Dew line

DEW Line A line of radar stations at ca 70th parallel on the North American Continent, undertaken in cooperation with the Canadian Government... 

The third plane identified in Fig. 12.1 is the vertical one perpendicular to the composition axis and indicated by MNQRSLM. When projected on a parallel plane, the lines from several such planes present a diagram such as that shown by Fig. 12.4. This is the PT diagram lines t/C, and KC2 are vapor-pressure curves for the pure species, identified by the same letters as in Fig. 12.1. Each interior loop represents the PT behavior of saturated liquid and of saturated vapor for a mixture of fixed composition the different loops are for different compositions. Clearly, the PT relation for saturated liquid is different from that for saturated vapor of the same composition. This is in contrast with the behavior of a pure species, for which the bubble line and the dew line coincide. At points A and B in Fig. 12.4 saturated-liquid and saturated-vapor lines intersect. At such points a saturated liquid of one composition and a saturated vapor of another composition have the same T and P, and the two phases are therefore in equilibrium. The tie lines connecting the coinciding points at A and at B are perpendicular to the PT plane, as illustrated by the tie line VX in Fig. 12.1. 

The line is projected in its true magnitude along the line syp, which is the limiting line of the mixture of composition x e is its ebvUitian line, and p the dew line they meet in the point y, projection of the critical point F, and at this point they are tangent to the projection of the critical line. 

Take a mixture of composition x, at a temperature T and under a pressure tc which serve as coordinates to a point in the plane TOtt. When this representative point is in the interior of the limiting curve sj p, the mixture of mean composition x is divided into two phases, a mixed liquid and a mixed vapor. One of these two phases disappears and the system becomes homogeneous when the representative point passes beyond the limiting line. It is the vapor phase which disappears if the representative point passes beyond the limiting line at a point which belongs to the ebullition line it is, on the contrary, the liquid phase which disappears if the representative point passes beyond the limiting line at a point belonging to the dew line. 

Take first a temperature T less than the critical temperature 0 of the mixture of composition x at this temperature cause the pressure to increase gradually from a very low value to a very great value the representative point will rise constantly along the straight line TT which meets the dew-line in a point B and the ebullition-line in a higher point E. 

The representative point rises along the line tY, which cuts the dew-line in a first point, then in a second point, of ordinate greater than the first. 

Dew line and line of ebullition for a mixture of given composition, 821.—243. Normal condensation, retrograde condensation, 822. 

FIG. 2-7 Enthalpy-concentration diagram for aqueous ammonia. From Thermodynamic and Physical Properties NH3-H20, Int Inst. Refrigeration, Paris, France, 1994 (88 pp.). Reproduced by permission. In order to determine equilibrium compositions, draw a vertical from any liquid composition on any boiling line (the lowest plots) to intersect the appropriate auxiliary curve (the intermediate curves). A horizontal then drawn from this point to the appropriate dew line (the upper curves) will establish the vapor composition. The Int. Inst. Refrigeration publication also gives extensive P-v-xtah es from —50 to 316°C. Other sources include Park, Y. M. and Sonntag, R. E., ASHRAE Trans., 96,1 (1990) 150-159 x, h, s, tables, 360 to 640 K) Ibrahim, O. M. and S. A. Klein, ASH E Trans., 99, 1 (1993) 1495-1502 (Eqs., 0.2 to 110 bar, 293 to 413 K) Smolen, T. M., D. B. Manley, et al.,/. Chem. Eng. Data, 36 (1991) 202-208 p-x correlation, 0.9 to 450 psia, 293-413 K)i Ruiter, J. P, 7nf. J. R rig., 13 (1990) 223-236 gives ten subroutines for computer calculations. 

FIG. 2-10 Enthalpy -concentration diagram for aqueous ethyl alcohol. Reference states Enthalpies of liquid water and ethyl alcohol at 0 °C are zero. NOTE In order to interpolate equilibrium compositions, a vertical may be erected from any liquid composition on the boiling line and its intersection with the auxiliary line determined. A horizontal from this intersection will establish the equilibrium vapor composition on the dew line. Bosnjakovic, Technische Thermodynamik, T. Steinkopjf, Leipzig, 1935.)... 

