## Chapter Objectives and Summaries

### CHAPTER 12 Heat transfer.

LEARNING OBJECTIVES
Knowledge of subject matter
• Identify and discuss how heat is transferred in given situations
• Distinguish between the methods of heat transfer: conduction, convection and radiation
• Identify and discuss why certain materials are good or bad at transferring heat
• The meaning of "Thermal Conductivity"
• Calculate the rate of heat flow in given situations
• Discuss methods of changing th rate of heat transfer to and from substances or structures
• Explain the green house effect in terms of heat transfer
• Solve problems involving heat transfer

SCIENTIFIC PROCESSES

• Collect and organise data on temperature transfer.
• Locate thermal data from tables.
• Design simple experiments to test the efficiency of heat transfer and its prevention.

COMPLEX REASONING PROCESSES

• Design a coherent strategy for complex 'real-world' problems related to heating and cooling.
• Select relevant data to confirm or refute theories about the efficiencies of various cooling measures.

### CHAPTER 12 SUMMARY

• Conduction is the process where heat energy is transferred through a medium by the vibration to the particles of the medium.
• In conduction the particles of the medium do not travel with the heat flow.
• Conduction occurs better where the particles are in close contact. Metallic solids are the best conductors.
• Insulators are materials that have very low thermal conductivity.
• Materials that trap air are poor conductors, as air is a poor conductor of heat.
• The rate of heat energy flow through a material is given by the equation:-
R = k (T2 - T1).A/d Where R is the rate of heat flow in Watts, k is the thermal conductivity in W.m-1 K-1, (T2 - T1) is the temperature difference on either side of the material in K, A is the surface area of the material in m2, and d is the thickness of the material in m.
• Convection is the process where heat energy is transferred through a medium by the movement of the particles of the medium. This movement of particles sets up convection currents.
• As convection requires the free movement of particles it is confined to liquids and gases.
• Radiation is the transfer of heat by means of electromagnetic waves, in particular, infra-red waves.
• The transfer of heat energy by radiation does not require a medium.
• White shiny materials can reflect radiation, while dark materials absorb radiation