density, heat transfer and heat loss in homes Flashcards
what is density?
a measure of how much matter is present in a given volume
what is the density of a solid like?
particles are very close together, tightly packed so they have a high density
what is the density of a liquid like?
particles are close together, still tightly packed so have high density but less dense than solids
what is the density of gas like?
particles are very far apart and so have a low density
what is conduction?
flow of heat through a material, from places of high temperature to low temperature
are metals good conductors?
yes
are plastics, wood, fabrics and glass good conductors?
no
what are bad conductors known as?
insulators
how do metals conduct heat?
metals contain ‘free electrons’ which gain energy when they are heated. They then move into cooler regions and collide with atoms. Their energy is passed on and temperature rises
what is convection?
flow of heat energy through a liquid or gas from a place of high temperature to low temperature
how is a convection current set up?
how liquid/ gas increases in volume and becomes less dense and lighter because the particles move faster and further apart. The hot liquid/ gas will rise. The colder, denser and heavier liquid/ gas will fall and gets heated. A convection current is set up.
what is radiation?
All hot or warm objects radiate heat in the form of infra-red radiation, the hotter the object the more heat energy it will emit
what are good emitters or infra red radiation?
dark surface because no heat is reflected away
what type of surface is a good absorber of heat radiation?
black surface
are shiny surfaces good emitters and absorbers?
no but they are good reflectors
why is it important to reduce heat loss?
saves money
reduces use of heating
reduces fossil fuel use
reduces pollution and use of fossil fuels
where is heat lost in a house?
windows and doors
floors
walls
roof
where is heat lost due to conduction?
walls, windows, floor and roof
where is heat lost due to convection?
draughts
where is heat lost due to radiation?
walls, roof and windows
how do you reduce heat loss in the roof?
loft insulation - traps air between fibres, air is an insulator and therefore prevents conduction. Air is also trapped in pockets which stops convection currents being set up
how do you reduce heat loss in windows?
double glazing - two panes of glass which trap air, air is an insulator and therefore prevents conduction. May be a vacuum between glass and this prevents conduction and convection
how do you prevent heat loss in walls?
cavity walls - foam is inserted which traps air which therefore stops conduction and convection
how do you prevent heat loss from draughts?
draught excluders - prevent flow of air and therefore convection currents
how do you prevent heat loss in floors?
underlay - trap air reducing condcution
how do you calculate payback time?
savings per year
