Vapor Pressure and Other Saturation

VAPOR PRESSURE AND OTHER SATURATION PROPERTIES OF WATER... 

Vapor Pressure and Other Saturation Properties of Water... 

VAPOR PRESSURE AND OTHER SATURATION PROPERTIES OF WATER AT TEMPERATURES UP TO 100 C (373.15 K) ... 

It is desirable for a VPI to provide inhibition rapidly and to have a lasting effect. Therefore, the compound should have a high volatility to saturate all of the accessible vapor space as quickly as possible, but at the same time it should not be too volatile, because it would be lost rapidly through any leaks in the package or container in which it is used. The optimum vapor pressure of VPI then would be just sufficient to maintain an inhibiting concentration on all exposed metal surfaces. Vapor pressures and other properties of some VPIs are given in Table 5.3. 

This shows that the presence of air in the gas phase has a very small influence on the vapor pressure of water. Repeating the same calculation procedure for other temperatures, we can show that the vapor pressure of water can with good accuracy be taken from the vapor pressure tables for saturated water (water has the same pressure as water vapor when they are in equilibrium), as though there were no air in the gas phase. So the vapor pressure of water is with good accuracy also in this case just a function of temperature, and Eq. (4.97) is valid. New vapor pressure tables will not be needed for calculations with humid air. 

We may evidently construct, for each of the cases of which we have spoken, a curve of dissociation tensionsj which possesses ail the properties of the vapor-pressure curve for saturated vapors. In each of the reactions studied by Debray the determinations of this investigator give us a certain number of points on the curve of dissociation tensions but these points are too few and too widely separated from each other to allow us to draw the curve. 

Natural waters formed of —99.7% of H2 0 are also constituted of other stable isotopic molecules, mainly H2 0 (—2%o), H2 0 ( 0.5%o), and HD 0 (—0.3%c), where H and D (deuterium) correspond to and H, respectively. Owing to slight differences in physical properties of these molecules, essentially their saturation vapor pressure, and their molecular diffusivity in air, fractionation processes occur at each phase change of the water except sublimation and melting of compact ice. As a result, the distribution of these water isotopes varies both spatially and temporally in the atmosphere, in the... 

In Fig. 3.6 a principal scheme of a pervaporation process is shown. The liquid feed mixture is heated to the highest temperature compatible with its own stability, the stabihty of the membrane and all other parts (e.g. gaskets, module elements) in the system. All partial vapor pressures are at saturation and fi ffid by the temperature and composition of the liquid mixture, and by the nature of the components. On the permeate side all noncondensable gases are removed by means of a vacuum pump, and the permeated vapors are condensed at a sufficiently low temperature in order to maintain a sufficiently low vapor pressure... 

Equation (8.37) is a practical working relationship for the infinite dilution aqueous molecular component partial molar enthalpy as a function of temperature. There is, however, an underlying assumption made. The relationship derived above assumes equilibrium between liquid and vapor, or, in other words a saturated liquid-vapor situation. In a subcooled liquid the enthalpy predicted by equation (8.37) should be corrected for the enthalpy difference between the pure component at the prevailing pressure and the saturation pressure. 

Table 42 shows that the saturation vapor pressure and orthobaric density of vapor and liquid have been measured repeatedly. We adopted experimental data of MEI [4.3] as reference values of p. These data were obtained statistically for a high-purity substance and with an error estimated by the authors at 0.1-0.2%. The results of comparison with the data of other researchers are shown in Fig. 34. 

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