Part 22

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 | |_______|_______|___________|_________|_________|_________|

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.

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, passes around the first thermometer cup, then through a one-eighth inch orifice in a disk between two flanges, 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.

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.

When steam passes through an orifice from a higher to a lower pressure, as is the case with the throttling calorimeter, no external work has to be done in overcoming a resistance. Hence, if there is no loss from radiation, the quantity of heat in the steam will be exactly the same after passing the orifice as before passing. If the higher steam pressure is 160 pounds gauge and the lower pressure that of the atmosphere, the total heat in a pound of dry steam at the former pressure is 1195.9 B. t. u. and at the latter pressure 1150.4 B. t. u., a difference of 45.4 B. t. u. As this heat will still exist in the steam at the lower pressure, since there is no external work done, its effect must be to superheat the steam. Assuming the specific heat of superheated steam to be 0.47, each pound passing through will be superheated 45.4/0.47 = 96.6 degrees. If, however, the steam had contained one per cent of moisture, it would have contained less heat units per pound than if it were dry. Since the latent heat of steam at 160 pounds gauge pressure is 852.8 B. t. u., it follows that the one per cent of moisture would have required 8.5 B. t. u. to evaporate it, leaving only 45.4 - 8.5 = 36.9 B. t. u. available for superheating; hence, the superheat would be 36.9/0.47 = 78.5 degrees, as against 96.6 degrees for dry steam. In a similar manner, the degree of superheat for other percentages of moisture may be determined. The action of the throttling calorimeter is based upon the foregoing facts, as shown below.

Let H = total heat of one pound of steam at boiler pressure, L = latent heat of steam at boiler pressure, h = total heat of steam at reduced pressure after passing orifice, t{1} = temperature of saturated steam at the reduced pressure, t{2} = temperature of steam after expanding through the orifice in the disc, 0.47 = the specific heat of saturated steam at atmospheric pressure, x = proportion by weight of moisture in steam.