Heat transfer Flashcards
Which solids are the best conductors of heat?
Metals - because they have fixed ionic lattice and free electrons
Which state of matter is the best conductor of heat?
Solids
Which state(s) of matter can form convection currents?
Fluids - liquids and gases
Name the 4 principle mechanisms for thermal transfer
Conduction
Convection
Radiation
Evaporation
Which part of the electromagnetic spectrum carries heat energy?
Infrared (IR)
What colour is the best emitter of IR radiation?
(Dull) black
Which colour is the worst emitter of IR radiation?
(Shiny) silver
Which colour is the best absorber of IR radiation?
(Dull) black
Which colour is the worst absorber of IR radiation?
(Shiny) silver
How does a convection current form?
- Material is heated and its particles gain energy
- The particles spread out and the material becomes less dense
- It rises
- Cooler fluid takes its place
- The cycle repeats
What happens to the temperature of a liquid when it evaporates?
Temperature decreases because fast moving particles leave the surface and so the average energy of the particles decreases.
What is the difference between temperature and heat?
Heat is the total energy of the particles
Temperature is the average energy of the particles
Which way will heat always flow?
From high temperature to low temperature
Why does the cooling system of a car engine have large, black “fins”?
Black because it is a good emitter
Large so the surface area is large increasing the rate of cooling
What are the main features of a vacuum (thermos) flask?
1 shiny silver bottle to reduce heat loss by radiation
2 vacuum between the two bottles to reduce convection
3 cap to reduce evaporation
