x and y
(MOLE FRACTION LIGHT COMPONENT)
Pressure vs. composition of binafy mixture at constant temperature a liquid phase present with composition z. At this high pressure, the liquid is called "subcooled."
If we now begin to drop the pressure, we will move down the vertical line drawn through composition z, shown in Figure 2.10. When pressure reaches the point labeled PBP, vapor will begin to appear. This therefore is called the bubble-point pressure of this mixture of composition z and at temperature T. The composition of this first bubble can be read off the y versus P curve by moving across horizontally at PBP.
As pressure is reduced further, more and more vapor is formed. Finally, at a pressure PDP all the liquid has vaporized. This is called the dew-point pressure of this mixture of composition z and at temperature T. The y versus P line is called the saturated-vapor line. At pressures below PDP only a single phase exists, "superheated vapor."
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