Part 14 (1/2)
H - h + s(t_{sup} - t_{sat}) F = ---------------------------- (3) 9704
Where s = mean specific heat of superheated stea in the trial fro in the trial, t_{sup} = final temperature of stea to pressure existing, (t_{sup} - t_{sat}) = degrees of superheat
The specific heat of superheated steaives factors of evaporation for saturated steae of conditions Except for the most refined work, intermediate values es indicate the pressure above the atmosphere As has been pointed out, the at to the altitude and the variation in the baro the properties of steaauge pressure plus the atmospheric pressure in pounds to the square inch This latter is generally assumed to be 147 pounds per square inch at sea level, but for other levels itat that place
Vacuues indicate the difference, expressed in inches of mercury, between atmospheric pressure and the pressure within the vessel to which the gauge is attached For approxiht of mercury may be considered equal to a pressure of one pound per square inch at the ordinary tees are used
Hence for any reading of the vacuue in inches, G, the absolute pressure for any baro in inches, B, will be (B - G) 204
If the barometer is 30 inches rees Fahrenheit and the vacuue 24 inches, the absolute pressure will be (30 - 24) 204 = 29 pounds per square inch
TABLE 19
FACTORS OF EVAPORATION CALCULATED FROM MARKS AND DAVIS TABLES
______________________________________________________________________ | | | |Feed | | |Tee | |Fahren-| | |heit | | |_______|______________________________________________________________| | | | | | | | | | | | 50 | 60 | 70 | 80 | 90 | 100 | 110 | |_______|________|________|________|________|________|________|________| | | | | | | | | | | 32 | 12143 | 12170 | 12194 | 12215 | 12233 | 12233 | 12265 | | 40 | 12060 | 12087 | 12111 | 12131 | 12150 | 12168 | 12181 | | 50 | 11957 | 11984 | 12008 | 12028 | 12047 | 12065 | 12079 | | 60 | 11854 | 11881 | 11905 | 11925 | 11944 | 11961 | 11976 | | 70 | 11750 | 11778 | 11802 | 11822 | 11841 | 11859 | 11873 | | 80 | 11649 | 11675 | 11699 | 11720 | 11738 | 11756 | 11770 | | 90 | 11545 | 11572 | 11596 | 11617 | 11636 | 11653 | 11668 | | 100 | 11443 | 11470 | 11493 | 11514 | 11533 | 11550 | 11565 | | 110 | 11340 | 11367 | 11391 | 11411 | 11430 | 11448 | 11462 | | 120 | 11237 | 11264 | 11288 | 11309 | 11327 | 11345 | 11359 | | 130 | 11134 | 11161 | 11185 | 11206 | 11225 | 11242 | 11257 | | 140 | 11031 | 11058 | 11082 | 11103 | 11122 | 11139 | 11154 | | 150 | 10928 | 10955 | 10979 | 11000 | 11019 | 11036 | 11051 | | 160 | 10825 | 10852 | 10876 | 10897 | 10916 | 10933 | 10948 | | 170 | 10722 | 10749 | 10773 | 10794 | 10813 | 10830 | 10845 | | 180 | 10619 | 10646 | 10670 | 10691 | 10709 | 10727 | 10741 | | 190 | 10516 | 10543 | 10567 | 10587 | 10606 | 10624 | 10638 | | 200 | 10412 | 10439 | 10463 | 10484 | 10503 | 10520 | 10535 | | 210 | 10309 | 10336 | 10360 | 10380 | 10399 | 10417 | 10432 | |_______|________|________|________|________|________|________|________| ______________________________________________________________________ | | | |Feed | | |Tee | |Fahren-| | |heit | | |_______|______________________________________________________________| | | | | | | | | | | | 120 | 130 | 140 | 150 | 160 | 170 | 180 | |_______|________|________|________|________|________|________|________| | | | | | | | | | | 32 | 12280 | 12292 | 12304 | 12314 | 12323 | 12333 | 12342 | | 40 | 12196 | 12209 | 12221 | 12231 | 12241 | 12250 | 12259 | | 50 | 12093 | 12106 | 12117 | 12128 | 12137 | 12147 | 12156 | | 60 | 11990 | 12003 | 12014 | 12025 | 12034 | 12044 | 12053 | | 70 | 11887 | 11900 | 11911 | 11922 | 11931 | 11941 | 11950 | | 80 | 11785 | 11797 | 11809 | 11819 | 11828 | 11838 | 11847 | | 90 | 11682 | 11695 | 11706 | 11717 | 11725 | 11735 | 11744 | | 100 | 11579 | 11592 | 11603 | 11614 | 11623 | 11633 | 11642 | | 110 | 11477 | 11489 | 11500 | 11511 | 11520 | 11530 | 11539 | | 120 | 11374 | 11386 | 11398 | 11408 | 11418 | 11427 | 11436 | | 130 | 11271 | 11284 | 11295 | 11305 | 11315 | 11324 | 11333 | | 140 | 11168 | 11181 | 11192 | 11203 | 11212 | 11221 | 11230 | | 150 | 11065 | 11078 | 11089 | 11099 | 11109 | 11118 | 11127 | | 160 | 10962 | 10975 | 10986 | 10997 | 11006 | 11015 | 11024 | | 170 | 10859 | 10872 | 10883 | 10893 | 10903 | 10912 | 10921 | | 180 | 10756 | 10768 | 10780 | 10790 | 10800 | 10809 | 10818 | | 190 | 10653 | 10665 | 10676 | 10687 | 10696 | 10706 | 10715 | | 200 | 10549 | 10562 | 10573 | 10584 | 10593 | 10602 | 10611 | | 210 | 10446 | 10458 | 10469 | 10480 | 10489 | 10499 | 10508 | |_______|________|________|________|________|________|________|________| ______________________________________________________________________ | | | |Feed | | |Tee | |Fahren-| | |heit | | |_______|______________________________________________________________| | | | | | | | | | | | 190 | 200 | 210 | 220 | 230 | 240 | 250 | |_______|________|________|________|________|________|________|________| | | | | | | | | | | 32 | 12350 | 12357 | 12364 | 12372 | 12378 | 12384 | 12390 | | 40 | 12267 | 12274 | 12282 | 12289 | 12295 | 12301 | 12307 | | 50 | 12164 | 12171 | 12178 | 12186 | 12192 | 12198 | 12204 | | 60 | 12061 | 12068 | 12075 | 12083 | 12089 | 12095 | 12101 | | 70 | 11958 | 11965 | 11972 | 11980 | 11986 | 11992 | 11998 | | 80 | 11855 | 11863 | 11869 | 11877 | 11883 | 11889 | 11895 | | 90 | 11750 | 11760 | 11766 | 11774 | 11780 | 11786 | 11792 | | 100 | 11650 | 11657 | 11664 | 11671 | 11678 | 11684 | 11690 | | 110 | 11547 | 11554 | 11562 | 11569 | 11575 | 11581 | 11587 | | 120 | 11444 | 11452 | 11459 | 11466 | 11472 | 11478 | 11484 | | 130 | 11341 | 11349 | 11356 | 11363 | 11369 | 11375 | 11381 | | 140 | 11239 | 11246 | 11253 | 11260 | 11266 | 11272 | 11278 | | 150 | 11136 | 11143 | 11150 | 11157 | 11163 | 11169 | 11176 | | 160 | 11033 | 11040 | 11047 | 11054 | 11060 | 11066 | 11073 | | 170 | 10930 | 10937 | 10944 | 10951 | 10957 | 10963 | 10969 | | 180 | 10826 | 10834 | 10841 | 10848 | 10854 | 10860 | 10866 | | 190 | 10723 | 10730 | 10737 | 10745 | 10751 | 10757 | 10763 | | 200 | 10620 | 10627 | 10634 | 10641 | 10647 | 10653 | 10660 | | 210 | 10516 | 10523 | 10530 | 10538 | 10544 | 10550 | 10556 | |_______|________|________|________|________|________|________|________|
The te a to each inch of reading of the vacuuiven 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| | Vacuurees |Cubic Foot| |Ins Hg| Pounds | heit | B t u |B t u|B t u| Pounds | |________|__________|_________|___________|________|________|__________| | | | | | | | | | 295 | 207 | 541 | 2218 | 10610 | 10832 | 0000678 | | 29 | 452 | 766 | 4464 | 10487 | 10933 | 0001415 | | 285 | 698 | 901 | 5809 | 10411 | 10992 | 0002137 | | 28 | 944 | 999 | 6787 | 10356 | 11035 | 0002843 | | 27 | 144 | 1125 | 804 | 10286 | 11090 | 000421 | | 26 | 193 | 1245 | 923 | 10220 | 11143 | 000577 | | 25 | 242 | 1326 | 1005 | 10173 | 11178 | 000689 | | 24 | 291 | 1401 | 1080 | 10131 | 11211 | 000821 | | 22 | 389 | 1517 | 1196 | 10064 | 11260 | 001078 | | 20 | 487 | 1611 | 1289 | 10010 | 11299 | 001331 | | 18 | 586 | 1689 | 1368 | 9964 | 11332 | 001581 | | 16 | 684 | 1758 | 1436 | 9924 | 11360 | 001827 | | 14 | 782 | 1818 | 1497 | 9888 | 11385 | 002070 | | 12 | 880 | 1872 | 1551 | 9856 | 11407 | 002312 | | 10 | 979 | 1922 | 1601 | 9826 | 11427 | 002554 | | 5 | 1224 | 2029 | 1708 | 9760 | 11468 | 003148 | |________|__________|_________|___________|________|________|__________|
From the steam tables, the condensed Table 21 of the properties of steam at different pressures may be constructed Fro conclusions
TABLE 21
VARIATION IN PROPERTIES OF SATURATED STEAM WITH PRESSURE ___________________________________________________ | | | | | | | Pressure |Terees | Liquid | Heat | Heat | | Absolute | Fahrenheit |B t u |B t u|B t u| |__________|____________|_________|________|________| | | | | | | | 147 | 2120 | 1800 | 9704 | 11504 | | 200 | 2280 | 1961 | 9600 | 11562 | | 1000 | 3278 | 2983 | 8880 | 11863 | | 3000 | 4175 | 3927 | 8113 | 12041 | |__________|____________|_________|________|________|
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 tee increase in the total heat is s 05, 31, and 47 per cent for 20, 100, and 300 pounds absolute pressure respectively above the total heat in one pound of steam at 147 pounds absolute The temperatures, on the other hand, increase at the rates of 75, 546, and 969 per cent The efficiency of a perfect steaine is proportional to the expression (t - t_{1})/t in which t and t_{1} are the absolute temperatures of the saturated steaines only approxiine in efficiency, yet they follow the saeneral law Since the exhaust temperature cannot be lowered beyond present practice, it follows that the only availablethe 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 econoher pressure, will result directly fro temperature
TABLE 22
