Document mpLkOyno1ZodEkOBedR8xjLQQ

American Society of Heating and Ventilating Engineers Guide, 1930 CAPACITY OF RETURNS WITH VARIOUS GRADES In general return lines when installed follow the contour of the land, and Table 3 gives sizes of return pipes for various grades. It is evident that at points where the grade is great, smaller pipes can be installed. Table 4 gives the number of pounds of steam condensed to water for various steam pressures which can be used in determining the size of steam main or return line. CAPACITY OF SUPPLY MAINS Table 5 gives the capacity of various sizes of pipes under various steam pressures, based on a velocity of 10,000 ft. per minute. The pipe loss will not vary under other velocities. For other velocities, at the same pressure drop, the capacity may be determined by dividing by 10,000 and multiplying by the actual velocity. Present practice in the design of underground lines is towards higher velocities, and 10,000 ft. per minute may be. considered as a minimum. Velocities as high as 35,000 ft. per minute are becoming quite common. As an example, at a velocity of 35,000 ft. per minute, the capacities would be three and one-half times the values given in the table. In assuming the higher velocities, the corresponding pressure drop should be checked. As already stated, with a maximum load, the pressure drop in a line will be such that a fixed pressure can be held at a distant point to meet definite requirements of a customer. For this reason, the practice has been quite well established among district heating companies for using pressure drop as the determining factor for fixing pipe sizes in order to give proper service at the end of any line. Following this practice velocities ranging from 25,000 to 50,000 ft. per minute me in use. The formula generally accepted for the flow of steam in pipes is that using Babcock's constant of K = 0.0027. Table 6, derived from this formula, is taken from Steam, and gives the amount of steam passing per minute that will flow through straight smooth pipes having a length of 240 diameters, for various initial pressures with 1 lb. difference between the initial and final pressures. To apply this table for other lengths of pipe and pressure losses than those assumed, let L = the length and d the diameter of the pipe, both in inches; l the loss in pounds; Q the weight under the conditions assumed in the table; and Qi the weight for the changed conditions. For any length of pipe, if the weight of steam passing is the same as given in the table, the loss will be: l = - ^240d If the pipe length is the same as assumed in the table, but the loss is different, the quantity of steam passing per minute will be: Q, =Ql* For any assumed pipe length and loss of pressure, the weight will be: a-<?(*)* 424 Chapter 25--District Heating Table 5 Pipe Sizes for Underground Supply Mains Based on a Velocity of 1A ` 10,000 Ft. per Minute Gage Pressure Lb. Steam peb Minute 200 Deg. Fahb. peb Hr. Pipe Loss B.t.u. peb Houb, peb Ft. Length Bare (10% of Bare) ^ Lb. Steam 2ondenbej> peb Hour peb Ft. Length --------------- --0 10 20 40 60 80 100 120 140 160 180 200 2.23 3.65 4.98 7.68 10.3 12.8 15.3 18.1 20.6 23.0 26.0 28.5 0 10 ' 20 40 60 80 100 120 140 160 180 200 8.70 14.2 19.4 29.8 40.0 49.7 59.8 70.5 ' 80.4 89.6 101.0 111.0 0 19.2 10 31.3 20 42.8 40 65.5 60 87.5 80 108 100 130 120 154 140 174 160 194 180 220 200 240 0 33.0 10 54.0 20 73.8 40 113 60 153 80 189 100 227 120 268 140 305 160 340 180 384 200 420 1 in. Pipe 131,100 217.200 298.200 461,400 627.000 780.000 936.000 1,110,000 1.272.000 1.416.000 1.608.000 1,764,000 2 in. Pipe 512,400 846,000 1.158.000 1.794.000 2.436.000 3.030.000 3.660.000 4.338.000 4.950.000 5.520.000 6.240.000 6.888.000 3 in. Pipe I,129,200 1,860,000 2.562.000 3.588.000 5.280.000 6.588.000 7.980.000 9.420.000 10,740,000 II,940,000 13.560.000 14.880.000 l in. Pipe 1.944.000 3.210.000 4.422.000 6.840.000 9.300.000 11.520.000 13.920.000 16.440.000 18.780.000 21,000,000 23.760.000 25.440.000 | 116 143 168 206 236 260 284 304 322 337 355 373 209 258 306 372 426 471 513 548 582 608 641 674 309 380 451 549 628 694 756 809 857 897 945 993 397 489 . 579 705 806 891 971 1039 1101 11521214 1275 11.6 14.3 16.8 20.6 23.6 26.0 28.4 30.4 32.2 33.7 35.5 37.3 20.9 25.8 30.6 37.2 42.6 47.1 51.3 54.8 58.2 60.8 64.1 67.4 30.9 38 45 55 63 69 76 81 86 90 94 99 39.7 48.9 57.9 70.5 80.6 89.1 97.1 103.9 110.1 115.2 121.4 127.5 0.0119 0.015 0.0179 0.0224 0.0262 0.0292 0.0322 0.0349 0.0374 0.0395 0.0420 0.0445 U.UZIO 0.0270 0.0327 0.0406 0.0472 0.0529 0.0582 0.0631 0.0675 0.0714 0.0760 0.0804 u.ujiy 0.0399 0.0480 0.0600 0.0693 0.0775 0.0864 0.0931 0 0999 0.1058 0.1110 0.1180 0.0404 0.0514 0.0617 0.0769 0.0895 0.1000 0.HO 0.119 0.128 0.135 0.144 0.152 425 '