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(3) How to calculate curved sections
Duct
No.
Outline diagram Conditions
section
90°
1
Smooth
Elbow
Rectangular
2
Radius
Elbow
Rectangular
Vaned
3
Radius
Elbow
90°
4
Miter
D
Elbow
Rectangular
Square
5
Square
Elbow
Rectangular
Vaned
6
Square
Elbow
Rectangular
Vaned
7
Square
Junction
Rectangular
Vaned
8
Radius
Junction
45°
9
Smooth
Elbow
10 Expansion
11 Contraction
Table 6 List of pressure losses in each duct section
Length of
C
equivalent
circular
value
pipe
R/D = 0.5
0.73
43D
= 0.75 0.38
23D
= 1.0
0.26
15D
= 1.5
0.17
10D
= 2.0
0.15
9D
W/D R/D
0.5
1.30
79D
0.75 0.47
29D
0.5
1.0
0.28
17D
1.5
0.18
11D
0.5
0.95
57D
0.75 0.33
20D
1-3
1.0
0.20
12D
1.5
0.13
8D
No. of
R/D
vanes
0.5
0.70
42D
0.75 0.16
10D
1
1.0
0.13
8D
1.5
0.12
7D
0.5
0.45
27D
0.75 0.12
7D
2
1.0
0.10
6D
1.5
0.15
9D
0.87
53D
1.25
76D
0.35
21D
Same loss as circular duct.
Velocity is based on inlet.
With or without
vanes,
1/2 times value
rectangular or
for similar 90°
circular
a = 5°
0.17
10D
10°
0.28
17D
20°
0.45
27D
30°
0.59
36D
40°
0.73
43D
Loss is for
hV
- hV
1
2
a = 30°
0.02
1D
45°
0.04
2D
60°
0.07
4D
Loss is for
V
2
CHAPTER 4
Duct
No.
Outline diagram Conditions
section
12 Transformer
14° or less
Abrupt
13
Entrance
Abrupt
14
Exit
Bellmouth
15
Entrance
Bellmouth
16
Exit
Re-entrant
17
inlet
Sharp edge
18
round orifice
Pipe inlet
(with
19
circular
hood)
Pipe inlet
(with
20
rectangular
hood)
Abrupt
21
contraction
Abrupt
22
expansion
Suction
inlet
23 (punched
narrow
plate)
Characteristics
Length of
C
equivalent
circular
value
pipe
0.15
9D
0.50
30D
1.0
60D
0.03
2D
1.0
60D
0.85
51D
V
/V
= 0
2.8
170D
1
2
0.25
2.4
140D
0.50
1.9
110D
0.75
1.5
90D
1
1.0
60D
Loss is for
V
2
20°
0.02
40°
0.03
β
60°
0.05
90°
0.11
120°
0.20
20°
0.03
40°
0.08
β
50°
0.12
90°
0.19
120°
0.27
V
/V
= 0
0.5
30D
1
2
0.25
0.45
27D
0.50
0.32
19D
0.75
0.18
11D
Loss is for
V
2
V
/V
= 0
1.0
60D
1
2
0.20
0.64
39D
0.40
0.36
22D
0.60
0.16
9D
0.80
0.04
2D
Loss is for
V
1
0.2
35
0.4
7.6
0.6
3.0
0.8
1.2
43
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