Analysis of the advantages of V cone flowmeter
1. Low requirements for installation of straight pipe sections
对安装直管段要求低，上游直管：0－3D；下游直管：0－1D。 The V-cone flowmeter has low requirements for the installation of straight pipe sections. The upstream straight pipe: 0-3D; the downstream straight pipe: 0-1D. Due to the characteristics of the shape and central installation position of the V-cone flow sensor, it directly interacts with the high-velocity region of the flow. The V-cone forces the high-velocity region to mix with the low velocity near the wall of the tube. It must be "flat" toward a fully developed flow shape, which can be re-formed upstream of the cone, so that using a V-cone sensor requires a shorter straight pipe section than other flow measuring instruments to form a fully developed flow in the tube . When the fluid flows near the V-cone, it can produce a flat flow distribution, so compared to other differential pressure instruments, it can play a more shaping role on the upstream interference factors. V cone upstream straight tube: 0-3D; downstream straight tube: 0-1D. This is beneficial to users of large diameter, expensive pipelines, or users of shorter running pipelines.
2.Wide range ratio
Flow (small flow) can be measured in the lower Reynolds number range (Re≥8000). The typical range ratio is 10: 1. Selecting appropriate parameters can achieve 50: 1. Because the V-cone hangs in the center of the pipe, it directly interacts with the high-velocity area, forcing the high-velocity area to mix with the low-velocity near the pipe wall; when the flow rate decreases, the V-cone continues to interact with the maximum velocity in the pipe. When other differential pressure instruments may not detect the differential pressure signal, the V cone sensor can still produce a differential pressure signal as low as 8000. This is the biggest advantage of the V-cone flowmeter when detecting small flow.
The accuracy of the primary element of the V-cone sensor is ± 0.5%. The accuracy of the system depends on the accuracy level of the V-cone sensor, the accuracy level of the differential pressure transmitter, and the secondary instrument.
4, good repeatability
The repeatability of the V-cone sensor is better than 0.1% 5. The V-cone sensor is resistant to wear and long-term stability. Since the shape of the V-cone is a shrinking fluid, it creates a vacuum effect on the surface of the cone and does not impact the abrupt surface. A boundary layer is formed along the surface of the cone to guide the fluid away from the β edge. This means that the β side will not be abraded by dirty fluid, so the β coefficient remains unchanged, and the V-cone sensor has good long-term stability.
Measurement principle and structural characteristics of 1 V cone flowmeter
V-cone is a differential pressure flowmeter. Like other differential pressure flowmeters, it is based on Bernoulli's law of the mutual conversion of energy in a closed pipe. That is, under the condition of a stable flow field, the flow velocity and differential pressure in the pipe The square root is proportional. Because this measurement principle is widely used, this article will not introduce it in detail. V-cone flowmeter is throttled by hanging a cone in the center of the pipeline. Because in the pipeline, the flow velocity distribution of the ideal flow field is: the velocity near the pipe wall is close to zero, the closer to the center of the pipeline, the greater the velocity, and the maximum velocity at the center of the pipeline (because the friction of the pipe wall reduces the flow of fluid through the pipe wall. speed). Therefore, when the fluid flows through the V-cone flowmeter, the cone directly interacts with the high-speed center portion of the fluid, forcing the high-speed center to be homogenized with the low-speed fluid near the pipe wall, thereby generating the correct differential pressure. This is even more the case when measuring at low flow rates. it works. However, other differential pressure flow meters with central openings (such as orifice plates) do not have this effect, so they cannot measure fluids with too low flow rates (reynolds numbers are too small). All differential pressure and flow measurements are based on the ideal fluid state, but due to the wide range of actual conditions on the site, this ideal state rarely exists. Any changes in the installation of the pipeline, such as elbows, valves, shrinkage, expansion, pumps, Tee, etc. will destroy the ideal flow field, so it is difficult for general flow meters to obtain accurate measurement values in the disturbed flow field. The V-cone overcomes these shortcomings. Due to its unique design, the shape and position of the cone rearrange the upstream velocity distribution and make the flow field ideal, so as to obtain accurate measurement values. Practice has shown that under extremely harsh installation conditions (such as two elbows on different planes immediately upstream of the cone), the V-shaped cone can also make the fluid velocity distribution flat and symmetrical, thereby ensuring measurement accuracy.
