Heat Transfer Flashcards
Why do solar water heaters have a layer of silver foil at the back?
To reflect the infrared radiation back into the pipe, so that the pipes stay warmer.
What is IR radiation?
> a wave on the EM spectrum that is responsible for the transfer of heat by radiation.
What are the properties of solids?
> vibrate about fixed positions
-fixed shape and volume.
What are the particle properties of liquids?
> closely packed
move around
> fixed volume but variable shape
What are the properties of gas particles?
> very far apart particle move randomly and v. Quickly
- no fixed shape or volume.
What are the particle energy levels for a solid, liquid and gas?
Low to medium to high.
What happens at first when you heat up a solid?
The particles gain energy and so vibrate more vigorously, taking up more space and so the solid expands.
What happens when you heat up a liquid?
> it gains energy, the particles gain more energy, vibrating more vigorously and so the liquid expands,
What happens when you heat a gas?
The particles gain more energy, vibrate more vigorously and so take up more energy so the gas expands.
What is conduction of heat energy?
The process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
Why is conduction faster in denser solids?
Because the particles are closer together and so will collide more often and pass energy between them.
What are insulators?
> particles more spaced out
not arranged in neat rows and columns
> no free electrons
Why are metals such good conductors
Because the delocalised electrons are free to move throughout the structure they can collide with other free electrons to pass on their energy.
> because they have a tightly packed regular arrangement
Where does convection occur and why?
In liquids and gases.
> relies on the ability of the particles to move around freely.
How does convection occur?
> more energetic particles move from a hotter region to a cooler region and take their heat energy with them.
