Heat Transfer Flashcards
What is convection?
The main form of heat transfer in liquids and gases
How is radiation different to conduction and convection?
It uses infrared radiation rather than particles
The bigger the temperature difference between an object and its surroundings, the _____ the speed of heat transfer
Faster
The hot object ____ more radiation than it ____
Emits
Absorbs
What kind of surfaces absorb radiation the best?
Dark, matt surfaces
What kind of surfaces emit radiation poorly?
Light, shiny surfaces
Why are shiny surfaces bad at absorbing and emitting radiation?
They reflect it
What happens to particles when you heat a substance?
They are given more kinetic energy and vibrate or move faster
Why is conduction faster in dense solids?
The particles are closer together and collide more
Why are insulators poor conductors?
Their particles are not very close together, so energy is passed on much slower
Why are metals good conductors?
Within the metal are free electrons, which move faster than atoms
What are the steps of convection in an immersion heater?
- Heat energy transferred by conduction from heater coils to water
- Particles around coils move faster with energy
- The greater distance between them means they are less dense
- Reduction in density allows them to rise above cooler water
- Hot water displaces the cold, which sinks towards the coils
- Convection currents circulate over and over
How does a radiator warm up a room?
Convection (sike)
Hot, less dense air by the radiator rises and denser, cooler air flows to replace it
What is conduction?
The main form of heat transfer in solids
Where is heat energy radiated from?
An object’s surface
Why are large surface areas good for transferring heat?
More infrared waves can be emitted or absorbed
What is the purpose of fins on an engine?
To increase surface area and cool down the engine faster
If two objects have the same surface areas but one has a lower volume, which will cool the quickest?
The lower volume object, as a larger proportion of it is in contact with its surroundings
What is the purpose of the vacuum in a vacuum flask?
To stop all conduction and convection
Why are the walls of a vacuum flask silvered?
To minimise radiation
How else may conduction be stopped in a vacuum flask (aside from the vacuum)?
Insulating foam
Plastic and cork/foam stopper
