Vapor-liquid phases

Effects of Two-Phase Vapor-Liquid Mixture on Relief Valve Capacity... 

Distribution Ratio (DR) The DR relates the concentration of an amine present in the steam phase to that concentration in the condensate phase (vapor-liquid distribution ratio). Consequently, it identifies in which condensate production region of a steam-condensate system any particular amine will concentrate and thus provide protection against corrosion. It also helps to indicates the portion of amine loss due to vaporization in a condenser or venting of a deaerator. The expression for DR is shown here ... 

Example 4.6 Mixtures of water and 1-butanol (n-butanol) form two-liquid phases. Vapor-liquid equilibrium and liquid-liquid equilibrium for the water-1-butanol system can be predicted by the NRTL equation. Vapor pressure coefficients in bar with temperature in Kelvin for the Antoine equation are given in Table 4.136. Data for the NRTL equation are given in Table 4.14, for a pressure of 1 atm6. Assume the gas constant R = 8.3145 kJ-kmoL -K-1. 

Mixtures of 2-butanol (.sec-butanol) and water form two-liquid phases. Vapor-liquid equilibrium and liquid-liquid equilibrium for the 2-butanol-water system can be predicted by the NRTL equation. Vapor pressure coefficients for the... 

B ecause the relief character of two-phase vapor-liquid material is markedly different from vapor relief, the nature of the relieved material must be known in order to design a proper relief. 

We shall now examine the consequences of Eqs. (18) and (21). For the case of two-phase vapor-liquid equilibria, there is only one degree of freedom and only one variable. Consequently, Eq. (18) leads to ... 

Wilcox et al 1941) phases. However, Ballard (2002) developed composition-independent sets of /f-values to provide the initial estimate for the component distribution between all possible phases vapor, liquid hydrocarbon, aqueous, si hydrate, sll hydrate, sH hydrate, ice, solid NaCl, solid KC1, and solid CaCl2. 

Lemon oil-carbon dioxide equilibrium was measured at 303. 308, and 313 K and in the pressure range of 4 to 9 MPa. Below 6 MPa, there was insufficient lemon oil in the vapor phase to obtain good samples for analysis. Above 9.0 MPa at 313 K, above 7.8 MPa at 308 K, and above 7.4 MPa at 303 K, the system exhibited a single phase. Nine experiments provided two-phase, vapor-liquid equilibrium data... 

Number of mixed phases (vapor, liquid, or solid) Pressure... 

Two-phase vapor-liquid flow of the type that can affect relief system design occurs as a result of vaporization and gas generation during a runaway reaction. Boiling can take place throughout the entire volume of liquid, not just at the surface. Trapped bubbles, retareded by viscosity and the nature of the fluid, reduce the effective density of the fluid and cause the liquid surface to be raised. When it reaches the height of the relief device, two-phase flow results. 

In engineering, we designate three fluid phases vapor, liquid, and supercritical (sometimes called dense phase). A fluid can be any one of these three phases. 

For mixtures, the phase envelopes expand from a curve to a region for the single component. Recall that in order for a single component to exist in two phase (vapor + liquid), the conditions had to fall exactly on the vapor pressure curve. For a mixture, there is a region over the pressure-temperature plane where two phases exist. 

In a two-phase vapor-liquid mixture at equilibrium, if all the components can vapor- ize and condense, a component in one phase is in equilibrium with the same compo-nent in the other phase. The equilibrium relationship depends on the temperature and pressure, and perhaps composition, of the mixture. Figure 3.15 illustrates two cases, one at constant pressure and the other at constant temperature. At the pairs of points A and B, and C and D, the respective pure components exert their respective vapor pressures at the equilibrium temperature. In between the pairs of points, as the overall composition of the mixture changes, two phases exist, each having a different composition for the same component as indicated by the dashed lines. Two useful linear ( ideal ) equations exist to relate the mole fraction of one component in the vapor phase to the mole fraction of the same component in the liquid phase. 

The prediction of the performance of three-phase multistage separation processes is dependent on the ability to describe the thermodynamics of three-phase behavior. The mathematical solution of three-phase distillation columns is similar to two-phase vapor-liquid columns, the difference being in the model used to calculate the /(-values. If the A -valuc model predicts two liquid phases, two liquid profiles must be considered in the column instead of one. 

Figure 3.2c shows the familiar cigar-shaped vapor—liquid envelope found in many elementary textbooks on phase equilibria. At a fixed overall composition (denoted by x in this figure) there exists a single vapor phase at very low pressures. As the pressure is isothermally increased, the two-phase vapor-liquid envelope is intersected and a dew or liquid phase now appears. The locus of points that separates the two-phase vapor-liquid region from the one-phase vapor region is called the dew point curve. The concentration of the equilibrium vapor and liquid phases within the two-phase boundary of the vapor-liquid envelope is determined by a horizontal tie line similar to the one depicted in this figure. 

As the pressure is further increased at this fixed overall composition, the amount of the liquid phase increases while the amount of the vapor phase shrinks until only a small bubble of vapor remains. If the pressure is still further increased, the bubble of vapor finally disappears, then a single liquid phase exists. The locus of points that separates the two-phase vapor-liquid region from the one-phase liquid region is called the bubble point curve. This vapor-liquid envelope can now be inserted into the three-dimensional P-T-x diagram in figure 3.2a. 

Equations of state can also be used to calculate three-phase (vapor-liquid-liquid) equilibria at Idgh pressures the principles for doing so are the same as those ured for caicolaling two-phase equilibrin but the numerical techniques for solviag the many simultaneous equations are now more complex. 

The addition of vapor to the flow leads to the existence of a two-phase vapor-liquid flow in the channel it is the existence of this flow and its interaction with the heat transfer processes that makes forced convective boiling so different from pool boiling. As more and more vapor enters the flow, the two-phase flow patterns or regimes develop in the following succession ... 

Estimate thermofluid characteristics of liquid-vapor phase change and related heat transfer processes such as circulation rate in natural or forced internal or external fluid circulation, pressure drops, and single- and two-phase vapor-liquid flow conditions. The initial analysis should be based on a rough estimation of the surface area from the energy balance... 

Seafloor temperature and pressure data for venting fluids indicate a wide variability relative to the two-phase (vapor-liquid) boundary for seawater (Fig. 4). Chloride concentrations in vent fluids (Table 1) range from 35 to 1090 mmol/kg due to subcritical boiling and/or supercritical phase-separation. For saline fluids such as seawater, phase-separation can occur above the critical point with condensation of brine droplets from a less saline residual vapor. Obviously, vent fluids decompress on ascent from subsurface reactions zones, which are inferred to be in cracking fronts just above the l-4... 

---