Rate of Heat Transfer Flashcards
What 3 things effect the rate of heat transfer?
Surface area, volume and material
Where is heat energy radiated from?
The surface of an object
How does surface area effect rate of heat transfer?
The bigger the surface area, the more infrared waves that can be emitted from (or absorbed by) the surface - so the quicker the transfer of heat.
What are ‘fins’? and What are they used for?
They are thin, metal plates that increase surface area in order to cool engines, on cars and motorbikes, more quickly
What are heat sinks designed to do?
Designed to transfer heat away from objects they’re in CONTACT with
What do heat sinks have that increases their rate of heat transfer?
Fins = Larger surface area = emit heat faster
If 2 objects have the same [ ], the same surface area but DIFFERENT volumes, the object with the [ ] volume will cool more quickly - as a higher proportion of the object will be in contact with its [ ]
temperature
smaller
surroundings.
Objects made from good insulators/conductors transfer heat away more quickly
conductors
Name the properties of a vacuum flask [7]
- Outer cap/cup
- Plastic cap filled with cork (stopper)
- Shiny mirrored surfaces on the inner walls
- Vacuum between inner walls
- Insulating foam between inner walls and the outer wall
- Air between the inner walls and outer wall
- Plastic case as the outer wall
How does the vacuumed, double-walled, inner walls prevent heat transfer?
It stops all convection and conduction through the sides
How does the Shiny mirrored surfaces on the inner walls prevent heat transfer?
Reduces heat loss through radiation
How does the Insulating foam prevent heat transfer?
It minimises heat conduction to or from the outer glass bottle
How does the Plastic cap filled with cork (stopper) prevent heat transfer?
Reduces any heat conduction through it
Why is it useful for humans and animals for their hair to stand up when it’s cold?
The hair traps a thicker layer of insulating air round the body. This limits the heat loss through convecction
Why do some people go pink when it’s hot? How does it help?
When you’re too warm, your body diverts blood to flow near the surface of your skin so that more heat can be lost by RADIATION
