What is the orientation of temperature lines within the SAT region of an enthalpy diagram?

The orientation of temperature lines within the Saturated (SAT) region of an enthalpy diagram is horizontal because, during a phase change of a refrigerant at constant pressure (such as from liquid to vapor or vice versa), the temperature remains constant. This phenomenon occurs at the saturation points where the refrigerant transitions between phases.

As the refrigerant absorbs or releases heat during this change of state, rather than increasing or decreasing in temperature, it maintains the same temperature while undergoing the transition. Therefore, the lines representing temperature on the enthalpy diagram in the SAT region are drawn horizontally, reflecting the fact that temperature does not change.

This understanding is crucial for interpreting how refrigerants behave under varying conditions in thermodynamic cycles, especially during the process of phase changes where energy is exchanged without a change in temperature.