Sensible heat occurs in the refrigeration system during two main processes: the refrigerant condensing process and the refrigerant evaporating process.
Refrigerant Condensing Process: After the high-pressure, high-temperature refrigerant gas leaves the compressor, it enters the condenser. In the condenser, the refrigerant releases its heat to the surrounding air or water, depending on the type of condenser used (air-cooled or water-cooled). As the refrigerant gives up heat and starts to cool down, it undergoes a phase change from a high-pressure gas to a high-pressure liquid. During this phase change, the temperature remains constant, and the heat being transferred is referred to as sensible heat.
Refrigerant Evaporating Process: After leaving the condenser, the high-pressure liquid refrigerant moves through the expansion valve or metering device into the evaporator. In the evaporator, the pressure of the refrigerant drops significantly, causing it to expand rapidly. As the refrigerant evaporates and absorbs heat from the surrounding air or the space being cooled, it undergoes another phase change from a high-pressure liquid to a low-pressure, low-temperature vapor. Again, during this phase change, the temperature remains constant, and the heat being absorbed is called sensible heat.
In both the condensing and evaporating processes, the sensible heat transfer results in a change in the refrigerant's temperature while the refrigerant remains in the same phase (gas or liquid). Sensible heat transfer is essential for the proper functioning of the refrigeration system, as it allows the refrigerant to absorb heat from the space being cooled in the evaporator and release that heat to the environment in the condenser, enabling the cooling cycle to continue.