Reducing Energy Loss (Edexcel IGCSE Physics: Double Science)

• There are many situations where energy transfers are actually unwanted:
  
  • Keeping a house warm
  • Keeping a drink hot or cold
  • Dressing to stay warm in cold weather

Insulated mugs are used to maintain the temperature of hot or cold drinks

 

• When an appliance is used for heating something (a kettle, a heater, a tumble dryer, a central heating system, etc.), the appliance requires a lot of energy
  • It can become expensive for a household to run such appliances
  • The production of electricity using fossil fuels produces greenhouse gases, which contribute to global warming
  • The combustion of (methane) gas produces greenhouse gases, which contribute to global warming

• Therefore, it is often useful to explore ways of reducing unwanted energy transfers

• Energy that is dissipated to the surroundings is often the main source of wasted energy transfers
• If these unwanted energy transfers can be prevented, or reduced, the useful energy transfers can be made more efficient

Reducing conduction

• Energy transfers by heating due to conduction are one of the most common sources of dissipated energy
• To reduce energy transfers by conduction, materials with a low thermal conductivity should be used
  • Materials with low thermal conduction are called insulators

 

Reducing convection

• Convection can also be a source of dissipated energy 
• To reduce energy transfers by convection, convection currents must be prevented from forming
• Therefore, the fluid (liquid or gas) that forms the currents must be prevented from moving

 

Insulation

• Insulation reduces energy transfers from both conduction and convection

 

• The effectiveness of an insulator is dependent upon:

• • The thermal conductivity of the material
    • The lower the conductivity, the less energy is transferred 
•  
  • The density of the material
    • The more dense the insulator, the more conduction can occur
    • In a denser material, the particles are closer together so they can transfer energy to one another more easily
•  
  • The thickness of the material
    • The thicker the material, the better it will insulate

 

• Insulating the loft of a house lowers its rate of cooling, meaning less energy is transferred to the surroundings (outside)
• The insulation is often made from fibreglass (or glass fibre)
  • This is a reinforced plastic material composed of woven material with glass fibres laid across and held together
  • The air trapped between the fibres makes it a good insulator

• The gaps or cavities between external walls are often filled with insulation
  • This is called cavity wall insulation
  • This is often done by drilling a hole through the external wall to reach the cavity and filling it with a special type of foam which is made from blown mineral fibre filled with gas
  • This lowers the conduction of heat through the walls from the inside to the outside

Cavity insulation

Less energy is transferred by conduction and convection if the cavity is insulated