Lecture_6a_4e

1 pp 1 2 p p 1 p p y 1 2 1 using eq 610 to substitute

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Unformatted text preview: =   P 1 + (P 2 − P  )y 1 1 Also, y 1 P = x 1 P . 1 Using Eq. (6.10) to substitute for x1 in the following equation, we get PP 12 P=  , P 1 + (P  − P  )y 1 2 1 (6.11) which is the desired equation. This equation is called the dew-point line equation because when pressure is increased on a vapor at composition y1 , the first drop of condensate (dew) is formed when the pressure reaches the value predicted by Eq. (6.11). The bubble-point line is a linear equation in pressure-composition space but the dew-point line is nonlinear. Fig. 6.2 gives good examples of both equations plotted together on the same graph. Fig. 6.2 Tie-lines: Horizontal lines (lines drawn at constant pressre in a P-x diagram or at constant temperature in a T-x diagram) that connect the compositions of liquid and vapor in equilibrium with each other are called tie-lines. The lever rule: The relative amounts of vapor and liquid present at a given total composition xT is given by the lever rule (note error i...
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