Appendix
EDMMT712101
180
VAM-HVE/HVLT Series
17.5.3 Local Pressure Loss for Duct
1) Local Pressure Loss
In the bend part of the duct and diagonal change, there is loss in quality that is different from the straight pipe such as the vortex. The
following formula expresses for pressure loss other than these straight pipes.
P =
ζ
·
γ
=
ζ
· Pv
ζ :
Local pressure loss
γ :
Specific weight of air ································ (1.2 kg/m
3
)
V : Air velocity ······················································· (m/s)
*Excluding merging flow, there is air velocity for the local upper flow.
Pv : Dynamic pressure ············································· (Pa)
2) Calculation of Local Pressure Loss for Duct
Example) in the case of a duct bend as shown in the lower figure
Condition = 1.5 v = 5.0 (m/s)
From Table-A
ζ
= 0.15
Pv =
γ
= × 1.2
Pv = 15 (Pa)
P =
ζ
(Local pressure loss) × Pv (Dynamic pressure)
= 0.15 × 15
≈
2.25 Pa
The right column in Table A is the value expressing for when this local pressure loss is converted to duct diameter. However, because
the value expressed here belongs to "friction resistance coefficient
γ
= 0.018 of time, "please use the following formula for other cases.
re : Partial resistance for equivalent length of straight pipe ··· (m)
re = d
d : Straight pipe diameter ····················································· (m)
ζ :
Local pressure loss
v
2
2
No.
1
2
3
4
5
6
Name
Shape diagram
Condition
H/W
–
–
0.25
0.5
1.0
4.0
0.5
0.75
1.0
1.5
θ
θ
0.5
0.75
1.0
1.5
2.0
–
0.5
0.75
1.0
1.5
0.5
0.75
1.0
1.5
0.5
0.75
1.0
1.5
0.5
0.75
1.0
1.5
0.71
0.33
0.22
0.15
0.13
1.20
1.30
0.57
0.27
0.22
1.30
0.52
0.25
0.20
1.20
0.44
0.21
0.17
0.92
0.40
0.19
0.15
1.30
1.20
1.20
1.10
0.02
0.03
0.05
0.11
0.13
0.08
0.12
0.19
R/dR/W
Circular
diagonal round
bend
Circular diagonal
square bend
Rectangular
diagonal round
bend
Rectangular
diagonal square
bend
Pipe entrance
(circular feed
attached)
Round shape
Pipe entrance
(rectangular
feed attached)
–
20˚
40˚
60˚
90˚
20˚
40˚
60˚
90˚
d
d
R
R
H
W
H
W
Vo
θ
Vo
θ
Local pressure
loss
ζ
Circular diagonal round bend
R
d
v
2
2
25
2
ζ
λ
Table-A
R
V
d
Summary of Contents for VAM Series
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