Guidelines For Dimensioning Ultraflow - Kamstrup ULTRAFLOW 54 Technical Description

TECHNICAL DESCRIPTION

8.7 Guidelines for dimensioning ULTRAFLOW

In connection with installations it has proved to be practical to work with larger pressures than the ones stated
below:
Nominal flow q
[m³/h]
The purpose of recommended back pressure is to avoid measuring errors due to cavitation or air in the water.
It is not necessarily cavitation in the flow sensor itself, but also bubbles from cavitating pumps or regulating
valves mounted before the sensor. It can take some time for these bubbles to dissolve in the water.
In addition, the water may contain air, which is dissolved in the water. The amount of air which can be dissolved in
water depends on the pressure and the temperature. This means that air bubbles can be formed because of a drop
of pressure e.g. due to an absolute speed rise in a contraction or over the meter.
The risk of these factors affecting accuracy is reduced by maintaining a fair pressure in the installation.
In relation to above table, the steam pressure at current temperature must also be considered. Table 20 applies to
temperatures up to approx. 80 °C. Furthermore, it must be considered that the above-mentioned pressure is the
back pressure at the sensor and that the pressure is lower after a contraction than before one (e.g. cones). This
means that the pressure – when measured elsewhere - might be different from the pressure at the sensor.
This can be explained by combining the continuity equation and Bernoulli's equation. The total energy from the
flow will be identical at any cross section. It can be reduced to: P + ½ρv
When dimensioning the flow sensor, this must be taken into consideration, especially if the sensor is used within
the scope of EN 1434 between q
3
2,5
2
1,5
1
0,5
0
80
40
Recommended
p
back pressure
[bar]
0.6 1
1.5 1.5
2.5 1
3.5 1
6 1.5
10 1
15 1.5
25 1
40 1.5
60 1
100 1.5
Table 20. Recommended minimum back pressure.
and q , and in case of heavy contractions of the pipe.
p s
85 90 95
Diagram 10. Steam pressure.
5512-385 GB/02.2014/Rev. H1
®
Max. flow q
s
[m³/h]
1.2
3
5
7
12
20
30
50
80
120
200
2
= constant.
Steampressure
100 105 110 115
[° C]
®
ULTRAFLOW 54 and 34
Recommended
back pressure
[bar]
2
2.5
2
2
2.5
2
2.5
2
2.5
2
2.5
120 125 130