Refrigeration and air conditioning

Refrigeration and Air Conditioning requires the movement of energy from a lower energy(ie. Lower Temperature) reservoir to a higher energy reservoir. This Process cannot occur without additional energy being supplied to the system. One common system used is the vapour-compression refrigeration cycle.

Vapour-compression refrigeration cycle
This Cycle consists of an evaporator, compressor, condenser and an expansion valve. The Refrigerant moves in this order through the cycle. In order to absorb energy from the low temperature reservior the Refrigerant must be below the temperature of the low temperature reservior when it enters the evaporator.

Evaporator
Facilitates the movement of energy from the low temperature reservior to the Refrigerant. This results in a temperature increase of the Refrigerant and a temperature decrease in the room or fridge.

Compressor
The system is able to work because of the energy input to the compressor (Wnet,in). The Compressor does work on the refrigerant to compress it. As a result of compression the refrigerants pressure and temperature increase (to a value higher than the high temperature reservior).

Condenser
The condenser facilitates the movement of energy from the refrigerant to the high temperature reservior. This results in the refrigerants temperature decreasing.

Expansion Valve
The Expansion Valve reduces the pressure and temperature via the effects of throttling.

Wikipedia

 * Air conditioning
 * Heat pump (can both heat and cool)