The principles of refrigeration are based on the laws of thermodynamics and the cycle of heat transfer. Here are the fundamental principles involved in refrigeration:
The First Law of Thermodynamics (Conservation of Energy): This principle states that energy cannot be created or destroyed, only transferred or converted from one form to another. In refrigeration, energy is transferred from a low-temperature region (the refrigerated space) to a high-temperature region (the surroundings or heat sink) using a refrigeration system.
The Second Law of Thermodynamics: This law describes the concept of heat flow from a hot object to a cold object. Heat naturally flows in the direction of decreasing temperature. In refrigeration, the second law is utilized to transfer heat from a low-temperature region to a high-temperature region using an external work input.
The Refrigeration Cycle: The refrigeration cycle is the thermodynamic process that enables the transfer of heat from a cold region to a hot region. It involves four essential components: compressor, condenser, expansion valve, and evaporator.
Compressor: The compressor is responsible for increasing the pressure and temperature of the refrigerant gas. It compresses the low-pressure refrigerant vapor, thereby raising its temperature.
Condenser: The high-pressure, high-temperature refrigerant gas from the compressor enters the condenser. In the condenser, heat is transferred from the refrigerant to the surroundings (typically air or water), causing the gas to condense into a high-pressure liquid.
Expansion Valve: The high-pressure liquid refrigerant passes through an expansion valve, which reduces its pressure and temperature. This sudden drop in pressure causes the refrigerant to partially evaporate and enter the evaporator as a low-pressure mixture of liquid and vapor.
Evaporator: In the evaporator, the remaining liquid refrigerant evaporates by absorbing heat from the refrigerated space. As the refrigerant vaporizes, it absorbs heat, cooling down the surrounding environment.
Latent Heat of Vaporization: During the evaporation process in the evaporator, the refrigerant absorbs heat from the refrigerated space. This heat transfer occurs through the latent heat of vaporization, where the refrigerant changes from a liquid phase to a vapor phase while absorbing a significant amount of heat.
By following this cycle, the refrigeration system continually absorbs heat from the refrigerated space, maintaining its low temperature, and rejects heat to the surroundings, keeping the temperature of the heat sink higher. This enables the system to create and maintain a temperature difference, allowing for cooling applications such as air conditioning, food preservation, and industrial processes.