Why do we sub-cool the refrigerant prior to the TXV?

Sub-cooling the refrigerant prior to the thermal expansion valve (TXV) is essential because it effectively reduces the amount of flash gas in the refrigerant flow. Flash gas refers to the refrigerant that has vaporized prematurely as it leaves the condenser. By ensuring that the refrigerant is fully in a liquid state before it enters the TXV, you maximize the efficiency of the cooling process.

When refrigerant is sub-cooled, it is cooled below its saturation temperature, which helps to ensure that as much as possible of the refrigerant is in liquid form. This is crucial because the TXV is designed to meter liquid refrigerant into the evaporator, where it will absorb heat and turn into a vapor. If flash gas enters the TXV, it can lead to inefficiencies, such as reduced cooling capacity and potential compressor damage due to the dilution of the liquid refrigerant entering the evaporator.

The other choices pertain to aspects of system function but do not directly address the primary purpose of sub-cooling. While increasing the system pressure and improving compressor efficiency are beneficial outcomes of proper refrigerant management, they are not the main reasons for sub-cooling prior to the TXV. Lowering the evaporation temperature is related to the refrigeration cycle's