Document 17gaVZwOgNrKVeX34g4R8x15

; 250._______________________ Chapter 14 _____ 1945 Guide when the rate of air elimination and condensation is high are clearly indicated in these curves. It is evident that the condensation flow during the initial warming-up period reaches a peak which is greater than the constant condensation rate which is eventually reached when the pressure becomes uniform. Moreover, the peak condensation rate is obtained when.the system steam pressure is lower than that existing during a period of constant condensing rate. It will also be noted that the peak rate of air elimination does not coincide with the higher condensing rate. STEAM FLOW The rate of flow of dry steam or steam with a small amount of water flowing in the same direction is in accordance with the general laws of gas flow and is a function of the length and diameter of the pipe, the density' . of the steam, and the pressure drop through the pipe. This relationship has been established by Babcock in the formula given at the top of Table 1. 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 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. 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 im portant that (1) the total pressure drop does not exceed the initial pressure of the system and in actual practice should never exceed one-half of the initial 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-atmos pheric which normally operate under controlled partial vacua, the orifice, and the vapor systems which at times operate under such partial vacua as may be obtained due to the condition of.the fire ; and (4) the equivalent head 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. . Steam Heating Systems and Piping ________ Table 1. Flow of Steam in Pipes P - loss in pressure in pounds. D = inside diameter of pipe in inches, X. = length of pipe in feet. d = weight of leu ft of steam. W -- pounds of steam per hour. P = 0.0000000367 ( 1 + 251 Pressure Loss IN Ounces Col. 1 Pips Size 5220Vlio Nominal Actual Internal Diameter Intebnal A&ea or Pipe Sq Inches Cou 2 Steam Press, Psio Col 3 V' Lbnoth or Pits nr * Feet Col 4 vr 0.25 65.28 i 1.049 . 0.864 0.536 -1.0" 0.187 20 2.240 0.50 1.00 92.28 130.5 m 1.380 m ' 1.610 1.496 2.036 1.178 --0.5a 0,190 1.828 0.0 0.193 40 1.580 60 1.290 2 184.6 2 2.067 3.356 3.710 0.3 0.195 . 80 1.120 m3 226.0 2.469 4.788 . 6.109 1.3 .0.201 100 1.000 4 261.0 3 3.068 7.393 11.183 2.3 0.207 120 0.912 _ 5' . 291.8 6 319.7 7 . 345.3 8 ' 369.1 10 412.7 12 452.0 14 488.3 16 522.0 20 583.6 24 639.3 28'. 690.5 32 738.2 40 825.4 48- 904.1 SO 1167.2 160 1650.7 320 2334.5 480 2859.1 3H 3.548 9.887 16.705 5.3 0.223 4 4.026 12.730 23.631 10.3 0.248 m 4.506 15.947 32.134 15.3* 0,270 5 5.047 20.006 43,719 20.3 0.290 6 6.065 28.886 71.762 30.3 0.326 7- 7.023 38.743 106.278 40.3 0.358 8 .7.981 . 50.027 .149.382 50.3. 0.388 9 8.941 62.786 201.833 60.3 0.415 10 10.020 . 78.854 272.592 75.3 0.452 12 12.000 113.098 437.503 100.3 0.507 14 ' 13.250 137.880 566.693 125.3 0.557 16 15.250 182.655 816.872- 150.3 0.603 Column 1. X 2 X 3 X 4 lb of steam 175.3 per hour that will flow through a straight pipe for a given condition. 200.3 Example 1: T oz drop -- 2. in. pipe -- 1.3 lb press. --' 100 ft equivalent length: 0.645 0.685 13&5 X 3.710 X 0.201 X 1 - 97.2 lb per hour. 97.2 X 4b -- 388.8 sq ft equivalent radiation. Table 1 does not allow for entrained water in low-pressure steam, condensation in covered pipe and roughness in com mercial pipe as found in practice. 140 160 180 200 250 300 350 400 450 500 600 700 800 900 1000 1200 1500 2000 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. factor 4 is the approximate equivalent in square feet of steam radiation of 1 tb of steam per hour.