What is the purpose of 'superheat' in a refrigeration system?

The purpose of superheat in a refrigeration system is to ensure that only vapor refrigerant enters the compressor. Superheat is defined as the temperature of the refrigerant vapor above its saturation temperature at a given pressure. It's measured at the outlet of the evaporator, just before the refrigerant enters the compressor. Allowing liquid refrigerant to enter the compressor can cause significant damage, as liquids are incompressible and can damage the compressor's valves, pistons, and other internal components. Liquid refrigerant can also wash away the lubricating oil, leading to increased friction and wear. By ensuring that the refrigerant is superheated, meaning it is entirely in the vapor phase and at a temperature above its saturation point, the risk of liquid refrigerant entering the compressor is eliminated. The proper amount of superheat is typically controlled by a thermostatic expansion valve (TXV), which regulates the flow of refrigerant into the evaporator to maintain a consistent level of superheat. For example, if the desired superheat is 10°F, the TXV will adjust the refrigerant flow to ensure that the refrigerant vapor leaving the evaporator is 10°F above its saturation temperature at that pressure. Maintaining proper superheat is critical for protecting the compressor and ensuring the reliable and efficient operation of the refrigeration system.