A thermos flask is designed to maintain the temperature of liquids, keeping hot drinks hot and cold drinks cold for extended periods. It features a double-walled glass construction with a vacuum between the walls, which minimizes heat transfer through conduction, convection, and radiation. The flask is secured with a cork or plastic stopper and is housed in a protective plastic case to absorb shocks.

1. THERMOS FLASK
•A thermos flask is a special kind
of flask or bottle
•It is used to keep a hot liquid hot
and a cold liquid cold for a long
time.

3. •It consists of a double-walled glass bottle.
• There is a vacuum in between the walls.
•Both the walls are made shiny on the vacuum side.
•The mouth of the bottle is fitted with a cork (or
plastic) stopper.
•The bottle is enclosed in a plastic case with the help of
cork pieces or spring as shock absorber.
•The case is provided with a cap over the stopper.

5. • The vacuum in between the walls of the bottle prevents any
transfer of heat by conduction and convection.
• The shining surface on the outer side of inner wall and inner
side of the outer wall reduces the transfer of heat by
radiation.
• The cork stopper prevents the transfer of heat by convection.
• Thus, the transfer of heat either from inside to outside or
from outside to inside is very little and the contents of the
bottle can remain at the same temperature for a long time.