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Vortex flowmeter selection points introduction

Vortex flowmeter selection points
1. Application overview
Since its application in the industrial field in the 1970s, the vortex flowmeter has been welcomed by users and has been rapidly developed due to its outstanding features. Developed like this, it has been among the universal flowmeters for more than 20 years and is rare in flowmeters. It is not surprising that due to the short application time, no matter whether the theoretical research or practical experience is weak, it is inevitable that some problems will arise. Many years of practice have proved that the selection (selection and use) of vortex flowmeter is the key link of the flowmeter. Therefore, the instrument manufacturer should strengthen the pre-sales service, that is, help the user to select the model and give guidance on installation and application. As long as you grasp this link, the flowmeter is a good performance flowmeter.
In the mid-to-late 1990s, the world's vortex flowmeters accounted for 3% to 5% of the total flow meters, 50,000 to 60,000 units per year, accounting for 4% to 6% of the total amount; It accounts for 6% to 8% of the total flow meter (excluding domestic gas meter and water meter and glass tube float flowmeter), and is 15,000 to 20,000 per year.
2. The choice of the diameter of the vortex flowmeter
The instrument diameter and specification selection of the vortex flowmeter is very important. It is similar to the design calculation of the differential pressure flowmeter throttling device. It should be selected according to some principles. The instrument caliber selection steps are as follows.
First, the following working parameters must be clarified.
1) fluid name, composition;
2) The maximum, common, and minimum flow of the working state;
3) highest, common, minimum working pressure and working temperature;
4) The viscosity of the working medium.
The output signal of the vortex flowmeter is proportional to the volume flow of the working state. Therefore, if the gas flow is known to be the standard state volume flow or mass flow, it should be converted into the volume flow qv under working conditions.
Qv=qn(pnTZ/pTnZn) m3/h (9)
Where qv,qn-- are the volume flow in the working state and the standard state, respectively, m3/h;
P, Pn-- are the absolute pressure in the working state and the standard state, respectively; Pa;
T, Tn - respectively, the working temperature and the thermodynamic temperature under standard conditions, K;
Z, Zn-- are the gas compression coefficients in the working state and the standard state, respectively.
Density ρ and volume flow qv of the working medium
ρ=ρn(pTnZn/ pnTZ) (10)
Where ρ,ρn-- are the medium density in the working state and the standard state, respectively, kg/m3;
The rest of the symbols are the same as above.
Qv =qm/ρ (11)
Where qm - mass flow, kg / h.
The sensor diameter is required below. The choice of sensor aperture is mainly to calculate the flow lower limit. It should satisfy two conditions: the minimum Reynolds number should not be lower than the limit Reynolds number (ReC=2×104) and the vortex strength should be greater than the allowable value of the sensor vortex strength for the stress vortex flowmeter at the lower limit flow (vortex strength and Lift force ρU2 proportional relationship), for liquids should also check whether the minimum working pressure is higher than the saturated vapor pressure at the working temperature, that is, whether cavitation will occur.
These conditions can be expressed by mathematical formulas as follows (12-14)

Where qVmin, qV0min--the minimum volume flow in the working state and the calibration state, respectively, m3/h;
(qVmin)ρ--the minimum volume flow when the vortex strength requirement is met, m3/h;
(qVmin)υ--the minimum volume flow when the minimum Reynolds number is met, m3/h;
ρ,ρ0-- respectively the density of the medium in the working state and the calibrated state, kg/m3;
υ,υ0--the kinematic viscosity of the medium under working condition and calibration state, m2/s;
Pmin - minimum working pressure, Pa;
△p--the pressure loss of the sensor at the maximum flow rate, Pa,
△p=CD(ρU2/2), CD≈2
U--pipeline average flow rate, m/s;
PV--the saturated vapor pressure of the liquid at the working temperature, Pa.
Compare (qVmin)ρ, and (qVmin)υ:
If (qVmin) υ ≥ (qVmin) ρ, the measurable flow range is (qVmin) ρ ~ qVmax, and the linear range is (qVmin) υ ~ qVmax;
If (qVmin) υ < (qVmin) ρ, the measurable flow range and linear range are (qVmin) ρ ~ qVmax.
The determination of the flow measurement range should also check whether it is within the optimal working range of the meter (ie 1/2 to 2/3 of the upper limit flow). Table 4 shows the flow measurement ranges for various calibers under certain calibration conditions for a vortex flowmeter of a certain type.

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