Vapor pressure liquids

Zg = compressibility fac tor of the saturated vapor Zl = compressibility fac tor of the saturated liquid = vapor pressure T = absolute temperature... 

Figure 2. Determine the vapor pressure/critical pressure ratio by dividing the liquid vapor pressure at the valve inlet by the critical pressure of the liquid. Enter on the abscissa at the ratio just calculated and proceed vertically to intersect the curve. Move horizontally to the left and read r< on the ordinate (Reference 1).

The nomograph combines all of these corrections (4) except the one for higher liquid vapor pressures. Physical properties of each of the inorganic gases are incorporated in the primary and secondary scales identifying the dissolved gas. 

Find the vapor pressure of the refrigerant in the condenser P ond at Tcond and the vapor pressure in the evaporator P vap at Tevap using a correlation for the saturated liquid - vapor pressure, such as the Antoine equation (see Chapter 4) ... 

Figure 10-20 Critical pressure ratio for cavitating and flashing liquids other than water. The abscissa is the ratio of the liquid vapor pressure at the valve inlet divided by the thermodynamic critical pressure of the liquid. The ordinate is the corresponding critical pressure ratio, re. (From Fisher Controls, 1987.)...

Bulk temperature Liquid vapor pressure Thermal activation Bubble content, intensity of collapse Enhanced secondary reaction rates... 

Choice of liquid Vapor pressure Surface tension Viscosity Chemical reactivity Intensity of collapse Transient cavitation threshold Transient cavitation threshold Primary or secondary sonochemistry... 

An attractive feature of K<)A is that it can replace the liquid or supercooled liquid vapor pressure in a correlation. K,-ja is an experimentally measurable or accessible quantity, whereas the supercooled liquid vapor pressure must be estimated from the solid vapor pressure, the melting point and the entropy of fusion. The use of KOA thus avoids the potentially erroneous estimation of the fugacity ratio, i.e., the ratio of solid and liquid vapor pressures. This is especially important for solutes with high melting points and, thus, low fugacity ratios. 

In the multimedia models used in this series of volumes, an air-water partition coefficient KAW or Henry s law constant (H) is required and is calculated from the ratio of the pure substance vapor pressure and aqueous solubility. This method is widely used for hydrophobic chemicals but is inappropriate for water-miscible chemicals for which no solubility can be measured. Examples are the lower alcohols, acids, amines and ketones. There are reported calculated or pseudo-solubilities that have been derived from QSPR correlations with molecular descriptors for alcohols, aldehydes and amines (by Leahy 1986 Kamlet et al. 1987, 1988 and Nirmalakhandan and Speece 1988a,b). The obvious option is to input the H or KAW directly. If the chemical s activity coefficient y in water is known, then H can be estimated as vwyP[>where vw is the molar volume of water and Pf is the liquid vapor pressure. Since H can be regarded as P[IC[, where Cjs is the solubility, it is apparent that (l/vwy) is a pseudo-solubility. Correlations and measurements of y are available in the physical-chemical literature. For example, if y is 5.0, the pseudo-solubility is 11100 mol/m3 since the molar volume of water vw is 18 x 10-6 m3/mol or 18 cm3/mol. Chemicals with y less than about 20 are usually miscible in water. If the liquid vapor pressure in this case is 1000 Pa, H will be 1000/11100 or 0.090 Pa m3/mol and KAW will be H/RT or 3.6 x 10 5 at 25°C. Alternatively, if H or KAW is known, C[ can be calculated. It is possible to apply existing models to hydrophilic chemicals if this pseudo-solubility is calculated from the activity coefficient or from a known H (i.e., Cjs, P[/H or P[ or KAW RT). This approach is used here. In the fugacity model illustrations all pseudo-solubilities are so designated and should not be regarded as real, experimentally accessible quantities. 

When calculating partition coefficients such as KAW, KqW or KqA from solubilities it is immaterial if the values used are of solids or liquids, but it is erroneous to mix the two states, e.g., a solid solubility and a liquid vapor pressure. 

Heats of fusion, AHfus, are generally expressed in kcal/mol or kJ/mol and entropies of fusion, ASlus in cal/mol-K (e.u. or entropy unit) or J/mol K. The fugacity ratio F, as discussed in Section 1.2.8, is used to calculate the supercooled liquid vapor pressure or solubility for correlation purposes. In the case of liquids such as benzene, it is 1.0. For solids it is a fraction representing the ratio of solid-to-liquid solubility or vapor pressure. 

Lei, Y.D., Chankalal, R., Chan, A., Wania, F. (2002) Supercooled liquid vapor pressures of the polycyclic aromatic hydrocarbons. J. Chem. Eng. Data 47, 801-806. 

Daubert, T. E., Jones, D. K. Project 821 Pure component liquid vapor pressure measurements. AIChE Symp. Ser., 86. 1990 pp. 29-39. 

If a liquid is placed in a sealed container, molecules will evaporate from the surface of the liquid and eventually establish a gas phase over the liquid that is in equilibrium with the liquid phase. The pressure generated by this gas is the vapor pressure of the liquid. Vapor pressure is temperature-dependent the higher the temperature, the higher the vapor pressure. If the liquid is made a solvent by adding a nonvolatile solute, the vapor pressure of the resulting solution is always less than that of the pure liquid. The vapor pressure has been lowered by the addition of the solute the amount of lowering is proportional to the number of solute particles added and is thus a colligative property. 

X 10 at 25 °C (subcooled liquid vapor pressure calculated from GC retention time data, Hinckley et ah, 1990)... 

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