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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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