Reducing Unwanted Thermal Energy Transfer

Reducing unwanted thermal energy transfer keeps hot things hot and cold things cold. The design addresses all three transfer methods: conduction, convection and radiation.

Vacuum flask

A vacuum flask reduces all three methods:

Feature	Reduces	How
Double-walled glass with vacuum between	Conduction and convection	No particles in a vacuum to conduct or convect
Silvered (shiny) inner surfaces	Radiation	Shiny surfaces are poor emitters and good reflectors of infrared
Insulating stopper	Conduction and convection	Reduces energy loss through the top
Plastic outer casing	Conduction	Plastic is a poor conductor

Home insulation

Method	Transfer method reduced	How
Loft insulation (fibreglass)	Conduction and convection	Traps air in fibres; trapped air is a poor conductor and cannot convect
Cavity wall insulation (foam)	Conduction and convection	Fills the gap between walls with foam, trapping air pockets
Double glazing	Conduction and convection	Trapped air (or gas) between panes reduces conduction; gas cannot convect in the narrow gap
Shiny foil behind radiators	Radiation	Reflects infrared back into the room
Draught excluders	Convection	Reduces air flow through gaps

Common errors and how to correct them

Saying “the vacuum stops heat.” Be precise: the vacuum prevents conduction and convection because there are no particles. Radiation still passes through a vacuum, which is why silvered surfaces are also needed.

Stating “insulation produces heat.” Insulation does not generate energy. It reduces the rate at which energy is transferred away.

How to apply this in an exam

For each insulation method, name the specific transfer method it reduces and explain how it does so in terms of particles, density, or surface properties. A complete answer addresses all three transfer methods.