Im doing revision for the next academic year and have lost this particular worksheet.A heat pump is on the back of a fridge and it is what keeps the fridge cold.
A heat pump is essentially a heat engine in reverse. Working in a reversed Carnot cycle it uses an energy input to move or pump heat from a cold source (e.g. the inside of a refrigerator) to a hot sink (the radiator on the back of a refrigerator). A vapour compression heat pump uses a compressor to raise the pressure and temperature of a refrigerant vapour (compression phase). It then condenses the vapour to a liquid in the hot sink heat exchanger exchanger (cooling phase), drops its pressure and temperature by expanding it through a restrictor or an expansion valve (expansion phase), finally evaporating the cold liquid to a gas in the cold source heat exchanger (heating phase) which in the case of a refrigerator is the cold space inside.
