Regarding flow measurement, a vortex flow meter has several benefits, including reduced leak risk, a large turndown range, straightforward installation without impulse lines, and no moving elements that need maintenance or repair. Since vortex meters consume so little energy, they can be deployed in outlying places.
In addition to their versatility, Vortex meters are corrosion-resistant and can measure the flow of liquids, gases, steam, and other media. High pressures and temperatures are not a problem for vortex flow meters.
What is a Vortex Flow Meter?
Scientists have developed a vortex meter to measure the volume of a liquid as it flows past an immovable object. The vortex shedding principle, by which vortices (or eddies) are shed sporadically downstream of an object, is the basis for the operation of vortex flow meters. Vortex shedding occurs at a rate proportional to the speed at which the liquid passes through the meter.
When measuring a flow, including moving pieces might cause complications; this is where vortex flow meters shine. They come in various materials, including plastic, brass, and industrial grade. Since there are no moving parts, there is less wear on the meter, and less sensitive to process changes.
Features And Versatility Of Vortex Flowmeters
The Vortex flowmeter is an IoT flow meter developed by the Karman Vortex principle and designed primarily for the flow measurement of gas, liquid, steam, and other media in industrial pipelines.
Fluid volume flow in closed pipes can be measured with the help of a vortex flowmeter. An IoT flow meter can be used to accurately measure the flow of gas, liquid, or steam in various industrial settings, including but not limited to the production process, energy monitoring, environmental protection, transportation, food processing, and more.
A vortex forms when a fluid traveling at a certain speed encircles a fixed object. Karman’s vortices will arise, with their apex roughly 1.2D downstream of the bluff body.
Strouhal deduced that the two quantities must be related after observing that the frequency of a vibrating stretched wire is precisely proportional to the speed of the surrounding air. Indicator of Vortex Flow
St = f * d / V0
S = Strouhal’s constant
F = frequency of the wires
d = Diameter of Wire
V0 = The Speed of Light in Space
The formation of this train of vortices is known as “vortex shedding,” and scientists have dubbed the phenomenon “Karman’s Vortex Street.”
The rate of vortex shedding depends linearly on the speed of the fluid but is also affected by the shape and width of the bluff body’s face. Since the pipe’s internal diameter and the width of the obstruction are both expected to be fairly constant, we can get the frequency as
V=Flow Rate in Sheddar Bars, in Meters Per Second
D=Inside Diameter of Pipe (in mm).
c=steadfast (the ratio of d to D).
Sheddar bar width (in mm) is represented by d.
Like a traditional vortex steam flow meter, the vortex meter’s pressure loss gradient will be displayed as an aperture. The lowest pressure will be at the shedder bar, analogous to the vena contracta in an orifice meter. Pressure will gradually return to its original level downstream of this location, although the drop will be long-lasting. To avoid cavitation, it is important to know how much pressure drops at the vena-contracta.
Remember that the d/D ranges from 0.22 to 0.26 for most vortex meters and that the frequency of vortices reduces with increasing meter size. The maximum diameter of a vortex meter is capped due to potential difficulties with meter resolution. There are arguments in favor of strict management.
On-board digital multipliers multiply the vortex frequency without adding any further room for error.
Patterns of Vortex Flow in Various Types of Meters
Digital signals from smart vortex meters convey more data than merely the flow rate. When the Reynolds number drops below 10,000, the flowmeter’s embedded microprocessor makes the necessary adjustments for a lack of straight pipe conditions, a mismatch between the bore and mating pipe diameters, thermal expansion of the bluff body, and a change in the K-factor.
Diagnostic subroutines are built into intelligent transmitters to alert users to any malfunctions. To diagnose issues with the meter or the application, smart transmitters can trigger testing processes. These on-demand examinations can also help with ISO 9000 certification.
Some vortex flowmeters have a mass-flow detection capability. One such configuration concurrently assesses the vortex frequency and the intensity of the vortex pulse. The density of the process fluid can be computed from these measurements, along with the mass flow, to an accuracy of +/- 2%.
In another configuration, sensors for measuring the fluid’s temperature and pressure and its vortex frequency are included. The density and mass flow rate are calculated based on the inputted information. This meter can measure mass flow rates with an accuracy of 1.25% for liquids and 2% for gases and steam. This meter is a handy, less expensive alternative to installing separate transmitters when knowing the pressure and temperature of a process is useful for other reasons.
Precision and Scope
Since the Reynolds number decreases with increasing viscosity, the vortex flowmeters’ rangeability also decreases. Tolerable precision and variation place a cap on maximum viscosity in the 8–30 centipoise range. Suppose the vortex meter has been sized appropriately for the application. In that case, it should have a rangeability greater than 20:1 for gas and steam service and greater than 10:1 for low-viscosity liquid applications.
For Reynolds values above 30,000, the typical error range for vortex meters is 0.5 to 1% of the rate. There is a rise in metering inaccuracy when the Reynolds number decreases. The margin of error can approach 10% of the true flow rate for Reynolds numbers below 10,000.
Unlike conventional flowmeters, the vortex meter is equipped with a cut-off point, which continues to offer some signal even at negligible rates. When the reading drops below this threshold, the meter’s output is immediately limited to 4 mA (in the case of analog transmitters). This threshold represents a Reynolds number of 10,000 or less. This is not an issue if the minimum flow that needs to be measured is greater than twice the cut-off flow. However, it is still a disadvantage if low flow rate data is needed for start-up, shutdown, or other upset procedures.
Potential Uses and Restrictions
Batching and other intermittent flow applications are not good fits for vortex meters. This is because the minimum Reynolds number limit of the meter can be reached if the dribble flow rate setting at the batching station is too low. The magnitude of the resulting inaccuracy increases as the batch size decreases.
In particular, low-pressure (low-density) gases do not generate a sufficiently robust pressure pulse if the fluid velocities are modest. As a result, the meter’s rangeability is likely to be poor in such settings, making it impossible to measure low flows accurately. However, the vortex flowmeter can still be considered if the meter is properly designed for typical flow and the reduced rangeability is acceptable.
In sludge and slurry service, when the process fluid tends to coat or build up on the bluff body, the K factor of the meter will eventually change. Flowmeters that generate vortices should be avoided in these circumstances. However, the application is more likely to be successful if the unclean fluid contains just trace amounts of non-coating solids. Although the bluff body and flow tube were significantly scarred and pitted by the end of the test, the K factor had changed by only 0.3% from the original factory calibration.