YOKOGAWA AE100D, Инструкция по эксплуатации

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IM 1F6A0-01E 2-14
2. GENERAL DESCRIPTION
■
Pressure Loss
At velocity of 10 m/s by water,
∆
P = 108 kPa
At velocity of 80 m/s by atmospheric air,
∆
P = 9 kPa
obtained from the following equations.
∆
P = 108
×
10
-5
·
ρ
f
·
υ
2
or
∆
P = 135
×
pf · Q
f2
D 4
where,
∆
P : Pressure loss (kPa )
ρ
f
: Density at operating condition (kg/m
3
)
υ
: Flow velocity (m/s)
Q
f
: Actual flow rate (m
3
/h)
D : Internal Diameter (mm)
Figure 7 shows pressure loss versus actual flow
rate. When nominal size 15 to 50mm and adjacent
pipeline is Sch 40, and nominal size 80 to 300 mm
and adjacent pipeline is Sch 80, the pressure loss
will be approximately 10% smaller than calculated
value.
(Example) Calculation of pressure loss
Calculate the pressure loss when the nominal size
is 50 mm and the flow rate of water at operating
temperature 80
°
C is 30m 3 /h.
1. Since the density of water at 80
°
C is 972kg/m 3 ,
substitute this value in equation (2):
∆
P = 135
×
972
×
30
2
51.1
4
= 17.3kPa
2. Obtain the pressure loss using equation (1). The
flow velocty when the flow rate is 30m
3
/h is given
by:
υ
=
354
×
Q
f
=
354
×
30
= 4.07m/s
D 2
51.1
2
Therefore, subtitute this value in equation (1):
∆
P = 108
×
10
-5
×
972
×
4.07
2
= 17.3kPa
3. Obtain the pressure loss using Figure 7. Since the
liquid pressure loss factor can be read as 18.5,
then:
∆
P = 98.1
×
18.5
×
972
×
10 -5
= 17.6kPa
■
Cavitation
(Minimum Back Pressure, Liquid service only):
Cavitation occurs when the flow line pressure is low
and flow velocity is high during fluid measurement,
preventing correct measurement of flow rate. The
optimum line pressure can be obtained from the
following equation.
P = 2.7 ·
∆
P + 1.3 · Po
Where,
P : Line pressure, 2 to 7 times as large as internal
diameter on downstream of flowmeter body
surface. (kPa absolute).
∆
P : Pressure loss (kPa).
Refer to the item above.
Po : Saturation liquid vapor pressure at operating
temperature (kPa absolute).
(Example) Confirmation of presence of cavitation
Suppose that the line pressure is 120 kPa abs and the
flow rate scale is 0 to 30 m
3
/h. It is only necessary to
confirm the pressure at the maximum flow rate ;
therefore, the saturated steam pressure of water at
80
°
C is as follows from the table of saturated steam
pressures:
Po = 47.4 kPa abs
Therefore, substitute this value in equation (3):
P = 2.7
17.3 + 1.3 47.4
= 108.3 kPa abs
Since the operating pressure of 120 kPa abs is higher
than 108.3 kPa abs, no cavitation occurs.
100
50
30
20
10
1
1 2 3 5 10 20 30 50 100 200 300 500 1000 2000 3000 5000
1 20 30 50 100 200 300 500 1000 2000 3000 5000 10000 50000
15m 25m 40m 50m 80m 100m 150m 200m 250m 300m
2
3
5
10000
5000
3000
2000
1000
200
300
500
Actual Gas and Steam Flow Rate m
3
/h
Liquid Pressure Loss Factor (C) Gas and Steam Pressure Loss Factor C
Actual Liquid Flow Rate(m
3
/h)
∆
P=C
× ×
10
-5
∆
P: Pressure loss (kg/cm 2 )
: Density (kg/m 3 )
F020502.EPS
Figure 2.5.2 Pressure Loss
········· (1)
··············· (2)
··············· (3)