Capacity | Immersion Tube Burners
Step 5--Air Pressure. From Table IV, at 70% efficiency (from Step 2), read an air pressure factor of 0.017. Tube back pressure = 0.017 × 12.7 osi × 103.6/10 = 2.28 osi.
Table I. Effective Tube Lengths and Firing Rates When Heating 180°F Water (Note: "Effective" Tube Lengths relate to heat transfer; "Equivalent" Lengths--Table III--apply to pressure drop.)
The required air pressure at the burner is then: Burner air pressure = 12.7 + 2.28 = 14.98 osi.
Step 6--Gas Pressure. From Table IV, read a natural gas pressure factor of 0.19. The gas pressure drop across the burner is then: Gas pressure drop = 0.19 × 12.7 = 2.42 osi. Adding the tube backpressure, Burner gas pressure = 2.42 + 2.28 = 4.70 osi .
300 350 400 450 500 550 600 700 800 900
13' 14' 15' 16' 17' 18'
500 583 666 750 833 916
16' 18' 19'
461 538 615
21'
428
22' 500
29' 466
37' 40' 42' 45' 47' 49' 53'
437 500 562 625 688 750 875
24'
571
31'
533
20' 692
25' 642
33' 600
21'
769
27'
715
35' 667 36' 733 38' 800
22' 846 23' 922 25' 1080 26' 1230 28' 1380 30' 1540 32' 1850 35' 2150 37' 2460 40' 2770 42' 3070 44' 3380 46' 3690 48' 4000
28' 786 29' 856 32' 1000 34' 1140 36' 1290 38' 1430 42' 1725 45' 2000 48' 2280 51' 2570 54' 2960 56' 3140 59' 3430 61' 3710 63' 4000
19' 1000 20' 1170 21' 1330 22' 1500
41'
934
Table II. Burner Capacities, in scfh air Multiply by 100 to obtain Btu/h HHV
43' 1070 46' 1200 49' 1330 53' 1600 58' 1870 62' 2130 65' 2400 69' 2660 72' 2940 76' 3200 79' 3460 82' 3730
56' 1000
60'
1120
1000 23' 1670
63' 1250 69' 1500
Burner Air pressure drop across burner, osi
Tube
1200
25' 2000
No.
1
5
6
8
12
16 Size
1400
27' 2330
75'
1750
1600 29' 2670
80' 2000 85' 2250 89' 2500 93' 2750 98' 3000 102' 3250 105' 3500 108' 3750 112' 4000 116' 4250
4762-4 4762-6
2 120 4 750 5 210 6 240 7 640 8 500 4"
1800
31' 3000
2000 33' 3330
4 570 10 200 11 200 12 700 15 500 18 300 6" 4762-7-A 5 250 11 700 12 800 14 800 18 200 21 000 8" 4762-7-B 8 000 17 900 19 600 22 600 27 700 32 000 8" 4762-8 10 500 23 500 25 700 29 700 36 300 42 000 8"
2200 34' 3670 2400 36' 4000
2600 2800 3000 3200 3400
65' 4280
85' 4000
Table III. Equivalent Lengths of Fittings (welded), for pressure drop calculations
60%
65%
70%
75%
80%
EFFICIENCY
EFFICIENCY
EFFICIENCY
EFFICIENCY
EFFICIENCY
Mitered
Short Sweep
Long Sweep
Pipe Size
90°
180°
90°
180° Bend
90°
180°
Step 3--Burner Size, Tube Diameter. Remembering that the blower will have to supply some extra pressure to overcome tube back pressure, use Table II and the square root law of flow to select a burner with 786 000 Btu/hr or more capacity, such as: 4762-4 Burner with 12.7 osi air pressure drop across the burner. From Table II, this burner requires a 4" tube. Multiply air pressure factor by burner air pressure to obtain pressure drop in each 10 feet equivalent length of tube. Multiply natural gas factor by burner air pressure drop to obtain gas pressure drop across burner. Add tube backpressure to get required gas pressure. Consult Fives for other gases. These factors are based on the primary air setting as shipped. They will be proportionally higher if the percent primary air is increased. "% tube efficiency" is really % available heat, which is the best possible fuel efficiency (with no wall or surface losses).
Elbow
Bend Elbow
Elbow Bend
4"
20'
35'
5'
8'
4'
6'
6"
30'
50'
8'
12'
6'
8'
8"
40'
60'
11'
14'
8'
10'
Do not use this table for heat transfer calculations.
Table IV. Air and Gas Pressure Factors
Air Pressure Factors
Natl. Gas
Burner Tube
Tube Efficiency
Pressure
No.
Size 60% 65% 70% 75% 80% Factors
4762-4 4762-6
4" 0.022 0.020 0.017 0.015 0.013 6" 0.012 0.011 0.010 0.008 0.007
0.19 0.15 0.08
4762-7-A 8" 0.004 0.004 0.004 0.003 0.003 4762-7-B 8" 0.010 0.008 0.008 0.007 0.006
*Losses from vats may be substantial. See pages 125-126, Volume I of the North American Combustion Handbook.
0.11
4762-8
8" 0.013 0.012 0.011 0.008 0.008
0.20
Step 4--Equivalent Tube Length for Pressure Drop. From Table III, find that each 4" mitered elbow produces a pressure drop equivalent to 20' of straight 4" pipe. Equivalent length of tube = 23.6' + (4 elbows × 20') = 23.6 + 80 = 103.6'
Bulletin 4762 Page 3
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