Thermodynamic heat transfer processes or refrigeration cycles are both the mathematical and conceptual models for air conditioner, refrigeration and heat pumping systems. A heat pump is an energy generating machine that enables for the conveyance of heat from a low-lying area at a high temperature to a colder region at a lower temperature. This process happens continuously throughout the whole life cycle of the device. It involves the movement of water and air that takes place through a manifold of heat exchangers. The concept of thermodynamics was developed in 1832 by J.S. Hamilton, though the basic principles have been around much longer than that. The modern version of these concepts are often referred to as Hamilton's Principles.
A refrigerator is used for a variety of different functions. It is sometimes referred to as the 'ultimate' form of refrigeration because it can cool water to almost any temperature without any external input of power or energy. A number of different types of refrigerators exist, including those that are part of a system and those that are stand alone units. The simplest form of a refrigeration cycle is the compressors used in air conditioning systems, which use a forced refrigerant to create a cooling effect.
A compressor uses a compression method to lower the temperature of cold air. The compressed air is then circulated through ducts to a cold gas generator, which is generally where the final heat output of the refrigeration cycle occurs. A series of compressors are used in this fashion, though some variation is possible depending on the need of the model. The final output is then compressed into a fluid that can be circulated through piping in the case of a condenser. These pipes are generally made of steel because they are resistant to damage from extended periods of cooling and they make for a long-lasting part.
Another variation of the compressors used in this type of refrigeration cycle is the expansion device. An expansion device generally consists of two tanks that are connected to each other with a flexible tube. The first tank holds cold water that has been pumped through the system while the second tank contains the heated air. A heating element is placed inside the expansion device, which warms the water before allowing it to enter the condenser unit. As the heated air passes through the evaporator coil, the evaporation process takes place, cooling the water that was in the original tank.
Refrigeration cycles using high pressure liquid refrigerant require two separate lines to complete the process. The low pressure liquid refrigerant is pumped through a cold gas generator that creates high pressure steam. This steam is then circulated through the lines, where it heats up the low pressure gas and condenses it into a high pressure liquid that exits the system via an exhaust. The high pressure liquid refrigerant is then pumped back into the system, where it combines with the cool high pressure gas, creating high pressure vapor. Check out this post that has expounded on the topic: https://en.wikipedia.org/wiki/Heat_pump_and_refrigeration_cycle.
High pressure steam and high pressure vapor will have to be separately generated. High pressure steam may be generated by using a diesel engine or a turbine driven by steam turbines. Some high pressure steam may also be created by using high pressure oil. The vapor that exits the refrigeration cycle (which is mostly hot) is cooled by a cooling fan. The fan draws the cooled moisture into the compressor where it is compressed and re-heated.