H - h + s(t_{sup} - t_{sat}) F = ---------------------------- (3) 970.4
Where s = mean specific heat of superheated steam at the pressure existing in the trial from saturated steam to the temperature existing in the trial, t_{sup} = final temperature of steam, t_{sat} = temperature of saturated steam, corresponding to pressure existing, (t_{sup} - t_{sat}) = degrees of superheat.
The specific heat of superheated steam will be taken up later.
Table 19 gives factors of evaporation for saturated steam boiler trials to cover a large range of conditions. Except for the most refined work, intermediate values may be determined by interpolation.
Steam gauges indicate the pressure above the atmosphere. As has been pointed out, the atmospheric pressure changes according to the alt.i.tude and the variation in the barometer. Hence, calculations involving the properties of steam are based on _absolute_ pressures, which are equal to the gauge pressure plus the atmospheric pressure in pounds to the square inch. This latter is generally a.s.sumed to be 14.7 pounds per square inch at sea level, but for other levels it must be determined from the barometric reading at that place.
Vacuum gauges indicate the difference, expressed in inches of mercury, between atmospheric pressure and the pressure within the vessel to which the gauge is attached. For approximate purposes, 2.04 inches height of mercury may be considered equal to a pressure of one pound per square inch at the ordinary temperatures at which mercury gauges are used.
Hence for any reading of the vacuum gauge in inches, G, the absolute pressure for any barometer reading in inches, B, will be (B - G) 2.04.
If the barometer is 30 inches measured at ordinary temperatures and not corrected to 32 degrees Fahrenheit and the vacuum gauge 24 inches, the absolute pressure will be (30 - 24) 2.04 = 2.9 pounds per square inch.
TABLE 19
FACTORS OF EVAPORATION CALCULATED FROM MARKS AND DAVIS TABLES
______________________________________________________________________ | | | |Feed | | |Temp- | | |erature| | |Degrees| Steam Pressure by Gauge | |Fahren-| | |heit | | |_______|______________________________________________________________| | | | | | | | | | | | 50 | 60 | 70 | 80 | 90 | 100 | 110 | |_______|________|________|________|________|________|________|________| | | | | | | | | | | 32 | 1.2143 | 1.2170 | 1.2194 | 1.2215 | 1.2233 | 1.2233 | 1.2265 | | 40 | 1.2060 | 1.2087 | 1.2111 | 1.2131 | 1.2150 | 1.2168 | 1.2181 | | 50 | 1.1957 | 1.1984 | 1.2008 | 1.2028 | 1.2047 | 1.2065 | 1.2079 | | 60 | 1.1854 | 1.1881 | 1.1905 | 1.1925 | 1.1944 | 1.1961 | 1.1976 | | 70 | 1.1750 | 1.1778 | 1.1802 | 1.1822 | 1.1841 | 1.1859 | 1.1873 | | 80 | 1.1649 | 1.1675 | 1.1699 | 1.1720 | 1.1738 | 1.1756 | 1.1770 | | 90 | 1.1545 | 1.1572 | 1.1596 | 1.1617 | 1.1636 | 1.1653 | 1.1668 | | 100 | 1.1443 | 1.1470 | 1.1493 | 1.1514 | 1.1533 | 1.1550 | 1.1565 | | 110 | 1.1340 | 1.1367 | 1.1391 | 1.1411 | 1.1430 | 1.1448 | 1.1462 | | 120 | 1.1237 | 1.1264 | 1.1288 | 1.1309 | 1.1327 | 1.1345 | 1.1359 | | 130 | 1.1134 | 1.1161 | 1.1185 | 1.1206 | 1.1225 | 1.1242 | 1.1257 | | 140 | 1.1031 | 1.1058 | 1.1082 | 1.1103 | 1.1122 | 1.1139 | 1.1154 | | 150 | 1.0928 | 1.0955 | 1.0979 | 1.1000 | 1.1019 | 1.1036 | 1.1051 | | 160 | 1.0825 | 1.0852 | 1.0876 | 1.0897 | 1.0916 | 1.0933 | 1.0948 | | 170 | 1.0722 | 1.0749 | 1.0773 | 1.0794 | 1.0813 | 1.0830 | 1.0845 | | 180 | 1.0619 | 1.0646 | 1.0670 | 1.0691 | 1.0709 | 1.0727 | 1.0741 | | 190 | 1.0516 | 1.0543 | 1.0567 | 1.0587 | 1.0606 | 1.0624 | 1.0638 | | 200 | 1.0412 | 1.0439 | 1.0463 | 1.0484 | 1.0503 | 1.0520 | 1.0535 | | 210 | 1.0309 | 1.0336 | 1.0360 | 1.0380 | 1.0399 | 1.0417 | 1.0432 | |_______|________|________|________|________|________|________|________| ______________________________________________________________________ | | | |Feed | | |Temp- | | |erature| | |Degrees| Steam Pressure by Gauge | |Fahren-| | |heit | | |_______|______________________________________________________________| | | | | | | | | | | | 120 | 130 | 140 | 150 | 160 | 170 | 180 | |_______|________|________|________|________|________|________|________| | | | | | | | | | | 32 | 1.2280 | 1.2292 | 1.2304 | 1.2314 | 1.2323 | 1.2333 | 1.2342 | | 40 | 1.2196 | 1.2209 | 1.2221 | 1.2231 | 1.2241 | 1.2250 | 1.2259 | | 50 | 1.2093 | 1.2106 | 1.2117 | 1.2128 | 1.2137 | 1.2147 | 1.2156 | | 60 | 1.1990 | 1.2003 | 1.2014 | 1.2025 | 1.2034 | 1.2044 | 1.2053 | | 70 | 1.1887 | 1.1900 | 1.1911 | 1.1922 | 1.1931 | 1.1941 | 1.1950 | | 80 | 1.1785 | 1.1797 | 1.1809 | 1.1819 | 1.1828 | 1.1838 | 1.1847 | | 90 | 1.1682 | 1.1695 | 1.1706 | 1.1717 | 1.1725 | 1.1735 | 1.1744 | | 100 | 1.1579 | 1.1592 | 1.1603 | 1.1614 | 1.1623 | 1.1633 | 1.1642 | | 110 | 1.1477 | 1.1489 | 1.1500 | 1.1511 | 1.1520 | 1.1530 | 1.1539 | | 120 | 1.1374 | 1.1386 | 1.1398 | 1.1408 | 1.1418 | 1.1427 | 1.1436 | | 130 | 1.1271 | 1.1284 | 1.1295 | 1.1305 | 1.1315 | 1.1324 | 1.1333 | | 140 | 1.1168 | 1.1181 | 1.1192 | 1.1203 | 1.1212 | 1.1221 | 1.1230 | | 150 | 1.1065 | 1.1078 | 1.1089 | 1.1099 | 1.1109 | 1.1118 | 1.1127 | | 160 | 1.0962 | 1.0975 | 1.0986 | 1.0997 | 1.1006 | 1.1015 | 1.1024 | | 170 | 1.0859 | 1.0872 | 1.0883 | 1.0893 | 1.0903 | 1.0912 | 1.0921 | | 180 | 1.0756 | 1.0768 | 1.0780 | 1.0790 | 1.0800 | 1.0809 | 1.0818 | | 190 | 1.0653 | 1.0665 | 1.0676 | 1.0687 | 1.0696 | 1.0706 | 1.0715 | | 200 | 1.0549 | 1.0562 | 1.0573 | 1.0584 | 1.0593 | 1.0602 | 1.0611 | | 210 | 1.0446 | 1.0458 | 1.0469 | 1.0480 | 1.0489 | 1.0499 | 1.0508 | |_______|________|________|________|________|________|________|________| ______________________________________________________________________ | | | |Feed | | |Temp- | | |erature| | |Degrees| Steam Pressure by Gauge | |Fahren-| | |heit | | |_______|______________________________________________________________| | | | | | | | | | | | 190 | 200 | 210 | 220 | 230 | 240 | 250 | |_______|________|________|________|________|________|________|________| | | | | | | | | | | 32 | 1.2350 | 1.2357 | 1.2364 | 1.2372 | 1.2378 | 1.2384 | 1.2390 | | 40 | 1.2267 | 1.2274 | 1.2282 | 1.2289 | 1.2295 | 1.2301 | 1.2307 | | 50 | 1.2164 | 1.2171 | 1.2178 | 1.2186 | 1.2192 | 1.2198 | 1.2204 | | 60 | 1.2061 | 1.2068 | 1.2075 | 1.2083 | 1.2089 | 1.2095 | 1.2101 | | 70 | 1.1958 | 1.1965 | 1.1972 | 1.1980 | 1.1986 | 1.1992 | 1.1998 | | 80 | 1.1855 | 1.1863 | 1.1869 | 1.1877 | 1.1883 | 1.1889 | 1.1895 | | 90 | 1.1750 | 1.1760 | 1.1766 | 1.1774 | 1.1780 | 1.1786 | 1.1792 | | 100 | 1.1650 | 1.1657 | 1.1664 | 1.1671 | 1.1678 | 1.1684 | 1.1690 | | 110 | 1.1547 | 1.1554 | 1.1562 | 1.1569 | 1.1575 | 1.1581 | 1.1587 | | 120 | 1.1444 | 1.1452 | 1.1459 | 1.1466 | 1.1472 | 1.1478 | 1.1484 | | 130 | 1.1341 | 1.1349 | 1.1356 | 1.1363 | 1.1369 | 1.1375 | 1.1381 | | 140 | 1.1239 | 1.1246 | 1.1253 | 1.1260 | 1.1266 | 1.1272 | 1.1278 | | 150 | 1.1136 | 1.1143 | 1.1150 | 1.1157 | 1.1163 | 1.1169 | 1.1176 | | 160 | 1.1033 | 1.1040 | 1.1047 | 1.1054 | 1.1060 | 1.1066 | 1.1073 | | 170 | 1.0930 | 1.0937 | 1.0944 | 1.0951 | 1.0957 | 1.0963 | 1.0969 | | 180 | 1.0826 | 1.0834 | 1.0841 | 1.0848 | 1.0854 | 1.0860 | 1.0866 | | 190 | 1.0723 | 1.0730 | 1.0737 | 1.0745 | 1.0751 | 1.0757 | 1.0763 | | 200 | 1.0620 | 1.0627 | 1.0634 | 1.0641 | 1.0647 | 1.0653 | 1.0660 | | 210 | 1.0516 | 1.0523 | 1.0530 | 1.0538 | 1.0544 | 1.0550 | 1.0556 | |_______|________|________|________|________|________|________|________|
The temperature, pressure and other properties of steam for varying amounts of vacuum and the pressure above vacuum corresponding to each inch of reading of the vacuum gauge are given in Table 20.
TABLE 20
PROPERTIES OF SATURATED STEAM FOR VARYING AMOUNTS OF VACUUM CALCULATED FROM MARKS AND DAVIS TABLES ______________________________________________________________________ | | | | | | | | | | | | Heat of | Latent | Total | | | | | Temp- | the Liquid| Heat | Heat | | | | | erature | Above | Above | Above |Density or| | | Absolute | Degrees | 32 De- | 32 De- | 32 De- |Weight per| | Vacuum | Pressure | Fahren- | grees | grees | grees |Cubic Foot| |Ins. Hg.| Pounds | heit | B. t. u. |B. t. u.|B. t. u.| Pounds | |________|__________|_________|___________|________|________|__________| | | | | | | | | | 29.5 | .207 | 54.1 | 22.18 | 1061.0 | 1083.2 | 0.000678 | | 29 | .452 | 76.6 | 44.64 | 1048.7 | 1093.3 | 0.001415 | | 28.5 | .698 | 90.1 | 58.09 | 1041.1 | 1099.2 | 0.002137 | | 28 | .944 | 99.9 | 67.87 | 1035.6 | 1103.5 | 0.002843 | | 27 | 1.44 | 112.5 | 80.4 | 1028.6 | 1109.0 | 0.00421 | | 26 | 1.93 | 124.5 | 92.3 | 1022.0 | 1114.3 | 0.00577 | | 25 | 2.42 | 132.6 | 100.5 | 1017.3 | 1117.8 | 0.00689 | | 24 | 2.91 | 140.1 | 108.0 | 1013.1 | 1121.1 | 0.00821 | | 22 | 3.89 | 151.7 | 119.6 | 1006.4 | 1126.0 | 0.01078 | | 20 | 4.87 | 161.1 | 128.9 | 1001.0 | 1129.9 | 0.01331 | | 18 | 5.86 | 168.9 | 136.8 | 996.4 | 1133.2 | 0.01581 | | 16 | 6.84 | 175.8 | 143.6 | 992.4 | 1136.0 | 0.01827 | | 14 | 7.82 | 181.8 | 149.7 | 988.8 | 1138.5 | 0.02070 | | 12 | 8.80 | 187.2 | 155.1 | 985.6 | 1140.7 | 0.02312 | | 10 | 9.79 | 192.2 | 160.1 | 982.6 | 1142.7 | 0.02554 | | 5 | 12.24 | 202.9 | 170.8 | 976.0 | 1146.8 | 0.03148 | |________|__________|_________|___________|________|________|__________|
From the steam tables, the condensed Table 21 of the properties of steam at different pressures may be constructed. From such a table there may be drawn the following conclusions.
