What do the two boundary lines separating the SAT region from the superheat and subcooled represent?

The boundary lines separating the saturated (SAT) region from the superheat and subcooled regions are critical for understanding the phase changes of a refrigerant. The left boundary line indicates the point where a refrigerant transitions from a saturated liquid (100% liquid phase) to the saturated mixture region. This means that at this boundary, all the refrigerant present is in a liquid state. Conversely, the right boundary line represents the point where the refrigerant is fully transitioned to vapor—here, it is 100% saturated gas. This distinction is crucial for thermodynamic calculations and for ensuring that the refrigerant operates within the designed limits of the system.

Understanding these boundary lines helps operators recognize when the refrigerant is in the saturated state, which is vital for efficient heat transfer and overall system performance. This knowledge also informs decisions regarding system operating conditions to avoid inefficient energy use or potential damage to the system components caused by operating in non-optimal conditions.