Thermal energy transfers
● Main types of heat transfers
○ Conduction
○ Convection
○ Radiation
● Heat is the transfer of energy from objects of different temperatures
● As objects warm up or cool down, their kinetic energy changes
● Conduction
○ It is the process by which heat or energy is directly transmitted through a substance
when there is a difference in temperature between the 2 substances
○ Conductor - it lets heat and energy transmit through it
○ Insulator - it doesn't let heat and energy transmit through it
○ Metals are better conductors as they have a lot of free electrons available
● Convection
○ The mode of heat energy transfer that mainly occurs in fluids due to difference in
densities
● Convection current
○ It is the movement of a fluid that carries energy from a warmer to a cooler place
● Radiation
○ Process of transferring energy by electromagnetic waves
○ The hotter the object, the higher frequency of radiation emitted
○ It does not require any medium to transfer energy meaning it can transfer across vacuum
○ Electromagnetic radiation transfers energy from a hot to a colder region
● Characteristics of infrared radiation
○ It is produced by warm or hot objects and is a form of electromagnetic radiation
○ Travels through empty space in the form of waves
○ Travels in straight lines
○ Warms the object that absorbs it
○ It is invisible to the naked eye and can only be detected by nerve cells in the skin
● Good absorber/bad reflector/best emitter → black and matt
● Bad absorber/good reflector → white and shiny
● Factors affecting rate of radiation
○ Temperature of surface
■ A hotter surface radiates more energy and emits more radiation than a cooler
surface (directly proportional)
○ Surface area
■ Larger radiation is emitted from a larger surface area. Energy is radiated at a
greater rate from a bigger surface area (directly proportional)
● Consequences of heat energy transfer
○ Heat energy travels from a hotter place to a cooler place (high to low temperatures)
○ Conduction is the only way that heat energy can travel through a solid. Energy travels
through the solids but the particles cannot move.
○ Convection is the main mode of heat energy transfer in fluids. Warm fluid moves around,
carrying energy with it
○ Radiation is the only way that the heat energy can travel through vacuum
Home insulation
● Loft insulation(roof)
○ Fiberglass is used and air is trapped inside
○ This prevents conduction of heat through the roofs
● Underfloor insulation (floor)
○ Using the insulating material and carpets to prevent conduction of heat through the floor
● Cavity walls (walls)
○ Air is trapped between the 2 layers of bricks, this again prevents conduction of heat
energy through the walls
○ When air is removed and there is vacuum between bricks, it prevents conduction and
convection
● Double/triple glazing of windows/thick curtain
○ It prevents conduction and convection through the windows
● Filling in the cavity of walls with foam or rockwool
○ It prevents conduction and convection through the walls
● Vacuum flask
○ No thermal energy transfer by conduction and convection
● Silvered surfaces
○ Inner silvered surfaces reflect radiation from hot fluids back into the flask. Outer
silvered surface reflects radiation in the external surroundings away from the flask.
● Foam plastic support
○ Reduce thermal energy transfer by conduction
● Plastic cap
○ Reduce thermal energy transfer by conduction, stops convection and evaporation
