3.9–3.10: Reducing unwanted energy transfers and insulation

How can lubrication reduce unwanted energy transfers?

It reduces friction between moving surfaces, reducing heating and energy dissipation.

How can thermal insulation reduce unwanted energy transfers?

It reduces the rate of thermal energy transfer to the surroundings.

How does increasing the thickness of a building’s walls affect its rate of cooling?

Thicker walls generally reduce the rate of cooling because they provide a longer path for thermal energy transfer.

How does increasing the thermal conductivity of a wall affect the rate of cooling?

Higher thermal conductivity generally increases the rate of thermal energy transfer through the wall.

What is thermal conductivity?

A measure of how readily a material transfers thermal energy.

Which type of material is generally a good thermal insulator?

A material with low thermal conductivity, such as trapped air or fibreglass insulation.

Why is trapped air useful as insulation?

Air is a poor thermal conductor, and when trapped it cannot circulate easily to transfer energy by convection.

How can draught excluders reduce energy transfer?

They reduce air movement through gaps, reducing heat loss by convection.

How can double glazing reduce heat loss?

The gap between the panes contains air or gas that reduces thermal energy transfer.

How can loft insulation reduce heat loss?

It reduces thermal energy transfer through the roof.

Why does reducing friction improve the efficiency of machines?

Less energy is dissipated as unwanted heating, so a greater proportion is transferred usefully.