Versus pressure diagram, constant

Figure 17. Impulse Versus Pressure Diagram for Constant Levels of Building Damage. (Reprinted with permission from ref. 15. Copyright 1983 Elsevier Science.)...

Solid-Fluid Equilibria The phase diagrams of binai y mixtures in which the heavier component (tne solute) is normally a solid at the critical temperature of the light component (the solvent) include solid-liquid-vapor (SLV) cui ves which may or may not intersect the LV critical cui ve. The solubility of the solid is vei y sensitive to pressure and temperature in compressible regions where the solvent s density and solubility parameter are highly variable. In contrast, plots of the log of the solubility versus density at constant temperature exhibit fairly simple linear behavior. 

For a solution or mixture of two or more distinct liquid components, an azeotrope is that composition (typically measured in mole fractions or percent weight and referred to as the azeotropic solution) with which there is either a maximum point (a negative azeotrope) or a minimum point (a positive azeotrope) in a boiling point versus composition diagram at constant pressure. 

On an enthalpy versus entropy diagram (Mollier diagram), the above equation shows the slopes of chords to the constant pressure curve between input and output conditions. The constant pressure curves are convex (d2h/ds2). If the input conditions are the same for both exchangers, inequality (5.120) and Figure 5.5 show that... 

If the data are taken with pressure held constant (isobaric), it is convenient to plot two curves on the same paper temperature versus x and temperature versusy. Figure 2.7 illustrates a typical T-xy diagram. To determine the composition of liquid and vapor phases in equilibrium with each other at a given temperature, and at the pressure under which the data were obtained, one merely draws a horizontal fine at the given temperature and reads off x and y values. 

Figure 8.2a shows a Pxy phase diagram for a binary mixture of a and h that follows Raoult s law. The liquid- and gas-phase mole fractions of species a are plotted versus total pressure while the temperature of the system is held constant. The liquid mole fraction versus pressure line (labeled T-Xa) is called the bubble-point curve. It gets this name because if we start at high pressure and decrease the system pressure at constant temperature, this curve marks the pressure at which the first bubble of vapor forms. That bubble s composition can be found where the tie line denoted in the figure intersects the Fya curve. Similarly, the vapor mole fraction versus pressure curve line (labeled P-y is termed the dew-point curve because this marks when the first drop of liquid forms when a superheated vapor mixture is isothermally compressed. 

Figure A2.5.1. Schematic phase diagram (pressure p versus temperature 7) for a typical one-component substance. The full lines mark the transitions from one phase to another (g, gas liquid s, solid). The liquid-gas line (the vapour pressure curve) ends at a critical point (c). The dotted line is a constant pressure line. The dashed lines represent metastable extensions of the stable phases.

Figure A2.5.3. Typical liquid-gas phase diagram (temperature T versus mole fraction v at constant pressure) for a two-component system in which both the liquid and the gas are ideal mixtures. Note the extent of the two-phase liquid-gas region. The dashed vertical line is the direction x = 1/2) along which the fiinctions in figure A2.5.5 are detemiined.

Figure A2.5.12. Typical temperatxire T versus mole fraction v diagrams for the constant-pressure paths shown in figure A2.5.11. Note the critical points (x) and the horizontal tliree-phase lines.

As indicated above, rather than keeping the temperature constant, we can replace the partial pressure of one of the gas components with the temperature as a variable. Figure 4.26 is a diagram of the Fe-S-0 system in which In pQi is plotted versus temperature. Here psq2 is fixed in order to allow a two-dimensional representation. 

Take, for example, the plot of G versus temperature for elemental sulfur, represented by the bottom diagram in Figure 2.1. We know from experiments and observation that there are four phases we have to consider for sulfur two solid forms (a low-temperature orthorhombic form, R, and high-temperature monoclinic form, M), liquid (L), and vapor (or gas, V). The lines of G versus T for each phase, which are partially solid and continue on as dashed lines, are constructed at constant pressure using Eq. (2.10),... 

Temperature (7) versus atom percent (X) liquid-vapor diagram for ethanol-water mixtures, which follow Dalton s4 law for partial pressures in the vapor phase, and Raoult s5 law for ideal solutions, but only approximately. One theoretical plate is the segment LM + MN another is NQ + QR. At point R there is a constant-boiling mixture. This is a variation of Fig. 4.7... 

Figure A2.5.5. Phase diagrams for two-component systems with deviations from ideal behaviour (temperature T versus mole fiaction x at constant pressure). Liquid-gas phase diagrams with maximum (a) and minimum (b) boiling mixtures (azeotropes), (c) Liquid-liquid phase separation, with a coexistence curve and a critical point.

Graphically, the partial molar properties rh and m2 can be read directly from a m - 2] -diagram as shown in Figure 4.2. At constant temperature and constant pressure, Eq. (4.19) is a straight line for m versus Zi ... 

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