Vortex street flowmeter application
The SKLU series vortex street flowmeter mainly uses in theindustry
pipeline medium fluid the flow measurement, like gas, liquid, vapor
andso on many kinds of medium. Its characteristic is the pressure
loss is small,the measuring range scope is big, the precision is
high, when survey operatingmode rate of volume flow nearly not
parameter and so on fluid density, pressure,temperature, viscosity
influences.
Not movable machine parts, therefore thereliability is high,
maintains the quantity to be small. The measuring
applianceparameter can the long-term stability. The vortex street
flowmeter uses thepiezoelectricity stress type sensor, the
reliability is high, may in - 20℃~+250the operating temperature
scope works.
Has the mock standard signal, also hasthe digital pulse signal
output, easy and number system necessary uses and so oncomputer, is
one kind quite advanced, the ideal flow instrument.
Vortex street flowmeter principle
Establishesthe triangle columnar order whirlpool in the fluid to
have the body, has thebody both sides from the whirlpool to produce
alternately has the rulewhirlpool, this kind of whirlpool is called
the Carmen whirlpool, if the figureto the right shows, turns on
lathe the vortex street to have the body downstreamin the whirlpool
to arrange asymmetrically.
Supposes the whirlpool theoccurrence frequency is f, was measured
that the medium mean velocity of streamis, the whirlpool has the
body to welcome the flow surface width is d, shows thebody latus
rectum is D, then obtains the following relationship:
f=SrU1/d=SrU/md (1)
In the formula U1--Thewhirlpool has the body both sides mean
velocity of stream, m/s;
Sr--Strouhal number;
m--Of the whirlpool has ratio of the body bothsides arch area and
the pipeline cross-section area
In the pipeline rate of volume flow qv is
qv=D2U/4=D2mdf/4Sr (2)
K=f/qv= [D2md/4Sr] - 1(3)
In the formula K--Flowmeter's scaling factor, the pulsecounts /m3
(P/m3).
K besides has the body, pipeline's geometry size withthe whirlpool
related, but also concerns with the Strouhal number. The
Strouhalnumber is the zero dimension parameter, it has the build
shape and the Reynoldsnumber with the whirlpool related, shown in
Figure 2 for the circle columnarwhirlpool has body's Strouhal
number and the pipeline Reynolds number relationalgraph. The figure
shows, in ReD=2×104~7×106 the scope, Sr may regard as theconstant,
this is the measuring appliance normal work scope. When survey
gasflow amount, the VSF current capacity formula is
(4)
Figure 2 Strouhal number and Reynolds numberrelations curve
In the formula qVn, qV--Respectively is under the standard
state(0oC or 20oC,101.325kPa) and under the operating mode rate of
volume flow, m3/h;
Pn, P--Respectively is under the standard state and the operating
modeabsolute pressure, Pa;
Tn, T--Respectively is under the standard state andthe operating
mode thermodynamic temperature, K;
Zn, Z--Respectively beunder standard state under and operating mode
gas loading coefficient.
Isobvious by the above equation, the VSF output's pulse frequency
signal not thefluid nature and the component change's influence,
namely the scaling factoronly has in certain Reynolds number scope
with the whirlpool the body andpipeline's shape size and so on
concerns. But must examine the mass flow as theflowmeter in the
mass balance and in the energy measurement, by now
flowmeter'soutput signal should simultaneously monitor the rate of
volume flow and thefluid density, the fluid nature and the
component has the immediate influence tothe flow measurement.
The vortex street flowmeter is carries on the solid
surroundingboundary rate of fluid flow survey based on the Carmen
whirlpool principle thenew flowmeter. Because it has the good
medium adaptiveness, does not need thetemperature pressure
compensation then direct measurement steam, the air, thegas, the
water, the liquid operating mode rate of volume flow, provides
thetemperature, the pressure transmitter to be possible the
surveyor's beaconsituation rate of volume flow and the mass flow,
is the throttle typeflowmeter's ideal substitution product.
In order to enhance the vortexstreet flowmeter thermostable and the
vibration-proof mobility energy, Ourcompany recently developed the
SDLU advanced version vortex street flow sensor,because its unique
structure and the selection cause this sensor to be possiblein the
high temperature (350℃), the strong vibration (≤1g) under the
badoperating mode uses.
In the practical application, often the maximumcurrent capacity far
is lower than measuring appliance's on limiting value,along with
the load change, the minimum current capacity often will be
lowerthan measuring appliance's lower limiting value, th
