The principle and main features of Verabar flowmeter

Differential pressure flowmeters are widely used in the industrial field, accounting for more than 70% of the total number of flowmeters used in the entire industrial world. With the rapid development of electronic technology, the level of transmitters and secondary instruments has undergone a qualitative leap, and the accuracy, sensitivity and function have reached a high level. Transmitters can now distinguish pressure differences as small as a few Pa. However, for decades, there has been no major breakthrough in the problem of primary measurement source components, which has become a bottleneck restricting the development of differential pressure flowmeters.

1. Structure of Verabar flowmeter

The probe of the Verabar steam flow meter is a single-piece double-cavity structure probe made of 316 stainless steel. Its cross section adopts a shape, and its front surface is roughened. The multiple pairs of pressure holes obtained by area integration cover the velocity profile of the entire pipeline. The pressure holes facing the fluid read the high-pressure average signal, and the low-pressure pressure holes on the side and rear of the probe and before the separation point of the fluid and the probe read the low-pressure average signal.

2. The principle of the Verabar flowmeter

When the fluid flows through the probe, a high-pressure distribution area is generated in front of it, and the pressure in the high-pressure distribution area is slightly higher than the static pressure of the pipeline. According to the principle of Bernoulli's equation, the fluid speeds up when flowing through the probe, and a low-pressure distribution area is generated at the rear of the probe, and the pressure in the low-pressure distribution area is slightly lower than the static pressure of the pipeline. After the fluid flows through the probe, a partial vacuum is generated at the rear of the probe, and vortices appear on both sides of the probe. The average velocity flow probe of the Verabar flowmeter can accurately detect the average differential pressure generated by the average velocity of the fluid.

Like other differential pressure flow meters, it follows the Bernoulli equation

qv=KC△p（1）

Where qv is the volume flow rate of the fluid;

K—discharge coefficient;

C—flow constant (constant);

△p—Differential pressure generated by the differential pressure generator.

C is a constant. To determine qv, K and △p must be determined.

2.1 Flow coefficient K

Based on aerodynamics, fluid mechanics theory, boundary layer theory and actual fluid test data, after extensive exploration, a mathematical analysis model of K for the Verabar flow probe was innovatively established.

K = 1 / [1 / (1-Cbβv) + C] (2)

Where Cb is the boundary layer coefficient;

βv—Blocking coefficient.

This is a supplement to the Bernoulli equation theory in specific applications.

1) K accuracy is +0.5%, confirmed by comprehensive testing by the world's independent flow laboratory.

2) K is linear and its change is independent of the change in Reynolds number, ensuring that the measurement results can achieve an accuracy of +0.5% at a range ratio higher than 10:1.

3) The flow coefficient of Verabar is more accurate and easier to know than other flow meters.

2.2 Differential pressure △p read by Verabar flowmeter

The accuracy and stability of △p depends on the unique scientific design of the Verabar flowmeter:

1) The probe with the shape is subjected to the least pulling force, so that the separation point between the fluid and the probe is fixed.

2) The complete metal cavity structure is adopted to avoid the leakage between chambers caused by the three-piece structure of other probes, increase the strength of the probe, and ensure its accuracy.

3) The low-pressure holes are located on both sides of the probe and before the separation point between the probe and the fluid, which prevents the low-pressure holes from being affected by eddy currents and blocked, making the low-pressure signal more stable and the measurement more accurate.

4) Surface roughening and anti-siltation groove: Control the boundary layer. Under various flow rates, the boundary layer of the fluid on the probe surface is a turbulent layer, ensuring that the probe can still obtain a stable signal when the fluid has a low flow rate.

5) The probe passes through the entire cross-section of the fluid in the pipeline and takes pressure from multiple pressure holes. The spacing between the pressure holes is obtained after area integration. The measured signal is a true signal reflecting the average velocity of the fluid.

3 Main Features

1) It can detect the temperature and pressure of the medium and automatically compensate the flow rate with an accuracy of up to +1.0%.

2) Able to ensure long-term stability of accuracy.

3) The anti-clogging design of the Verabar flowmeter probe completely gets rid of the drawbacks of easy clogging of insertion-type flowmeters such as Anyuba flowmeter, bringing the level of uniform-velocity tube flowmeters to the highest level.

4) No mechanical moving parts, not easy to corrode, high reliability, good stability and low maintenance.

5) A hand valve is installed at the valve interface to make installation and maintenance easier, reduce the number of assembly parts, and reduce the hardware connection cost.

6) The perfectly designed three-way connector allows direct connection to the transmitter without the need for a three-valve group and a pressure-inducing pipe.

7) The flexible QuickJackHotTap operating system can easily and quickly insert and retract the probe.

8) The safety spring locking device keeps the probe well sealed and firmly installed. When the pipe size changes or when the pressure, temperature and mechanical force change, the probe can always maintain stress contact with the opposite pipe wall.

9) Small pressure loss and low energy consumption.

4 Application of Verabar flowmeter

Verabar flowmeter can be used in major petrochemical enterprises to measure the flow of various single-phase gas, liquid and steam media under full pipe conditions. It can be installed on square and round pipes of various materials, with pipe diameters ranging from 38mm to 14m. In particular, the application of non-stop installation technology is very popular among users.

5. Installation of flow meter

In order to facilitate maintenance and not affect the normal delivery of fluids, the flowmeter installation should ensure that the front straight pipe section is greater than 7D (D is the pipe diameter) and the rear straight pipe section is greater than 1D. In specific flow measurement applications, only correct installation can make the measurement go smoothly. The following is the correct installation position of the Verabar flowmeter and transmitter when measuring different fluids.

1) When measuring gas, it is recommended to install the Verabar flowmeter 160° above the horizontal pipeline; for vertical pipelines, it is recommended to install the transmitter above the Verabar flowmeter, and the transmitter and integrated probe 90° below the pipeline.

3) When measuring steam, it is recommended to install the Verabar flowmeter 160° below the horizontal pipeline; for vertical pipelines, it is recommended to install the transmitter below the Verabar flowmeter and the integrated probe 90° below the pipeline.