Water saturation line properties

Va.por Pressure. Vapor pressure is one of the most fundamental properties of steam. Eigure 1 shows the vapor pressure as a function of temperature for temperatures between the melting point of water and the critical point. This line is called the saturation line. Liquid at the saturation line is called saturated Hquid Hquid below the saturation line is called subcooled. Similarly, steam at the saturation line is saturated steam steam at higher temperature is superheated. Properties of the Hquid and vapor converge at the critical point, such that at temperatures above the critical point, there is only one fluid. Along the saturation line, the fraction of the fluid that is vapor is defined by its quaHty, which ranges from 0 to 100% steam. 

For slightly metastable states of superheated water no problems arise in describing its thermophysical properties. They differ little Ifom properties on the saturation line. But a problem will arise at the approach of the spinodal, when isothermal compressibility, thermal expansion and isobaric heat capacity tend to infinity. 

Such data are available also in the compendium by Riddick et al. (1986) on the properties of solvents and in the book by Marcus Ion Solvation (1985) among other sources. The latter book also summarizes interpoiation functions for some of these variables. Some of these data are also available there for heavy water, D2O and for sub-cooled liquid water, down to -35 °C, and heated liquid water along the saturation line to the critical point and at elevated pressures. 

The United Kingdom Committee on the Properties of Steam has published U.K. Steam Tables in SI Units . These tables, although published in 1970, use IPTS-48. The tables include values for the specific enthalpy, entropy, volume, and heat capacity. Data are given for the saturation line for the temperature range 0.01 to 374.15 °C, pressure range 0.006 11 to 221.2 bar, and for water substances at pressures 0 to 1000 bar and temperatures 0 to 800 °C. 

Analysis of profiles shown in Figs. A3.5—A3.12 for subcritical water [figures (a)] and critical/supercritical water [figures (b)] shows similar trends. However, for subait-ical water, there are two different values of any thermophysical property on the saturation line one for liquid and one for vapor (steam). However, for example, at pressure of 7 MPa, values of specific heat of water (5.4025 kJ/kg K) and steam (5.3566 kJ/kg K) can be very close (see Fig. A3.9(a)). Also, it can be clearly seen that pressure has almost negligible effect of liquid properties. Just closer to the saturation line, some small differences can be seen in property profiles at various pressures. 

Cis double bonds produce a kink, or a bend, of about 30 degrees for each double bond into the backbone, and these can flip over to the trans form under high temperatures. Trans double bonds allow the molecule to lie in a straight line however, the human body cannot convert the trans form into nutrients and so prevents the metabolic activities from converting it to the active cis forms. This can lead to a deficiency in essential fatty acids. The more double bonds, and therefore more kinks, the more beneficial it is to human health. By completely changing the physical and chemical properties, the kinks allow essential protein associations to form more easily, thus permitting more saturated fatty acids to disperse and interact with water or blood. 

Lines 21-40. Physical data. The usual crystalline shape, density (note two values reported,), sublimation notation, boiling point data, and so on. K at 25" is the ionization constant of the acid the pH ofthe saturated solution (2.8 at 25°C) is given. The solubility data (Soly) are very complete, including water solutions at various temperatures, a bit about the phase diagram of the compound, and solubility in other solvents. Note that numerical data are given where possible. Lines 41-67. Properties of some slots of benzoic acid. 

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