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Thermos Flask

Heat and Temperature of Class 7

About Thermos Flask

In daily life we required a container that use as a vacuum flask that keeps hot things hot and cold things cold. In this purpose Scottish chemist and physicist Sir James Dewarinvented the thermos bottlein 1892.This thermo flask is used to store hot or cold drinks. These are also used in scientific, medical or daily purpose work to store chemicals and drugs.

A vacuum flaskdoes not allow heat transfer by conduction, convection and radiation. To prevent the heat a thermos flask is used that constructed with a glass vessel with double walls, the space between which is evacuated. Due to this evacuation it prevents the transfer of heat to or from the container, as in a vacuum conduction and convection can’t take place. By silvering and shiny the glass on both sides that minimize the radiation .

The silver coating on the inner bottle prevents heat transfer by radiation, and the role of the vacuum between its wall is to prevents heat moving by convection. Again the thinness of the glass walls stops heat entering or leaving the flask by conduction. The upper case surrounding the flask provides additional insulation.

The three processes through which heat is transferred - conduction, convection and radiation are prevented in a thermos flask.

Most flasks have a small mouth, which reduces heat exchange. These are closed with a   stopper made of cork or hollow plastic. This fragile inner container is encased in metal or plastic for protection.

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