Steam:
Its Generation and Use

HEATING LIQUIDS AND BOILING BY STEAM. (<?). Efficiency of surface, where all the air is expelled. For vertical surface, each square foot will transmit 230 heat units per hour, for each degree of difference in the temperature of the two sides. For horizontal and inclined surface, each square foot will transmit 330 heat units per hour for each degree of difference in temperature between the two sides. (&'). Steam required. Each 966 heat units will require the condensation of one pound of steam at 2120, or 1,000 units at 75 lbs. pressure. Babcock <S> Wilcox Boilers in Ponce de Leon Hotel, St. Augustine, Fla. The philosophy of drying or evaporating moist- ure by heated air rests upon the fact that the ca- pacity of air for moisture is rapidly increased by rise in temperature. If air at 520 is heated to 720, its capacity for moisture is doubled, and is four times what it was at 320. The following table gives the weight of a saturated mixture of air and aqueous vapor at different temperatures up to 1600 —the practical limit of heating air by steam, together with the weight of vapor, in pounds and per centage, and total heat, the portion contained in the vapor and the quantity of air required per pound of water. By the inspection of this table it will be seen why it is more economical to dry at the higher tempera- tures. The atmos- phere is seldom satu- rated with moisture, and in practice it will be found generally necessary to heat the air about 30° above the temperature of saturation. The best effect is produced where there is artifi- cial ventilation, by fan or by chimney, and the course of the heated air is from above downwards. Each pound of steam condensed will evaporate one pound of water (nearly) from the tempera- ture of evaporation. Each horse-power of boil- er will heat 30,000 lbs. water i° per hour, or evaporate 30 lbs. water in the same time. 1 SATURATED MIXTURES OF AIR AND AQUEOUS VAPOR. DRYING BY STEAM. There are three modes of drying by steam, ist. By bringing wet substances in direct con- tact with steam-heated surfaces, as by passing cloth or paper over steam-heated cylinders, or clamping veneers between steam-heated plates. 2. By radiated heat from steam pipes, as in some lumber kilns, and laundry drying rooms. 3d. By causing steam-heated air to pass over wet surfaces, as in glue works, etc. The second is rarely used except in combina- tion with the third. The first is the most eco- nomical, the second less so, and the third least. Under favorable circumstances, it may be esti- mated that one horse-power of steam will evap- orate 24 pounds water by the first method, 20 by the second, and 15 by the third. 35 40 45 5° 65 70 75 80 85 9° 95 100 Io5 110 "5 120 i si c g i) - lbs. 3080 2526 2088 1714 1326 1203 1004 868 125 130 135 140 ’45 150 *55 160 I 8.004 7.920 7-834 7-752 7.688 7-589 7-5°7 7-425 7.342 7.262 7-’78 7.108 7.009 6.924 6.830 6.74t 6.650 6-551 6-454 6-347 6.238 6.131 6.015 5.891 5-764 5-679 0.034 0.041 0.049 0.059 0.070 0.082 0.097 o. 114 0.134 0.156 o. 182 0.212 O.245 O.283 O.325 °-373 0.426 0.488 0-554 0.630 o.7’4 0.806 0.909 1.022 i 145 T'333 0.42 0.52 0.62 0.76 0.91 1.08 1.29 1.49 1.79 2.15 2-5+ 2.98 3-5° 4.08 4-76 5-23 6.41 7-46 8-55 9.90 11.44 I3-I4 ’7-33 19.88 23.47 <U 3 X u 42.8 59-8 77-7 97-6 118.3 140.1 164-9 189.7 221.6 253-6 289.7 33° •2 373-4 422.0 474-7 533-9 599-1 672.4 750-5 839-4 936-7 1042.7 ii60.6 1288.4 1427.4 1638.7 86.69 76-59 68.98 66.29 64.58 64-31 64-76 66.21 66.74 68.02 69.66 71.19 72.87 74-58 76.22 77.88 79-52 81.14 82.62 84.13 85.57 86.89 88.18 89-39 90-53 91-93 234-4 192.2 158.9 i3°-4 108.5 91.6 76.4 66.0 55-o 45-6 38-4 32-5 27.6 23-5 2C.O 17.I 14.6 12.6 9.1 7-7 6.6 5-6 4-8 3-3 723 599 505 427 363 308 263 224 192 163 140 118 102 87 74 63 53 43