• DIAGRAM

Connecting Science © Hodder Education 2009

• DIAGRAM

Connecting Science © Hodder Education 2009

How a vacuum flask works

• Use the hot spots for the labels on the diagram to find out how the vacuum flask minimises heat loss by conduction, convection and radiation.

• DIAGRAM

Connecting Science © Hodder Education 2009

Vacuum

• The narrow gap between the two silvered walls is evacuated – it contains no air.

• There is no convection in this vacuum space.• No heat can be transferred by conduction in the

vacuum space.

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• DIAGRAM

Connecting Science © Hodder Education 2009

Plastic stopper

• Conduction can only occur at the points where the walls meet the rest of the flask.

• Trapped air between the plastic cup and the stopper acts as an insulator.

• This reduces heat transfer by conduction and convection.

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• DIAGRAM

Connecting Science © Hodder Education 2009

Silvered walls

• The walls around the vacuum flask are made of glass with a silvery coating made of aluminium .

• The shiny surfaces reduce heat loss by radiation (radiated energy is reflected off shiny surfaces).

• The walls could also be made of stainless steel, which can be polished.

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• DIAGRAM

Connecting Science © Hodder Education 2009

Cork support

• Conduction can only occur at the points where the walls meet the rest of the flask, at the top and through the supports.

• Cork is a good insulator.• It reduces heat loss by conduction.

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