HEAT UNITS PER POUND AND WEIGHT PER CUBIC FOOT OF WATER BETWEEN 32 DEGREES FAHRENHEIT AND 340 DEGREES FAHRENHEIT _________________________________ | | | | |Terees | per | per | | Fahrenheit| Pound |Cubic Foot| |___________|__________|__________| | | | | | 32 | 000 | 6242 | | 33 | 101 | 6242 | | 34 | 201 | 6242 | | 35 | 302 | 6243 | | 36 | 403 | 6243 | | 37 | 504 | 6243 | | 38 | 604 | 6243 | | 39 | 705 | 6243 | | 40 | 805 | 6243 | | 41 | 905 | 6243 | | 42 | 1006 | 6243 | | 43 | 1106 | 6243 | | 44 | 1206 | 6243 | | 45 | 1307 | 6242 | | 46 | 1407 | 6242 | | 47 | 1507 | 6242 | | 48 | 1607 | 6242 | | 49 | 1708 | 6242 | | 50 |1808 | 6242 | | 51 | 1908 | 6241 | | 52 | 2008 | 6241 | | 53 | 2108 | 6241 | | 54 | 2208 | 6240 | | 55 | 2308 | 6240 | | 56 | 2408 | 6239 | | 57 | 2508 | 6239 | | 58 | 2608 | 6238 | | 59 | 2708 | 6237 | | 60 | 2808 | 6237 | | 61 | 2908 | 6236 | | 62 | 3008 | 6236 | | 63 | 3107 | 6235 | | 64 | 3207 | 6235 | | 65 | 3307 | 6234 | | 66 | 3407 | 6233 | | 67 | 3507 | 6233 | | 68 | 3607 | 6232 | | 69 | 3706 | 6231 | | 70 | 3806 | 6230 | | 71 | 3906 | 6230 | | 72 | 4005 | 6229 | | 73 | 4105 | 6228 | | 74 | 4205 | 6227 | | 75 | 4205 | 6226 | | 76 | 4404 | 6226 | | 77 | 4504 | 6225 | | 78 | 4604 | 6224 | | 79 | 4704 | 6223 | | 80 | 4803 | 6222 | | 81 | 4903 | 6221 | | 82 | 5003 | 6220 | | 83 | 5102 | 6219 | | 84 | 5202 | 6218 | | 85 | 5302 | 6217 | | 86 | 5401 | 6216 | | 87 | 5501 | 6215 | | 88 | 5601 | 6214 | | 89 | 5700 | 6213 | | 90 | 5800 | 6212 | | 91 | 5900 | 6211 | | 92 | 6000 | 6209 | | 93 | 6099 | 6208 | | 94 | 6199 | 6207 | | 95 | 6299 | 6206 | | 96 | 6398 | 6205 | | 97 | 6498 | 6204 | | 98 | 6598 | 6203 | | 99 | 6697 | 6202 | | 100 | 6797 | 6200 | | 101 | 6897 | 6199 | | 102 | 6996 | 6198 | | 103 | 7096 | 6197 | | 104 | 7196 | 6195 | | 105 | 7295 | 6194 | | 106 | 7395 | 6193 | | 107 | 7495 | 6191 | | 108 | 7595 | 6190 | | 109 | 7694 | 6188 | | 110 | 7794 | 6186 | | 111 | 7894 | 6185 | | 112 | 7993 | 6183 | | 113 | 8093 | 6182 | | 114 | 8193 | 6180 | | 115 | 8292 | 6179 | | 116 | 8392 | 6177 | | 117 | 8492 | 6175 | | 118 | 8592 | 6174 | | 119 | 8691 | 6172 | | 120 | 8791 | 6171 | | 121 | 8891 | 6169 | | 122 | 8991 | 6168 | | 123 | 9090 | 6166 | | 124 | 9190 | 6165 | | 125 | 9290 | 6163 | | 126 | 9390 | 6161 | | 127 | 9489 | 6159 | | 128 | 9589 | 6158 | | 129 | 9689 | 6156 | | 130 | 9789 | 6155 | | 131 | 9889 | 6153 | | 132 | 9988 | 6152 | | 133 | 10088 | 6150 | | 134 | 10188 | 6149 | | 135 | 10288 | 6147 | | 136 | 10388 | 6145 | | 137 | 10487 | 6143 | | 138 | 10587 | 6141 | | 139 | 10687 | 6140 | | 140 | 10787 | 6138 | | 141 | 10887 | 6136 | | 142 | 10987 | 6134 | | 143 | 11087 | 6133 | | 144 | 11187 | 6131 | | 145 | 11286 | 6129 | | 146 | 11386 | 6127 | | 147 | 11486 | 6125 | | 148 | 11586 | 6124 | | 149 | 11686 | 6122 | | 150 | 11786 | 6120 | | 151 | 11886 | 6118 | | 152 | 11986 | 6116 | | 153 | 12086 | 6114 | | 154 | 12186 | 6112 | | 155 | 12286 | 6110 | | 156 | 12386 | 6108 | | 157 | 12486 | 6106 | | 158 | 12586 | 6104 | | 159 | 12686 | 6102 | | 160 | 12786 | 6100 | | 161 | 12886 | 6098 | | 162 | 12986 | 6096 | | 163 | 13086 | 6094 | | 164 | 