Document 44oqBnyBy9X3e62K17g96OegN

48 CHAPTER 3 1950 Guide Table 3. Properties of Saturated Steam: Pressure Table* . fSUam- *>y J H. Keenan and F. G. Kiyi Thermodynamics 49 p. = saturation pressure of pure water vapor, pounds per square inch or inches of Hg " Moist air can be saturated at any given values of temperature and pressure, though this requires that it have a definite humidity ratio W, and that the coexisting condensed phase contain a definite, but very small quantity of dissolved air. On the other hand, pure water vapor (steam) cannot be saturated at any given values of tem perature and pressure because its composition is invariable. It can, however, be saturated at any given temperature (below the critical temperature), though this requires that it have a definite pressure p. and that the coexisting condensed phase have the same temperature and pressure. The values of saturation pressure listed in Table 1 have been computed from the formulas of Goff and Gratch.` Thermodynamic Properties of Water at Saturation Table 2 offers revisions to existing steam table data' with extension downward to --160 F. These revisions and extension were a necessary preliminary to the construction of Table 1. A detailed explanation of the methods employed in constructing Table 2 is given in a paper* by John A. Goff and S. Gratch. As in Table 1 the temperature scale used as argument in Table 2 is the Fahrenheit scale defined in terms of absolute temperature T by Equation 1, whereas the Fahrenheit scale used as argument in existing steam tables is that derived from the International Centigrade scale by means of Equation 2. The symbols used as column headings in Table 2 are the same as those used in the steam tables and have the same meanings; therefore, a detailed explanation seems unnecessary. Properties of water above 212 F from Keenan and Keyes' are given in Table 3. DEGREE OF SATURATION At given values of temperature and pressure the humidity ratio W of moist air can have any value between zero (dry air) and W, (moist air at saturation). For convenience a parameter p called alternatively degree of saturation is introduced through the definition, W = nW. (3) Obviously the degree of saturation p can have any value from zero (dry air) to unity (moist air at saturation). To a degree of approximation within the estimated uncertainty of the Table 4. Coefficients A, B, C Appearing in Equations 4ai, 5a, 6a, Maximum Values of Corrections Defined bt Equations 4a,,5a, 6a. Degree of Saturation at Which These Maxima Occur, ji*i. Maximum Value of Correction Defined bt Equation 6b. Degree of Saturation at Which This Maximum Occurs, Um(Standard Atmospheric Pressure) t (F) AB (ftVlbn) (Bttt/lb.) c (Btu/F/ lb) Pmax (ftVIba) (BtS/lb,) tnax (Btu/F/ lb) Jmax l*ta (Btu/F/ (bo) 96 0.0018 0.0286 0.00004 0.0004 0.0069 0.00001 0.4925 0.0015 0.3650 . 112 0.0042 0.0650 0.00009 0.0010 0.0155 0.00002 0.4878 0.0025 0.3632 128 0.0096 0.1439 0.00020 0.0022 0.0332 0.00005 0.4805 0.0040 0.3602 144 0.0215 0.3149 0.00042 0.0047 0.0693 0.00009 0.4691 0.0065 0.3557 160 0.0487 0.6969 0.00091 0.0099 0.1418 0.00019 0.4511 0.0106 0.3485 176 0.1169 1.636 0.00207 0.0207 0.2903 0.00037 0.4213 0.0179 0.3363 192 0.3363 4.608 0.00567 0.0451 0.6180 0.00076 0.3662 0.0333 0.3129