Document YGekXax3GJJJ9vQr6xkK5vQwE

506 CHAPTER 21 1956 Guide Table 2. Flow of Steam in Pipes 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. ' I PdD* W = 5220 */ / 3.6 \ ll * + ' P = 0.0000000367 ( 1 + Loss HI Ounces Col. 1 I Pipe Sob I 5220VIloTo-] Nominal Actual Internal Diameter Area or Pipe So Inches Col.2 1 * Avo Steam Pexaa. rsto Col.3 rr V Length Qt Fnrr Col. 4 Jloo V-r 0.25 0.50 1.00 2 3 4 5 6 7 8 10 12 14 , 16 20 24 28 32 40 48 80 160 320 480 65.28 92.28 130.5 i m m 1.049 1.380 1.610 0.864 1.496 2.036 0.536 -- 1.0a 0.187 1.178 --0.5a 0.190 1.828 0.0 0.193 184.6 2 2.067 3.356 3.710 0.3 0.195 226.0 23S 2.469 4.788 6.109 1.3 0.201 261.0 3 3.068 7.393 11.183 2.3 0.207 291.8 319.7 3M 3.548 9.887 16.705 5.3 0.223 4 4.026 12.730 23.631 10.3 0.248 345.3 435 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 7.023 38.743 106.278 40.3 0.358 488.3 8 7.981 50.027 149.382 50.3 0.388 522.0 9 8.941 62.786 201.833 60.3 0.415 583.6 10 10.020 78.854 272.592 75.3 0.452 639.3 12 12.000 113.098 437.503 100.3 0.507 690.5 14 13.250 137.880 566.693 125.3 0.557 738.2 16 15.250 182.655 816.872 150.3 0.603 825.4 904.1 1167.2 1650.7 2334.5 2859.1 Column 1 X 2X3 x 4 - lb of steam 175.3 pipe for a given condition. 200.3 Example t: 1 0* drop -- 2 in. pipe -- 1.3 lb press. -- 100 ft equivalent length: 0.645 0.685 130.5 X 3.710 X 0.201 X 1 - 07.2 lb per hour. 97.2 X 4b > 388.8 sq ft equivalent radiation. 1 Table 2 does not allow for entrained water in low-pressure 1 steam, condensation In covered pipe and roughness In com[ merdal pipe as found in practice. 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 0.224 * Pounds per square inch gage = 2.04 in. Vacuum, Mercury Column. . u.,,- b The factor 4 is the approximate equivalent in square feet of steam radiation of 1 lb of steam per nour. Steam Heating Systems 507 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 rim 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 units, 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.A.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 f 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