TABLE 21
VARIATION IN PROPERTIES OF SATURATED STEAM WITH PRESSURE ___________________________________________________ | | | | | | | Pressure |Temperature | Heat of | Latent | Total | | Pounds | Degrees | Liquid | Heat | Heat | | Absolute | Fahrenheit |B. t. u. |B. t. u.|B. t. u.| |__________|____________|_________|________|________| | | | | | | | 14.7 | 212.0 | 180.0 | 970.4 | 1150.4 | | 20.0 | 228.0 | 196.1 | 960.0 | 1156.2 | | 100.0 | 327.8 | 298.3 | 888.0 | 1186.3 | | 300.0 | 417.5 | 392.7 | 811.3 | 1204.1 | |__________|____________|_________|________|________|
As the pressure and temperature increase, the latent heat decreases.
This decrease, however, is less rapid than the corresponding increase in the heat of the liquid and hence the total heat increases with an increase in the pressure and temperature. The percentage increase in the total heat is small, being 0.5, 3.1, and 4.7 per cent for 20, 100, and 300 pounds absolute pressure respectively above the total heat in one pound of steam at 14.7 pounds absolute. The temperatures, on the other hand, increase at the rates of 7.5, 54.6, and 96.9 per cent. The efficiency of a perfect steam engine is proportional to the expression (t - t_{1})/t in which t and t_{1} are the absolute temperatures of the saturated steam at admission and exhaust respectively. While actual engines only approximate the ideal engine in efficiency, yet they follow the same general law. Since the exhaust temperature cannot be lowered beyond present practice, it follows that the only available method of increasing the efficiency is by an increase in the temperature of the steam at admission. How this may be accomplished by an increase of pressure is clearly shown, for the increase of fuel necessary to increase the pressure is negligible, as shown by the total heat, while the increase in economy, due to the higher pressure, will result directly from the rapid increase of the corresponding temperature.
TABLE 22
HEAT UNITS PER POUND AND WEIGHT PER CUBIC FOOT OF WATER BETWEEN 32 DEGREES FAHRENHEIT AND 340 DEGREES FAHRENHEIT _________________________________ | | | | |Temperature|Heat Units| Weight | | Degrees | per | per | | Fahrenheit| Pound |Cubic Foot| |___________|__________|__________| | | | | | 32 | 0.00 | 62.42 | | 33 | 1.01 | 62.42 | | 34 | 2.01 | 62.42 | | 35 | 3.02 | 62.43 | | 36 | 4.03 | 62.43 | | 37 | 5.04 | 62.43 | | 38 | 6.04 | 62.43 | | 39 | 7.05 | 62.43 | | 40 | 8.05 | 62.43 | | 41 | 9.05 | 62.43 | | 42 | 10.06 | 62.43 | | 43 | 11.06 | 62.43 | | 44 | 12.06 | 62.43 | | 45 | 13.07 | 62.42 | | 46 | 14.07 | 62.42 | | 47 | 15.07 | 62.42 | | 48 | 16.07 | 62.42 | | 49 | 17.08 | 62.42 | | 50 | 18.08 | 62.42 | | 51 | 19.08 | 62.41 | | 52 | 20.08 | 62.41 | | 53 | 21.08 | 62.41 | | 54 | 22.08 | 62.40 | | 55 | 23.08 | 62.40 | | 56 | 24.08 | 62.39 | | 57 | 25.08 | 62.39 | | 58 | 26.08 | 62.38 | | 59 | 27.08 | 62.37 | | 60 | 28.08 | 62.37 | | 61 | 29.08 | 62.36 | | 62 | 30.08 | 62.36 | | 63 | 31.07 | 62.35 | | 64 | 32.07 | 62.35 | | 65 | 33.07 | 62.34 | | 66 | 34.07 | 62.33 | | 67 | 35.07 | 62.33 | | 68 | 36.07 | 62.32 | | 69 | 37.06 | 62.31 | | 70 | 38.06 | 62.30 | | 71 | 39.06 | 62.30 | | 72 | 40.05 | 62.29 | | 73 | 41.05 | 62.28 | | 74 | 42.05 | 62.27 | | 75 | 42.05 | 62.26 | | 76 | 44.04 | 62.26 | | 77 | 45.04 | 62.25 | | 78 | 46.04 | 62.24 | | 79 | 47.04 | 62.23 | | 80 | 48.03 | 62.22 | | 81 | 49.03 | 62.21 | | 82 | 50.03 | 62.20 | | 83 | 51.02 | 62.19 | | 84 | 52.02 | 62.18 | | 85 | 53.02 | 62.17 | | 86 | 54.01 | 62.16 | | 87 | 55.01 | 62.15 | | 88 | 56.01 | 62.14 | | 89 | 57.00 | 62.13 | | 90 | 58.00 | 62.12 | | 91 | 59.00 | 62.11 | | 92 | 60.00 | 62.09 | | 93 | 60.99 | 62.08 | | 94 | 61.99 | 62.07 | | 95 | 62.99 | 62.06 | | 96 | 63.98 | 62.05 | | 97 | 64.98 | 62.04 | | 98 | 65.98 | 62.03 | | 99 | 66.97 | 62.02 | | 100 | 67.97 | 62.00 | | 101 | 68.97 | 61.99 | | 102 | 69.96 | 61.98 | | 103 | 70.96 | 61.97 | | 104 | 71.96 | 61.95 | | 105 | 72.95 | 61.94 | | 106 | 73.95 | 61.93 | | 107 | 74.95 | 61.91 | | 108 | 75.95 | 61.90 | | 109 | 76.94 | 61.88 | | 110 | 77.94 | 61.86 | | 111 | 78.94 | 61.85 | | 112 | 79.93 | 61.83 | | 113 | 80.93 | 61.82 | | 114 | 81.93 | 61.80 | | 115 | 82.92 | 61.79 | | 116 | 83.92 | 61.77 | | 117 | 84.92 | 61.75 | | 118 | 85.92 | 61.74 | | 119 | 86.91 | 61.72 | | 120 | 87.91 | 61.71 | | 121 | 88.91 | 61.69 | | 122 | 89.91 | 61.68 | | 123 | 90.90 | 61.66 | | 124 | 91.90 | 61.65 | | 125 | 92.90 | 61.63 | | 126 | 93.90 | 61.61 | | 127 | 94.89 | 61.59 | | 128 | 95.89 | 61.58 | | 129 | 96.89 | 61.56 | | 130 | 97.89 | 61.55 | | 131 | 98.89 | 61.53 | | 132 | 99.88 | 61.52 | | 133 | 100.88 | 61.50 | | 134 | 101.88 | 61.49 | | 135 | 102.88 | 61.47 | | 136 | 103.88 | 61.45 | | 137 | 104.87 | 61.43 | | 138 | 105.87 | 61.41 | | 139 | 106.87 | 61.40 | | 140 | 107.87 | 61.38 | | 141 | 108.87 | 61.36 | | 142 | 109.87 | 61.34 | | 143 | 110.87 | 61.33 | | 144 | 111.87 | 61.31 | | 145 | 112.86 | 61.29 | | 146 | 113.86 | 61.27 | | 147 | 114.86 | 61.25 | | 148 | 115.86 | 61.24 | | 149 | 116.86 | 61.22 | | 150 | 117.86 | 