Heat Transfer Flashcards
How are heat and temperature two different quantities?
Heat is a form of energy and is therefore measured in units of Joules.
Temperature is a measure of how hot or how cold an object is, it is measured using a thermometer. The difference in temperature will decide the direction in which heat energy will move. Heat energy always flows from a high to a low temperature.
What is conduction?
This is concerned with the movement of heat through solid materials
Best conductors between copper, aluminium, brass and iron from best to worst
Copper
Aluminium
Brass
Iron
Why do good conductors always feel cold to touch while good insulators always feel warm?
The metal conducts heat our of your hand quickly so the hand is cooler and sense it as cold
Four uses for conductors
Steel saucepans good conductor.
Radiators conduct heat from warm water.
BBQ grills.
Solar panels.
Four uses for insulators
Wooden/plastic handles of saucepan.
Wall insulation.
Jumper.
Lagging of pipes.
What is the best and second best insulators?
Best - vacuum because no material is present to conduct the heat.
Second - pockets of trapped gas/air
Explanation of conduction
In metals atoms, the outer shell electrons are fairly easy to remove and they are free to move around within the metal (free electrons). When all solids are heated the atoms begin to vibrate more vigorously and little heat energy is passed on to neighbouring atoms but it’s a very slow process because of the massive size of the atom
Heat transfer in metals and non-metals?
Metals - via interatomic vibration and movement of delocalised electrons.
Non-metals - via by interatomic vibration only.
What is convection?
This is concerned with the movement of heat through liquids and gases
How does convection work with liquids?
As a Bunsen heats water at the bottom of a flask it becomes less dense and rises to the top. Cold water which is more dense moves in to take its place. A convection current is then established.
How does convection work with gases?
A candle heats the air around it which rise. Cold air which is more dense takes its place by smoke from a splint being drawn through with it.
What is heat radiation?
Concerned with the movement of heat using electromagnetic rays known as Infra-red rays.
They are part of the electromagnetic spectrum, are the hottest part and can travel through a vacuum.
What are the best and worst absorbers of radiant heat?
Dark matt colours are the best absorbers and shiny surfaces are the worst absorbers.
Bright clothes in the summer reflect the sun’s heat rays.
What are the best and worst emitters of radiant heat?
Dark matt colours are the best emitters and shiny surfaces are the worst.
Applications of absorbing or emitting heat
Factory’s roofs - painted silver on inside to reflect radiant heat back in reducing heat loss and heating costs.
Thermal solar water panels - painted black to enhance the heat absorption.
How do the structure of houses prevent heat loss?
Constructed using double walls, separated by a cavity which can be filled with an insulating material.
Double-glazing, 2 panes of glass separated by a trapped pocket of air.
Using good quality carpet.
Using good heavy curtains.
