4 Operation
Manual TRZ 03· EN08 ·2018 September, 10th
53
K
Q
DN
p
Q
rel
rel
2
With:
Q
^
rel
:
is the relative volume flow pulsation (peak-to-peak)
Q
¯ : is the mean volumetric flow
𝑝
𝑟𝑒𝑙
̂
: is the relative pressure pulsation (peak-to-peak)
DN:
is the nominal diameter of the gas meter
K:
is a constant depending on standard density, velocity of sound,
compressibility, pressure at base conditions, temperature,
and station-specific parameters.
With this relation, it is possible to estimate volume flow pulsation on the basis of
pressure pulsation, which can be measured more easily. Direct measurement of
volume flow pulsation is preferable, however, since the results are more reliable.
The crucial factor is the pulsation at the location of measurement.
4.1.3
Consequences
Notice
In the case of pulsating flow, the turbine meter shows a measured value
which is too high.
Due to the pulse applied by the flow on the impeller which increases quadratically
with the flow velocity, the resultant rotational speed is higher than the mean value
of the flow velocity. The influence with high gas density is less but increases with a
high mass moment of inertia (heavy impeller) or fast-running wheels.
The influence is less with high gas density but increases with high mass moment
of inertia (heavy impeller) or fast-running wheels.
Warning
Furthermore, high pulsation amplitudes may result in premature wear of
shaft bearings due to in-creased load.