61.20 | | 151 | 118.86 | 61.18 | | 152 | 119.86 | 61.16 | | 153 | 120.86 | 61.14 | | 154 | 121.86 | 61.12 | | 155 | 122.86 | 61.10 | | 156 | 123.86 | 61.08 | | 157 | 124.86 | 61.06 | | 158 | 125.86 | 61.04 | | 159 | 126.86 | 61.02 | | 160 | 127.86 | 61.00 | | 161 | 128.86 | 60.98 | | 162 | 129.86 | 60.96 | | 163 | 130.86 | 60.94 | | 164 | 131.86 | 60.92 | | 165 | 132.86 | 60.90 | | 166 | 133.86 | 60.88 | | 167 | 134.86 | 60.86 | | 168 | 135.86 | 60.84 | | 169 | 136.86 | 60.82 | | 170 | 137.87 | 60.80 | | 171 | 138.87 | 60.78 | | 172 | 139.87 | 60.76 | | 173 | 140.87 | 60.73 | | 174 | 141.87 | 60.71 | | 175 | 142.87 | 60.69 | | 176 | 143.87 | 60.67 | | 177 | 144.88 | 60.65 | | 178 | 145.88 | 60.62 | | 179 | 146.88 | 60.60 | | 180 | 147.88 | 60.58 | | 181 | 148.88 | 60.56 | | 182 | 149.89 | 60.53 | | 183 | 150.89 | 60.51 | | 184 | 151.89 | 60.49 | | 185 | 152.89 | 60.47 | | 186 | 153.89 | 60.45 | | 187 | 154.90 | 60.42 | | 188 | 155.90 | 60.40 | | 189 | 156.90 | 60.38 | | 190 | 157,91 | 60.36 | | 191 | 158.91 | 60.33 | | 192 | 159.91 | 60.31 | | 193 | 160.91 | 60.29 | | 194 | 161.92 | 60.27 | | 195 | 162.92 | 60.24 | | 196 | 163.92 | 60.22 | | 197 | 164.93 | 60.19 | | 198 | 165.93 | 60.17 | | 199 | 166.94 | 60.15 | | 200 | 167.94 | 60.12 | | 201 | 168.94 | 60.10 | | 202 | 169.95 | 60.07 | | 203 | 170.95 | 60.05 | | 204 | 171.96 | 60.02 | | 205 | 172.96 | 60.00 | | 206 | 173.97 | 59.98 | | 207 | 174.97 | 59.95 | | 208 | 175.98 | 59.93 | | 209 | 176.98 | 59.90 | | 210 | 177.99 | 59.88 | | 211 | 178.99 | 59.85 | | 212 | 180.00 | 59.83 | | 213 | 181.0 | 59.80 | | 214 | 182.0 | 59.78 | | 215 | 183.0 | 59.75 | | 216 | 184.0 | 59.73 | | 217 | 185.0 | 59.70 | | 218 | 186.1 | 59.68 | | 219 | 187.1 | 59.65 | | 220 | 188.1 | 59.63 | | 221 | 189.1 | 59.60 | | 222 | 190.1 | 59.58 | | 223 | 191.1 | 59.55 | | 224 | 192.1 | 59.53 | | 225 | 193.1 | 59.50 | | 226 | 194.1 | 59.48 | | 227 | 195.2 | 59.45 | | 228 | 196.2 | 59.42 | | 229 | 197.2 | 59.40 | | 230 | 198.2 | 59.37 | | 231 | 199.2 | 59.34 | | 232 | 200.2 | 59.32 | | 233 | 201.2 | 59.29 | | 234 | 202.2 | 59.27 | | 235 | 203.2 | 59.24 | | 236 | 204.2 | 59.21 | | 237 | 205.3 | 59.19 | | 238 | 206.3 | 59.16 | | 239 | 207.3 | 59.14 | | 240 | 208.3 | 59.11 | | 241 | 209.3 | 59.08 | | 242 | 210.3 | 59.05 | | 243 | 211.4 | 59.03 | | 244 | 212.4 | 59.00 | | 245 | 213.4 | 58.97 | | 246 | 214.4 | 58.94 | | 247 | 215.4 | 58.91 | | 248 | 216.4 | 58.89 | | 249 | 217.4 | 58.86 | | 250 | 218.5 | 58.83 | | 260 | 228.6 | 58.55 | | 270 | 238.8 | 58.26 | | 280 | 249.0 | 57.96 | | 290 | 259.3 | 57.65 | | 300 | 269.6 | 57.33 | | 310 | 279.9 | 57.00 | | 320 | 290.2 | 56.66 | | 330 | 300.6 | 56.30 | | 340 | 311.0 | 55.94 | |___________|__________|__________|
The gain due to superheat cannot be predicted from the formula for the efficiency of a perfect steam engine given on page 119. This formula is not applicable in cases where superheat is present since only a relatively small amount of the heat in the steam is imparted at the maximum or superheated temperature.
The advantage of the use of high pressure steam may be also indicated by considering the question from the aspect of volume. With an increase of pressure comes a decrease in volume, thus one pound of saturated steam at 100 pounds absolute pressure occupies 4.43 cubic feet, while at 200 pounds pressure it occupies 2.29 cubic feet. If then, in separate cylinders of the same dimensions, one pound of steam at 100 pounds absolute pressure and one pound at 200 pounds absolute pressure enter and are allowed to expand to the full volume of each cylinder, the high-pressure steam, having more room and a greater range for expansion than the low-pressure steam, will thus do more work. This increase in the amount of work, as was the increase in temperature, is large relative to the additional fuel required as indicated by the total heat.
In general, it may be stated that the fuel required to impart a given amount of heat to a boiler is practically independent of the steam pressure, since the temperature of the fire is so high as compared with the steam temperature that a variation in the steam temperature does not produce an appreciable effect.
The formulae for the algebraic expression of the relation between saturated steam pressures, temperatures and steam volumes have been up to the present time empirical. These relations have, however, been determined by experiment and, from the experimental data, tables have been computed which render unnecessary the use of empirical formulae.
Such formulae may be found in any standard work of thermo-dynamics. The following tables cover all practical cases.
Table 22 gives the heat units contained in water above 32 degrees Fahrenheit at different temperatures.
Table 23 gives the properties of saturated steam for various pressures.
Table 24 gives the properties of superheated steam at various pressures and temperatures.
These tables are based on those computed by Lionel S. Marks and Harvey N. Davis, these being generally accepted as being the most correct.
