Thermal Insulation
- Thermal energy transfers from hotter areas to cooler areas by the processes of:
- Conduction
- Convection
- Radiation
Conduction, convection and radiation demonstrated in a mug of hot tea
- Objects will always lose heat until they are in thermal equilibrium with their surroundings
- Thermal equilibrium is reached when objects have cooled to room temperature
- Insulation can be used to reduce the rate at which heat transfers
Reducing Conduction
- Insulators are materials that are poor conductors of heat
- Fabrics, such as wool and cotton, are good insulators
Different materials have different properties of conductivity
- These materials are usually low density and often contain pockets of trapped air
- This makes them very effective because air is a poor conductor
- Surrounding a warm object with a material that contains trapped air will reduce the rate at which it loses heat
- Likewise, surrounding a cold object with such a material will reduce the amount of heat reaching the object
Reducing Convection
- Insulating materials that contain trapped air are also effective at reducing convection
- Trapped air is unable to move around, forming convection currents
- By placing a lid on a hot drink, or saucepan, convection can be further reduced
Reducing Radiation
- Infrared radiation is emitted from all hot materials
- It is a wave of electromagnetic radiation
- Shiny materials are poor emitters of radiation
- By covering the material with a shiny (non-metal) coating the rate of heat loss can be further reduced
