The fraction of the total mass in the vapor phase is called quality, and denoted by X quality of a liquid-vapor system In terms of the quality and specific volumes, the average specific volume can be expressed as V=X (1-X) In reference to Figure 2B-5,ab=v-Vf,ac=vg-vI Ity T (b) Figure 2B-5: Liquid vapor equilibrium in a two-phase medium 2. B2-work and Heat Transfer with Two-Phase Media We examine the work and heat transfer in quasi-static processes with two-phase systems For definiteness, consider the system to be a liquid-vapor mixture in a container whose volume car be varied through movement of a piston, as shown in Figure 2B-5. The system is kept at constant temperature through contact with a heat reservoir at temperature T. The pressure is thus also constant, but the volume, v, can change. For a fixed mass, the volume is proportional to the specific volume v so that point b in Figure 2B-5 must move to the left or the right as V changes This implies that the amount of mass in each of the two phases, and hence the quality, also changes because mass is transferred from one phase to the other. We wish to find the heat and work transfer associated with the change in mass in each phase. The change in volume can be related to he changes in mass in the two phases as dV=vdm。+v,dm2B-5 The fraction of the total mass in the vapor phase is called quality, and denoted by X. X m m m g f g = + = quality of a liquid-vapor system. In terms of the quality and specific volumes, the average specific volume can be expressed as: v Xv X v =⋅ +− ⋅ g f ( ) 1 In reference to Figure 2B-5, ab v v ac v v =− = − f g f , . ab ac v v v v X f g f = − − = = quality. (a) T L L-V T T V p a b c vf v v vg (b) Figure 2B-5: Liquid vapor equilibrium in a two-phase medium 2.B.2 - Work and Heat Transfer with Two-Phase Media We examine the work and heat transfer in quasi-static processes with two-phase systems. For definiteness, consider the system to be a liquid-vapor mixture in a container whose volume can be varied through movement of a piston, as shown in Figure 2B-5. The system is kept at constant temperature through contact with a heat reservoir at temperature T. The pressure is thus also constant, but the volume, V, can change. For a fixed mass, the volume is proportional to the specific volume v so that point b in Figure 2B-5 must move to the left or the right as V changes. This implies that the amount of mass in each of the two phases, and hence the quality, also changes because mass is transferred from one phase to the other. We wish to find the heat and work transfer associated with the change in mass in each phase. The change in volume can be related to the changes in mass in the two phases as, dV v dm v dm = + g g f f