Document XO7jm9Ve2vBb77pJqa8w44d2x

472 CHAPTER 20 Table 2. Flow op Steam in Pipes P loss iirpressure 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. fV = pounds of steam per hour. w P = 0.0000000367 ( 1 + 1951 Guido PnmftT7to Loss IN Col. 1 Pipe Size i~P~ Actual Pipe Nomina! Internal Sq Inches Diameter Col. 2 1* Steam 1 Press. P610 Col. 3 rr V or Pipe Feinet Col. 4 V? 0.25 .0.50 65.28 92.28 i 1M 1.049 1.380 0.864 1.496 0.536 -- 1.0a 0.187 1.178 -0.5a 0.190 20 2.240 40 1.580 1.00 130.5 IK 1.610 2 184.6 2 2.067 3 226.0 2K 2.469 4 261.0 3 3.068 2.036 3.356 4.788 7.393 1.828 3.710 6.109 11.183 0.0 0.193 60 0.3 0.195 80 1.3 0.201 100 2.3 0.i07 . 120 1.290 1.120 1.000 0.912 5 291.8 m 3.548 9.887 16.705 5.3 0.223 140 0.841 6 319.7 4 4.026 12.730 23.631 10.3 0.248 160 0.793 7 345.3 iK 4.506 15.947 32.134 15.3 0.270 180 0.741 8 369.1 5 5.047 20.006 43.719 20.3 0.290 200 0.710 10 412.7 6 6.065 28.886 71.762 30.3 0.326 250 0.632 12 452.0 7 7.023 38.743 106.278 40.3 0.358 300 0.578 14 488.3 8 7.981 50.027 149.382 50.3 0.388 350' 0.538 16 522.0 9 8.941 62.786 201.833 60.3 0.415 400 0.500 20 583.6 10 10.020 78.854 272.592 75.3 0.452 450 0.477 24 639.3 12 12.000 113.098 437.503- 100.3 0.507 500 0.447 28 690.5 14 13.250 137.880' 566.693 125.3' 0.557 600 0.407 32 738.2 16 15.250 182.655 816.872 150.3 0.603 700. 0.378 40 825.4 Column 1 X 2 X 3 x.4 - lb of'steam 175.3 0.645 800 0.354 48 904.1 pipe for a given condition. 200.3 0.685 900 0.333 Example t: 1 oz drop -- 2 in. pipe 80 1167.2 -- 1.3 lb press. -- 100 ft equivalent length: 1000 0.316 160 1650.7 130.5 X 3.710 X 0.201 X 1 - 97.2 lb per hour. 97.2 X 4b * 388.8 sq ft equivalent radiation. 1200 0.289 320 2334.5 Table 2 does not allow for entrained water in low-pressure steam, condensation in covered pipe and roughness in com- 1500 . 0.258 mercxal pipe as found in practice. 480 2859.1 2000 0.224 * Pounds per square inch gage *= 2.04 in..Vacuum, Mercury Column. b The factor 4 is the approximate equivalent in square feet of steamradiation of 1 lb of steam per hour. . Steam Heating Systems 473 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 units, or the dry-return, and the boiler water line. All systems should be designed for a low initial pressure and a reason ably small pressure drop for two reasons: first, the present tendency in steam heating unmistakably points toward a constant lowering of pres sures even to those below atmospheric; second, a system designed in this manner will operate under higher pressures without difficulty. 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 ^