的优势分析 Advantages of 2 V cone flowmeter
The range ratio is wide. Because the cone can make the fluid flow field uniform, the measurable flow rate is lower than that of a general differential pressure flowmeter, that is, the lower limit of the range is lower than that of a general differential pressure flowmeter, so the range can be extended downward, and the range ratio can be 15: 1, the Reynolds number as low as 8000 can still maintain the linearity of the signal.
Long life, fluid flow through the cone without sudden fluctuations, but instead becomes a boundary layer along the cone, and guides the fluid away from the rear corner of the cone, which makes the angle of the cone free from abrasion and flow of unclean fluid. The coefficient β rate can be unchanged for a long time and ensure accurate measurement for a long time. Therefore, the flow meter can be used for a long time in dirty places without regular maintenance and periodic verification (of course, regular maintenance and verification of the secondary meter is still necessary). Small pressure loss The permanent pressure loss is lower than the orifice plate and close to Venturi.
The signal is stable. When the differential pressure generated by the throttling element also causes the eddy current behind the element, each type of differential pressure instrument has a signal fluctuation, even if the fluid is stable. For the standard orifice plate, the long eddy currents caused large signal fluctuations at low frequencies, which seriously interfered with the accuracy of differential pressure readings, while the eddy currents generated after the V-cone were very short, so the signal fluctuations were low-frequency. Amplitude, which makes the V-cone produce a stable signal.
The wide range of β values and the unique geometry of the V-cone allow a wide range of β values. The standard β values are 0.45, 0.55, 0.65, 0.75, 0.85, and specific β values can be used to ensure user-specific differential pressure output. The V-cone completely purged design without retention zone avoids the retention of residue, condensate or particles in the fluid. It can be widely used to measure dirty media without causing damage to the cone. Can measure vapor-liquid two-phase flow (liquid phase does not exceed 5%) and guarantee accuracy. Wide range of pipelines V-cone flowmeters are available in both pipe and plug-in versions, with sizes ranging from 1/2 "to 72".
Practical application of 3 V cone flowmeter
A 16 "pipe in an old plant of an ethylene plant requires an additional flowmeter due to the transformation, but the pipeline is short and the installation space is limited. It is not possible to make major changes to the pipeline. Because the installation of a flowmeter cannot affect production, it can only be stopped for maintenance. During this period, the construction time is also urgent. The pipeline medium is quenched water, normal flow rate is 2220t / h, temperature is 85 ° C, pressure is 1.06MPa. In this case, a V-cone flowmeter was selected because of its straight pipe requirements Only the first 3D and the first 1D, so it meets the problem of straight pipe sections caused by short pipelines. After being put into use, the flowmeter's condition is quite satisfactory to the user in terms of accuracy and stability, and the transformation has been successful. Another example, a factory measuring coke oven Due to the impurities contained in the gas pipeline, the damage to the measuring elements is serious. The factory originally used standard orifice plates for measurement, which not only has low accuracy but also needs to be replaced one year, which has a great impact on process production. The factory has also been replaced Other types of measuring flowmeters, but the effect is not obvious. Later, the factory switched to V-cone flowmeters, which not only improved the measurement accuracy, but also avoided regular Maintenance and periodic verification. The V-cone flowmeter has been used for several years, and the condition is still good. The user is quite satisfied, and several other flowmeters with the same problem have been replaced. Although it seems that the investment is more than the orifice plate at a time. However, due to the extension of the service life, the actual cost of use has not increased, but it has decreased.
Recommended applications for 4 V cone flowmeters
Suitable for the following occasions:
1) Small and medium diameter gas;
2) dirty media;
3) Where the straight pipe section is insufficient;
4) Where high accuracy is required.
有着相当明显的优势，所以其使用前景相当光明。 Because the V-cone flowmeter has quite obvious advantages, its application prospect is quite bright. Of course, as a type of differential pressure flowmeter, it cannot completely replace the position of the orifice plate and venturi due to cost. Compared with vortex flowmeters and electromagnetic flowmeters, it also has disadvantages such as the installation of pressure guiding pipes. But for suitable occasions, using a V-cone flowmeter should be an option worth considering