Heat | Chapter 4 | 8th Science - Thermos flask (Vacuum flask) | 8th Science : Chapter 4 : Heat
Chapter: 8th Science : Chapter 4 : Heat
Thermos flask (Vacuum flask)
Thermos flask (Vacuum flask)
The thermos flask (Vacuum flask) is
an insulating storage vessel that keeps its content hotter or cooler than the
surroundings for a longer time. It is primarily meant to enhance the storage
period of a liquid by maintaining a uniform temperature and avoiding the
possibilities of getting a bad taste.
The vacuum flask was
invented by Scottish scientist Sir James Dewar in 1892. In his honour it is
called as Dewar flask. It’s also known as Dewar bottle.
Working of Thermos flask
A thermos flask has double walls,
which are evacuated. It is silvered on the inside. The vacuum between the two
walls prevents heat being transferred from the inside to the outside by
conduction and convection.
With very little air between the
walls, there is almost no transfer of heat from the inner wall to the outer
wall or vice versa. Conduction can only occur at the points where the two walls
meet, at the top of the bottle and through an insulated support at the bottom.
The silvered walls reflect radiated heat back to the liquid in the bottle.
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