum bottle vok. Dewar Gefäß, n; Vakuummantelgefäß, n rus. сосуд Дьюара, m pranc. dewar, m; vase de Dewar, m …   Fizikos terminų žodynas

  • Dewar flask — Diuaro indas statusas T sritis chemija apibrėžtis Termosas suskystintoms dujoms laikyti. atitikmenys: angl. Dewar flask; vacuum bottle; vacuum flask; vacuum vessel rus. сосуд Дьюара …   Chemijos terminų aiškinamasis žodynas

  • Dewar flask — /ˈdjuə flask/ (say dyoohuh flahsk) noun a double walled silvered glass flask in which the space between the walls is evacuated, used for storing liquids at a low temperature, especially liquid air. {named after Sir James Dewar} …   Australian English dictionary

  • Dewar flask — noun A type of double walled vacuum flask with silver lining. Syn: Dewar vessel …   Wiktionary


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