TEMPERATURE−ENTROPY DIAGRAM FOR WATER AND STEAM

It is the plot of the saturation temperature of water and steam corresponding to various absolute pressure vs entropies at those saturation temperatures, as shown in Fig. 2.2. The curve on the left marked water line (saturated liquid line) shows the relationship between entropy and temperature before steam is formed. The dry steam line (saturated vapour line) shows the relationship between entropy and temperature when all the water has been converted into steam. The area in between two regions is called the wet region. The area to the right of the dry steam lines is called the region of superheat. The lines of constant dryness, constant volume, and constant total heat are also drawn on the diagram. The temperature at which the distinction between the entropy of water and that of dry steam disappears is called the critical temperature (374.15°C). The pressure corresponding to this temperature is called the critical pressure (221.2 bar).

Figure 2.2 Temperature−entropy diagram for water and steam