a、b、d"… and saturated vapor state at different pressures will form the saturated liquid line(x=0)and saturated vapor line(x=1). These two lines d, d superheated meet at the critical point C, forming a dome as shown in Fig. 6-2. All the compressed liquid states are located in the region to the wet vapor left of the saturated liquid line, called the compressed liquid region. All the Figure 6-3T-s Diagram of Phase Change Processes located to the ight of the saturated vapor line, called the superheated vapor region. In these two regions, the substance exists in a single phase, liquid or vapor. All the states that involve both phases in equilibrium are located under the dome, called the saturated liquid-vapor mixture region, or the wet region At the critical point, there is no longer difference between saturated liquid and saturated vapor The temperature, pressure, and specific volume of a substance at the critical point are called the critical temperature Te, critical pressure pe and critical specific c volume espectively. At pressures above the critical pressure, there is not a distinct phase change process. Instead, the specific volume of the substance continually increases, and at all times there is only one phase present. Eventually, it resembles a vapor, but we can never tell when the change has occurred. Above the critical state, there is no line that separates the compressed liquid region and the superheated vapor region. However, it is customary to refer to the substance as superheated vapor at temperatures above the critical temperature and as compressed liquid at temperatures below the critical temperature Critical properties of a substance are determined by the type of the substances, each substance has nly a group of critical properties. The critical properties of water vapor are t=373990,p=22064 MPa and 1=0003106m3/kg Similarly, the T-sdiagram of water vapor can be drawn, as shown in Fig. 6-3. The same haracteristics of the p-vand the T-sdiagram can be summarized as the following There are two lines on the diagram, which are the saturated liquid line (x=0) and saturated vapor line (x=0), and these two lines meet at one point: the critical point; and the two lines divide region into three region; during a phase-change process from liquid to vapor, substance will experience five kinds of states: unsaturated liquid state, saturated liquid state, wet vapor, saturated vapor state and superheated vapor state 6.3 Water Vapor Tables The ideal-gas equation of state is pv= RT. Water vapor differs from ideal gases and does not follow this equation. The equation of state for water vapor is very complicated and seldom directly used in practical engineering calculations. Therefore, property tables and charts are often compiled and plotted on the basis of experimental and theoretical data for practical application In the following, steam tables are used to demonstrate the use of thermodynamic property tables Property tables of other substances are used in the same manner. For various substances, the thermodynamic properties are listed in more than one table. In fact, a separate table is prepared for each region of interest, such as the superheated vapor, compressed liquid, and saturated(mixture) regions101 a b d    、 、 …and saturated vapor states a b d    、 、 … ... at different pressures will form the saturated liquid line（ x = 0 ）and the saturated vapor line（ x =1 ）. These two lines meet at the critical point C, forming a dome as shown in Fig. 6-2. All the compressed liquid states are located in the region to the left of the saturated liquid line, called the compressed liquid region. All the superheated vapor states are located to the right of the saturated vapor line, called the superheated vapor region. In these two regions, the substance exists in a single phase, liquid or vapor. All the states that involve both phases in equilibrium are located under the dome, called the saturated liquid–vapor mixture region, or the wet region. At the critical point, there is no longer difference between saturated liquid and saturated vapor. The temperature, pressure, and specific volume of a substance at the critical point are called the critical temperature Tc , critical pressure c p and critical specific volume, respectively. At pressures above the critical pressure, there is not a distinct phase change process. Instead, the specific volume of the substance continually increases, and at all times there is only one phase present. Eventually, it resembles a vapor, but we can never tell when the change has occurred. Above the critical state, there is no line that separates the compressed liquid region and the superheated vapor region. However, it is customary to refer to the substance as superheated vapor at temperatures above the critical temperature and as compressed liquid at temperatures below the critical temperature. Critical properties of a substance are determined by the type of the substances, each substance has only a group of critical properties. The critical properties of water vapor are c t = 373.99 ℃, c p = 22.064 MPa and c v = 0.003106 m3 /kg. Similarly, the T s − diagram of water vapor can be drawn, as shown in Fig. 6-3. The same characteristics of the p − v and the T − s diagram can be summarized as the following: There are two lines on the diagram, which are the saturated liquid line （ x = 0 ） and saturated vapor line （ x = 0 ）; and these two lines meet at one point: the critical point; and the two lines divide the entire region into three regions: unsaturated liquid region, wet region and superheated vapor region; during a phase-change process from liquid to vapor, substance will experience five kinds of states: unsaturated liquid state, saturated liquid state, wet vapor, saturated vapor state and superheated vapor state. 6.3 Water Vapor Tables The ideal-gas equation of state is pv RT = . Water vapor differs from ideal gases and does not follow this equation. The equation of state for water vapor is very complicated and seldom directly used in practical engineering calculations. Therefore, property tables and charts are often compiled and plotted on the basis of experimental and theoretical data for practical application. In the following, steam tables are used to demonstrate the use of thermodynamic property tables. Property tables of other substances are used in the same manner. For various substances, the thermodynamic properties are listed in more than one table. In fact, a separate table is prepared for each region of interest, such as the superheated vapor, compressed liquid, and saturated (mixture) regions. Figure 6-3 T s − Diagram of Phase Change Processes