Heat Transfer Flashcards
What are the methods of heat transfer?
Conduction
Convection
Radiation
What is conduction?
Transfer of heat energy through particles of a solid
In metals, atoms arranged very close together in regular pattern.
Heat energy can pass rapidly across most metals
What is an insulator?
A material that doesn’t transfer heat energy easily
What is a conductor?
They transfer heat by process of conduction
What is convection?
Transfer of heat energy in liquid or gas.
If we heat beaker of water, water at bottom heats up & rises.
This is seen by adding dye to bottom of beaker of water
What is convection current?
Pattern of liquid or gas rising & falling
How does convection current work?
When liquid absorbs heat energy, particles gain energy & move further apart as they have more kinetic energy
As particles are more widely spaced, they have lower density than those in cooler liquid
This lower density in warmer liquid causes it to rise & is replaced by older liquid of higher density
Why are most metals good conductors?
They have free electrons that can move & transfer heat energy as well as atoms in conductor vibrating faster. Heat transferred inform of kinetic energy
What is radiation?
Transfer of heat energy by waves passing out from a hot surface
What are some examples of radiation?
Earth receiving heat energy from sun, through vacuum of space. Heat energy transferred in infrared waves
Heat off fire
Heat radiating out from any object
What are the reactions of black surfaces to radiation?
Best emitters & best absorbers
What are white surfaces’ reaction to radiation?
Worst emitters & worst absorbers
Differences between gloss & matt surfaces towards radiation?
Matt surfaces better emitters & absorbers than most gloss surfaces
How does conduction work?
Atoms in metal arranged in regular structure & very close together
In metal atoms, outer electrons not tightly attached; they’re free/delocalised
This means these electrons can move easily throughout whole metallic structure
As electrons move, they carry heat energy from one part of metal to another
Why can insulators not conduct heat?
Outer electrons aren’t free , so they can’t pass throughout structure
Only way heat energy can transfer s by passing fro atom to atom - much slower process
