Heat transfer Flashcards
What are some different factors that effect the rate of heat transfer?
The size of the surface area.
Fins.
The type of material.
If the materials in contact with it are insulators and conductors.
Are metals good conductors of heat?
Yes
What are bad conductors of heat called?
Insulators
Gas particles:
Almost no forces Particles have more energy Free to move Random directions High speed
Liquid particles:
Weaker forces Particles are close together Can move past each other Have more energy than solids Move at low speeds
Solid particles:
Strong forces
Particles are close together
Fixed pattern
Can only vibrate about their fixed position
What do fins in and engine do?
Increase surface area to speed up cooling.
If two objects at the same temperature have the same surface area but different volumes, which one will cool more quickly?
The one with the smaller volume.
Give an example of how an animal controls heat transfer.
Arctic foxes: small ears
small surface area to minimise heat loss
by radiation.
Desert foxes: huge ears
large surface area to allow them to loose
heat loss by radiation.
Describe how a vacuum limits heat transfer.
The glass bottle is double-walled with a vacuum between the two walls to stop conduction and convection through the sides.
Heat energy is transferred from the heater coils to the what?
Water (conduction)
The particles near the coils get ___________ so they start moving around faster
More energy
Heating a room with a radiator relies on?
Convection currents
Hot, less dense air by the radiator what flows to replace it?
Denser, cooler air
Convection simply cant happen in solids because ….
particles cant move
What happens when Gas cools?
The particles in the gas slow down and lose kinetic energy
How does water vapour condense?
It condenses in the air when it comes into contact with cold surfaces
Why does invisible water vapour condense?
It condenses to form tiny water droplets as it spreads into cooler air
What is Condensation?
When a Gas turns to a Liquid
What is Evaporation?
When a Liquid turns to a Gas
What is melting?
When a solid turns to a liquid
What is freezing?
When a liquid turns to a solid
What is sublimation?
When a solid turns straight away to a gas (the liquid part is skipped out)
In order for a solid to turn into a liquid and a liquid to turn into a gas what needs to happen to the particles?
The particles need to gain more kinetic energy (in order to break bonds)
What state of matter has the most kinetic energy within its particles?
A Gas
What state of matter has the least kinetic energy within its particles?
A Solid
Explain the process of conduction
~ In conduction, one particle gets heated up and passes on its kinetic energy to it’s neighbouring particle (and so on…)
Why do metals make good conductors?
The metal contains free ions (electrons) which whizz around quickly and pass on the kinetic energy to random particles
What do draught excluders do?
They are placed at the bottom of doors to minimise cold draughts by CONVECTION CURRENTS
What does Double Glazing do?
It is an extra layer of glass placed in a window to minimise heat loss by CONDUCTION
What do cavity walls do?
They are an additional layer of brick placed in walls to reduce heat loss by CONDUCTION
What is Cavity Wall Insulation?
Foam placed in between cavity walls to reduce heat loss by CONVECTION
What do radiator reflectors do?
They are a piece of shiny foil placed behind radiators to reflect the heat back into the home
What is loft insulation?
A thick layer of fibreglass wood laid out across the floor and ceiling of the loft which reduces heat loss by CONDUCTION AND CONVECTION
What do thick curtains do?
They are big bits of cloth over the window which reduces heat loss by CONDUCTION AND RADIATION
What is the formula for Payback Time?
Payback time = initial cost/annual saving
If the initial cost for installing loft insulation was £200 and the annual saving was £50. What would be the payback time?
200/50 = 4 years
What is payback time measured in?
Years (sometimes can be months e.g. 15/30 can equal to 6 months)
The better the insulator the (…….) the U-Value?
Lower
