Vortex flowmeter: operating principle

Vortex flowmeters are based on taking into account the periodicity of the pressure change, which is formed in the flow after a certain obstacle present in the pipeline, or during the oscillation and vortex formation of the jet.

Advantages

The first devices of this type appeared in the 60s of the last century. Their main disadvantage was a small range of measurement parameters and a significant error. The electronic modern vortex flowmeter has become more sophisticated, effective and has acquired many advantages, which include the following:

• Relative simplicity of the measurement system;
• The data are always stable, independent of temperature and available pressure;
• Measures that are highly accurate;
• Measuring linear signals;
• Reliable and simple construction;
• Wide range of measurements;
• Static elements;
• Presence of self-diagnosis function in some models.

disadvantages

Rosemount Vortex Flowmeter Is designed for operation in pipes with a diametrical size of 20 to 300 mm, since pipelines with a smaller size are characterized by inconstant vortex formation, and operation with a larger size is quite difficult. In this case, there is no possibility of using at a low flow rate, due to the complexity of measuring the signal and a significant reduction in pressure. Also, vibration and sound types of pulsation affect the operation of the device. As a hindrance is a vibrating pipeline and compressors. They can be eliminated by means of a straight-jumper mounted at the input, or by installing an additional inverter with counter-coupling and electronic filters, in the event of a difference in measuring signals and pulsating frequencies.

Classification

There are three versions of devices that are divided by the type of converter:

• A vortex flowmeter in which a real body plays the role of a primary converter. Gradually, on both sides, vortexes are formed in it after a detour of the immobile body, due to which the pulsation is formed.
• Mechanisms with a rotating flow of the primary converter, which creates a pressure pulsation by taking a funnel-like shape in the expanded part of the pipeline.
• Vortex flowmeters having a jet as a converter. In this case, the pulsation of pressure is provided by the oscillations of the jet.

The first two versions of the instruments are more suitable for determining the vortex flowmeter. But in view of the volatile nature of the flow of the third type, it also belongs to this category. The greatest similarity in the characteristics of the process is noted in the first and third versions.

Vortex flowmeter with streamlined converter

When the body is walking the flow changes the trajectory of the direction of the jets, at the same time their velocity increases and the pressure decreases. The reverse change occurs after the midsection of the object. On its reverse part, low pressure is formed, and on the front - high. After the passage of the body, the boundary layer leaves, and under the influence of low compression a vortex is created, and also when the trajectory of motion changes. This is typical for both parts of the streamlined body. The alternating formation of vortices on both sides is realized, since they interfere with the formation of each other. This marks the creation of the Karman path.

A special flow body has working planes with self-cleaning due to vortices, even under the condition of a heavily polluted medium they are always clean.

The dimensions and sweep of the flow are directly proportional to the periodicity of the appearance of the vortices, which corresponds to the velocity at an unchanged size, and as a consequence to the volumetric flow. If the stable formation of vortices occurs at a low consumption of the material, the measuring range of the flowmeter will be 20 l / min.

Streamline body structure

The flowmeter counter vortex, as a rule, is based on a prismatic element of a trapezoidal, triangular or rectangular type. The design of the first variant goes towards the water flow. Given some loss of pressure, such elements form oscillations with sufficient regularity and strength. In addition, special convenience is noted when converting output signals.

Vortex flowmeter in some cases can use two streamlined devices to increase the output signals, in this case they are located at a set distance. On the side parts of the rectangular second prisms there are piezoelements hidden by elastic thin membranes, so that there is no possibility of exposure to acoustic interference.

Types of transformations

There are several ways to convert output signals from vortex changes. The fastest flow with streamlined elements and systematic pressure changes have become most widespread. The sensor element consists of one or two wire-type thermoanemometers. Used ultrasonic, integrating, capacitive and inductive flow converter. For correct operation, the vortex flowmeter must have a free, even part of the pipe in front of it.

The complexity of operation in pipes with increased diameter is caused by the following reasons:

• Decrease in the regularity of the vortex formation;
• Low productivity of vortex formation;
• Decrease in the total number of oscillations.

Funnel-shaped vortex flowmeters: the principle of operation

In these devices, the transducers have a mechanism that ensures the swirling of the flow transmitted through a part of the pipeline to its expanded side or through cylindrical small nozzles. The shape in the form of a funnel is formed in the tube, and around its axis the axis rotates around the core of the vortex. The flow in the upper part has a pressure that pulsates simultaneously with the angular displacement of the nucleus, while it is equal to the flow of volume or linear velocity. Conductor thermo-anemometers or electromechanical elements convert the speed or the frequency of pulsations for measuring channels. The process consists of two phases: first, the transfer of the volume flow to the frequency of the precession of the vortex is formed, then the frequency turns into a signal.

Flowmeter based on an oscillating jet

Passing through the nozzle, the gas or liquid flow is in the diffuser with a section in the form of a rectangle. In some cases, the flow is alternately pressed at a certain time to the different walls of the diffuser. The electrifying property of the jet of the relaxation device reduces the pressure in the upper region of the bypass tube, while in the lower part it remains the same and a motion is created that transfers the jet to the lower part of the diffuser. Afterwards, the character of the motion changes in the rim, and the oscillation of the jet arises.

The jet, clasped in the lower element of the diffuser in the converters of the hydraulic return connection, leaves only partially through the outlet branch pipe. In the leading upper channel, the fraction of the jet is diverted and, when passing through the first nozzle, it is transferred to the lower position into the flow from the second nozzle. Then the part is separated and goes to the outlining upper channel, the oscillation process occurs after the transfer is down, with a simultaneous change of pressure in both sides of the flow.

The converter of this type is more rational. Due to this, a strict oscillation path is formed and there is a direct effect of the oscillation frequency on the flow rate.

The largest distribution of vortex flowmeters Yokogawa Purchased in pipelines with a small diameter, maximum up to 90 mm. In some cases, devices of this type are used as replacement of partial converters.

Today, the quality of manufacturing of flowmeters is constantly evolving and new functions appear, despite the fact that such devices have a fairly long period of use. Developers are looking for more effective design solutions, creating technological options that are more effective.