Document oD5yBZ99Re6OEzjwOpod4bEVg

494 CHAPTER 21 Table 2. Flow of Steam in Pipes rfar 1954 Guide P = loss in pressure in pounds per square inch. D = inside diameter of pipe in inches. L = length of pipe in feet. d = weight of 1 cu ft of steam. W = pounds of steam per hour. W p = 0--.-0-0--0-0--0--0-0--3--6-7---( - 3.6 I PdD` 5220 Vo+s: 1V*L Lobs Oumnces Col 1 Pm Sizx 5220Vw Actual `Nominal' Internal Diameter 1Internal Ahju or Pm Sq Inches COLZ . 4ih Ave Steam Psxsa. P610 Col. 3 . V4' Length : IN Feet Col. 4 0 0.25 0.50 1.00 2 3 4 5 6 7 8 10 12 14 16 20 24 28 32 40 48 80 160 320 65.28 | i 1.049 0.864 0.536 -1.0a 0.187 92.28 Wa 1.380 1.496 1.178 -0.5a 0.190 130.5 184.6 iH- 1.610 2 2.067 2.036 3.356 1.828 3.710 0.0 0.193 0.3 0.195 226.0 VA 2.469 4.788 6.109 1.3 0.201 261.0 3 3.068 7.393 11.183 2.3 0.207 291.8 3A 3.548 9.887 16.705 5.3 0.223 319.7 4 4.026 12.730 23.631 10.3 0.248 345.3 4)4 4.506 15.947 32.134 15.3 0.270 369.1 5 5.047 20.006 43.719 20.3 0.290 412.7 6 6.065 28.886 71.762 30.3 0.326 452.0 7 1 8488.3 1 9522.0 583.6 10 ' 639.3 12 7.023 7.981 8.941 10.020 12.000 38.743 106.278 40.3 0.358 50.027 149.382 50.3 0.388 62.786 78.854 113.098 201.833 272.592 437.503 60.3 75.3 100.3 0.415 |0.452 10.507 690.5 738.2 825.4 14 13.250 137.880 566.693 125.3 16 15.250 182.655 816.872 150.3 1 Column 1X2 X 3 X 4 - lb of steam 173.3 0.557 I 0.603 | 0.645 I 904.1 1 pipe for a given condition. 200.3 0.685 1167.2 ~f B Example t: - 1.3 lb press. 1 -- oz drop -- i in. pipe 100 ft equivalent length: 1650.7 11 0173025XX 43b.71o0 X3SSU..82Us1q Xft leq-uivalenitd rPadiautoiounx.. 2334.5 Table 2 does not allow for entrained water in low-pressure 480 2859.1 :se&s.vs isasi 20 40 60 80 100 120 140 160 180 200 250 300 350 400 450 500 600 700 800 900 1000 1200 1500 2000 2.240 1.580 1.290 1.120 1.000 0.912 0.841 0.793 0.741 0.710 0.632 0,578 0.538 0.500 0.477 0.447 0.407 0.378 0.354 0.333 0.316 0.289 0.258 1 0.224 Steam Heating Systems 495 has been established by Babcock in the formula given at the top of Table 2. In Columns 1, 2, 3, and 4 of this table, the numerical values of the factors for different pressure losses, pipe diameters, steam densities and lengths of pipe have been worked out in convenient form so that the steam flowing in any pipe may be calculated by multiplying together the proper factors in each column, as shown in the example at the bottom of the table. Pipe Sizes The determination of pipe sizes for a given load in steam heating depends on the following principal factors: 1. The initial pressure and the total pressure drop which may be allowed between the source of supply and at the end of the return system. ' 2. The maximum velocity of steam allowable for quiet and dependable operation of the system, taking into consideration the direction of condensate flow. -3. The equivalent length of the run from the boiler or source of steam supply to the farthest heating unit. 4. The direction of flow of the condensate, whether against or with the steam. Initial Pressure and Pressure Drop Theoretically,, there are several factors to be considered such as initial pressure and pressure required at the end of the line, but it is most impor tant that: (1) the total pressure drop does not exceed the initial gage pressure of the system, and in actual practice it should never exceed onehalf of the initial gage pressure; (2) the pressure drop is not.so great as to cause excessive velocities; (3) there:is a constant initial pressure, except on systems specially designed for varying initial pressures, such as the sub-atmospheric, which normally operate under controlled partial vacua and orifice and vapor systems, which at times operate under such partial vacua as may be obtained due to the condition of the fire; and (4) the rise in water due to pressure drop does not exceed the difference in level, for gravity return systems, between the lowest point on the steam main, the heating emits, or the dry-return, and the boiler water line. The present tendency in steam heating unmistakably points toward a constant lowering of initial pressures, even to those below atmospheric, and to the use of reasonably small pressure drops because a system de signed in this manner will operate under higher pressures without dif ficulty. When a system designed for a relatively high initial pressure and a relatively high pressure drop is operated at a lower pressure, it is likely to be noisy and have poor circulation. The total pressure drop should never exceed one-half of the initial gage pressure when condensate is flowing in the same direction as the steam. Where the condensate must flow counter to the steam, the governing factor is the velocity permissible without interfering with the condensate flow. A.S.H.V.E. Research Laboratory experiments limit this to the capacities given in Table 3 for horizontal pipes at varying grades. Maximum Velocity The capacity of a steam pipe in any part of a steam system depends upon the quantity of condensate present, the direction in which the con densate is flowing, and the pressure drop in the pipe. Where the quantity of condensate is limited and is flowing in the same direction as the steam, only-the pressure drop need be considered. When the condensate must .flow against the steam, even in limited quantity, the velocity of the steam must not exceed limits above which the disturbance between the steam and