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...3 MECHANICAL INSTALLATION
3.2 Location – Flow Conditions
The probe may be installed in one of two positions in the pipe;
either on the centre line or at the mean axial velocity point
(
1
⁄
pipe diameter). It may also be traversed across the pipe to
8
determine the velocity profile.
3.2.1 International Standard for Flow Measurement
ISO 7145 '(BS 1042) Measurement of fluid flow in closed
conduits' Part 2 'Velocity area methods' describes methods of
calculating volumetric flow from velocity measurements.
Section 2.2: 1982 'Method of measurement of velocity at one
point of a conduit of circular cross section' describes the
inference of volumetric flow from measurement of velocity at a
single point. Several conditions must be fulfilled to validate the
method, which uses calculations based on empirical data.
Where the validating conditions can be met, the method
described in Section 2.2 is the most practical. It is possible to
measure the velocity either on the centre line, which reduces
sensitivity to positional errors, or at the assumed point of mean
flow velocity.
5 Diameters
A – Flow Direction
B – Fluid Level
Fig. 3.3 Flow Conditions
4
See Table 3.1
M
T
y
p
e
f o
d
s i
u t
b r
a
n
c
e
u
p
t s
e r
a
m
f
o r
m
h t
e
m
e
m
e
a
s
r u
n i
g
c
o r
s
- s
h t
e
s
e
t c
o i
n
a
9 °
0
e
b l
o
w
r o
a
t
b -
e
n
d
°
S
e
v
r e
l a
9
0
c
o
p
a l
n
r a
b
e
n
d
s
°
S
e
v
r e
l a
9
0
n
o
- n
c
o
p
a l
n
r a
b
e
n
d
s
T
t o
l a
a
n
g
e l
c
o
n
v
e
g r
e
t n
°
1
8
o t
3
6
T
t o
l a
a
n
g
e l
d
v i
e
g r
e
t n
°
1
4
o t
2
8
F
u
y l l
o
p
e
n
e
d
b
u
t t
r e
y l f
v
a
v l
e
F
u
y l l
o
p
e
n
e
d
p
u l
g
v
a
v l
e
* Expressed in multiples of the diameter of the conduit.
Downstream from the measurement cross-section, the
straight length shall be at least equal to five duct diameters
whatever the type of disturbance.
Table 3.1 Straight Pipe Lengths
Table 3.1 is an extract from ISO 7145 (BS 1042): Section 2.2:
1982 and is reproduced with the permission of BSI. Complete
copies of the standard can be obtained by post from BSI
Publications, Linford Wood, Milton Keynes, MK14 6LE.
Information. Where the above ideal conditions
cannot be achieved, the flow profile must be tested for
symmetry in order to obtain reliable flow results.
i
i n
m
u
m
u
p
t s
e r
a
m
t s
a r
g i
t h
e l
F
r o
a
F
r o
a
a
s
u
e r
m
e
t n
t a
m
e
a
s
u
e r
m
p
i o
t n
f o
m
e
a
n
h t
e
a
x
s i
f o
i x
l a
v
e
o l
i c
y t
c
o
n
d
u
5
0
2
5
5
0
2
5
8
0
5
0
3
0
1
0
5
5
2
5
4
5
2
5
3
0
1
5
n
t g
* h
e
t n
o
n
h t
e
t i
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