TABLE 23
PROPERTIES OF SATURATED STEAM
REPRODUCED BY PERMISSION FROM MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS"
(Copyright, 1909, by Longmans, Green & Co.) ____________________________________________________________________ |Pressure,| Temper- |Specific Vol-|Heat of |Latent Heat|Total Heat| | Pounds |ature De-| ume Cu. Ft. |the Liquid,| of Evap., |of Steam, | |Absolute |grees F. | per Pound | B. t. u. | B. t. u. | B. t. u. | |_________|_________|_____________|___________|___________|__________| | 1 | 101.83 | 333.0 | 69.8 | 1034.6 | 1104.4 | | 2 | 126.15 | 173.5 | 94.0 | 1021.0 | 1115.0 | | 3 | 141.52 | 118.5 | 109.4 | 1012.3 | 1121.6 | | 4 | 153.01 | 90.5 | 120.9 | 1005.7 | 1126.5 | | 5 | 162.28 | 73.33 | 130.1 | 1000.3 | 1130.5 | | 6 | 170.06 | 61.89 | 137.9 | 995.8 | 1133.7 | | 7 | 176.85 | 53.56 | 144.7 | 991.8 | 1136.5 | | 8 | 182.86 | 47.27 | 150.8 | 988.2 | 1139.0 | | 9 | 188.27 | 42.36 | 156.2 | 985.0 | 1141.1 | | 10 | 193.22 | 38.38 | 161.1 | 982.0 | 1143.1 | | 11 | 197.75 | 35.10 | 165.7 | 979.2 | 1144.9 | | 12 | 201.96 | 32.36 | 169.9 | 976.6 | 1146.5 | | 13 | 205.87 | 30.03 | 173.8 | 974.2 | 1148.0 | | 14 | 209.55 | 28.02 | 177.5 | 971.9 | 1149.4 | | 15 | 213.0 | 26.27 | 181.0 | 969.7 | 1150.7 | | 16 | 216.3 | 24.79 | 184.4 | 967.6 | 1152.0 | | 17 | 219.4 | 23.38 | 187.5 | 965.6 | 1153.1 | | 18 | 222.4 | 22.16 | 190.5 | 963.7 | 1154.2 | | 19 | 225.2 | 21.07 | 193.4 | 961.8 | 1155.2 | | 20 | 228.0 | 20.08 | 196.1 | 960.0 | 1156.2 | | 22 | 233.1 | 18.37 | 201.3 | 956.7 | 1158.0 | | 24 | 237.8 | 16.93 | 206.1 | 953.5 | 1159.6 | | 26 | 242.2 | 15.72 | 210.6 | 950.6 | 1161.2 | | 28 | 246.4 | 14.67 | 214.8 | 947.8 | 1162.6 | | 30 | 250.3 | 13.74 | 218.8 | 945.1 | 1163.9 | | 32 | 254.1 | 12.93 | 222.6 | 942.5 | 1165.1 | | 34 | 257.6 | 12.22 | 226.2 | 940.1 | 1166.3 | | 36 | 261.0 | 11.58 | 229.6 | 937.7 | 1167.3 | | 38 | 264.2 | 11.01 | 232.9 | 935.5 | 1168.4 | | 40 | 267.3 | 10.49 | 236.1 | 933.3 | 1169.4 | | 42 | 270.2 | 10.02 | 239.1 | 931.2 | 1170.3 | | 44 | 273.1 | 9.59 | 242.0 | 929.2 | 1171.2 | | 46 | 275.8 | 9.20 | 244.8 | 927.2 | 1172.0 | | 48 | 278.5 | 8.84 | 247.5 | 925.3 | 1172.8 | | 50 | 281.0 | 8.51 | 250.1 | 923.5 | 1173.6 | | 52 | 283.5 | 8.20 | 252.6 | 921.7 | 1174.3 | | 54 | 285.9 | 7.91 | 255.1 | 919.9 | 1175.0 | | 56 | 288.2 | 7.65 | 257.5 | 918.2 | 1175.7 | | 58 | 290.5 | 7.40 | 259.8 | 916.5 | 1176.4 | | 60 | 292.7 | 7.17 | 262.1 | 914.9 | 1177.0 | | 62 | 294.9 | 6.95 | 264.3 | 913.3 | 1177.6 | | 64 | 297.0 | 6.75 | 266.4 | 911.8 | 1178.2 | | 66 | 299.0 | 6.56 | 268.5 | 910.2 | 1178.8 | | 68 | 301.0 | 6.38 | 270.6 | 908.7 | 1179.3 | | 70 | 302.9 | 6.20 | 272.6 | 907.2 | 1179.8 | | 72 | 304.8 | 6.04 | 274.5 | 905.8 | 1180.4 | | 74 | 306.7 | 5.89 | 276.5 | 904.4 | 1180.9 | | 76 | 308.5 | 5.74 | 278.3 | 903.0 | 1181.4 | | 78 | 310.3 | 5.60 | 280.2 | 901.7 | 1181.8 | | 80 | 312.0 | 5.47 | 282.0 | 900.3 | 1182.3 | | 82 | 313.8 | 5.34 | 283.8 | 899.0 | 1182.8 | | 84 | 315.4 | 5.22 | 285.5 | 897.7 | 1183.2 | | 86 | 317.1 | 5.10 | 287.2 | 896.4 | 1183.6 | | 88 | 318.7 | 5.00 | 288.9 | 895.2 | 1184.0 | | 90 | 320.3 | 4.89 | 290.5 | 893.9 | 1184.4 | | 92 | 321.8 | 4.79 | 292.1 | 892.7 | 1184.8 | | 94 | 323.4 | 4.69 | 293.7 | 891.5 | 1185.2 | | 96 | 324.9 | 4.60 | 295.3 | 890.3 | 1185.6 | | 98 | 326.4 | 4.51 | 296.8 | 889.2 | 1186.0 | | 100 | 327.8 | 4.429 | 298.3 | 888.0 | 1186.3 | | 105 | 331.4 | 4.230 | 302.0 | 885.2 | 1187.2 | | 110 | 334.8 | 4.047 | 305.5 | 882.5 | 1188.0 | | 115 | 338.1 | 3.880 | 309.0 | 879.8 | 1188.8 | | 120 | 341.3 | 3.726 | 312.3 | 877.2 | 1189.6 | | 125 | 344.4 | 3.583 | 315.5 | 874.7 | 1190.3 | | 130 | 347.4 | 3.452 | 318.6 | 872.3 | 1191.0 | | 135 | 350.3 | 3.331 | 321.7 | 869.9 | 1191.6 | | 140 | 353.1 | 3.219 | 324.6 | 867.6 | 1192.2 | | 145 | 355.8 | 3.112 | 327.4 | 865.4 | 1192.8 | | 150 | 358.5 | 3.012 | 330.2 | 863.2 | 1193.4 | | 155 | 361.0 | 2.920 | 332.9 | 861.0 | 1194.0 | | 160 | 363.6 | 2.834 | 335.6 | 858.8 | 1194.5 | | 165 | 366.0 | 2.753 | 338.2 | 856.8 | 1195.0 | | 170 | 368.5 | 2.675 | 340.7 | 854.7 | 1195.4 | | 175 | 370.8 | 2.602 | 343.2 | 852.7 | 1195.9 | | 180 | 373.1 | 2.533 | 345.6 | 850.8 | 1196.4 | | 185 | 375.4 | 2.468 | 348.0 | 848.8 | 1196.8 | | 190 | 377.6 | 2.406 | 350.4 | 846.9 | 1197.3 | | 195 | 379.8 | 2.346 | 352.7 | 845.0 | 1197.7 | | 200 | 381.9 | 2.290 | 354.9 | 843.2 | 1198.1 | | 205 | 384.0 | 2.237 | 357.1 | 841.4 | 1198.5 | | 210 | 386.0 | 2.187 | 359.2 | 839.6 | 1198.8 | | 215 | 388.0 | 2.138 | 361.4 | 837.9 | 1199.2 | | 220 | 389.9 | 2.091 | 363.4 | 836.2 | 1199.6 | | 225 | 391.9 | 2.046 | 365.5 | 834.4 | 1199.9 | | 230 | 393.8 | 2.004 | 367.5 | 832.8 | 1200.2 | | 235 | 395.6 | 1.964 | 369.4 | 831.1 | 1200.6 | | 240 | 397.4 | 1.924 | 371.4 | 829.5 | 1200.9 | | 245 | 399.3 | 1.887 | 373.3 | 827.9 | 1201.2 | | 250 | 401.1 | 1.850 | 375.2 | 826.3 | 1201.5 | |_________|_________|_____________|___________|___________|__________|
[Ill.u.s.tration: Portion of 6100 Horse-power Installation of Babc.o.c.k & Wilc.o.x Boilers Equipped with Babc.o.c.k & Wilc.o.x Chain Grate Stokers at the Campbell Street Plant of the Louisville Railway Co., Louisville, Ky.
