Heat Transfer and Kinetic Theory

Infrared Radiation
1. Infrared radiation transfers heat energy
2. Dark, matt surfaces are best at absorbing and emitting infrared radiation
3. Light, shiny surfaces are worst at absorbing and emitting infrared radiation and reflect a lot of the radiation
4. If an object is cooler than its surroundings it will absorb more infrared radiation than it emits
5. If an object is warmer than its surroundings it will emit more infrared radiation than it absorbs
6. Everything absorbs and emits infrared radiation
Kinetic Theory
1. Gases
  1. Almost no forces of attraction
  2. Particles move in a random direction at high speeds
  3. High energy levels
2. Solids
  1. Strong forces of attraction keep it in a fixed pattern
  2. Low amount of energy so it can only vibrate in fixed positions
3. Liquids
  1. Weak forces of attraction
  2. The particles can move in random directions at low speeds
Conduction
1. A type of heat transfer that occurs mainly in solids but also in liquids and gases
2. The particles vibrate and transfer their heat energy to neighbouring particles
3. More dense materials are better conductors because their particles are closer together
4. Materials that have particles that are far apart transfer heat via conduction slower and are known as insulators
5. Metals are good conductors because they contain free electrons which allows them to transfer energy faster
Convection
1. Occurs mainly in liquids and gases
2. Particles vibrate more as they heat up and so take up less space and become less dense
3. Less dense particles rise taking the energy with them
4. Convection currents occur when the less dense particles rise and are replaced by the denser particles
Condensation
1. Condensation is the process of turning a gas into a liquid
2. If particles lose energy they slow down and the attractive forces between them grow stronger and if the forces are strong enough the particles join and become a liquid
3. Factors affecting the rate of condensation
  1. Temperature of the surface the gas touches
  2. Airflow
  3. Density of gas
  4. Temperature of the gas
Evaporation
1. Evaporation is the process of a liquid turning into a gas
2. If the particles have enough energy and are travelling in the right direction they can escape the attractive forces of the other particles and evaporate
3. Factors affecting the rate of evaporation
  1. Airflow over the liquid
  2. Surface area of the liquid
  3. Temperature of the liquid
  4. Density of the liquid
Rate of Heat Transfer
1. Factors affecting rate of heat transfer
  1. Surface Area
  2. Type of material
  3. Colour
  4. Surface area to volume ratio
    1. The smaller this is, the faster the transfer
2. Controlling Heat Transfer
  1. Vacuum Flask
    1. The flask uses two walls to create a vacuum to stop heat loss through conduction and convection
    2. The flask walls are silver and shiny to stop heat loss through radiation
    3. The insulated support stops the flask walls from cracking under the pressure and minimises heat loss from conduction
    4. The stopper is made of plastic and filled with cork and foam to reduce heat loss through conduction
  2. Humans and Animals
    1. Hairs on your skin stand up to trap a thicker layer of insulating air to limit heat transfer by convection
    2. Blood is diverted to the surface where heat can be lost as radiation resulting in pinker skin tone
    3. Arctic foxes have small ears to minimise heat loss via radiation
    4. Desert foxes have large ears to maximise heat loss via radiation

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Heat Transfer and Kinetic Theory

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	Created by Joseph Tedds over 9 years ago