Heat can be transferred through three processes: conduction, convection, and radiation. Conduction involves the transfer of heat between particles in direct contact. Convection refers to the transfer of heat by the movement of fluids like gases and liquids. Radiation involves the transfer of heat by electromagnetic waves and does not require a medium. The vacuum flask harnesses these principles of heat transfer to keep liquids hot or cold by using double walls, a vacuum between the walls, and silvered surfaces to minimize conduction, convection, and radiation between the interior and exterior.

1. Heat Transfer

2. Heat Transfer
 Heat travels from a region of higher
temperature to a region of lower
temperature.
 This process is carried out by
 Conduction
 Convection
 Radiation

3. Conduction
 Conduction is the process which heat
is transferred through a medium from
one particle to the next.

4. Convection
 Convection is the process where heat is
transferred through a fluid (gas and liquid)
by the movement of heated particles of the
liquid
 Recall movement of molecules in kinetic
theory and the energy of the molecules.

5. Convection in Liquids
 Hot liquids rise as
they expand under
heat (less dense)
 Cool liquids fall
(relatively denser)
 Movement of liquids
due to this effect is
called the ‘convection
current’

6. Radiation
 Radiation is a form of heat transfer
that requires no medium to travel.
 Heat is transmitted
in the form of
energy waves.
 Energy travels until
it gets absorbed
somehow.

7. Conduction, Convection and
Radiation – Applying knowledge
 The Vacuum Flask
(Thermos Flask)
 Keeps water hot
(or cold) by
harnessing
knowledge of heat
transfer reduction

8. Parts of the Vacuum Flask
 Double Glass Walls
 Silvered Surfaces
 Vacuum
 Insulation Supports
 Insulated Cover
- poor conductor
- prevents radiation (poor
absorber and emitter)
- No conduction or convection
- Reduce conduction and
support the vacuum chamber
- Prevent conduction of heat
and convection of hot air

9.  The insulated lid stops the heat escaping
(and entering) by convection

10.  The vacuum between the two walls
stops the heat escaping (and entering)
by conduction
vacuum

11. The silvered inner and
outer stops the heat
escaping (and entering) by
radiation
silvered outer
silvered
inner