The Carnot Vapour Compression Refrigeration cycle is the thermodynamic cycle that is widely used by commercial manufacturers and producers of refrigerators, air-conditioners, freezers, and other equipment for the same cooling and freezing applications. There are four major components involved in the Carnot vapor compression refrigeration and air conditioning cycle in which a refrigerant is used as a cooling medium that flows through these 4 components:
The low pressure, low temperature, liquid state refrigerant enters the Evaporator. The Evaporator through the refrigerant is used to absorb heat. In the Evaporator is where the cooling of the items that you put inside your fridge take place. Heat exchange will take place between the refrigerant and the heat sources. The food items will then be cooled down while the previously cold refrigerant will be heated up and be turned to vapor. The boiling point (saturation temperature) of the refrigerant must be lower than the temperature of the heat source (such as food, drinks, beverage, vegetables, fruits that you put inside your fridge) so that by the 2nd Law of Thermodynamics, "Heat flows from a hot body to a cold body", the heat will flow from the heat source to the refrigerant. Upon exiting the Evaporator and absorbing the heat, the previously liquid refrigerant is now turned into a low pressure, high temperature, gas/vapor state refrigerant.
The low pressure, high temperature, gas/vapor state refrigerant enters the Compressor. In order for the refrigerant to reject the heat (in order for the refrigerant to get cooled down) in the condenser, the boiling point or saturation temperature of the refrigerant must be higher than the condenser (heat sink) temperature. The purpose of the Compressor is to raise the saturation temperature of the refrigerant as well as to increase the refrigerant's pressure. Upon exiting the Compressor, the previously low pressure, high temperature, gas/vapor state refrigerant is now turned into a gas or vapor state refrigerant with high pressure, and higher temperature than when it entered the Compressor.
The high pressure, high temperature, gas state refrigerant enters the Condenser or Heat Sink. The purpose of the Condenser is to cool down and condense the vapor state refrigerant and turn it into a liquid state refrigerant. Typical condensers used in refrigeration and air-conditioning are Air-cooled Condensers which are basically made up of multiple thin coils that are used to liquefy the refrigerant and discharge the heat to the surrounding air or atmosphere in the environment. When the refrigerant exits the Condenser, it is now high pressure, high temperature, and in liquid form.
Thermal Expansion Valve
The high pressure, high temperature, liquid state refrigerant enters the Thermal Expansion Valve (TEV). The purpose of the TEV is to lower down the pressure and bring back the refrigerant to its original saturation temperature so that the cycle is completed and prepares the refrigerant to start another cycle. Another important function of the TEV is to regulate the amount of flow of liquid refrigerant to the evaporator. This is determined by how much food and drink items were place in your refrigerator and how cold you want them to be. The thermostat, (the usually circular button that has numbers indicating Cold, Colder, Coldest) that you turn inside your fridge is where you control to the desired settings. On the exit to the Thermal Expansion Valve, the refrigerant is now turned into low pressure, low temperature, liquid refrigerant that is now again ready to absorb heat from whatever food, drink, milk, fruits, veggies, cheese, soda, and other heat sources that you place inside your fridge or refrigerator. Thus completes the Carnot Vapour-Compression Refrigeration cycle.
1. Basics of Refrigeration and Air Conditioning