On February 5, 2002, George W. Bush visited the RODS laboratory and used it as a model for a 300 million spending proposal to equip all 50 states with biosurveillance systems. In a speech delivered at the nearby Masonic temple. Bush compared the RODS system to a modem DEW line (referring to the Cold War balhstic missile early warning system). 

To read the Pxy graph we follow the same principles as with Txy graphs. The horizontal axis reads composition (mol fraction of component 1). Points inside the VLE envelope represent a two-phase system, and the horizontal axis gives the overall composition. The tie line is horizontal and points to the composition of the vapor (on the dew line) and the composition of the liquid (on the bubble line). The lever rule applies and can be used to find the liquid and vapor fractions. 

Solution The solution is shown graphically in Fieure 8-4. The initial state is A. The final state is B and is located such that the tie line intersects the dew line at y, = 0.9. The corresponding pressure is read off the graph and is found to be Pb = 1.01 bar. The final system consists of two phases, a vapor that contains the desired 90% in heptane and a liquid that contains 50% heptane. 

Notice that in this graph the composition of the vapor lies to the right of 1 and the two lobes of the vapor-liquid region lie at opposite sides of the tie line ABV. The vapor-liquid region of phase (1) (isobutane-rich) is quite small. The vapor region also is very small because of the steepness of the dew line. 

This equation defines the dew line. The simplest way to calculate the dew line is to set the temperature and solve... 

This equation describes the dew line to the right of point The procedure is the same as above. We fix the value... 

The simplest way to calculate this dew line is to fix the mole fraction and calculate the dew pressure from the above equation. For example, with x/u, = o.i we find... 

Fig. 2.5-1 Boiling and dew line above) and enthalpy-concentration diagram of the binary mixture ethane/propane at 14 bar (Matschke 1962)...

Calculation of the required condenser surface is not trivial. In contrast to the common applications where saturated vapors are condensed the permeate is a superheated vapor mixture. For design calculations the selection of appropriate heat-transfer coefficients has to consider the cooling to saturation conditions, the presence of noncondensable gases, and the partial condensation of the components along the respective dew lines. Total condensation of the more volatile components of the permeate vapor will often not be possible, but any losses of permeate vapor through the vacuum pump have to cope with the respective emission control regulations. An important factor is the solubility of the components of the permeate in the liquid phase. An additional condenser at the high-pressure side of the vacuum pump is a feasible option. 

For Cv l 1 a part of the dew line in the temperature-entropy diagram shows a positive slope (ds/dT>0) as is typical for large-heat-capacity fluids. 

In order to calculate the isothermal supersaturation, the dew line of the respective mixture hat to be known For a given... 

The results for an equimolar CO -air mixture, obtained with several series of expansions, are presented in Fig.4. The pressure-temperature diagram in the upper part shows the experimental Wilson points and the dew line, which is extrapolated below the triple point For comparison, the frost line is plotted, too. The lower diagram shows the same Wilson points in a plot of the partial density of CO versus temperature. Here, the full curve represents the Wilson line for pure CO, obtained in the preceding investigation [1]. Obviously, spontaneous condensation of CO in the equimolar CO -air mixture begins nearly at the same partial density as with pure CO. ... 

Fig.4. Wilson points of an equimolar COp-air mixture in plots of total pressure and of partial COp density versus temperature. The dew line of the mixture is extrapolated below the triple point of CO ...

Boiling Diagram The boiling line and dew line are plotted at constant pressure. The boiling line d(x) connects the bubble points at boiling temperature as a function of the composition of the liquid mixture. The dew line I O ) shows the eondensation temperature of the saturated vapor mixture as a function of its composition in the vapor. 

Boiling lines and dew lines for an ideal mixture at a given pressure p may be derived from Dalton s and Raoult s laws to give... 

Boiling lines and dew lines may be calculated stepwise for a chosen temperature t9. Pg i and Pg 2 are the saturated pressures of pure components 1 and 2 corresponding to temperature i9. 

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