ULTRAFLOW® 54 DN15-125
Kamstrup A/S · Technical description · 5512-2464_D1_GB_09.2021
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This can be explained by combining Bernoulli’s equation and the continuity equation. Based on Bernou
lli's equation, the
total pressure of the flow will be the same for any cross section. It can be reduced to:
𝑝
𝑠𝑡𝑎𝑡.
+ 𝑝
𝑑𝑦𝑛𝑎𝑚.
= 𝑝
𝑠𝑡𝑎𝑡.
+
1
2
𝜌𝑣
2
= 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
(Bernoulli’s equation)
𝑝
𝑠𝑡𝑎𝑡.
is the static pressure.
[𝑃𝑎 =
𝑁
𝑚
2
=
𝑘𝑔
𝑠
2
∙𝑚
] ; 1 𝑏𝑎𝑟 = 10
5 𝑁
𝑚
2
𝑝
𝑑𝑦𝑛𝑎𝑚.
is the dynamic pressure.
[𝑃𝑎 =
𝑁
𝑚
2
=
𝑘𝑔
𝑠
2
∙𝑚
]; 1 𝑏𝑎𝑟 = 10
5 𝑁
𝑚
2
𝜌
is the water density.
[
𝑘𝑔
𝑚
3
]
𝑣
is the water flow rate.
[
𝑚
𝑠
]
The continuity equation determines that the product of pipe cross sectional area
𝐴
and average flow velocity
𝑣
, which
corresponds to the volume flow rate passing through, is constant for an incompressible fluid like e.g. water. Therefore,
the flow velocity is increased in a contraction and the static pressure decreases.
𝑞 = 𝐴
1
∙ 𝑣
1
= 𝐴
2
∙ 𝑣
2
= ⋯ = 𝐴
𝑖
∙ 𝑣
𝑖
= 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
(Continuity equation)
When dimensioning a flow sensor, you must take the above into consideration, especially if the sensor is used within the
scope of EN 1434 between q
p
and q
s
, and in case of major pipe contractions. In general, the maximum design flow in the
system must NOT exceed the nominal flow q
p
of the flow sensor.
6.1.5
Pressure loss
Pressure loss in a flow sensor is stated as maximum pressure loss at q
p
. According to EN 1434, the max pressure loss at
q
p
must not exceed 0.25 bar, unless the energy meter includes a flow controller or functions as a pressure reducing
equipment.
The pressure loss increases with the square of the flow and is usually stated as a direct proportionality between the flow
and the square root of the pressure loss:
𝛥𝑝 =
1
𝑘
𝑣
2
𝑞
2
⇔ 𝑞 = 𝑘
𝑣
× √𝛥𝑝
where:
𝑞
= volume flow rate
[𝑞] =
𝑚
3
ℎ
𝑘
𝑣
= volume flow rate at 1 bar pressure loss
[𝑘
𝑣
] =
𝑚
3
ℎ∙√𝑏𝑎𝑟
𝛥𝑝
= pressure loss
[∆𝑝] = 𝑏𝑎𝑟; 1 𝑏𝑎𝑟 = 10
5
𝑃𝑎
