Document Xz9N33MZE0Kw2mQga9nnNxn6B

456 CHAPTER 20 1950 Guide Table 2. Flow op Steam in Pipes P = loss in pressure in pounds per square inch. Z>.= inside diameter ofpipe in inches. L length of pipe-in feet. d = weight of 1 cu ft of steam.. W = pounds of steam per hour. ' ______ / -POP W = 5220 -a/ / 3.6\ , ll 1+ -g- 1-Z '' ' P = 0.0000000367 ( 1 + ~g ) ftaasra* : Lose ' Dt OlRtCBS Col. 1 Puts Sob "V- Nominal - Actual. Internal Diameter- Internal Area or Sq- Pip* Inches Col. 2 Aro Steam Passa. PBXQ Col. 3 V." Length op Pip* C4 Fbet Col. 4 VT 0.25 - 65.28. l. 1.049 .0.864 . Q.536 -1.0* 0.1S7 20 2.240 0.50 92.28 IX 1.380 1.496 1.00 130.5 1H 1.610 2.036 2 184.6 2 2.067 3.356 3 226.0 2X 2.469 . 4.788 1.178 -0.5* 0.190 40 1.828 3.710 6.109 0.0 0.1931; 60 0.3 0395 J; 80 1.3 0.2011 100 1.580 1.290 1.120 1.000 4 261.0 .3 3.068 ' 7.393 11.183 2.3 0.207 120 0.912 5 291.8 3J4 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 *X .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 0.3261 250 0.632 12 452.0 "7' 7.023 38,743 '106,278. 40.3 0.358 300 0.578 14 488.3 8 .16 . 522.0 9 7.981 8.941 50.027 149.382 50.3 6.388 62.786 201.833 60,3 0.415 35p 0.538 .400., 0.500 20 583.6 10 - 10.020: 78.854 272.592 75:3 6.452 450 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 0.401 32 738.2 16 15.250 182.655 816.872. 150.3 0.603 700. 0.378 40 825.4 .. 904-1 80 1167.2 160 1650.7 320 2334.5 480 2859.1 Column 1 X 2 X 3 X 4 lb of steam 175.3 or that will flow throug pipe for a given condition. 200.3 Example I: . 1 02 drop -- 2 in. pipe -- 1.3 lb press. -- 100 ft equivalent length: 0.645 0.685 800 900 . 1000 130.5 X 3.710 X 0.201 X 1 - 97.2.1b per hour. . 97.2 X 4b a 383.8 sq ft equivalent radiation. 1200 Table 2 does not allow for entrained water in low-pressure steam, condensation in covered pipe and roughness in com- 1500 merdal pipe as found in practice. ,2000 0.354 0.333 0.316 0.289 0.258 0.224 ' * Pounds per square inch gage 2.04 in. Vacuum, Mercury Column. _ .\ The factor 4 is theapproximate equivalent in square feet of steam radiation of 1 lb ofsteam per hour. Steam Heating Systems and Piping 457 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 muTfimnnn 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 diy-retum, 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