Quantity of Heat and Heat Transfer

Heat

Heat

a form of energy

Heat Capacity

the amount of heat energy needed to change the temperature by 1 kelvin

SI unit of Heat Capacity

joule per kelvin

Heat Capacity Formula

heat energy need to change temperature = heat capacity x change in temperature

Specific Heat Capacity

the heat energy needed to change the temperature of one kilogram of that substance by one kelvin

SI unit of Specific Heat Capacity

joule per kilogram per kelvin

Specific Heat Capacity Formula

heat energy added/lost = mass x specific heat capacity x change in temperature

Latent Heat

the heat energy needed to change the state of a substance without a change in temperature

SI unit for Latent Heat

joule

Specific Latent Heat

the heat energy needed to change the state of one kilogram of a substance without a change in temperature

Specific Latent Heat Unit

joule per kilogram

Specific Latent Heat of Fusion

the heat energy needed to change one kilogram of a substance from a solid to a liquid without a change in temperature

Specific Latent Heat of Vaporisation

the heat energy needed to change one kilogram of a substance from a liquid to a gas without a change in temperature

Application of Specific Latent Heat

heat pump

How a Heat Pump Works

low pressure liquid turns into low pressure vapour with added heat, goes through compressor and becomes high pressure vapour, gives off heat and condense into high pressure liquid, goes through expansion valve and returns to low pressure liquid

Types of Heat Transfer

convection, conduction, radiation

Convection

movement of heat through a fluid by circulating currents caused by heat

How Convection Occurs

lower part of liquid is heated, expands and becomes less dense, less dense objects float on denser objects, therefore heated liquid rises above cooler liquid

Conduction

transfer of heat through a substance by the passing on of vibrations from molecule to molecule

Radiation

transfer of heat energy from one place to another in the form of electromagnetic waves

Solar Constant

average amount of the sun’s energy falling per second perpendicularly on one metre squared of the earth’s atmosphere

Solar Constant Value

1.35 kW m^-2

Solar Heating

using the suns energy to heat something

Solar Panels

photocells convert suns energy into electrical energy

U-Value

amount of heat energy conducted per second through one metre squared of a structure when the difference of 1 degree celsius is maintained between its ends

SI unit for U-Value

W m^-2 K^-1

High U-Value

bad insulation

Low U-Value

good insulation