What happens to Enthalpy during vertical changes in the sub-cooled or SAT region?

During vertical changes in the sub-cooled or saturation (SAT) region of a refrigeration cycle, enthalpy does not change significantly. This is because both the sub-cooled liquid and saturated liquid regions represent states where the temperature and pressure of the working fluid remain relatively constant while the substance is being compressed or expanded vertically on a pressure-enthalpy diagram.

In the sub-cooled region, as liquid refrigerant is further cooled at constant pressure, its enthalpy remains stable since it is already in a liquid state and is not undergoing any phase change. Similarly, in the saturation region, whether it is in the saturated liquid or vapor phase, any vertical movement often represents a change in pressure or temperature at equilibrium, but the enthalpy remains constant during these transitions.

Thus, during these vertical changes, the enthalpy is effectively stable, which validates the choice that there is no change in enthalpy.