13186 | 6092 | | 165 | 13286 | 6090 | | 166 | 13386 | 6088 | | 167 | 13486 | 6086 | | 168 | 13586 | 6084 | | 169 | 13686 | 6082 | | 170 | 13787 | 6080 | | 171 | 13887 | 6078 | | 172 | 13987 | 6076 | | 173 | 14087 | 6073 | | 174 | 14187 | 6071 | | 175 | 14287 | 6069 | | 176 | 14387 | 6067 | | 177 | 14488 | 6065 | | 178 | 14588 | 6062 | | 179 | 14688 | 6060 | | 180 | 14788 | 6058 | | 181 | 14888 | 6056 | | 182 | 14989 | 6053 | | 183 | 15089 | 6051 | | 184 | 15189 | 6049 | | 185 | 15289 | 6047 | | 186 | 15389 | 6045 | | 187 | 15490 | 6042 | | 188 | 15590 | 6040 | | 189 | 15690 | 6038 | | 190 | 157,91 | 6036 | | 191 | 15891 | 6033 | | 192 | 15991 | 6031 | | 193 | 16091 | 6029 | | 194 | 16192 | 6027 | | 195 | 16292 | 6024 | | 196 | 16392 | 6022 | | 197 | 16493 | 6019 | | 198 | 16593 | 6017 | | 199 | 16694 | 6015 | | 200 | 16794 | 6012 | | 201 | 16894 | 6010 | | 202 | 16995 | 6007 | | 203 | 17095 | 6005 | | 204 | 17196 | 6002 | | 205 | 17296 | 6000 | | 206 | 17397 | 5998 | | 207 | 17497 | 5995 | | 208 | 17598 | 5993 | | 209 | 17698 | 5990 | | 210 | 17799 | 5988 | | 211 | 17899 | 5985 | | 212 | 18000 | 5983 | | 213 | 1810 | 5980 | | 214 | 1820 | 5978 | | 215 | 1830 | 5975 | | 216 | 1840 | 5973 | | 217 | 1850 | 5970 | | 218 | 1861 | 5968 | | 219 | 1871 | 5965 | | 220 | 1881 | 5963 | | 221 | 1891 | 5960 | | 222 | 1901 | 5958 | | 223 | 1911 | 5955 | | 224 | 1921 | 5953 | | 225 | 1931 | 5950 | | 226 | 1941 | 5948 | | 227 | 1952 | 5945 | | 228 | 1962 | 5942 | | 229 | 1972 | 5940 | | 230 | 1982 | 5937 | | 231 | 1992 | 5934 | | 232 | 2002 | 5932 | | 233 | 2012 | 5929 | | 234 | 2022 | 5927 | | 235 | 2032 | 5924 | | 236 | 2042 | 5921 | | 237 | 2053 | 5919 | | 238 | 2063 | 5916 | | 239 | 2073 | 5914 | | 240 | 2083 | 5911 | | 241 | 2093 | 5908 | | 242 | 2103 | 5905 | | 243 | 2114 | 5903 | | 244 | 2124 | 5900 | | 245 | 2134 | 5897 | | 246 | 2144 | 5894 | | 247 | 2154 | 5891 | | 248 | 2164 | 5889 | | 249 | 2174 | 5886 | | 250 | 2185 | 5883 | | 260 | 2286 | 5855 | | 270 | 2388 | 5826 | | 280 | 2490 | 5796 | | 290 | 2593 | 5765 | | 300 | 2696 | 5733 | | 310 | 2799 | 5700 | | 320 | 2902 | 5666 | | 330 | 3006 | 5630 | | 340 | 3110 | 5594 | |___________|__________|__________|
The gain due to superheat cannot be predicted froiven 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 e of the use of high pressure stea 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 443 cubic feet, while at 200 pounds pressure it occupies 229 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 volu e for expansion than the low-pressure steam, will thus do more work This increase in the ae relative to the additional fuel required as indicated by the total heat
In general, it iven amount of heat to a boiler is practically independent of the steah as compared with the steam temperature that a variation in the steam temperature does not produce an appreciable effect
The forebraic 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 ther tables cover all practical cases