In a vapor-compression refrigeration system, which phases does the refrigerant primarily operate in?

In a vapor-compression refrigeration system, the refrigerant predominantly operates in the liquid and vapor phases. This operation is critical to the refrigeration cycle, which involves the absorption of heat from a low-temperature space and the expulsion of that heat to a higher-temperature area.

During the evaporation process, the refrigerant absorbs heat, causing it to change from a liquid to a vapor. This phase change is what allows the system to effectively draw heat from the space being cooled. The vapor is then compressed, raising its pressure and temperature, and subsequently released into the condenser where it releases heat and changes back into a liquid state.

This cycle of transitioning between liquid and vapor phases is essential for the efficiency and functionality of the refrigeration system, making the correct answer liquid and vapor. The other phases—such as solid or combinations involving either solid or gas—are not utilized in the standard vapor-compression cycle, as the refrigeration process relies on the heat-exchange properties of the liquid and vapor states for effective cooling.