This Company Operates a Total of 14,000 Horse Power of Babc.o.c.k & Wilc.o.x Boilers]
TABLE 24
PROPERTIES OF SUPERHEATED STEAM
REPRODUCED BY PERMISSION FROM MARKS AND DAVIS "STEAM TABLES AND DIAGRAMS"
(Copyright, 1909, by Longmans, Green & Co.) __________________________________________________________________ | | | | | | | Degrees of Superheat | |Pressure| |_______________________________________________| | Pounds |Saturated| | | | | | | |Absolute| Steam | 50 | 100 | 150 | 200 | 250 | 300 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 162.3 | 212.3 | 262.3 | 312.3 | 362.3 | 412.3 | 462.3 | | 5 v| 73.3 | 79.7 | 85.7 | 91.8 | 97.8 | 103.8 | 109.8 | | h| 1130.5 |1153.5 |1176.4 |1199.5 |1222.5 |1245.6 |1268.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 193.2 | 243.2 | 293.2 | 343.2 | 393.2 | 443.2 | 493.2 | | 10 v| 38.4 | 41.5 | 44.6 | 47.7 | 50.7 | 53.7 | 56.7 | | h| 1143.1 |1166.3 |1189.5 |1212.7 |1236.0 |1259.3 |1282.5 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 213.0 | 263.0 | 313.0 | 363.0 | 413.0 | 463.0 | 513.0 | | 15 v| 26.27 | 28.40| 30.46| 32.50| 34.53| 36.56| 38.58| | h| 1150.7 |1174.2 |1197.6 |1221.0 |1244.4 |1267.7 |1291.1 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 228.0 | 278.0 | 328.0 | 378.0 | 428.0 | 478.0 | 528.0 | | 20 v| 20.08 | 21.69| 23.25| 24.80| 26.33| 27.85| 29.37| | h| 1156.2 |1179.9 |1203.5 |1227.1 |1250.6 |1274.1 |1297.6 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 240.1 | 290.1 | 340.1 | 390.1 | 440.1 | 490.1 | 540.1 | | 25 v| 16.30 | 17.60| 18.86| 20.10| 21.32| 22.55| 23.77| | h| 1160.4 |1184.4 |1208.2 |1231.9 |1255.6 |1279.2 |1302.8 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 250.4 | 300.4 | 350.4 | 400.4 | 450.4 | 500.4 | 550.4 | | 30 v| 13.74 | 14.83| 15.89| 16.93| 17.97| 18.99| 20.00| | h| 1163.9 |1188.1 |1212.1 |1236.0 |1259.7 |1283.4 |1307.1 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 259.3 | 309.3 | 359.3 | 409.3 | 459.3 | 509.3 | 559.3 | | 35 v| 11.89 | 12.85| 13.75| 14.65| 15.54| 16.42| 17.30| | h| 1166.8 |1191.3 |1215.4 |1239.4 |1263.3 |1287.1 |1310.8 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 267.3 | 317.3 | 367.3 | 417.3 | 467.3 | 517.3 | 567.3 | | 40 v| 10.49 | 11.33| 12.13| 12.93| 13.70| 14.48| 15.25| | h| 1169.4 |1194.0 |1218.4 |1242.4 |1266.4 |1290.3 |1314.1 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 274.5 | 324.5 | 374.5 | 424.5 | 474.5 | 524.5 | 574.5 | | 45 v| 9.39 | 10.14| 10.86| 11.57| 12.27| 12.96| 13.65| | h| 1171.6 |1196.6 |1221.0 |1245.2 |1269.3 |1293.2 |1317.0 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 281.0 | 331.0 | 381.0 | 431.0 | 481.0 | 531.0 | 581.0 | | 50 v| 8.51 | 9.19| 9.84| 10.48| 11.11| 11.74| 12.36| | h| 1173.6 |1198.8 |1223.4 |1247.7 |1271.8 |1295.8 |1319.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 287.1 | 337.1 | 387.1 | 437.1 | 487.1 | 537.1 | 587.1 | | 55 v| 7.78 | 8.40| 9.00| 9.59| 10.16| 10.73| 11.30| | h| 1175.4 |1200.8 |1225.6 |1250.0 |1274.2 |1298.1 |1322.0 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 292.7 | 342.7 | 392.7 | 442.7 | 492.7 | 542.7 | 592.7 | | 60 v| 7.17 | 7.75| 8.30| 8.84| 9.36| 9.89| 10.41| | h| 1177.0 |1202.6 |1227.6 |1252.1 |1276.4 |1300.4 |1324.3 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 298.0 | 348.0 | 398.0 | 448.0 | 498.0 | 548.0 | 598.0 | | 65 v| 6.65 | 7.20| 7.70| 8.20| 8.69| 9.17| 9.65| | h| 1178.5 |1204.4 |1229.5 |1254.0 |1278.4 |1302.4 |1326.4 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 302.9 | 352.9 | 402.9 | 452.9 | 502.9 | 552.9 | 602.9 | | 70 v| 6.20 | 6.71| 7.18| 7.65| 8.11| 8.56| 9.01| | h| 1179.8 |1205.9 |1231.2 |1255.8 |1280.2 |1304.3 |1328.3 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 307.6 | 357.6 | 407.6 | 457.6 | 507.6 | 557.6 | 607.6 | | 75 v| 5.81 | 6.28| 6.73| 7.17| 7.60| 8.02| 8.44| | h| 1181.1 |1207.5 |1232.8 |1257.5 |1282.0 |1306.1 |1330.1 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 312.0 | 362.0 | 412.0 | 462.0 | 512.0 | 562.0 | 612.0 | | 80 v| 5.47 | 5.92| 6.34| 6.75| 7.17| 7.56| 7.95| | h| 1182.3 |1208.8 |1234.3 |1259.0 |1283.6 |1307.8 |1331.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 316.3 | 366.3 | 416.3 | 466.3 | 516.3 | 566.3 | 616.3 | | 85 v| 5.16 | 5.59| 6.99| 6.38| 6.76| 7.14| 7.51| | h| 1183.4 |1210.2 |1235.8 |1260.6 |1285.2 |1309.4 |1333.5 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 320.3 | 370.3 | 420.3 | 470.3 | 520.3 | 570.3 | 620.3 | | 90 v| 4.89 | 5.29| 5.67| 6.04| 6.40| 6.76| 7.11| | h| 1184.4 |1211.4 |1237.2 |1262.0 |1286.6 |1310.8 |1334.