Heat Transfer or Heat Energy

1. Heat Transfer or Heat Energy

2. Learning objective and Outcomes Objective • The objective of this topic is to understand the methods of heat transfer Outcomes At the end of this session, students should be able to: • Recognise heat as a form of energy • Recognise the three types of energy transfer (Conduction, Convection and Radiation) • Describe convection in liquid or gas • Describe the process of heat radiation and that black is a good radiator

3. Questions • If a cup of hot coffee and an ice cube were left on the table in this room what would happen to them? • The cup of coffee will cool until it reaches room temperature. The ice cube will melt and then the liquid will cool to room temperature. • Why? • They both have to adapt the rates at which the temperature changes in the room

4. Why does heat transfer happen? Heat is a type of energy called thermal energy. Heat can be transferred (moved) by three main processes: 1. Conduction 2. Convection 3. Radiation During heat transfer, thermal energy always moves in the same direction: HOTCOLD Heat energy only flows when there is a temperature difference from a warmer area to a cooler area.

5. Conduction • Conduction is the process of heat transfer through a medium or material without any movement of the medium or material

6. Conduction As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this? As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this?

7. Why does metal feel colder than wood, if they are both at the same temperature? Metal is a conductor, wood is an insulator. The metal conducts the heat away from your hands, the wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

8. Some materials conduct heat more rapidly than others • Such materials are called thermal conductors • Most metals are good thermal conductors

9. Examples of Poor Conductors of Heat

10. Comparing Different Thermal Conductivities • Which is the best conductor? --> Brass --> Iron --> Water • Which is the least conductor? --> Air

11. Second method of heat transfer Convection

12. Definition! • Convection is the transfer of heat from one place to another by the movement of currents in liquids or gases

13. How does convection in a liquid occur?

14. Heating fluids What happens to the particles in a liquid or a gas when you heat them? The particles spread out and become less dense. What is a fluid? A liquid or gas. This effects fluid movement.

15. Fluid movement Cooler, more d____, fluids sink through w_____, less dense fluids. ense armer In effect warmer liquids and gases r___ up. ise Cooler liquids and gases s___. ink

16. Demostrations of Convection using Water movement Cools at the surface Convection current Hot water rises Cooler water sinks

18. Why is it windy at the seaside?

19. Why is convection important in fridges? Why is the freezer compartment at the top of a fridge? Where is the freezer compartment put in a fridge? It is put at the top, because cool air sinks, so it cools the food on the way down. It is warmer at the bottom, so this warmer air rises and a convection current is set up.

20. Third method of heat transfer Radiation

21. Radiation is the transfer of heat, in the form of waves, from one place to another without a medium.

22. The third method of heat transfer How does heat energy get from the Sun to the Earth? There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. RADIATION ?

23. Investigating thermal emission

24. Investigating thermal absorption

25. What are infrared waves? Heat can move by travelling as infrared waves. These are electromagnetic waves, like light waves, but with a longer wavelength. This means that infrared waves act like light waves: • They can travel through a vacuum. • They travel at the same speed as light – 300,000,000 m/s. • They can be reflected and absorbed. Infrared waves heat objects that absorbthem and are alsoknown as thermal radiation.

26. Radiation Radiation travels in straight lines True/False Radiation can travel through a vacuum True/False Radiation requires particles to travel True/False Radiation travels at the speed of light True/False

27. Dull metal Shiny black Shiny metal Dull black Emission experiment Four containers were filled with warm water. Which container would have the warmest water after ten minutes? shiny metal The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation. radiation dull black emitting

28. Dull metal Shiny black Shiny metal Dull black Absorption experiment Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? dull black The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation. radiation shiny metal absorbing

29. Vacuum Flask

30. 1. Which of the following is not a method of heat transfer? A. Radiation B. Insulation C. Conduction D. Convection

31. 2. In which of the following are the particles closest together? A. Solid B. Liquid C. Gas D. Fluid

32. 3. How does heat energy reach the Earth from the Sun? A. Radiation B. Conduction C. Convection D. Insulation

33. 4. Which is the best surface for reflecting heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black

34. 5. Which is the best surface for absorbing heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black