The graphical representations of Figures 2.8 and 2.9 are valuable for understanding the general features of the p-v-T properties of water but are of little use for quantitative analysis. For this purpose, extensive tables of the thermodynamic properties of water have been compiled. Such tabular information is available for many condensable substances in addition to water. For the latter, the property listings are called the steam tables, although they contain data for liquid water and ice as well as for the vapor phase. The steam considered in the tables is pure, undiluted by other gases such as air. Mixtures of water vapor and noncondensible gases are considered in Chapter 5.
In addition to listing the numerical values of the p-v-T properties illustrated in Figures 2.8 and 2.9, the steam tables present a complete listing of the thermal properties h and s. Tables 2.2-2.5 are condensed versions of these tabulations. Complete tables can be found in the appendices of References 4 and 5.
Table 2.2 contains properties of saturated water, both gaseous (denoted by subscript^) and liquid (subscript f). These are the numerical values along the heavy-line, two-phase envelope in the T-v projection of Figure 2.9. The first two columns of Table 2.2 gives the coordinates of the L/V line in the p-T projection of Figure 2.9. That is, these data represent the vapor pressure of liquid water. Like the line in right-hand graph of Figure 2.9, the p-T properties in the saturated-water table start at the triple point and end at the critical point.
The intervals of temperature,and jpressure in Table 2.2 are designed so that intermediate values can be obtained with reasonable accuracy by linear interpolation. Using Table 2.2, for example, the vapor pressure at 73°C is determined by solving the following equation for p^ (73°C):
Psai(73°C)-psg,(70°C) _ jPjb>(73°C)-312 ^ 73-70 Psa (75°C) - pM (70°C) 386-312 75-70
The variable absent from Table 2.2 is the volume v. The reason is that in a two-phase region, Equation (2.20) shows that the system volume depends on the quality -(steam mass fraction) in addition to the specific volumes vf and vg of the saturated liquid and vapor phases. The latter are listed in the third and fourth columns of the table. The quality x is not a thermodynamic property; it can vary between 0 and 1. Internal energy (u), enthalpy (h) and entropy (s) are handled in the same manner as described above for the specific volume (v).
Was this article helpful?
Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.