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 324.1 | 374.1 | 424.1 | 474.1 | 524.1 | 574.1 | 624.1 | | 95 v| 4.65 | 5.03| 5.39| 5.74| 6.09| 6.43| 6.76| | h| 1185.4 |1212.6 |1238.4 |1263.4 |1288.1 |1312.3 |1336.4 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 327.8 | 377.8 | 427.8 | 477.8 | 527.8 | 577.8 | 627.8 | | 100 v| 4.43 | 4.79| 5.14| 5.47| 5.80| 6.12| 6.44| | h| 1186.3 |1213.8 |1239.7 |1264.7 |1289.4 |1313.6 |1337.8 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 331.4 | 381.4 | 431.4 | 481.4 | 531.4 | 581.4 | 631.4 | | 105 v| 4.23 | 4.58| 4.91| 5.23| 5.54| 5.85| 6.15| | h| 1187.2 |1214.9 |1240.8 |1265.9 |1290.6 |1314.9 |1339.1 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 334.8 | 384.8 | 434.8 | 484.8 | 534.8 | 584.8 | 634.8 | | 110 v| 4.05 | 4.38| 4.70| 5.01| 5.31| 5.61| 5.90| | h| 1188.0 |1215.9 |1242.0 |1267.1 |1291.9 |1316.2 |1340.4 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 338.1 | 388.1 | 438.1 | 488.1 | 538.1 | 588.1 | 638.1 | | 115 v| 3.88 | 4.20| 4.51| 4.81| 5.09| 5.38| 5.66| | h| 1188.8 |1216.9 |1243.1 |1268.2 |1293.0 |1317.3 |1341.5 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 341.3 | 391.3 | 441.3 | 491.3 | 541.3 | 591.3 | 641.3 | | 120 v| 3.73 | 4.04| 4.33| 4.62| 4.89| 5.17| 5.44| | h| 1189.6 |1217.9 |1244.1 |1269.3 |1294.1 |1318.4 |1342.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 344.4 | 394.4 | 444.4 | 494.4 | 544.4 | 594.4 | 644.4 | | 125 v| 3.58 | 3.88| 4.17| 4.45| 4.71| 4.97| 5.23| | h| 1190.3 |1218.8 |1245.1 |1270.4 |1295.2 |1319.5 |1343.8 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 347.4 | 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | | 130 v| 3.45 | 3.74| 4.02| 4.28| 4.54| 4.80| 5.05| | h| 1191.0 |1219.7 |1246.1 |1271.4 |1296.2 |1320.6 |1344.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 350.3 | 400.3 | 450.3 | 500.3 | 550.3 | 600.3 | 650.3 | | 135 v| 3.33 | 3.61| 3.88| 4.14| 4.38| 4.63| 4.87| | h| 1191.6 |1220.6 |1247.0 |1272.3 |1297.2 |1321.6 |1345.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 353.1 | 403.1 | 453.1 | 503.1 | 553.1 | 603.1 | 653.1 | | 140 v| 3.22 | 3.49| 3.75| 4.00| 4.24| 4.48| 4.71| | h| 1192.2 |1221.4 |1248.0 |1273.3 |1298.2 |1322.6 |1346.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 355.8 | 405.8 | 455.8 | 505.8 | 555.8 | 605.8 | 655.8 | | 145 v| 3.12 | 3.38| 3.63| 3.87| 4.10| 4.33| 4.56| | h| 1192.8 |1222.2 |1248.8 |1274.2 |1299.1 |1323.6 |1347.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 358.5 | 408.5 | 458.5 | 508.5 | 558.5 | 608.5 | 658.5 | | 150 v| 3.01 | 3.27| 3.50| 3.75| 3.97| 4.19| 4.41| | h| 1193.4 |1223.0 |1249.6 |1275.1 |1300.0 |1324.5 |1348.8 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 361.0 | 411.0 | 461.0 | 511.0 | 561.0 | 611.0 | 661.0 | | 155 v| 2.92 | 3.17| 3.41| 3.63| 3.85| 4.06| 4.28| | h| 1194.0 |1223.6 |1250.5 |1276.0 |1300.8 |1325.3 |1349.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 363.6 | 413.6 | 463.6 | 513.6 | 563.6 | 613.6 | 663.6 | | 160 v| 2.83 | 3.07| 3.30| 3.53| 3.74| 3.95| 4.15| | h| 1194.5 |1224.5 |1251.3 |1276.8 |1301.7 |1326.2 |1350.6 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 366.0 | 416.0 | 466.0 | 516.0 | 566.0 | 616.0 | 666.0 | | 165 v| 2.75 | 2.99| 3.21| 3.43| 3.64| 3.84| 4.04| | h| 1195.0 |1225.2 |1252.0 |1277.6 |1302.5 |1327.1 |1351.5 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 368.5 | 418.5 | 468.5 | 518.5 | 568.5 | 618.5 | 668.5 | | 170 v| 2.68 | 2.91| 3.12| 3.34| 3.54| 3.73| 3.92| | h| 1195.4 |1225.9 |1252.8 |1278.4 |1303.3 |1327.9 |1352.3 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 370.8 | 420.8 | 470.8 | 520.8 | 570.8 | 620.8 | 670.8 | | 175 v| 2.60 | 2.83| 3.04| 3.24| 3.44| 3.63| 3.82| | h| 1195.9 |1226.6 |1253.6 |1279.1 |1304.1 |1328.7 |1353.2 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 373.1 | 423.1 | 473.1 | 523.1 | 573.1 | 623.1 | 673.1 | | 180 v| 2.53 | 2.75| 2.96| 3.16| 3.35| 3.54| 3.72| | h| 1196.4 |1227.2 |1254.3 |1279.9 |1304.8 |1329.5 |1353.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 375.4 | 425.4 | 475.4 | 525.4 | 575.4 | 625.4 | 675.4 | | 185 v| 2.47 | 2.68| 2.89| 3.08| 3.27| 3.45| 3.63| | h| 1196.8 |1227.9 |1255.0 |1280.6 |1305.6 |1330.2 |1354.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 377.6 | 427.6 | 477.6 | 527.6 | 577.6 | 627.6 | 677.6 | | 190 v| 2.41 | 2.62| 2.81| 3.00| 3.19| 3.37| 3.55| | h| 1197.3 |1228.6 |1255.7 |1281.3 |1306.3 |1330.9 |1355.5 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 379.8 | 429.8 | 479.8 | 529.8 | 579.8 | 629.8 | 679.8 | | 195 v| 2.35 | 2.55| 2.75| 2.93| 3.11| 3.29| 3.46| | h| 1197.7 |1229.2 |1256.4 |1282.0 |1307.0 |1331.6 |1356.2 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 381.9 | 431.9 | 481.9 | 531.9 | 581.9 | 631.9 | 681.9 | | 200 v| 2.29 | 2.49| 2.68| 2.86| 3.04| 3.21| 3.38| | h| 1198.1 |1229.8 |1257.1 |1282.6 |1307.7 |1332.4 |1357.0 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 384.0 | 434.0 | 484.0 | 534.0 | 584.0 | 634.0 | 684.0 | | 205 v| 2.24 | 2.44| 2.62| 2.80| 2.97| 3.14| 3.30| | h| 1198.5 |1230.4 |1257.7 |1283.3 |1308.3 |1333.0 |1357.