5. Applications of Heat Transfer

Learning outcomes
  • I can identify situations where conduction, convection, and radiation occur together.
  • I can explain how insulation reduces heat transfer.
  • I can describe how heat transfer is used in buildings, cooking, and engineering.
  • I can explain how evaporation can cool objects and living organisms.
  • I can evaluate methods of improving thermal efficiency in practical applications.

Convection: Heat Transfer in Liquids and Gases

Liquids and gases can also transfer heat, but instead of conduction through particles locked in place, the fluid itself moves — this is called convection.
When a fluid is heated, the particles near the heat source gain energy, spread out, and become less dense. The warmer, less-dense region rises, while cooler, denser fluid sinks to take its place. This cycle sets up a convection current that continuously carries energy through the liquid or gas.

Convection explains why warm air rises above radiators, why sea breezes blow toward the shore on hot days, and why water circulates in a kettle as it boils. Any situation where a fluid is heated unevenly will create convection currents.

Summary

  • Good thermal conductors: metals such as copper, aluminium, silver (used for cooking pots, radiators).

  • Poor conductors / insulators: wood, plastic, rubber, wool, polystyrene.

  • Conduction in solids: energy passes through lattice vibrations; in metals, mobile electrons speed up the process.

  • Convection in liquids/gases: heating lowers density, causing warm regions to rise and cooler regions to sink, setting up currents that move thermal energy through the fluid.