Heat Transfer Mechanisms

Overview

Energy is transferred to an object's thermal energy store when heated, increasing its temperature.
Heating occurs through three main mechanisms:
- Conduction (in solids)
- Convection (in fluids)
- Radiation (through empty space)

Occurs primarily in solids.
Process:
- Vibrating particles transfer energy to neighboring particles.
- Example: Heating one end of a metal with a Bunsen burner.
- Energy is transferred to the kinetic energy store of particles, increasing their vibration.
- Energy is passed along a solid through particle collisions, eventually spreading heat evenly.
Why Solids?
- Particles are closely held together, causing frequent collisions and efficient energy transfer.
Thermal Conductivity:
- Measure of how well objects transfer energy by conduction.
- Metals have high thermal conductivity (rapid heat transfer).
- Plastics and most fluids have low thermal conductivity (used as insulators).

Occurs mainly in fluids (liquids and gases).
Process:
- Particles gain kinetic energy and move faster through random diffusion.
- More energetic particles move from warmer to cooler regions, causing expansion.
- Cycle of rising less dense warm fluid and sinking cooler fluid, creating convection currents.
Real-Life Example:
- Container of fluid: Heated particles rise, cooler particles sink, repeating the cycle.
- Seen in oceans, buildings with radiators, etc.
Reducing Convection:
- Stop free flow of fluids, e.g., using blankets to trap warm air.

Energy transfer without particles, allowing travel through a vacuum.
Process:
- Energy carried by infrared waves.
- All objects absorb and emit radiation simultaneously.
- Hotter objects emit more radiation, e.g., feeling heat from a barbecue without touching.

Conduction and convection involve particle-based energy transfer.
- Conduction: Energy transfer between particles.
- Convection: Movement of particles themselves.
Radiation allows heat transfer in vacuums via infrared radiation.

End of Lecture.