7.0 HEAT TRANSFER

Heat (thermal energy) always moves from a region of higher temperature to a region of lower temperature. It does so by one or more of three processes: conduction, convection, and radiation. This chapter explains each mechanism in detail, with everyday examples, experiments, and applications. Understanding heat transfer is essential for designing everything from cooking utensils to spacecraft.

7.1 CONDUCTION

Conduction is the process by which heat is transferred through a material without the material itself moving. It is the main method of heat transfer in solids.

7.1.1 Mechanism of Conduction

In a solid, particles are fixed in position but vibrate. When one end of a solid is heated:

• The particles at the hot end gain kinetic energy and vibrate more vigorously.
• These vibrating particles collide with their less energetic neighbours, passing on some of their energy.
• This transfer of energy continues from particle to particle, gradually warming the entire solid.

In metals, there is an additional, much faster mechanism: free electrons. Metals have a 'sea' of delocalised electrons that can move freely throughout the structure. These electrons gain kinetic energy at the hot end and travel rapidly through the metal, colliding with other particles and transferring heat very efficiently. This is why metals are generally good conductors.

7.1.2 Conductors vs. Insulators

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