Heat transfer Flashcards
What are three was heat is transferred?
Radiation
Conduction
Convection
What is heat radiation?
The transfer of heat energy by Infrared radiation
What energy transfers, transfer their energy by particles?
Conduction
Convection
What is the main form of heat transfer in solids?
Conduction
What is the main form of heat transfer in liquids and solids?
Convection
What can be emitted by liquids solids and gases?
Infrared Radiation
What can absorb and emit infrared radiation?
Any object, whether or not conduction or convection are taking place
The bigger the temperature difference between a body and its surroundings, the….
…faster energy is transferred by heating
What is infrared radiation? (waves)
Emission of electromagnetic waves
When do objects absorb and emit IR?
Continually
Where is IR emitted from?
The surface of an object
An object that’s hotter than its surrounding emits ….(+/-)…. radiation than it absorbs
What happens to the temperature of the object?
More - it cools down
An object that’s cooler than its surrounding emits ….(+/-)…. radiation than it absorbs
What happens to the temperature of the object?
Less - it warms up
The hotter an object is the more….
radiation it radiates in a given time
What does radiation depend on?
Surface colour and texture
What absorbs IR better than light shiny surfaces, such as glass or silver?
Dark, matt surfaces
What emit more IR than shiny light surfaces?
Dark matt surfaces
What do light shiny surfaces do to IR?
They reflect a lot of the IR falling on them
What uses shiny light surfaces to reflect IR? How?
Vacuum flasks have silver inner surfaces to keep heat out or in.
Where do solar hot water pipes run?
Under the black surface, or painted pipes under glass.
How is the water in pipes in solar panels heated?
What can this water be used for?
Radiation from the sun is absorbed by the black surface to heat the water
Washing or to be pumped into radiators to heat the building
Kinetic theory describes how…
Kinetic theory explains ….
The energy an object (or particle) has because of its movement is called its….
… particles move in solids liquids and gases
… the three states of matter
… kinetic energy
What are the three states of matter, give examples….
Solid - ice
Liquid - water
Gas - water vapour
What is the difference between particles of different state?
Their arrangement and energy of particles are different
Solids:
What forces hold the particles close together in a ….. ….. arrangement?
How much energy do the particles have and what does this mean?
Strong forces of attraction, fixed regular arrangement
The particles don’t have much energy so they vibrate in their fixed positions
Liquids:
How strong are the forces of attraction between the particles?
How are the particles arranged?
They have …… energy than particles in a solid.
They move in ….. directions at ….. speeds
Weaker
They are close together but can move past each other, they are in an irregular arrangement
More
Random…. low
Gases:
How much force of attraction is there between the particles?
How much energy do the particles have?
How do the particles move?
Almost none
More than liquids and solids
They are free to move and travel in random directions and at high speeds
When you heat a substance you give its particles….. they then…
This is what causes solids to …. and liquids to ….
More kinetic energy - the vibrate and move faster
Solids to melt
Liquids to boil
Conduction of heat occurs in what state of particles? (s.l,g)
Mainly in solids
What is the process where vibrating particles pass on their extra kinetic energy to neighboring particles
Conduction
Conduction continues throughout the solid and gradually some ….. is passed all the way through the solid causing a ….. at the end of the solid.
This causes an …. in the heat …. from its surface.
extra kinetic energy…. increase in temperature.
Increase… radiating
Conduction is usually faster in what type of solid?
Why? (collide)
Denser solids
Because the particles are closer together and so will collide more often and pass energy between them
Materials that have larger spaces between their particles conduct….
these are called ….
….heat energy much more slowly
Insulators
Why are materials good conductors? why are metals so good at conducting?
Because of their free electrons, these are free to move inside the metal.
How does conduction happen through a metal heated at one end?
So why does conduction happen faster in a metal than another material?
At the hot end electrons move faster and collide with the free electrons, transferring energy, these pass on their energy to the next electron.
Electrons transfer energy faster as they are free to move when atoms vibrating and passing their energy is slower
When does convection occur in gases and liquids?
Why doesn’t it occur in solids?
When the particles with more energy move from the hotter region to the cooler region and take their energy with them
Because the particles aren’t free to move about.
How to immersion kettles and hot water tanks work?
By convection currents
Describe how an immersion heater works:
- The coils and water:
- Particles near the coils…..
- So the water becomes … …. because….
- What happens to the hot water?
- So the cold water is …
- So the cold water now gets….
- Heat energy is transferred through radiation from the coils to the water
- get more energy so move around faster
- less dense, because there is more space between the particles so it expands
- It’s less dense so it rises above the cool water
- Displaced as the hot water takes its place so it sinks down to the coil
- heated by the coils and rises so you get convection currents circling the heat energy through the water.
Where are convection currents most effective?
In round containers, squarish in size as tall thin ones don’t allow good convection, the water can rise but an’t sink.
Convection currents are all about …..
changes in density
What inside object uses convection currents? Why?
Radiators, the hot air the water has heated rises in the room as it’s less dense so the cool dense air must sink to fall back to the radiator to heat up.
