There is a distinct nomenclature used for systems with more than one phase. In this, the terms "vapor"and"gas "seem to be used interchangeably. In the zone where both liquid and vapor exist there are two bounding situations. When the last trace of vapor condenses, the state becomes turated liquid. When the last trace of liquid evaporates the state becomes saturated vapor(or di vapor). If we put heat into a saturated vapor it is referred to as superheated vapor. Nitrogen at room temperature and pressure(at one atmosphere the vaporization temperature of nitrogen is 77 K) is a superheated vapor Figure 2B-3: Constant pressure curves in T-V coordinates showing vapor dome Figure 2B-3 shows lines of constant pressure in temperature-volume coordinates. Inside the vapor dome the constant pressure lines are also lines of constant temperature It is useful to describe the situations encountered as we decrease the pressure or equivalently increase the specific volume, starting from a high pressure-low specific volume state(the upper left-hand side of the isotherm in Figure 2B-2). The behavior in this region is liquid-like with very little compressibility. As the pressure is decreased, the volume changes little until the boundary of the vapor dome is reached. Once this occurs, however, the pressure is fixed because the temperature is constant. As the piston is withdrawn, the specific volume increases through more liquid evaporating and more vapor being produced. During this process, since the expansion is sothermal we specified that it was), heat is transferred to the system. The specific volume will increase at constant pressure until the right hand boundary of the vapor dome is reached. At this point, all the liquid will have been transformed into vapor and the system again behaves as a single-phase fluid For water at temperatures near room temperature, the behavior would be essentially that of a perfect gas in this region. To the right of the vapor dome, as mentioned above, the behavior is qualitatively like that of a perfect gas Referring to Figure 2B-4, we define notation to be used in what follows. The states a and c denote he conditions at which all the fluid is in the liquid state and the gaseous state respectively 2B-32B-3 There is a distinct nomenclature used for systems with more than one phase. In this, the terms “vapor” and “gas” seem to be used interchangeably. In the zone where both liquid and vapor exist, there are two bounding situations. When the last trace of vapor condenses, the state becomes saturated liquid. When the last trace of liquid evaporates the state becomes saturated vapor (or dry vapor). If we put heat into a saturated vapor it is referred to as superheated vapor. Nitrogen at room temperature and pressure (at one atmosphere the vaporization temperature of nitrogen is 77 K) is a superheated vapor. Figure 2B-3: Constant pressure curves in T-v coordinates showing vapor dome Figure 2B-3 shows lines of constant pressure in temperature-volume coordinates. Inside the vapor dome the constant pressure lines are also lines of constant temperature. It is useful to describe the situations encountered as we decrease the pressure or equivalently increase the specific volume, starting from a high pressure-low specific volume state (the upper left-hand side of the isotherm in Figure 2B-2). The behavior in this region is liquid-like with very little compressibility. As the pressure is decreased, the volume changes little until the boundary of the vapor dome is reached. Once this occurs, however, the pressure is fixed because the temperature is constant. As the piston is withdrawn, the specific volume increases through more liquid evaporating and more vapor being produced. During this process, since the expansion is isothermal (we specified that it was), heat is transferred to the system. The specific volume will increase at constant pressure until the right hand boundary of the vapor dome is reached. At this point, all the liquid will have been transformed into vapor and the system again behaves as a single-phase fluid. For water at temperatures near room temperature, the behavior would be essentially that of a perfect gas in this region. To the right of the vapor dome, as mentioned above, the behavior is qualitatively like that of a perfect gas. Referring to Figure 2B-4, we define notation to be used in what follows. The states a and c denote the conditions at which all the fluid is in the liquid state and the gaseous state respectively