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 386.0 | 436.0 | 486.0 | 536.0 | 586.0 | 636.0 | 686.0 | | 210 v| 2.19 | 2.38| 2.56| 2.74| 2.91| 3.07| 3.23| | h| 1198.8 |1231.0 |1258.4 |1284.0 |1309.0 |1333.7 |1358.4 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 388.0 | 438.0 | 488.0 | 538.0 | 588.0 | 638.0 | 688.0 | | 215 v| 2.14 | 2.33| 2.51| 2.68| 2.84| 3.00| 3.16| | h| 1199.2 |1231.6 |1259.0 |1284.6 |1309.7 |1334.4 |1359.1 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 389.9 | 439.9 | 489.9 | 539.9 | 589.9 | 639.9 | 689.9 | | 220 v| 2.09 | 2.28| 2.45| 2.62| 2.78| 2.94| 3.10| | h| 1199.6 |1232.2 |1259.6 |1285.2 |1310.3 |1335.1 |1359.8 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 391.9 | 441.9 | 491.9 | 541.9 | 591.9 | 641.9 | 691.9 | | 225 v| 2.05 | 2.23| 2.40| 2.57| 2.72| 2.88| 3.03| | h| 1199.9 |1232.7 |1260.2 |1285.9 |1310.9 |1335.7 |1360.3 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 393.8 | 443.8 | 493.8 | 543.8 | 593.8 | 643.8 | 693.8 | | 230 v| 2.00 | 2.18| 2.35| 2.51| 2.67| 2.82| 2.97| | h| 1200.2 |1233.2 |1260.7 |1286.5 |1311.6 |1336.3 |1361.0 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 395.6 | 445.6 | 495.6 | 545.6 | 595.6 | 645.6 | 695.6 | | 235 v| 1.96 | 2.14| 2.30| 2.46| 2.62| 2.77| 2.91| | h| 1200.6 |1233.8 |1261.4 |1287.1 |1312.2 |1337.0 |1361.7 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 397.4 | 447.4 | 497.4 | 547.4 | 597.4 | 647.4 | 697.4 | | 240 v| 1.92 | 2.09| 2.26| 2.42| 2.57| 2.71| 2.85| | h| 1200.9 |1234.3 |1261.9 |1287.6 |1312.8 |1337.6 |1362.3 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 399.3 | 449.3 | 499.3 | 549.3 | 599.3 | 649.3 | 699.3 | | 245 v| 1.89 | 2.05| 2.22| 2.37| 2.52| 2.66| 2.80| | h| 1201.2 |1234.8 |1262.5 |1288.2 |1313.3 |1338.2 |1362.9 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 401.0 | 451.0 | 501.0 | 551.0 | 601.0 | 651.0 | 701.0 | | 250 v| 1.85 | 2.02| 2.17| 2.33| 2.47| 2.61| 2.75| | h| 1201.5 |1235.4 |1263.0 |1288.8 |1313.9 |1338.8 |1363.5 | |________|_________|_______|_______|_______|_______|_______|_______| | t| 402.8 | 452.8 | 502.8 | 552.8 | 602.8 | 652.8 | 702.8 | | 255 v| 1.81 | 1.98| 2.14| 2.28| 2.43| 2.56| 2.70| | h| 1201.8 |1235.9 |1263.6 |1289.3 |1314.5 |1339.3 |1364.1 | |________|_________|_______|_______|_______|_______|_______|_______|
t = Temperature, degrees Fahrenheit.
v = Specific volume, in cubic feet, per pound.
h = Total heat from water at 32 degrees, B. t. u.
[Graph: Temperature of Steam--Degrees Fahr.
against Temperature in Calorimeter--Degrees Fahr.
Fig. 15. Graphic Method of Determining Moisture Contained in Steam from Calorimeter Readings]
MOISTURE IN STEAM
The presence of moisture in steam causes a loss, not only in the practical waste of the heat utilized to raise this moisture from the temperature of the feed water to the temperature of the steam, but also through the increased initial condensation in an engine cylinder and through friction and other actions in a steam turbine. The presence of such moisture also interferes with proper cylinder lubrication, causes a knocking in the engine and a water hammer in the steam pipes. In steam turbines it will cause erosion of the blades.
The percentage by weight of steam in a mixture of steam and water is called the _quality of the steam_.
The apparatus used to determine the moisture content of steam is called a calorimeter though since it may not measure the heat in the steam, the name is not descriptive of the function of the apparatus. The first form used was the "barrel calorimeter", but the liability of error was so great that its use was abandoned. Modern calorimeters are in general of either the throttling or separator type.
Throttling Calorimeter--Fig. 14 shows a typical form of throttling calorimeter. Steam is drawn from a vertical main through the sampling nipple, pa.s.ses around the first thermometer cup, then through a one-eighth inch orifice in a disk between two f.l.a.n.g.es, and lastly around the second thermometer cup and to the atmosphere. Thermometers are inserted in the wells, which should be filled with mercury or heavy cylinder oil.
[Ill.u.s.tration: Fig. 14. Throttling Calorimeter and Sampling Nozzle]
The instrument and all pipes and fittings leading to it should be thoroughly insulated to diminish radiation losses. Care must be taken to prevent the orifice from becoming choked with dirt and to see that no leaks occur. The exhaust pipe should be short to prevent back pressure below the disk.