Two phase line

For lines having plerrty available pressure, its line size is limited by erosion velocity, which is calculalcd using Eq. (1) using density of the two phase mixture, p nuK, in 1b/R3. p mix is calculated as follow  

For lines with limited available pressure, preliminary line sizing criterion for vapor Or liquid in Table I can be used, depending the two phase mixture is close to vaipur or liquid. 

Two phase How is more complicated than single phase flow. Depending on the amount of vapor and liquid in the How, Its How pattern is different. Further complication is the line orientation(hoiizontal, vertical, or i nclination) will aHTect the flow pattern in line. Different two phase flow patterns in horizontal and verdcat lines 

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Future operation pressures Sizing of lines must consider operating pressures expected as the reser oir depletes. Diameter requirement calculations should be made using both initial and future conditions to determine the governing case. Often in gas and two-phase lines the greatest flow velocity occurs late in life when flowing pressures are low even though flow rates may be lower than initial conditions. 

Whenever two-phase flow is encountered in facility piping it is usually in flowlines and interfield transfer lines. Some designers size liquid lines downstream of control valves as two-phase lines. The amount of gas involved in these lines is low and thus the lines are often sized as singlephase liquid lines. Oversizing two-phase lines can lead to increased slugging and thus as small a diameter as possible should be used consistent with pressure drop available and velocity constraints discussed in Volume 1. 

A condition of phase equilibrium is the equality of the chemical potentials in the two phases. Therefore, at all points along the two-phase line, //(g) = p( ). But, as we have noted above, the approach to the critical point brings the liquid and gas closer and closer together in density until they become indistinguishable, At the critical point, all of the thermodynamic properties of the liquid become equal to those of the gas. That is, Hm(g) = Um(g) - /m(l),... 

This is just the three-phase (triangle) analog of the two-phase (line) lever rule balance condition of Section 7.3.2. 

Note that the text box name txtPrt2 replaces the code word Print in GW Basic. When the system test is true for two-phase, line 720, then... 

Isochores with v < v, are above the Lh-G two-phase coexistence line isochores with v > are below the line. The isochore with v = v, coincides with the Lh-G coexistence line over the entire range from the triple point t to the critical point c. Beyond the critical point it is a continuous extension of the coexistence line. The isochores are remarkable by their near linearity. The curvature, generally small, is the largest at states close to the two-phase line. 

In Figure 8.12 the outer envelope is the locus of saturated equimolar liquid states and saturated equimolar vapor states. However, note that Figure 8.12 is not a phase-equilibrium diagram in Figure 8.12 every point on the two-phase line represents an equimolar mixture, but phases in vapor-liquid equilibrium generally do not have the same composition. Consequently, Figure 8.12 contains no tie lines across the two-phase region. Outside the saturation envelope, the mixtures are stable one-phase fluids. Underneath that envelope, the mixtures may be metastable one-phase fluids or they may be unstable to one phase (that is, they may exist as two-phases). 

In 8.2.6 we foxmd that the slope of any two-phase line on a pure-component PT diagram obeys the Clapeyron equation. 

So a one-phase ternary has T = 2 these states span areas on a triangular diagram. At fixed T and P, a two-phase ternary has T = 1, which defines a line. Two-phase lines appear in pairs, each giving the composition of one phase. Areas between two-phase lines are traversed by tie lines, and, if the overall mole fractions are known, the relative amounts in the two phases can be found by lever rules. 

Second, recall the many analogies that occur in the phase behavior of binary mixtures. For example, many features that occur on binary vapor-liquid phase diagrams have counterparts on liquid-solid diagrams. Some of those equivalent features are listed in Table 9.2. Furthermore, such equivalences include not only the kinds of behavior but may also extend to the general shapes of two-phase lines. That is, many... 

Thermowell installation in liquor spaces in two-phase lines... 

FIGURE 1.51 Analytical results of surge voltages on a two-phase line. 

In order to understand how thermodynamic data is tabulated, it is helpful to look at a phase diagram. A simple one-component diagram is shown in Figure 7.7. Here, you can see the curves marking the phase boundaries, or two-phase lines, where, for... 

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