Document k9EyBOr3EqwJeBbyVw5JB8p1D

American Society of Heating and Ventilating Engineers Guide, 1924-25 reason why mains should be a certain percentage greater area than the sum of the connections, and still lower power consumption can be ob tained by using larger branches and mains of equal area. While the rule of thumb method of determining size of mains works very well in many cases, yet it is always desirable to figure the mains and branches of the proper size to give the velocity which has been found best suited to the work to be done. Ln certain special cases where explosive or poisonous dusts such as aluminum buffings, grain dust, powdered sugar, or lead dust are handled, increasing the size of the mains unduly would introduce a serious hazard. TABLE 110. CUBIC FEET OF AIR HANDLED PER MINUTE THROUGH AVERAGE COLLECTING HOODS 0.71 10Based on Coefficient of Orifice of with Per Cent Added forXbakage Diameter of Connection Pipe In. 1 Maintained Suction--In. Water Gage 1M 2 2M 3 4 5 m 2 2Vi 3 334 4 4M 5 6 7 8 9 10 38 68 107 153 209 273 345 427 614 .835 1092 1381 1705 47 84 131 188 256 334 423 523 751 1023 1337 1694 2090 54 97 161 217 296 386 488 605 867 1181 1546 1953 2409 61 108 168 243 330 431 546 676 970 1322 1727 2184 2695 67 118 185 266 362 473 598 741 1062 1448 1892 2387 2959 76 136 214 306 418 546 690 854 1228 1670 2184 2762 3410 86 153 238. 343 466 609 775 955 1373 1870 2440 3091 3806 An exhaust system to be effective must remove.a certain amount of air from each hood or other connection, and in addition must maintain sufficient velocity throughout the piping; system to convey , the dust or refuse material to the separator. Any system which is mechanically well constructed and handles the requisite air at the connections and, maintains sufficiently high velocities, is an effective system from the standpoint of the work done. However, to keep the operating cost low it is advantageous to.do the work with as low velocities as the.character istics of the material will permit. The skilled designer will keep both of these requirements in mind and produce a system which is both effective and economical of power. The maintained resistance of the exhaust system is composed of three factors: (1) Loss through the hoods; (2) Collector drop; and (3) Fric tion drop in the pipes. A. Suction at the various hoods must be chosen from experience. Loss through the hoods can be calculated by an experienced engineer but may be taken very roughly at one-half the suction. B. Collector drop in inches of water is given by the following formula: Drop = c(----Y V 1000 ) 214 American Society of Heating and Ventilating Engineers Guide, 1924-25 where ; C -- a constant which depends upon the type of collector and is found to range from 0.25 to 0.75; V = velocity in feet per minute of air entering the collector. C. Friction drop in the pipes must be computed for each section where there is a change in area or in velocity. Find the velocities in each sec tion of pipe starting with the branch furtherest from the fan. The friction drop for these sections can be determined by reference to Table 111. Total friction loss in the piping system is the friction drop in furthest TABLE 111. FRICTIONAL RESISTANCE OF STRAIGHT CONVEYOR PIPE To Flow of Air Per 100 Feet of Pipe per Min. 2000 2200 2400 2600 2800 3000 3200 3400 3600 . 3800 4000 4200 4400 4800 . 5200 5600 6000 Loss of Pressure in Inches for Given Diameter Pipe 4' .. 1.92 2.32 2.77 3.26 3.76 4.33 4.93 5.56 6.23 6.95 7.69 8.48 9.26 11.05 13.00 15.25 17.30 5' 1.53 1.85 2.22 2.60 3.01 3.46 3.94 4.45 4.98 5.55 6.15 6.78 7.41 8.85 10.50 12.05 13.85 6' 1.28 1.55 1.84 2.17 2.52 2.88 3.28 3.71 . 4.154.62 5.13 5.65 6.18 .7.38 8.66 10.05 11.52 7' 1.09 1.32 1.58 1.86 2.15 , 2.47 2.82 3.18 3.56 3.97 4.40 4.85 5.30 6.32 7.44 8.61 9.89 8' 0.962 1.16 1.39 1.63 1.89 2.08: 2.47 2.78 3.12 3.48 3.85 4.25 4.63 5.55 6.50 7.55 8.66 10' 0.770 0.932 1.01 1.30 1.51 1.73 1.97 2.22 2.49 2.78 3.08 3.49 3.71 4.43 5.21 6.03 6.92 12' 0.640 : 0.778 0.924 1.08 1.26 1.44 1.64 1.85 2.08 2.32 2.57 2.83 3.09 3.69 4.34 5.05 5.76 14' 16' 18' 20' 22' 24' 30' 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 , 4200 4400 4800. 5200 5600 6000 0.550 0.655 0.790 0.930 1.07 1.24 1.41 1.59 1.78 1.99 . 2.26 2.43 2.66 3.17 3.72 4.32 4.95 0.482 0.582 0.693 0.810 0.932 1.08 1.23 1.43 1.56 1.74 1.92 2.12 2.33 2.77. 3.25 3.78 4.33 0.428 0.578 0.617 0.722 0.838 0.961 1.09 1.24 1.38 1.54 1.71 1.88 2.06 2.46 2.89 3.35 3.85 0.385 0.465 0.553 0.650 0.754 0.865 0.985 1.11 1.25 1.39 1.54 1.70 1.85 2.22 2.61 3.02 3.46 0.350 0.423 0:504 0.590 0.685 0.788 0.895 1.01 1.13 1.26 1.40 1.54 1.68 2.02 2.36 2.74 . 3.14 0.320 0.388 0.462 0.542 0.628 0.722 0.820 0.925 1.04 1.16 1.28 1.42 1.54 1.85 2.16 2.52 2.89 0.257 0.310 0.369 0.434 0.503 0.577 0.657 0.742 0.832 0.926 1.03 1.13 1.24 1.48 1.75 2.01 2.31 FRICTIONAL RESISTANCE OF ELBOWS Elbows having a radius equal to the pipe diameter set up a resistance equivalent to a section of straight pipe approximately 10 diameters long. With a radius of 1>$ times the diameter the resistance is about the same as seven diameters of straight pipe. 215