Different lines or areas of the T-s diagram represent qualitatively different classes of thermodynamic states.
The T-s diagram, illustrated in Figure 1, has been consistently used in thermodynamics textbooks for decades to explain the thermodynamic properties of water.
This state transformation occurs at a constant temperature (and pressure) and is therefore shown as a horizontal line in the T-s diagram. Finally, a pump compresses the liquid, thereby increasing its temperature.
From a human factors point of view, the T-s diagram provides an especially good mapping because it makes it easy to see the invariant properties of the Rankine cycle.
For example, an actual turbine is not perfectly efficient, as indicated in the T-s diagram by a deviation from vertical in the line representing the turbine phases of the cycle.
The pressure and temperature at each of these points can then be graphed as data points on the T-s diagram. Recall that temperature, pressure, and entropy are partially redundant, so knowing the temperature and pressure is sufficient to identify a point in the T-s diagram.
Instead of presenting a large number of independent data points, the Rankine display exploits the features of the T-s diagram described earlier.