Heat Transfer and Temperature Change

Heat Capacity

The heat capacity of an object is the heat energy needed to change it’s temperature by 1K.

Specific Heat Capacity

The specific heat capacity of a substance is the heat energy needed to change the temperature of 1 kilogram of that substance by 1 kelvin.

SI unit of Specific Heat Capacity

Joules per kilogram per kelvin $\left(Jkg^{-1}K^{-1}\right)$

Latent Heat

The latent heat of a substance is the heat energy needed to change it’s state without a change in temperature.

L=Q

Specific Latent Heat

The specific latent heat (l) of a substance is the amount of heat energy needed to change the state of 1 kilogram of that substance without a change in temperature.

Specific Latent Heat of Fusion

The specific latent heat of fusion of a substance is the amount of heat energy needed to change 1 kilogram of that substance from a solid to a liquid without a change in temperature (i.e. at its melting point). The same amount of heat energy is given out when the substance changes from a liquid to a solid at its melting point.

Specific Latent Heat of Vaporisation

The specific latent heat of vaporisation of a substance is the amount of heat energy needed to change 1 kilogram of that substance from a liquid to a gas without a change in temperature (i.e. at its boiling point). The same amount of energy is given out when the substance changes from a gas to a liquid at its boiling point.

SI unit of all specific latent heat

Joules per kilogram $\left(Jkg^{-1}\right)$

Heat Pump

A heat pump is a device that uses electricity to transfer heat from a cooler region to a warmer one.

Conduction

Conduction is the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule. There is no overall motion in the substance.

Convection

Convention is the transfer of heat through a fluid by means of circulating currents of fluid caused by the heat.

Radiation

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

U-value

The U-value of a structure is the amount of heat energy conducted per second through 1m² of that structure when a temperature difference of 1⁰C (i.e. 1K) is maintained between its ends.

SI unit for U-value

Watts per meter squared per kelvin $\left(Wm^{-2}K^{-1}\right)$

Energy Efficiency

Percentage efficiency = useful power output divided by power input times 100