Boiling line

The shaded region is that part of the phase diagram where liquid and vapor phases coexist in equilibrium, somewhat in analogy to the boiling line for a pure fluid. The ordinary liquid state exists on the high-pressure, low-temperature side of the two-phase region, and the ordinary gas state exists on the other side at low pressure and high temperature. As with our earlier example, we can transform any Type I mixture... 

Figure 2.31. Schematic representation of the P/T equilibria in a simple two-component system (forming continuous solid and liquid solutions). In (a) a perspective view of the P-T-X diagram is shown in (b) its projection on the P/T plane. Notice the two single-component systems represented, for instance, for the component B by the three lines SB/G (sublimation line of B representing the gas/so lid equilibrium), SB/LB (melting equilibrium of B) and the boiling line LB/G. The solid solution is indicated by a. Notice in (a) the isobaric and isothermal sections of the diagrams (compare with Fig. 2.1).

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.)... 

The temperature at the phase interface lies, as can be seen in Fig. 4.22, between the temperature on the dew point line (case b) and the temperature on the boiling line (case a). The associated vapour and liquid compositions can be read off the abcissa, points A and B in Fig. 4.22. 

In order to prevent this phenomenon, to be avoided above all in nuclear reactors, a sufficiently large safety margin should be maintained from the maximum heat flux. Obviously not all of the states along the boiling line illustrated in Fig. 4.37 are stable, rather under certain conditions instabilities can occur. 

The onset of nucleate boiling (line XX in Fig. 15.88) occurs above the x = 0 line at low heat flux (i.e., there is a net bulk superheat of the liquid) but at qualities less than 0 for high heat fluxes, corresponding to the region of subcooled nucleate boiling. For heat transfer to a single-phase liquid, the wall superheat (ATsat)w can be calculated from... 

Isothermal tie lines in the area of vapor-liquid equilibrium with the boundaries of the dew and the boiling line can be found by connecting the points on these lines, here the points = 0.26, T = 290 K and yl = 0.54, T = 290 K. (Dealing with liquid-liquid equilibria such tie lines are also called tie lines.) Note that a... 

These three enthalpies can all be determined. We would find hg on Figure 2-4 on the saturated liquid (boiling-line) at x = Xg. 

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. 

For an azeotropic mixture the isothermal partial pressure curve (Xj), Piix, the isobaric boiling line i (Xi) and dew line i9 yi) and the isobaric equilibrium curve (x,), exhibit maxima/minima (maximum boiling or bubble point and therefore minimum vapor pressure minimum boiling or bubble point and therefore maximum vapor pressure see Fig. 1-20)... 

If the boiling line liquid isotherm) and dew line (vapor isotherm) are known, the composition of the vapor phase corresponding to a given composition of the liquid phase may be calculated from Eq. (1-104). The positions of the equilibrium lines in the triangle are determined stepwise. 

Figure 1 Phase diagram of carbon dioxide. The supercritical region is to the right and above the critical point at the end of the line separating vapor from iiquid (sometimes called the boiling line).

The pressure-temperature phase (PT) diagram of CO2 is shown in Figure 2.1. The critical point (CP) occurs at a temperature of 31.1 °C. At this temperature the boiling line terminates and the gas and liquid phases merge into a single supercritical fluid phase. 

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