Heat Transfer Flashcards
What are the three types of heat transfer?
Conduction, convection and radiation.
What are the differences between heat and temperature?
Heat:
– is a form of energy;
– is measured in joules;
– a flow of heat causes a change in temperature.
Temperature:
– measures how hot or cold something is;
– is measured in ºC;
– a difference in this causes heat to flow.
Heat can be transferred through a medium (e.g. liquids, gases) or a material.
Through what mediums can heat be transferred by conduction?
Conduction occurs in SOLIDS only.
Heat can be transferred through a medium (e.g. liquids, gases) or a material.
Through what mediums can heat be transferred by convection?
Convection occurs in LIQUIDS and GASES.
Heat can be transferred through a medium (e.g. liquids, gases) or a material.
Through what mediums can heat be transferred by radiation?
Radiation occurs in GASES and in a VACUUM.
How is heat transferred within a non-metal?
The atoms in the material vibrate against other neighbouring atoms. This is usually a slow process and heat energy is conducted from the hot end to the cold end.
How is heat transferred within a metal?
The electrons in the material become free and travel rapidly through the metal. As a result, this process is fast.
Give five examples of insulators.
– Plastic
– Wood
– Glass
– Rubber
– Concrete
Give five examples of conductors.
(Most of these are metals)
– Iron
– Steel
– Silver
– Copper
– Aluminium
Why is conduction the most effective method of heat transfer in solids?
Conduction happens best in solids as the atoms are tightly packed together, and so can transfer the energy to other atoms by vibrating against each other.
Best conductor ______
______
______
______
Worst ______
– Copper (Best conductor)
– Other metal solids
– Non-metal solids
– Liquids
– Gases (Worst)
How does convection occur in a liquid?
Warm water is less dense than cold water as the particles are further apart than they are in cold water. The warm water rises and the cold water falls. We say that a convection current has been set up and will stop when all the liquid has reached the same temperature. (Thermal equilibrium)
How does convection occur in a gas?
Warm air is less dense than cold air as the particles are further apart than they are in cold air. The warm air rises and the cold air falls. We say that a convection current has been set up and will stop when all the gas has reached the same temperature. (Thermal equilibrium)
What is thermal radiation?
Heat/thermal radiation is the transfer of energy by waves.
Where is thermal radiation most effective?
Heat/thermal radiation is most effective in a vacuum.
What type of surface absorbs heat radiation the best?
Dark and dull/matt surfaces absorb and emit heat radiation very easily.
What type of surface absorbs heat radiation the least?
Shiny and light-coloured surfaces are not good absorbers or emitters of heat radiation. Instead, they reflect heat radiation.
What methods can be taken to reduce heat loss from the walls and roof of a home?
– Fibre glass
– Cavity wall insulation
– (Silvered) Foam
What methods can be taken to reduce heat loss from the windows and doors of a home?
– Double glazed windows can be installed.
– Draught excluders can be put onto doors.
