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516 CHAPTER 21 1952 Guide Table 3. Heat-cabbying Capacity of Type L Coppeb Tubing with. Tempebatube Dbop of 20 Deg* . Nominal Tube Sizes | in. to 4 in., and Friction SO to 720 milinches per foot. (A = Capacity, Mbh. B = Velocity, inches per second) (One milinch equals 0.001 in.) . Milinch Friction Loss peb Foot of Tube Nominal Tube Size In. 720 600 . 480 360 300 240 180 . 150 120 90. .75 ,60 A: 10 9 .. B 27. 24 .A H. B A' HB 20 . 18 35 30 36 30 37 34 A' HB 51 46 42 38 A 104 94 1 B 48 45 A 1H B 185 169 55 51 A 1H B 300 270 62 57.- A 625 / 560 2 B . 76 68 A . '1130) 1010 :2H b ; 90 - 80 A ' 1840 1650 3 B 98 90 .A .3)6 B 27n5o0 . 2480 100 A 3900 3505 4 .B 120 108 8 6.8 6.2 21 18 16.5 5.4 4.6 : 14 13 4 11 16 13.5 12 10.8 9 8 25 21 19 17 15 13 26 22.1 . 20 17.8 30 24 21 19 15. 13.1 17 15 40' 34 ' 31 33 27 24 28 ' 23.2 20.5 21 19 17 82 70 39 ' 34 63 ... 56 - 47 r 42 30 25 ' 22 19 149 125 112 100 84 75 45 39 35 30 25 22 235 200 180 160 134 120 51 43 39. 35 30 25 .495 420 375 335- '-280 250 59 51 47 42.' 36 32 890 750 : 680 600 ' V500 450 ' 69 58 49. 47 42 37 1450 1210 1100 980 80 66 59' 52 820 740 47- 42 2170 1840 1650 1450 1210 1100 89 75 66 57 51 . '45' 3100 2600 2350 : 2090 1760 1580 96 83 73 63 55. 49 3.6 3 2.8- 2.4 10 8.5 8 7 -7 6 5.4 4.7 12 10 9 8 11.8 9.9 9 7.9 13 11 10 9 18.1 15:3 13:9 12.1 14 12 11.5 10 37 32 17 14.5 28 25 13. 12 66 56 50 44 19 17 16 13 105 90 81 71 22 19 17 ..,15 200 188 170 150 27 22 . 20 : 18; 395 335 ' 305 33 26 23 270 21' 650 550 490 420 36 30 27 23 980 820 . 740 650 40: 35 ; 30 26 1390' 1180 1080 44 37.. 34 950 29 - a For other temperature drops the pipe capacities may be changed correspondingly. For example,-with temperature drop of 30 deg the capacities shown in this table are to be multiplied by 1.5. spectively. These figures would also illustrate forced circulation if a pump or circulator were shown in the return line at the boiler. One-pipe gravity systems require very precise design owing to the small circulating head available. Also, circulation in them is slow, and tem perature drop is large toward the end of the main, and consequently these systems are usually considered impractical. . One^pipe forced systems compared with gravity systems provide more rapid'circulation, with consequent smaller1 temperature drop in mains and more uniform water temperature in all radiators, and are therefore preferred. Special flow and return fittings are available for improving the circulation to risers. '= Two-pipe systems have separate flow and return mains.' If the return main is direct as shown in Fig. 5 the radiator at the end of the system has RPiPi tf Fig. 4. One-Pipe System Fig. 5. A Two-Pipe Dibect Retubn System Fig. 6. A Two-Pipe Revebsed Retubn System Hot Water Heating Systems 517 Table 4'.'. Friction (in Milinches) of Central Circular Diaphragm Orifices in Unions (One milinch equals 0.001 in.) Diameter or Orifices (Iitchsb) 1 2 ,. . Vrloott or Water hi Pin in Inches per Second . | -3 |(; 4 | .6 | 8 10 |' 12. j 18 . V. . %-iu. Pipe. 24 1 34 0.25 0.30 0.35 : 0.40 , 0.45 0.50 0.55 1300 2900 5000 11,300 20,800 32,000 45,000 650 1450 2500 5700 10,400 16,000 23,000 57,000 330 740 1300 2900 5200 . 8000 12,000 26,000 47,000 170 380 660 1500 2600 - 4000 6800: 13,000 24,000 53,000 185 330 ;740 -1300 2000 2900 6500 12,000 27,000 155 . 350. 620 970 1400 3200 5700 13,000 75 170 300 480 700 1600 2800 6400 0,35 0.40 0.45 0.50 0.55 0.60 0.65 900 2000 3500 460 1000 1800 270 570 1000 160 330 580 190 330 200 120 1-in. Pipe 7800 14,000 22,000 4000 7200 .12,000 2300 . 4100, . 6400 1400 ' 2300 .. 3700 750 1300 2200 440. . . 800 1300 260 460 720 32,000 17,000 9300 5400 3000 1800 1100 37,000 65,000 21,000 37,000 12,000 22,000 50,000 7000 13,000 28,000 "4200' 7400 17,000 2400 4300 10,000 0.45 0.50 0.55 0.60 0.65 0.70 0.75 1000 660 430 280 190 2250 1450 950 630 420 285 190 4000 2600 1700 1100 750 510 330 lVfin. Pipe. 8900 5800 3800 2500 1700 1150 750 16,000 10,400 6800 4400 3000 2000 1300 25,000 36,000 16,400 23,000 10,500 15,000 .6900 10,000 4700' 1 6700 3100 , 4500 2100 3000 53,000 34,000 22,000 15,000 10,000 6700 60,000 40,000 27,000 60,000 18,000 40,000 12,000 26^000 0.55 0.60 0.65 0.70 0.75 0.80 0.85 Ifoin. Pipe 850 1900 3300 7400 13,000 21,000 30,000 600 1300 2300 5400 8600 16,800 2i;ooo 50,000 400 850 1500 3600 7200 10,400 14,000 30,000 53,000 260 600 1100 2600 4400 7000 10,000 21,000 39,000 180 400 760 1800 3000 5000' 7000 14,000 28,000 300 540 . 1200 2200 . 3200 : 5000 10,200 19,000 45,000 200 380 860 1600 2300 3000 7800 13,000 30,000 0.70 0.80 0.90 1.00 1.10 1.20 1.30 890 1850 3500 470 975 1800 255 560 1000 160 340 610 214 375 195 S-in. Pipe 7400 3900 2200 1320 850 460 275 14,000 7400 4200 2520 1600 950 525 22,300 11,700 6500 4000 2500 1360 980 33,000 17,000 9500 5800 3700 1910 1375 37,000 20,500 12,500 7900 4200 3100 ;` i 38,000 23,000 49,000 14,000 30,000 8100 16,800 4400 8850 Not*.--The losses of head tor the orifices In the lK-in. and 2-in. pipe were calculated from those in the smaller pipes, the calculations being .based on the assumption that, for any.given velocity, the loss of head is a function of the ratio of the diameter of the pipe to that of the orifice. ' This had been found to be practically true in the tests to determine the losses of head in orifices in 3-in..;l-in..-and`l)4-in. pipe, conducted by the Texas Engineering Experiment Station, and also in the tests to determine the losses of bead in 4-in.. 6-in., and 12-in. pipe, conducted by the Engineering Experiment Station of the University of Illinois. (BulUltn 109. Table 6. p. 38. Davis and Jordan).