x=0 and saturated vapor linex=1, meeting at the critical point C, are firstly plotted on the diagram. The saturated liquid line initiates from the origin of coordinates. In the wet region the isobars and isotherms are identical and are inclined straight lines. In the superheated region the isobars and isotherms diverge: the isobars run upwards and the isotherms turn to approach horizontal lines. In the wet region, lines of constant quality (x=const)are also plotted, which merge at the critical point C. Isochors(constant-volume lines) are also plotted on the h-s diagram, which run more steeply ds, compared with the isobars, as shown by the dotted line in Fig.6- It is convenient to use h-s diagram to determine the properties of water vapor. However, the accuracy of the readings depends on the person who uses it. Therefore, in practice, it is often to analyze thermodynamic processes of water vapor with the aid of h-s diagram and tables for water vapor simultaneously to simplify the calculations and to ensure the accuracy Usually, the entire h-s diagram is just partly given out. It is the part of the wet region with quality greater than 0.6 because the lines in the region with quality less than 0.6 is too dense and the data seldom used in projects. The h-s diagram of steam for application in engineering practice is hown in Appendix Figure 2 6.5 Thermodynamic Processes of Water Vapor The main purpose of analyzing thermodynamic processes of water vapor is to determine the final state and state properties of the process and to determine the thermodynamic energy and enthalpy changes of steams to obtain the energy conversion relations, including those between work output and heat ddition during the process. In general, steam tables and h-s diagram are used. The analysis is based on the first and the second laws of thermodynamics. Here we just discuss reversible processes. The (1)Based on the given conditions, determine the initial state and related properties (2)Based on the characteristics of the process and one of the properties given for the final state determine the final state and its properties (3) Based on the initial and final states, calculate the q, Au and w during the process Energy conversion relationships of water vapor are discussed respectively for the four basic thermodynamic processes as following 6.5.1 Isochoric process Durin isochoric (constant-volume) process, when heat is transferred to water, its pressure and temperature increase. The work output is zero as the volume remains constant. The heat addition leads to the increase in the internal energy of the water. And the increment of internal energy is equal to the heat addition. On h-s diagram, the process is depicted by the curve 1-2 in Fig. 6-5 The work output can be calculated by w=pdv=0 le amount of heat addition is The change in internal energy of the steam is △a=h2-h1-(P2-P1) The technical work available is w,=-]vdp=v(P1-P2)104 x = 0 and saturated vapor line x =1, meeting at the critical point C, are firstly plotted on the diagram. The saturated liquid line initiates from the origin of coordinates. In the wet region the isobars and isotherms are identical and are inclined straight lines. In the superheated region the isobars and isotherms diverge: the isobars run upwards and the isotherms turn to approach horizontal lines. In the wet region, lines of constant quality ( x =const) are also plotted, which merge at the critical point C. Isochors (constant-volume lines) are also plotted on the h − s diagram, which run more steeply upwards, compared with the isobars, as shown by the dotted line in Fig.6-4. It is convenient to use h − s diagram to determine the properties of water vapor. However, the accuracy of the readings depends on the person who uses it. Therefore, in practice, it is often to analyze thermodynamic processes of water vapor with the aid of h − s diagram and tables for water vapor simultaneously to simplify the calculations and to ensure the accuracy. Usually, the entire h − s diagram is just partly given out. It is the part of the wet region with quality greater than 0.6 because the lines in the region with quality less than 0.6 is too dense and the data seldom used in projects. The h − s diagram of steam for application in engineering practice is shown in Appendix Figure 2. 6.5 Thermodynamic Processes of Water Vapor The main purpose of analyzing thermodynamic processes of water vapor is to determine the final state and state properties of the process and to determine the thermodynamic energy and enthalpy changes of steams to obtain the energy conversion relations, including those between work output and heat addition during the process. In general, steam tables and h − s diagram are used. The analysis is based on the first and the second laws of thermodynamics. Here we just discuss reversible processes. The analyzing procedure is as following: ⑴ Based on the given conditions, determine the initial state and related properties. ⑵ Based on the characteristics of the process and one of the properties given for the final state, determine the final state and its properties. ⑶ Based on the initial and final states, calculate the q u w , and  during the process. Energy conversion relationships of water vapor are discussed respectively for the four basic thermodynamic processes as following. 6.5.1 Isochoric Process During an isochoric (constant-volume) process, when heat is transferred to water, its pressure and temperature increase. The work output is zero as the volume remains constant. The heat addition leads to the increase in the internal energy of the water. And the increment of internal energy is equal to the heat addition. On h s − diagram, the process is depicted by the curve 1-2 in Fig.6-5. The work output can be calculated by 0 2 1 w =  pdv = The amount of heat addition is q = u The change in internal energy of the steam is ( ) 2 1 p2 p1 u = h − h −v − The technical work available is = − = − 2 1 1 2 w vdp v( p p ) t