Heat transfer and Energy efficiency

Question 1

Why do radiators have large surface areas?

Answer 1

To maximise the amount of heat they transfer.

Question 2

Describe two ways in which a vacuum flask reduces heat transfer.

Answer 2

One of the below:

1) shiny mirrored surfaces reflect the heat back into the flask
2) double-walled, reducing heat loss through conduction and convection
3) A plastic cap with cork for insulation
4) Vacuum to reduce convection and conduction

Question 3

What is the equation for payback time?

Answer 3

Initial cost over annual saving.

Question 4

How does cavity wall insulation reduce heat transfer?

Answer 4

Foam is quirted into the gaps between the bricks reducing convection and radiation and the air pockets in the foam reduce conduction.

Question 5

Would you want a high or low u-value and why?

Answer 5

Low, because u-value is how fast heat can transfer through a material.